Flavor Quality, Objective Measurement

Flavor Quality: Objective Measurement In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; Amer...

Author: Richard A. Scanlan

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Flavor Quality: Objective Measurement

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Flavor Quality: Objective Measurement Richard A . Scanlan, EDITOR Oregon State University

A symposium sponsored by the Division of Agricultural and Food Chemistry at the 172nd Meeting of the American Chemical Society, San Francisco, Calif., September 1, 1976

ACS

SYMPOSIUM

SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D. C. 1977

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

51

Data

Library of Congress

Flavor quality, objective measurement. (ACS symposium series; 51 ISSN 0097-6156) Includes bibliographical references and index. 1. Food—Analysis—Congresses. 2. Flavor—Congresses. I. Scanlan, Richard Α., 1937. II. American Chem ical Society. Division of Agricultural and Food Chemis try. III. Series: American Chemical Society. ACS sym posium series; 51. TX545.F53 ISBN 0-8412-0378-4

Copyright ©

664'.07 ACSMC8

77-8286 51 1-118

1977

A m e r i c a n Chemical Society All Rights Reserved. N o part of this book may be reproduced or transmitted i n any form or by any means—graphic, electronic, i n c l u d i n g photo copying, recording, taping, or information storage and retrieval systems—without written permission from the A m e r i c a n C h e m i c a l Society. PRINTED IN T H E UNITED STATES O F AMERICA

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

ACS Symposium Series Robert F. G o u l d , Editor

Advisory Donald G. Crosby Jeremiah P. Freeman E. Desmond Goddard Robert A. Hofstader John L. Margrave Nina I. McClelland John B. Pfeiffer Joseph V. Rodricks Alan C. Sartorelli Raymond B. Seymour Roy L. Whistler Aaron Wold

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

FOREWORD The A C S S Y M P O S I U

a m e d i u m for p u b l i s h i n g symposia q u i c k l y i n book form. T h e f o r m a t of the S E R I E S p a r a l l e l s that of its predecessor, A D V A N C E S IN CHEMISTRY

S E R I E S , except that i n o r d e r to save t i m e the

p a p e r s are n o t typeset b u t are r e p r o d u c e d as t h e y a r e s u b m i t t e d b y the authors i n c a m e r a - r e a d y

form.

A s a further

means of s a v i n g t i m e , the p a p e r s are n o t e d i t e d o r r e v i e w e d except b y t h e s y m p o s i u m c h a i r m a n , w h o becomes t h e book.

e d i t o r of

Papers p u b l i s h e d i n the A C S S Y M P O S I U M

SERIES

are o r i g i n a l c o n t r i b u t i o n s n o t p u b l i s h e d elsewhere i n w h o l e or major p a r t a n d i n c l u d e reports of r e s e a r c h as w e l l as r e v i e w s since s y m p o s i a m a y e m b r a c e b o t h types of p r e s e n t a t i o n .

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PREFACE Λ Λ ν β Γ the past 15 years w e h a v e w i t n e s s e d r e m a r k a b l e a d v a n c e m e n t s i n areas r e l a t i n g to objective m e a s u r e m e n t of flavor q u a l i t y . A l o o k at several of the a n a l y t i c a l t e c h n i q u e s u s e d t o d a y i n

flavor

research

p r o v i d e s examples of this. T h e c o m m o n use of glass c a p i l l a r y gas c h r o m a t o g r a p h i c c o l u m n s a n d h i g h pressure l i q u i d c h r o m a t o g r a p h i c systems a l l o w s s e p a r a t i o n of l a b i l e c o m p o u n d s w h i c h w e r e v i r t u a l l y i m p o s s i b l e to separate several years ago c a r r i e r gas separators has analysis m u c h m o r e efficient.

U s e of c o m p u t e r s w i t h mass spectrometers

a n d other i n s t r u m e n t s has i n c r e a s e d o u r a b i l i t y to m a k e correct s t r u c t u r a l assignments. T h e s e advances h a v e b e e n e x t r e m e l y h e l p f u l , a n d u n d o u b t e d l y w e c o u l d also p o i n t to s i m i l a r advances i n sensory e v a l u a t i o n , i n s t a t i s t i c a l a p p l i c a t i o n s , a n d i n other areas r e l a t i n g to m e a s u r e m e n t of flavor q u a l i t y . P e r h a p s at this p o i n t w e s h o u l d r e m i n d ourselves that flavor is the sensa t i o n p e r c e i v e d w h e n one takes f o o d or b e v e r a g e i n t o t h e m o u t h .

Ulti

m a t e l y it is this sensation w h i c h w e attempt to define a n d measure, a n d w e u s u a l l y t r y to d o so b y m e a s u r i n g those t h i n g s i n the f o o d w h i c h effect, or are r e s p o n s i b l e for, the

flavor

sensation. H o w successful are

w e ? W h a t t y p e of p r o b l e m s do w e encounter, a n d w h a t t y p e of r e s e a r c h w i l l b e necessary to solve these p r o b l e m s ? T h e p a p e r s i n this s y m p o s i u m o n objective m e a s u r e m e n t of flavor q u a l i t y p r o v i d e i n f o r m a t i o n h e l p f u l to the s o l u t i o n of these questions. RICHARD A. SCANLAN

D e p a r t m e n t of F o o d a n d S c i e n c e a n d T e c h n o l o g y O r e g o n State U n i v e r s i t y C o r v a l l i s , OR 97331 March

25, 1977

ix

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1 Objective Measurements of Flavor Quality: General Approaches, Problems, Pitfalls, and Accomplishments WALTER G. JENNINGS Department of Food Science and Technology, University of California, Davis, CA 95616

After I had accepte paper for this series, and for very good reasons. First, I can think of a number of individuals who beyond any doubt are better qualified to discuss this multi-disciplinary area than I am, and second, the title itself is enough to flash a warning light. While the complexity of this attribute we call "flavor" has been stressed by several workers (e.g. 1), Moncrief (2) argued that taste and odor are the major components. Certainly i t is generally agreed that flavor requires the participation of sensory receptors, which makes it an individual, and at least within certain limits, a variable characteristic. Because of this, flavor is necessarily a highly subjective trait. Rereading my title, I find that I'm committed to discussing objective measurements of a subjective characteristic and my first thought is, "I'm in trouble." But as long as we recognize this contradiction and are willing to accept a degree of compromise, hopefully we can make some progress. An early quest for an objective measurement of quality has been cited from the 13th and 14th centuries, when "ale conners" or "ale tasters" in England were assigned the task of setting the price on batches of brew based on their individual flavor judgments. In an effort to achieve a greater degree of objectivity, this was combined with a test of the ale strength: some of the ale was poured on a bench, and the ale Conner sat in i t . After a predetermined interval, "he made to stand up"; i f his leather breeches stuck to the bench, the ale was of the right quality (3). To most of us, an "objective measurement of flavor quality" means establishing a chemical or physical method for measuring the amount of a substance responsible for a particular flavor attribute. This requires first establishing which compound or compounds are responsible for a particular attribute, which has been done in relatively few instances, at least in complex mixtures. The problem is further complicated by the fact that synergism and antagonism can exist between compounds that elicit flavor responses. In many cases, flavor is due to an integrated 1 In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

response to at l e a s t several compounds, and as we change the r e l a t i v e r a t i o s and/or absolute amounts of these compounds, the f l a v o r responses change i n a manner t h a t i s u s u a l l y u n p r e d i c t a b l e . Moskowitz (4) argued t h a t the a c t i v i t i e s of the f l a v o r chemist, who i s u s u a l l y concerned w i t h e s t a b l i s h i n g the c o n t r i b u t i o n of i n d i v i d u a l components to f l a v o r , diverge from but are complement a r y to psychometric e f f o r t s concerned w i t h the q u a l i t y of f l a v o r mixtures. Two general approaches have been u t i l i z e d i n attempts to o b t a i n o b j e c t i v e measurements of f l a v o r q u a l i t y . One has been concerned with the measurement or r e c o r d i n g of the minute e l e c t r i c a l response of o l f a c t o r y or t a s t e c e l l s e l i c i t e d by odor or t a s t e s t i m u l i (e.g. 5_, 6 ) , but a great deal of work remains to be done i n t h i s a r e a . Another widely used approach has involved s n i f f i n g the o u t l e t of problems are immediatel response to a mixture of compounds, and the gas chromatograph provides a d i f f e r e n t i a l r a t h e r than an i n t e g r a t e d response to those compounds. Secondly, i t can be most d i s t u r b i n g when the panel reports t h a t i n t e r e s t i n g odors e x i s t between the peaks (e.g. 8 , 9) which emphasizes the f a c t t h a t f o r some substances, the gas cïïromatograph has not y e t matched the s e n s i t i v i t y of the human nose. Even s o , useful r e s u l t s can be obtained by t h i s r o u t e . B a r y l k o - P i k i e l n a et a l . (10) s p l i t the e f f l u e n t from a gas c h r o matographic column to a s s i g n q u a l i t a t i v e odor assessments to the i n d i v i d u a l peaks of a sugar-amino a c i d r e a c t i o n m i x t u r e . McLeod and Coppock (TJJ used a s i m i l a r technique to a s s i g n odor e v a l u a t i o n s to f r a c t i o n s from b o i l i n g beef. A number of workers i n t e r ested i n c o r r e l a t i n g t h e i r a n a l y t i c a l r e s u l t s w i t h sensory response have a l s o used the odors of i n d i v i d u a l peaks, sometimes to good advantage (vide i n f r a ) . Tucknott and W i l l i a m s (12) pointed out t h a t s n i f f i n g the e f f l u e n t from a gas chromatograph s u f f e r s from a number of other shortcomings, and suggested t h a t the e f f l u e n t gas c o n t a i n i n g peaks of i n t e r e s t be trapped i n i n d i v i d u a l d i s p o s a b l e syringes f o r subsequent odor assessment. Clark and Cronin (13) u t i l i z e d a novel method; peaks were trapped i n short s e c t i o n s of support coated open t u b u l a r (SCOT) g l a s s columns, which were then crushed under water to produce a s o l u t i o n f o r sensory a n a l y s i s . Parliment (14) bubbled the gas chromatographic e f f l u e n t i n t o water to prepare s o l u t i o n s f o r t a s t e - t e s t i n g , which he reported was i n some cases more s a t i s f a c t o r y than s n i f f - t e s t i n g . When we r e s o r t to gas chromatography, we have of course r e s t r i c t e d our o b j e c t i v e measurements to v o l a t i l e compounds; i t i s a l l too easy to f o r g e t t h a t t a s t e i s a l s o a major c o n t r i b u t o r to f l a v o r (1). Weiss and S c h a l l e r (T5_, 16) s t u d i e d the i n f l u e n c e of several v a r i a b l e s - - e . g . t i t r a t a b l e a c i d i t y , pH, d i s s o l v e d gases-on the sensory p r o p e r t i e s of apple j u i c e ; a number of such s t u d i e s

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1.

JENNINGS

Approaches,

Problems,

Pitfalls,

and

Accomplishments

3

on other products have been p u b l i s h e d . R e c e n t l y , Noble (17) used gel chromatography to f r a c t i o n a t e f l a v o r components of tomato. Another major problem i s o b t a i n i n g gas chromatographic r e s u l t s t h a t r e f l e c t with high q u a l i t a t i v e and q u a n t i t a t i v e f i d e l i t y the v o l a t i l e composition of the m a t e r i a l i n q u e s t i o n . Compositional changes are f r e q u e n t l y caused i n the p r e p a r a t i o n of a sample s u i t a b l e f o r gas chromatography, and a d d i t i o n a l e r r o r s may be introduced by the gas chromatographic a n a l y s i s i t s e l f . Many m a t e r i a l s r e q u i r e some type of treatment to f r e e the compounds of i n t e r e s t from m a t e r i a l s t h a t would otherwise i n t e r fere w i t h the a n a l y s i s (e.g. water and n o n - v o l a t i l e components) before the sample can be i n j e c t e d i n t o the gas chromatograph. A l s o , some type of c o n c e n t r a t i o n i s f r e q u e n t l y r e q u i r e d so t h a t the l i m i t e d amount of sampl able q u a n t i t i e s of the compounds to be s t u d i e d . Most o f the procedures t h a t are used to achieve these ends i n v o l v e d i s t i l l a t i o n , e x t r a c t i o n and/or e v a p o r a t i o n , or a d s o r p t i o n , a l l of which cause q u a n t i t a t i v e changes and some of which may engender q u a l i t a t i v e changes i n the concentrated sample, so that i t no longer r e f l e c t s the composition of the s t a r t i n g m a t e r i a l . In e f f o r t s to surmount these d i f f i c u l t i e s , many i n v e s t i g a t o r s p r e f e r to use d i r e c t i n j e c t i o n s of headspace gas f o r a n a l y s i s , but the chromatogram i s then r e s t r i c t e d to those components whose p a r t i a l pressures are r e l a t i v e l y h i g h . A great deal of a t t e n t i o n has been given to the use of porous polymers i n c o n c e n t r a t i n g headspace v o l a t i l e s by l e s s strenuous means ( e . g . 1J3, 19^, 20). Sample p r e p a r a t i o n remains a c r i t i c a l l y important a r e a , and forms the subject of another symposium at t h i s meeting. Another source of problems l i e s i n the gas chromatographic a n a l y s i s i t s e l f ; not a l l compounds are s t a b l e to the c o n d i t i o n s of the a n a l y s i s , and the chromatogram may not a c c u r a t e l y r e f l e c t the composition of the m a t e r i a l i n j e c t e d . A d d i t i o n a l l y , minor components t h a t are not w e l l resolved from l a r g e r c o n s t i t u e n t s may be of c r i t i c a l importance to a given f l a v o r a t t r i b u t e , but unless these are unambiguously separated from the other compon e n t s , we are f r e q u e n t l y not even aware of t h e i r e x i s t e n c e i n the sample. Recent developments i n w a l l - c o a t e d open t u b u l a r g l a s s c a p i l l a r y columns (WCOT: 21^, 22, 23) make i t p o s s i b l e to r e s o l v e many of these p r e v i o u s l y poorly separated components. A d d i t i o n a l l y , the more i n e r t c h a r a c t e r of the g l a s s columns has permitted a n a l y s i s of some c o n s t i t u e n t s (notably s u l f u r - c o n t a i n i n g compounds) t h a t are almost s u r e l y of great importance to some f l a v o r s and which have r e s i s t e d packed-column or m e t a l - c a p i l l a r y a n a l y s i s (e.g. 24, 25, 26). Glass i n l e t s p l i t t e r s of much higher l i n e a r i t y (27, 2 8 ) , when combined w i t h the open t u b u l a r g l a s s c a p i l l a r y column, are capable of producing chromatograms t h a t r e f l e c t much more a c c u r a t e l y the composition of the i n j e c t e d sample.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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FLAVOR QUALITY:

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MEASUREMENT

U n f o r t u n a t e l y , column e f f i c i e n c y - - ! . e . the inherent power to separate the components of a m i x t u r e - - i s i n v e r s e l y p r o p o r t i o n a l to column c a p a c i t y . The maximum t h e o r e t i c a l e f f i c i e n c y of WCOT columns, expressed i n t h e o r e t i c a l p l a t e s per meter, i s a p p r o x i mately 1000/r, where r i s the inner column radius i n mm (29). A compromise i s a l s o u s u a l l y necessary i n the thickness of the f i l m of l i q u i d phase, as columns with t h i n n e r f i l m s have higher e f f i c i e n c i e s but impose severe l i m i t a t i o n s on sample c a p a c i t y , and columns w i t h t h i c k e r f i l m s possess higher c a p a c i t i e s at the expense of column e f f i c i e n c y (e.g. 2£, 30). While the lower c a p a c i t i e s of small diameter (e.g. 0.25 mm) WCOT columns are s t i l l s u f f i c i e n t f o r a p p l i c a t i o n s such as gas chromatographymass spectrometry, t h e i r use f o r the sensory a n a l y s i s of i n d i v i dual f r a c t i o n s poses very d i f f i c u l t problems. Some i n v e s t i g a t o r s have compromised on l a r g e or columns whose roughene SCOT columns) increase the surface area of the l i q u i d phase (e.g. 33, 34). Because of t h i s c a p a c i t y requirement, there remains a use and a need for packed columns. I t i s , however, c r i t i c a l l y important to d u p l i c a t e the a n a l y s i s on a high r e s o l u t i o n system, so the i n v e s t i g a t o r i s not misled by peaks that may play a c r u c i a l r o l e i n the sensory q u a l i t i e s and that are not w e l l resolved on the lower r e s o l u t i o n high c a p a c i t y system. The i n v e s t i g a t o r must a l s o f r e q u e n t l y compromise i n s e l e c t i n g gas chromatographic parameters, balancing the degree of separation d e s i r e d against the length of time required f o r the a n a l y s i s , and, f o r t h e r m a l l y l a b i l e m a t e r i a l s , the amount of heat to which the samples are exposed (35). A t t e n t i o n must a l s o be given to the s u i t a b i l i t y of the system f o r the separation of the components of a given m i x t u r e . Once the problems of sample preparation and sample a n a l y s i s are overcome, one has at best a w e l l - r e s o l v e d chromatogram, w i t h out overlapping or co-chromatographing components, which may q u a l i t a t i v e l y and q u a n t i t a t i v e l y r e f l e c t the composition of the o r i g i n a l m a t e r i a l . I t cannot be overemphasized t h a t even t h i s i s r a r e l y achieved. S t i l l to be reckoned w i t h are the myriad problems and sources of e r r o r inherent i n the sensory t e s t i n g procedures. Most of us would now agree that i t i s not s u f f i c i e n t f o r the chemist, untrained i n sensory a n a l y s i s , to c a s u a l l y s n i f f the o u t l e t of h i s gas chromatograph and record h i s impressions. Sensory a n a l y s i s , t o o , has come a long way, and a meaningful study should use s e l e c t e d panels of t r a i n e d personnel u t i l i z i n g q u a n t i t a t i v e procedures amenable to s t a t i s t i c a l e v a l u a t i o n . Martin (36) described procedures used i n the s e l e c t i o n and t r a i n i n g of p a n e l i s t s f o r various types of sensory e v a l u a t i o n s . Larmond (37) emphasized the importance of c o n t r o l l i n g p h y s i c a l s t i m u l i to which the p a n e l i s t s are subjected. Best (38) described the a n a l y s i s of t a s t e - t e s t d a t a , and H a r r i e s (39) reviewed the c o m p l e x i t i e s of sensory assessment. Stone et a l .

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1.

JENNINGS

Approaches,

Problems,

Pitfalls,

and

Accomplishments

5

(40) described a sensory e v a l u a t i o n technique termed " q u a n t i t a t i v e d e s c r i p t i v e a n a l y s i s " which uses an i n t e r v a l s c a l e and a panel of at l e a s t s i x t r a i n e d p a n e l i s t s , and Moskowitz (41_) has argued f o r a method he terms "magnitude e s t i m a t i o n " , i n which numbers are assigned to s t i m u l i so t h a t the r a t i o s of judgments r e f l e c t sensory r a t i o s . Taking a l l of these f a c t o r s i n t o account--changes engendered by sample p r e p a r a t i o n ; poor s e p a r a t i o n , a r t i f a c t s and e r r o r s i n the gas chromatographic a n a l y s i s ; s i n s of omission and s i n s of commission i n the sensory a n a l y s i s - - t h e i n v e s t i g a t o r may f i n a l l y be i n a p o s i t i o n to t r y and r e l a t e v a r i a t i o n s i n the sensory p r o p e r t i e s to v a r i a t i o n s i n the chromatographic p a t t e r n . Here a g a i n , however, r e s u l t s can be o v e r - i n t e r p r e t e d . Szczesniak (42) and Persson et a l . (43^, 44) both emphasize t h a t even a s i g n i f i c a n t c o r r e l a t i o n betwee r a t i n g e s t a b l i s h e s only a p r e d i c t i v e r e l a t i o n s h i p , not a causal one. Two general approaches, which are not n e c e s s a r i l y mutually e x c l u s i v e , have been used i n attempts to c o r r e l a t e the a n a l y t i cal data with sensory a t t r i b u t e s . One has involved attempts to e s t a b l i s h the q u a l i t a t i v e and/or q u a n t i t a t i v e f l a v o r p r o p e r t i e s of i n d i v i d u a l compounds, sometimes with a t t e n t i o n to the synergism or antagonism t h a t they e x h i b i t i n mixtures w i t h other compounds, or i n one s o l v e n t as opposed to another. Meilgaard (45, 46) and Clapperton e t a l . (47) have accumulated a l a r g e amount of information on the f l a v o r c h a r a c t e r i s i t i c s and t h r e s h o l d values of aroma v o l a t i l e s i n beer. As emphasized by these workers, the odor p u r i t y of the compounds t e s t e d i s c r i t i c a l l y important to t h i s type of study. They p o i n t o u t , as one example, that Murahashi (48) reported l - o c t e n - 3 - o l as possessing a mushroom aroma, w h i l e Hoffmann (49) a s c r i b e d the odor to 1,3dioxalans formed on decomposition of the a l c o h o l . L a t e r Meilgaard (46) found t h a t the odor i n question was due to contamination by l - o c t e n - 3 - o n e , which had a m e t a l l i c aroma i n f a t s o l u t i o n s , and a mushroom aroma i n aqueous medium; the p u r i f i e d alcohol had an odor he reported as " s p i c y , perfumed and g r a s s l i k e . " S i m i l a r l y , Boelens et a l . (50), who i d e n t i f i e d a large number of compounds i n onion o i l , suggested t h a t 2 , 4 - d i m e t h y l thiophene and 3,4-dimenthythiophene possessed an odor of f r i e d onions. R e c e n t l y , G a l e t t o and Hoffman (5>1) synthesized these compounds, and reported t h a t alone or i n combination w i t h other compounds they d i d not make a s i g n i f i c a n t c o n t r i b u t i o n to the f r i e d onion aroma. The other major approach has involved attempts to c o r r e l a t e f l a v o r w i t h gas chromatographic p a t t e r n s . Guadagni et a l . worked on such c o r r e l a t i o n s f o r apple (7); these and other e f f o r t s have been reviewed by Powers (52), ASTM (53, 54) and von Sydow (55); a d d i t i o n a l e f f o r t s i n c l u d e those of Salo et a l . (56) and Salo (57).

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

Bednarczyk and Kramer (58) reported that four gas chromato graphic peaks accounted f o r 85% of a sensory p a n e l ' s f l a v o r response to ginger e s s e n t i a l o i l . C i t e d as prime c o n t r i b u t o r s to the c h a r a c t e r i s t i c ginger a t t r i b u t e were 3-sesquiphellandrene and ar-curcumene; α t e r p i n e o l and c i t r a l s c o n t r i b u t e d a lemony a t t r i b u t e , and an undesirable woody or soapy note was caused by nerolidol. Using l i n e a r r e g r e s s i o n a n a l y s i s , Fore et a l . (59) found a high c o r r e l a t i o n between the f l a v o r score of stored peanut b u t t e r and the r a t i o between 2-methyl propanal and hexanal as d e t e r mined gas chromatographically. Dravnieks et a l . (60.) used stepwise d i s c r i m i n a t e a n a l y s i s to c l a s s i f y , by gas chromato graphic techniques, the odor of c o r n . G a l e t t o and Bednarczyk (61) used m u l t i p l e r e g r e s s i o n techniques i n e s t a b l i s h i n g t h a t the amount of methyl propy d i p r o p y l t r i s u l f i d e as determined gas chromatographically showed a high degree of c o r r e l a t i o n w i t h o v e r a l l onion f l a v o r . Tassan and R u s s e l l (62) used a micro olfactometer to evaluate the odors of i n d i v i d u a l cumin c o n s t i t u e n t s trapped from a gas chromato graph, and reported that v a r i a t i o n s i n four aldehydes i n f l u e n c e d the main odor c h a r a c t e r ; 3-p-menthen-7-al was shown to be necessary f o r the c h a r a c t e r i s t i c odor of heated cumin. Karlsson-Ekstrom and von Sydow (63) using a p s y c h o p h y s i c a l s t a t i s t i c a l approach, found t h a t the sensory changes that occur when black c u r r a n t s are heated could be w e l l c o r r e l a t e d w i t h a decrease i n monoterpene hydrocarbons and an increase i n dimethyl s u l f i d e and a l i p h a t i c aldehydes. Persson and von Sydow (640 examined the sum, d i f f e r e n c e s , r a t i o s , geometric means and v e c t o r i a l sums of peaks from gas chromatographic analyses for t h e i r c o r r e l a t i o n w i t h f l a v o r scores of frozen and r e f r i g e r a t e d cooked s l i c e d beef. A number of d i f f e r e n t models i n v o l v i n g both sensory response and gas chromatographic data e x h i b i t e d high c o e f f i c i e n t s of c o r r e l a t i o n . Studies on canned beef (43) e s t a b l i s h e d that a high degree of c o r r e l a t i o n e x i s t e d between 15 odor p r o p e r t i e s and four gas chromatographic peak combinations. In l a t e r work the methods were extended to a v a r i e t y of meat products and found to hold true (44). Akesson et a l . (65) used headspace sampling techniques and open t u b u l a r gas chromatography combined with a f l a v o r p r o f i l e technique to see i f sensory p r o p e r t i e s and preference values f o r a v a r i e t y of food m a t e r i a l s could be p r e d i c t e d by gas chromato graphic d a t a . T e s t i n g a large number of models t h a t used gas chromatographic peak areas i n various combinations and i n several types of f u n c t i o n s , they found that the assessment of sensory q u a l i t i e s was r e l a t e d monotonicly to gas chromatographic d a t a , w h i l e estimated preference values were i n most cases r e l a t e d i n a more complex non-mototonic way. Using the proper models, very accurate p r e d i c t i o n s could be made. Von Sydow (66)

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1.

JENNINGS

Approaches,

Problems,

Pitfalls,

and

Accomplishments

7

g e n e r a l i z e d t h a t a l l compounds present above t h r e s h o l d l e v e l s c o n t r i b u t e to the aroma of foods, and t h a t the number of important aroma c o n t r i b u t o r s i s v a r i a b l e , but i s u s u a l l y high i n t h e r m a l l y processed foods or foods of animal o r i g i n . He emphas i z e d t h a t the instrumental technique must be g e n t l e , so that the sample i n v e s t i g a t e d represents the true s i t u a t i o n i n the food, and that the sensory technique must be d e t a i l e d and s e n s i t i v e . The development of numerical and psychophysical models capable of r e l a t i n g the physicochemical data with the sensory data i s crucial. I t would appear t h a t we may f i n a l l y have a r r i v e d at a p o i n t where we have the opportunity to combine improved methods of sample p r e p a r a t i o n , gas chromatographic s e p a r a t i o n , sensory a n a l y s i s and computerized data a n a l y s i s to achieve some r e a l i s t i c r e s u l t s i n the search f o q u a l i t y i n at l e a s t som depend to a large degree on how w e l l we combine advances i n sample preparation w i t h high r e s o l u t i o n gas chromatography, v a l i d sensory procedures and advanced methods of data a n a l y s i s . This r e q u i r e s judgments and e v a l u a t i o n s on the part of the investigator. No s i n g l e sample preparation procedure can be accepted as uniformly s a t i s f a c t o r y ; one or another may be s u p e r i or depending on the sample composition and the compounds of interest. Gas chromatographic parameters must be s e l e c t e d c a r e f u l l y , w i t h a t t e n t i o n to the sample c o m p o s i t i o n , i t s s t a b i l i t y under the c o n d i t i o n s of a n a l y s i s and whether one's immediate goal i s r e s o l u t i o n or c a p a c i t y . Neither are a l l procedures f o r sensory or data a n a l y s i s — i n c l u d i n g those c i t e d i n t h i s p a p e r - - e q u a l l y v a l i d under a l l circumstances, nor are a l l of them acceptable to experts i n t h i s f i e l d (e.g. 4 0 , 41_, 5i8). And no degree of s o p h i s t i c a t e d computer a n a l y s i s can compensate f o r c a r e l e s s sensory procedures, or f o r an incompletely resolved chromatogram i n which peaks of sensory importance have f a i l e d to separate. But we do now have increased c a p a b i l i t y i n a l l of these a r e a s , and the next few years should see some e x c i t i n g results. I would l i k e to conclude by thanking several c l o s e f r i e n d s , e s p e c i a l l y E r i k von Sydow, Morten M e i l g a a r d , Rose Marie Pangborn and Gerry R u s s e l l f o r t h e i r help i n preparing t h i s i n f o r m a t i o n . There are of course many other i n v e s t i g a t i o n s which could and perhaps should have been included i n t h i s p r e s e n t a t i o n . I can only apologize f o r such o m i s s i o n s , but i n a very short time the data I have presented w i l l be l a r g e l y o b s o l e t e , as the papers that f o l l o w t h i s b r i e f i n t r o d u c t i o n extend our e f f o r t s and knowledge i n t h i s very important a r e a .

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8

flavor quality: objective measurement

Literature Cited 1. Amerine, Μ. Α., Pangborn, R. Μ., Roessler, Ε. B. "Principles of Sensory Evaluation of Food", page 3. Academic Press New York, London, 1965 2. Moncrief, R. W. in "The Chemistry and Physiology of Flavors", 3rd Edit., page 650. Avi Publishing, Westport, Conn. 1967 3. Corran, H. S. "A History of Brewing", page 40. Davis and Charles, London, 1975 4. Moskowitz, H. R. Lebensmittel Wissenshaft-Technologie (1975) 8, 237 5. Boeckh, J. in "Geruch und Geschmackstoffe", pages 1-18. Hans Karl, Nurenberg, Germany, 1975 6. Getchell, T. V. and Getchell, M. L. Ann. New York Acad. Sci. (1974) 237, 7. Guadagni, D. G., Okano Technol., (1966) 20, 518 8. Jennings, W. G. Lebensmittel Wissenschaft-Technologie (1969) 2, 75 9. Jennings, W. G. Food Technol. (1972) 26, 25 10. Barylko-Pikielna, N., Daniewski, M. and Mielniczuk, Z. Die Nahrung (1974) 18, 125 11. MacLeod, G. and Coppock, B. M. J. Agr. Food Chem. (1976) 24, 835 12. Tucknott, O. G. and Williams, A. A. Chem. and Ind. (1974) No. 19, 784 13. Clark, R. G. and Cronin, D. A. J. Sci. Food Agric. (1975) 26, 1009 14. Parliment, T. H. Chem. and Ind. (1976) No. 9, 418 15. Weiss, J., Schaller, A. Confructa (1970 a) 15, 93 16. Weiss, J., Schaller, A. Confructa (1970 b) 15, 140 17. Noble, A. C. J. Agr. and Food Chem. (1976) 24, 321 18. Dravnieks, Α., Krotoszynski, Β. Κ., Whitfield, J., O'Donnell, A. and Burgwald, T. Environ. Sci. Technol. (1971) 5, 1220 19. Jennings, W. G., Wohleb, R. and Lewis, M. J. J. Food Sci. (1972) 37, 69 20. Jennings, W. G., Wohleb, R. H. and Lewis, M. J. M.B.A.A. Tech. Quarterly (1974) 11, 104 21. Jennings, W. G., Wohleb, R. H. Chemie, Mikrobiol. Tech. der Lebensmittel (1974) 3, 33 22. Jennings, W. G., Yabumoto, Κ., Wohleb, R. H. J. Chromatogr. Sci. (1974) 12, 344 23. Jennings, W. G. Chromatographia (1975) 8, 690 24. Whithycombe, D. Α., Walradt, J. P. Paper 13, 170th ACS National Meeting, Chicago, Ill. Aug. 25-29, 1975 25. Shibamoto, T. and Russell, G. F. J. Agr. Food Chem. (1976), 24, 843 26. Buttery, R. G., Guadagni, D. G., Ling, L. C., Seifert, R. M. and Lipton, W. J. Agr. Food Chem. (1976) 24, 829

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1. jennings

Approaches, Problems, Pitfalh, and Accomplishments

9

27. Jennings, W. G. J. Chromatog. S c i . (1975) 13, 185 28. Jennings, W. G. Food Chem. (1977) (in press) 29. Kaiser, R. "Chromatographie in der Gasphase", vol. 2, 3rd E d i t . : page 72. Bibliographisches Institut Mannheim, 1975 30. Ettre, L. S. "Open Tubular Columns in Gas Chromatography", page 15, Plenum Press, 1965 31. Verzele, Μ., Verstappe, Μ., Sandra, P . , van Luchene, E. and Vuye, A. J. Chromatogr. S c i . (1972) 10, 668 32. Roeraade, J. Chromatographia (1975) 8, 511 33. Cronin, D. A. J. Chromatog. (1970) 48, 406 34. Schieke, J. D . , Comins, N. R. and Pretorius, V. J. Chroma tog. (1975) 115, 373 35. Jennings, W. G. and Adam, S. Anal. Biochem. (1975) 69, 61 36. Martin, S. L. Foo 37. Larmond, E. Food 38. Best, D. J. Food Technol. in Australia (1974) 26, 20 39. Harries, J. M. J. S c i . Food Agr. (1973) 24, 1571 40. Stone, Η . , Sidel, J., Oliver, S . , Woolsey, A. and Singleton, R. C. Food Technol. (1974) 28 (11) 24 41. Moskowitz, H. R. Food Technol. (1974) 28 (11), 16 42. Szczesniak, A. S. Food Technol. (1968) 22, 981 43. Persson, T., von Sydow, E., Åkesson, C. J. Food S c i . (1973) 38, 682 44. Persson, T. and von Sydow, E. J. Food S c i . (1974) 39, 537 45. Meilgaard, M. C. M.B.A.A. Tech. Quarterly (1975) 12, 107 46. Meilgaard, M. C. M.B.A.A. Tech. Quarterly (1975) 12, 151 47. Clapperton, J. F., Dalgliesh, C. E. and Meilgaard, M. C. M.B.A.A. Tech. Quarterly (1976) (in press) 48. Murahashi, S. S c i . Papers Inst. Phys. Chem. Res. (Tokyo) (1938) 34, 155 cf. Chem. Abst. 32, 37556 49. Hoffmann, G. "Lipids and their Oxidation", page 224, Schultz, H. W. e d . , Avi Publishing, Westport, Conn. 1962 50. Boelens, M . , de Valois, P. J., Wobben, H. J., Van den Gen, A. J. Agr. Food Chem. (1971) 19, 984 51. Galetto, W. G. and Hoffman, P. G. J. Agr. Food Chem. (1976) 24, 852 52. Powers, J. J. Food Technol. (1968) 22, 383 53. ASTM. "Correlation of Subjective-Objective Methods in the Study of Odor and Taste". Spec. Tech. Pub. #440. 1968 54. ASTM. "Reviews of Correlations of Objective-Subjective Methods in the Study of Odor and Taste". Spec. Tech. Pub. #451. 1969 55. von Sydow, E. Food Technol. (1971 ) 25, 40 56. Salo, P. Lebensmittel Wissenschaft-Technologie (1973) 6, 52 57. Salo, P . , Nykanen, L., Soumalainen, H. J. Food S c i . (1972) 37, 394 58. Bednarczyk, A. A. and Kramer, A. Chem. Senses and Flavor (1975) 1, 377

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10

flavor quality: objective measurement

59. Fore, S. P . , Goldblatt, L. Α . , Dupuy, H. P. J . Amer. Peanut Res. Educ. Ass. (1972) 4, 177 60. Dravnieks, Α . , Reilich, H. G . , Whitfield, J. J . Food S c i . (1973) 38, 34 61. Galetto, W. G. and Bednarczyk, A. A. J . Food S c i . (1975) 40, 1165 62. Tassan, C. G. and Russell, G. F. J . Food S c i . (1975) 40, 1185 63. Karlsson-Ekström, G. and von Sydow, E. Lebensmittel Wissenschaf-Technologie (1973) 6, 86 64. Persson, T . , von Sydow, E. J . Food S c i . (1972) 37, 234 65. Åkesson, C . , Persson, T. and von Sydow, E. (1976). Personal communication. To be published. 66. von Sydow, E. (1976). Personal communication. To be published.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

C o r r e l a t i o n of O d o r Intensities a n d V a p o r Pressures with

Structural Properties of O d o r a n t s

ANDREW DRAVNIEKS Odor Sciences Center, IIT Research Institute, Chicago, Ill. 60616

The relationship of perceived odor intensity to the concentration of odorants in headspace samples of various materials tends to follow a similar mathematical function but with different coefficients for different odorants. The task of obtaining experimental data for all compounds of interest would be overwhelming. It is desirable, therefore, to evolve procedures which would enable generalization and estimation of these coefficients from some molecular properties. (1,2) The most readily accessible properties are those derivable from the structural chemical formulas of the compounds. Attempts in this direction achieved some success (3) but were obtained for a relatively narrow selection of compounds. The present study expands odor data to include a more diversified selection of odorants. Furthermore, the properties derivable from the molecular structures were selected in such a way that they could be inventoried directly from inspection of the one-line Wiswesser notation formulas of compounds. Such formulas u t i l i z e specific symbols for certain structural charact e r i s t i c s of molecules (e.g., U for double bond, R for benzene ring, Q for hydroxyl group), and in principle permit their enumeration by computerized methods. Odor Intensity Measurements Concentration of odorants in headspace vapors of a flavorpossessing sample can be measured by appropriate analytical means. The intensity of the odor sensation experienced when smelling the sample can be derived from such data i f the dose-response r e l a tionship is known; dose is described by the types and concentrations of the odorants in the headspace, and response by the intensity of the resulting odor sensation. Three principal methods exist to describe how strong an odor is: 11

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

(1)

Magnitude e s t i m a t i o n : "Smell the odor and give a number or some other type of response ( f i n g e r span, length of a l i n e ) i n p r o p o r t i o n to the experienced odor i n t e n s i t y " . The choice of the numbers i s e i t h e r l e f t to the best judgement of the subject or may be "pegged", p r e s c r i b i n g that the i n t e n s i t y of another reference stimulus i s given some d e f i n i t e value, f r e q u e n t l y 10 (ten). The r e s u l t i n g numbers are p r o p o r t i o n a l to the perceived odor i n t e n s i t i e s . Figure 1 i l l u s t r a t e s r e s u l t s of the magnitude e s t i m a t i o n of two odorants at s e v e r a l a i r d i l u t i o n l e v e l s . (2) Category s c a l i n g : "Judging the i n t e n s i t y on a s c a l e of zero to f i v e (or some other f i x e d numerical s c a l e ) " . The r e s u l t ing numbers are not p r o p o r t i o n a l to the perceived odor i n t e n s i t y . Typicaïly7~an ô d ô " ô n e u n i t higher than another on 0-5 s c a l e i s a c t u a l l y perceived to be stronger by a f a c t o r of 3 or 4. (3) Reference s c a l e : "Compar a reference s c a l e c o n s i s t i n g of a s e r i e s of known concentrat i o n s of a s e l e c t e d odorant and i n d i c a t e the best i n t e n s i t y match". The magnitude estimate method gives the t r u e s t r e p r e s e n t a t i o n of the perceived i n t e n s i t y . The reference s c a l e method permits the e a s i e s t documentation and t r a n s f e r of information on the odor intensity. The f o l l o w i n g f u n c t i o n s approximately r e l a t e the magnitude of the perceived odor i n t e n s i t y S, category s c a l e number Ν and the odorant c o n c e n t r a t i o n C Ν = m log S

1.

s=

2.

The c o e f f i c i e n t s m and k depend on the choice of u n i t s f o r S; m, a l s o on the choice of u n i t s f o r the category s c a l e . In a d d i t i o n , k and η depend on the type of odorants. Equation 2, known as the psychophysical power f u n c t i o n (sometimes r e f e r r e d to as Stevens law) b e t t e r d e s c r i b e s the r e l a t i o n between odor i n t e n s i t y and odorant c o n c e n t r a t i o n f o r the great m a j o r i t y of odorants over a broad range of concentrations than the t r a d i t i o n a l WeberFechners law. For a few odorants, Equation 2 seems to hold true only over a c e r t a i n range or ranges of concentrations. Recently, a 1-butanol (n-butanol) reference s c a l e (4) has been e s t a b l i s h e d as a recommended p r a c t i c e , ASTM E544, f o r r e f e r encing odor i n t e n s i t y ("sample smells as strong as X ppm v o l / v o l of 1-butanol i n a i r " ) . F i g u r e 2 i l l u s t r a t e s one p h y s i c a l form of t h i s s c a l e . For n-butanol,

,0.66

3.

S = kC log

S = l o g k + 0.66

log C

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

DRAVNiEKs

Structural

Properties

of

Odorants

ο

RELATIVE VAPOR PRESSURE OF ODORANT ( SATURATED VAPOR=l )

Figure 1. Effect of dilution on odor intensity; obtained by magnitude estimation method

Figure 2. A form of vapor dilution olfactometer to serve as an ASTM 544 odor suprathresnold. Intensity referencing scale based on 1-butanol.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

Moskowitz, et a l (5) have proposed to d e f i n e the odor i n t e n s i t y of 250 ppm v o l / v o l of n-butanol i n a i r as 10. With C taken i n ppm ( v o l / v o l ) u n i t s , Equation 3 becomes: S = 0.261

C

0 , 6 6

4.

I t permits t r a n s l a t i o n of 1-butanol referenced values of i n t e n s i t y to a open-ended numerical s c a l e (both ends open) i n which the numbers are approximately p r o p o r t i o n a l to the perceived odor intensities. In such a s c a l e , odor i n t e n s i t i e s <1 approach per ception thresholds and occur at odor threshold concentration ranges of the r e s p e c t i v e odorants. R e l a t i o n s between the butanol, category, and S-value s c a l e s are i l l u s t r a t e d i n Figure 3. Measuring s e v e r a l concentrations of a sample odorant v s n-butanol s c a l e , convertin by Equation 4, and p l o t t i n one can obtain values of k and η ( p o s i t i o n ) ( s l o p e ) f o r the sample odorant. For odorants, η i s u s u a l l y i n the range of 0.2-0.8. When an odorant stimulus i s d e l i v e r e d f o r s m e l l i n g as a vapor d i l u t e d with a i r , the flow r a t e of t h i s mixture of constant odorant c o n c e n t r a t i o n becomes an a d d i t i o n a l v a r i a b l e . The ASTM E544 1-butanol s c a l e i s standardized to 160 ml/min a i r from glass n o z z l e s , c f . Figure 2. Figure 4 i l l u s t r a t e s how the odor i n t e n s i t y of the same 1-butanol vapor concentration i n a i r increases as the d e l i v e r y flow r a t e from a s n i f f i n g port i s changed. I t i s evident that f o r an e q u i t a b l e comparison of the a b i l i t i e s of d i f f e r e n t odorants to generate odor of c e r t a i n i n t e n s i t i e s , the comparison should be at i d e n t i c a l flow r a t e s . Dose-Response Parameters From Equation 2, the dose-response r e l a t i o n s h i p f o r odors can be c h a r a c t e r i z e d by a p l o t of l o g (response) vs. l o g (concentra t i o n ) , F i g u r e 5. l o g S = l o g k + η l o g (C)

5.

The slope i s represented by n, and the p o s i t i o n i s r e l a t e d to k. The odor threshold i s a s u b s i d i a r y parameter, s i g n i f y i n g the concentration at which the response S becomes i n d i s t i n c t at some selected s t a t i s t i c a l significance l e v e l . Because of the d i f f e r ence i n the s l o p e s , the odor i n t e n s i t y at the same m u l t i p l e of odor threshold concentration can be q u i t e d i f f e r e n t f o r d i f f e r e n t odorants. Thus, expressing the odor i n t e n s i t i e s i n terms of m u l t i p l e s of the odor threshold concentrations i s a proce dure which ignores d i f f e r e n c e s i n the slopes of dose/response functions. For example, an e a s i l y n o t i c e a b l e odor i n t e n s i t y f o r thiophenol i s at 100 to 1000 m u l t i p l e s of i t s odor threshold

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

DRAVNIEKS

Structural

oc

Properties

5= VERY

ζ

1,000

0 ζ

< h

Odorants

CATEGORIES:

10,000

<

-

STRONG

—

4= STRONG 3= EASILY

ιοο

NOTICEABLE

-

2 = FAINT

D m ι

ΙΟ

C Σ α.

1=JUST

-

PERCEPTIBLE

1

Figure

3.

Rehtions

50

4.

Change

between

100

STIMULUS

Figure

of

200

FLOWRATE,

various

odor intensity

500

1000

2000

scales

5000

10000

flowrate

from

ML/MIN

of odor intensity with stimulus a sniffing port

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

F L A V O R QUALITY: OBJECTIVE

16

MEASUREMENT

c o n c e n t r a t i o n , while f o r 2,4-hexadienal i t i s at 20 to 50 m u l t i p l e s of i t s own t h r e s h o l d . Patte, Etcheto, and L a f f o r t (6) have published a l i s t of slopes η f o r 110 compounds. A c a l c u l a t i o n from t h e i r t a b l e s i n d i c a t e d that the mean value of η i s 0.41, and the d i s p e r s i o n of the values f o r d i f f e r e n t odorants i s c h a r a c t e r i z e d by a standard d e v i a t i o n of 0,14. Thus, the estimated 95 percent of odorants have η values i n the range between 0.15 and 0.70, and most are between 0.25 and 0.55. Since the f l a v o r i n d u s t r y deals mostly with odors w e l l above t h e i r t h r e s h o l d s , parameters k and η may be more s u i t a b l e f o r c h a r a c t e r i z i n g the dose/response f u n c t i o n of an odorant that a s i n g l e value of t h r e s h o l d value which says nothing about the change i n the response with c o n c e n t r a t i o n . C h a r a c t e r i z a t i o n of Molecula A number of molecular or physico-chemically measurable prop^ e r t i e s of odorants have been considered and sometimes s u c c e s s f u l l y c o r r e l a t e d to some c h a r a c t e r i s t i c s of t h e i r odors:* a. Molecular volumes ( L a f f o r t ) b. Gas-chromatographic r e t e n t i o n volumes i n s e v e r a l types of s t a t i o n a r y p h a s e s ( L a f f o r t & Dravnieks) c. Hydrogen-bonding, e l e c t r o n acceptor/donor, e t c . p r o p e r t i e s d. A d s o r p t i v i t i e s at w a t e r / o i l i n t e r f a c e s (Davies) e. Molecular shapes and s i z e s (Amoore) f. R e l a t i v e arrangement of f u n c t i o n a l groups (Beets) g. S p e c t r a l , e.g., f a r i n f r a r e d and Raman c h a r a c t e r i s t i c s (Wright) h. B u i l d i n g blocks of molecules (Dravnieks). Each of these s e l e c t i o n s i s c o r r e l a t e d to others i n some way. Thus, s p e c t r a l c h a r a c t e r i s t i c s r e f l e c t types and arrangements of f u n c t i o n a l groups, GC p r o p e r t i e s are the r e s u l t of s i m i l a r f a c t o r s and molecular s i z e s , e t c . In some f l a v o r work, the i d e n t i t y of a compound may not be known, while i t s GC c h a r a c t e r i s t i c s can be measured. Here, the group under (b) i s u s e f u l . In many cases, the i d e n t i t y of the compound i s known from mass-spectrometric or i n f r a r e d data. The most u n i v e r s a l l y a v a i l a b l e p r o p e r t i e s are those that can be d i r e c t l y derived from s t r u c t u r a l formulas. Recently, Wiswesser o n e - l i n e chemical n o t a t i o n formulas (7) are coming more i n use f o r computerized storage of chemical i n f o r m a t i o n , such as on i n f r a r e d , mass-spectrometric, and odor threshold data.(8) These formulas r e f l e c t the s t r u c t u r e s by u t i l i z i n g a s e r i e s of symbols and formal l o g i c a l r u l e s , so that each compound has one unique sequence of symbols that can be c a r r i e d by a punched card and used to search * Names i n parentheses i n d i c a t e researchers that emphasized some s p e c i f i c e f f e c t s and r e f l e c t t h e i r work; Ann. N.Y. Acad. S c i . , V o l 116 (1964) and V o l 237 (1974).

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

DRAVNIEKS

Structural

Properties

of

17

Odorants

f o r v a r i o u s types of data on the same compound i n d i f f e r e n t data c o l l e c t i o n s . As an example, the formula f o r s k a t o l e i s : T56 BMJ D where T56 represents a h e t e r o c y c l i c r i n g with 5 or 6 atoms respec t i v e l y , BM i n d i c a t e s the presence of NH (=M group) i n one of the r i n g s i n a c e r t a i n p o s i t i o n represented by B, and D i n d i c a t e s a methyl group attached to the r i n g s t r u c t u r e i n a p o s i t i o n r e p r e sented by D. Wiswesser formulas provide an e x c e l l e n t base f o r scanning f o r the presence of c e r t a i n molecular s t r u c t u r a l c h a r a c t e r i s t i c s . Thus, i f c o r r e l a t i o n s can be found between such c h a r a c t e r i s t i c s and odors, i t should become p o s s i b l e to (1) f i r s t i n s p e c t the dat c o l l e c t i o n t f i n d i f experimental odor data already e x i s (2) i f not, to estimat probabl compound from the c o r r e l a t i o n s based on experimental data. S e l e c t i o n of Data Katz and T a l b e r t (9) have published data on odor i n t e n s i t i e s of warning agents, u s i n g category s c a l i n g on a 0 to 5 s c a l e . Con c e n t r a t i o n s to o b t a i n an i n t e n s i t y score of 3 (= e a s i l y n o t i c e able) were s e l e c t e d f o r c o r r e l a t i o n s f o r 52 compounds from t h e i r publication. In our own work, odors of 59 compounds l i s t e d i n Table I at d i f f e r e n t concentrations were rated v s . 1-butanol s c a l e , and the concentrations producing an i n t e n s i t y S == 5 (Equation 4) obtained by i n t e r p o l a t i o n . By a comparison of our and K a t z - T a l b e r t s data f o r some compounds, i t was estimated that t h e i r score of 3 was approximately equivalent to the odor i n t e n s i t y of ppm v o l / v o l Ι-butanoï i n a i r . Thus, c o n c e n t r a t i o n values to o b t a i n a p p r o x i mately i d e n t i c a l odor i n t e n s i t i e s f o r 107 (111 data p o i n t s s i n c e 4 substances were evaluated i n both s t u d i e s ) were a v a i l a b l e f o r correlation. A supplementary e f f o r t was a search f o r c o r r e l a t i o n s between vapor pressures and Wiswesser n o t a t i o n c h a r a c t e r i s t i c s . Very f r e q u e n t l y , data on vapor pressures of odorants are not a v a i l a b l e , so that i t i s impossible to estimate to what extent a ££turated vapor of an odorant need to be d i l u t e d to o b t a i n concentrations that would y i e l d s e l e c t e d odor i n t e n s i t y l e v e l . In these c o r r e l a t i o n s , vapor pressure data on 326 compounds were used and assembled from s e v e r a l sources (11,12). Halogen-containing organic compounds were not i n c l u d e d i n t h i s data base, s i n c e t h e i r f l a v o r s i g n i f i c a n c e i s low. f

Method of C o r r e l a t i o n F u n c t i o n a l groups may e x h i b i t a d i f f e r e n t i n f l u e n c e on the

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

18

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

Table I. Concentrations of Vapors i n A i r , PPM V o l / V o l , to Produce Odor I n t e n s i t y Equivalent to 87 PPM (Vol/Vol) of 1-Butanol (S=5)* 12% (PPM) Katz-Talbert This work Compound G

Acetone Acetonitrile Acetophenone Allylalcohol Benzaldehyde Benzene Butanoic a c i d 2- Butanone Butylbutanoate Butylether Carbon t e t r a c h l o r i d e Chlorobenzene Chloroform Cineole Citral Cyclohexane 1,2-Dichloroethane Dimethylbenzylcarbinol 2,4-Dimethylpentane 1,4-Dioxane Ethanol Ethylbutanoate Eugenol Guaiacol Hexanoic a c i d 1-Hexanal 1- Hexanol 3- Hexanol 2- Hexanone Indole 1-Iodobutane d-Limonen e Linalool

3.55 3.73 -1.19 1.46 (=29 PPM) 0.49 (=3 PPM) 2.97

1.56 (=36 PPM) 1.08 (=12 PPM)

1,01 1.03 3.84 0.98 3.49 -1.06 -1.42 3.67 2.84 0.38 3.97 2.48 4.14 0.17 -1.07 -1.20 -0.98 0.43 1.08 0-83 0.67 -0.85 1.90 1.27 -1.88

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

DRAVNIEKS

Table I.

Structural

Properties

of

19

Odorants

(Continued) Lo£

Compound

This work

Menthol Mesitylene Methyl isopentanoate Methyl pentanoate 2-Methyl-2-propanol Methyl s a l i c y l a t e Nitrobenzene 1-Nitropropane 1- Octene 2- 0ctene 2- 0ctyne 3- Pentanone Phenylethanol Alpha-Pinene Propanoic a c i d 1- Propanol 2- Propanol Proplybutanoate iso-Propylpropionate Pyridine Styrene 1,1,2,2-Tetrachloroethane Thiophene Toluene Vanillin m-Xylene * Note:

(PPM) Katz-Talbert

0.50 1.49 0.82 1.12 3.79 0.54 0.50

1.36 0.00 1.03 0.14 1.34 0.72 3.07 3.41 0.97 0.80 0.84 (=7 PPM) 0.98 1,62 0.68 2.37 -2.30 1.37

1.26 (=18 PPM)

f o r four of the odorants, Katz-Talbert values were a v a i l a b l e i n d i c a t i n g concentrations needed to produce odor i n t e n s i t y of category 3 on t h e i r s c a l e . Values of ppm f o r these substances are shown i n parentheses.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

20

F L A V O R Q U A L I T Y : OBJECTIVE

MEASUREMENT

molecular p r o p e r t i e s depending on (1) t h e i r p o s i t i o n i n the molecule, (2) molecular s i z e , and (3) the presence of other funct i o n a l groups. Therefore, i n c h a r a c t e r i z i n g the s t r u c t u r e of the molecule i t i s not s u f f i c i e n t to e.g., c l a s s i f y these by the presence of -OH groups. The s i z e of the molecule needs to be considered as w e l l as the presence of groups that may enhance the exposure of the -OH group, such as being on a r i n g s t r u c t u r e , or i n a terminal p o s i t i o n , or elsewhere i n the v i c i n i t y of bulky groups that may obscure the -OH, e.g., next to a branched - C H 3 group. Molecular weight was used as one of the molecular d e s c r i p t o r s , followed by 38 a t t r i b u t e s derived from i n s p e c t i o n of Wiswesser n o t a t i o n s . These r e f l e c t e d : presence, number, and p o s i t i o n a l types of hydroxyl group presence of c a r b o x y l i c a c i d groups presence and p o s i t i o n a number and p o s i t i o n a number and p o s i t i o n a l types of carboxyl, aldehyde, e s t e r , ether groups number of benzene r i n g s number of amino, imino, and -N= groups number of -S- groups number of cyano, n i t r i l e , thiocyanate, and i s o t h i o c y a n a t e groups number of n i t r o groups number of ternary and quaternary atoms number of halogen atoms ( C l , Br, I) number of h e t e r o c y c l i c r i n g s number of s u b s t i t u e n t s on rings longest hydrocarbon chain i n the molecule (one of the a t t r i b u t e s r e l a t e d t o the s o l u b i l i t y i n o i l s and i n s o l u b i l i t y i n water) Odor p r o p e r t i e s i n a homologous s e r i e s vary with the molecular s i z e and frequently reach a maximum at a c e r t a i n s p e c i f i c s i z e . A l s o , they are i n f l u e n c e d by the types of the other funct i o n a l groups present. To permit c o n s i d e r a t i o n of these f a c t o r s , combinations o f the enumerated p r o p e r t i e s were a l s o introduced as p o t e n t i a l candidates f o r c o r r e l a t i o n s . One set of p r i n c i p a l combinations c o n s i s t e d of products of molecular weight and the numbers i n d i c a t i n g presence of the most of the quoted f u n c t i o n a l groups. Such terms r e f l e c t i n t e r a c t i o n e f f e c t s : e.g., s i g n i f i cance of hydroxyl group may decrease as the molecular weight i n c r e a s e s . The other s e t included products o f the square of molecular weight and f u n c t i o n a l group i n d i c a t o r s . The squarec o n t a i n i n g term provides f o r a maximum e f f e c t at a c e r t a i n molecular weight, but a l e s s e r (or i n reverse) e f f e c t at lower and higher molecular weight. A d d i t i o n a l f a c t o r s were introduced to r e f l e c t the p o s s i b i l i t y o f i n t e r a c t i o n s between the presence of f u n c t i o n a l groups and the presence of ternary and quaternary atoms and double bonds. In t o t a l , 118 i n d i c e s c h a r a c t e r i z i n g molecular

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

DRAVNIEKS

Structural

Properties

of

Odorants

21

c h a r a c t e r i s t i c s and some of t h e i r i n t e r a c t i o n s , most l i k e l y to have an e f f e c t on odor, r e s u l t e d . An updated form of Biomed 02R Stepwise Regression A n a l y s i s program and a Univac 1108 were used to search f o r the c o r r e l a tions. R e s u l t s and D i s c u s s i o n I s o - i n t e n s i t y Concentrations. These are concentrations that produce approximately equal suprathreshold odor i n t e n s i t i e s . In t h i s case, an odor i n t e n s i t y , S = 5, equivalent to that of 87 ppm of 1-butanol f o r our data s e t ; or an i n t e n s i t y score of 3 f o r the K a t z - T a l b e r t s e t . A v a r i a b l e to account f o r a p o s s i b l e systematic d i f f e r e n c e between these two s e t s was introduced as a candidate term i n the r e g r e s s i o n equation Figure 6 i l l u s t r a t e ppm c o n c e n t r a t i o n to e x h i b i Equation j6. C o e f f i c i e n t of determination (squared c o r r e l a t i o n c o e f f i c i e n t ) between the c a l c u l a t e d and the a c t u a l value was 0.74. Thus, 74 percent of the v a r i a n c e i n the concentrations needed to o b t a i n the d e f i n e d odor i n t e n s i t y was accomodated by the equation. The value of F - r a t i o was 18.2: the p r o b a b i l i t y of such c o r r e l a t i o n by chance i s ρ « 0.001. Standard d e v i a t i o n f o r the c a l c u l a t e d vs. a c t u a l value was 0.78. There was a systematic d i f f e r e n c e between our and KatzT a l b e r t data s e t s , which i s understandable because of d i f f e r e n t sample p r e s e n t a t i o n and odor i n t e n s i t y r a t i n g methods. In t h e i r work, the l o g (ppm) needed to o b t a i n the i n t e n s i t y score of 3 was by 0.6 l o g u n i t s lower than that to o b t a i n S = 5 i n our work. F i g u r e 7 i l l u s t r a t e s the obtained r e s u l t . The upper part i s a histogram i n d i c a t i n g the experimental d i s t r i b u t i o n of concen t r a t i o n s , by ranges, found to e x h i b i t the t a r g e t i n t e n s i t y S = 5 (or score 3 f o r K a t z - T a l b e r t d a t a ) : e.g., 21 substances e x h i b i t e d t h i s odor l e v e l at concentrations between 0.1 and 1 ppm i n a i r . The lower p a r t of the f i g u r e i s a histogram of d e v i a t i o n s of the experimental values from the c a l c u l a t e d values r e s u l t i n g from the use of Equation 6_. The set of numbers above t h i s histogram estimates the r e s u l t i n g odor i n t e n s i t i e s S f o r cases when an o d o r a n t s experimental i s o - i n t e n s i t y c o n c e n t r a t i o n value i s d i f f e r e n t from the c a l c u l a t e d value. Thus, i f the substance disobeyed the c a l c u l a t e d value to the extent of 0.5 l o g u n i t s to the l e f t ( a c t u a l needed c o n c e n t r a t i o n to o b t a i n S = 5 was 3 (= 10""0·5) times lower than the c a l c u l a t e d v a l u e ) , a stimulus prepared to c o n t a i n the c a l c u l a t e d c o n c e n t r a t i o n would e x h i b i t an i n t e n s i t y of 8 i n s t e a d of 5 (assuming that the odor i n t e n s i t y v a r i e s p r o p o r t i o n a l l y to 0.41 power of the odorant c o n c e n t r a t i o n , see above). There may be s e v e r a l reasons f o r the r e s i d u a l data s c a t t e r : (1) Match v s . 1-butanol s c a l e i n repeated measurements of the same odor stimulus by d i f f e r e n t panels has a standard f

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

22

FLAVOR

QUALITY: OBJECTIVE

MEASUREMENT

2 Q_

VOLUMETRIC DILUTION FACTOR AIR

SATURATED Figure

5.

•4

WITH ODORANT

Dose-response

LOG ( P P M ) TO INTENSITY

plots for several

GIVE

odorants

ODOR

S=5

| - 3 οοο

ce t—

•

5-2 ο ο

V

Ω Ο.

M

θ

0

ο

c' ;·*··

8 o p

0

ο°·ο*.

A

·

ο. «· *

*

·

#

ο THIS WORK •

-31 -3

-2

-1

EXPERIMENTAL

Figure

6.

0 L0G(PPM

KATZ

*1

+Î

& TALBERT

*3

.4

CONCENTRATION)

Results of isointensity tion correlations

concentra-

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

DRAVNIEKS

Structural

Properties

of

23

Odorants

Regression Equation f o r I s o i n t e n s i t y Concentrations (S = 5 f o r our data; i n t e n s i t y score 3 f o r Katz & T a l b e r t Data) Equation 6 F-Ratios f o r Log (PPM v/v) = 6.903 Separate Terms -1.3296 (Log MW) 115 -0.596 (Log MW) (VQ) 24 -1.030 (SH) 21 +0.517 (G) 19 -0.004 (MW) (U) 16 +0.216 (L + T) (max. No.) 15 -1.276 (R) (Q) 13 -0.396 (L + Τ)(X + Y + L + Τ + R) 12 -1.116 (R) (V) 9 -0.0002 (MW) +1526 (R +1.816 (I) 5 +0.742 (L + Τ) (V) 4 Ω cq \Katz-Talbert = 1 ° - " * 0 u r Data = 0 c f . next page f o r explanation of symbols. 2

2

Q

5

1

3

Regression Equation f o r Vapor Pressure Equation 7 log (mm vapor pressure at 25 C) = 4.152 -0.0354 (MW) -0.746 (Q) +0.131 (max. No.) +0.719 (X + Y) -0.887 (V i n L & T) -0.586 (terminal Q) -0.338 (VH) -0.712 (CN or NC) +0.206 (0) +0.237 <0V) -0.298 (X + Y + L + T + R) -0.680 (Z i n LT) +0.082 (No. of Subst.) -0.280 (U i n L & T) +0.174 (L + T)

F-Ratios f o r Separate Terms 1085 74 62 61 30 21 15 10.5 8.7 8.5 8.2 7.9 5.1 4.1 3.2

See notes to Equation 6 f o r the meanings of the term symbols.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

24

F L A V O R Q U A L I T Y : OBJECTIVE

MEASUREMENT

Symbols i n Regression Equations (for a l l except molecular weight the number of the corresponding symbols i n Wiswesser n o t a t i o n formula i s used as the v a r i a b l e ) MW VQ SH G U L Τ max.

= molecular weight = C a r b o x y l i c a c i d group = mercaptan = chlorine = double bonds = c a r b o c y c l i c r i n g (but not benzene) = heterocyclic ring No. = l a r g e s t A r a b i c numeral i n the formula, denoting the longest methyl group segment i n the molecule R = benzene r i n g Q = hydroxyl group X = C atom with four bonds extending to separate atoms which are not hydrogen Y = same as X but with three bonds extending as above V = carbonyl group CN, NC = cyanide and isocyanide groups 0V = e s t e r l i n k a g e (oxygen bridge 0 and carbonyl V) I = i o d i n e (there i s only one i o d i n e compound i n the s e r i e s - 1-iodobutane) Other symbols appearing i n vapor pressure r e g r e s s i o n equation, see below: VH = aldehyde group Ζ = NH2 group No. of Subst. - number of s u b s t i t u t e d p o s i t i o n on r i n g s

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d e v i a t i o n of the order of 0.2 l o g (ppm 1-butanol) u n i t s . Expressed i n odor i n t e n s i t y u n i t s , values of S between 4 and 7 may occur f o r a stimulus with S = 5. This would account i n part f o r the s c a t t e r i n the lower part of F i g u r e 7. (2) The expression of s t r u c t u r e s from Wiswesser formulas i s not yet s u f f i c i e n t l y r e f i n e d to r e f l e c t some o d o r - s i g n i f i c a n t property, or the experimental substance's odor i s contaminated by components not represented by the formula. The l a r g e s t d i f f e r e n c e s between the c a l c u l a t e d and e x p e r i mental values occurred f o r the f o l l o w i n g compounds: benzaldehyde, skatole, propylmercaptan, d i t h i o e t h y l g l y c o l , m e t h y l s u l f i d e , a l p h a - c h l o r o e t h y l s u l f i d e ( a l l these from Katz-Talbert data publ i s h e d i n 1930); and a l l y l a l c o h o l , dioxane, dimethylpentane, 1-hexanal, e t h y l b u t y r a t e , acetophenone, g u a i a c o l , d-limonene, and carbon t e t r a c h l o r i d e i n our data. There i s a good reason to suspect odor-important substances are the f i r s homologous s e r i e s , u s u a l l y d i f f i c u l t to f i t i n t o physico-chemical c o r r e l a t i o n s developed f o r the higher members of the same s e r i e s . I s o - i n t e n s i t y Concentrations and Vapor Pressures. When saturated vapors of substances are d i l u t e d by the same f a c t o r , they are at the same thermodynamic s t a t e with respect t o the corresponding condensed phases. Substances compared f o r the same property at the same vapor d i l u t i o n tend to a c t more s i m i l a r l y than when compared a t the same molar concentration (as i n the case of concentrations expressed i n ppm v / v ) . I t was of i n t e r e s t to compare vapor d i l u t i o n f a c t o r s needed to o b t a i n odor i s o i n t e n s i t y concentrations. T h i s was p o s s i b l e only f o r those compounds f o r which s a t u r a t i o n vapor pressures at 25°C were a v a i l a b l e from v a r i o u s handbooks. The upper part of F i g u r e 8 repeats the upper part of Figure 7. The lower part i s a histogram by ranges of d i l u t i o n s from saturated vapor. In transforming from ppm c o n c e n t r a t i o n s to d i l u t i o n s , the range has contracted from 7 to 5 l o g u n i t s . Substances with s i m i l a r f u n c t i o n a l group occupy even a l e s s e r range. I t i s p o s s i b l e that c o r r e l a t i o n s v s . Wiswesser formula c h a r a c t e r i s t i c s would c o n s i d e r a b l y improve i f d i l u t i o n to obtain odor i n t e n s i t y S = 5 would be introduced as one of the s t a r t i n g independent v a r i a b l e s . T h i s , however, would r e q u i r e knowledge of vapor pressures, c f . next subsection. F i g u r e 8 has some p r a c t i c a l a p p l i c a t i o n s i n olfactometry where odor s t i m u l i f r e q u e n t l y are prepared by s a t u r a t i n g a i r with the vapor of the odorant and followed by subsequent d i l u t i o n with a d d i t i o n a l a i r . D i l u t i n g the vapor by a f a c t o r of 100 would b r i n g a considerable f r a c t i o n of odorants i n t o the weak to moderate odor i n t e n s i t y range. Vapor Pressures.

Lack of knowledge of vapor pressures f o r

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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£20

Figure 7. Limitations of obtained isointensity vs. concentrations correlation

PREDICTED PPM for S=5 [EXPERIMENTAL PPM 1 PREDICTED PPM

0 +5 LOG (PPM) V/V 40

J 1 20 . contain -OH

Figure 8. Isointensity concentrations in terms of dilution ratio for saturation vapor pressure

LOG [DILUTION FACTOR) FROM SATURATED VAPOR

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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many odorants makesit d i f f i c u l t to estimate t h e i r concentrations i n o l f a c t o m e t r i c work. Since Wiswesser n o t a t i o n formulas contain well-organized s t r u c t u r a l i n f o r m a t i o n , a t e s t was conducted to determine i f vapor pressures can be c o r r e l a t e d to such properties. Two s t a t i s t i c a l experiments were conducted. In one, use of i n t e r a c t i o n terms was minimized — l o g (molecular weight), square terms, e t c . were not introduced. T h i s procedure was considered proper s i n c e l o g (vapor pressure) f o r a homologous s e r i e s f o l l o w s a n e g a t i v e l y sloped l i n e a r trend with respect to the molecular weight, and the corresponding members of d i f f e r e n t homologous s e r i e s tend to be separated by a constant l o g a r i t h m i c increment. In the other s t a t i s t i c a l experiment, a l l i n t e r a c t i o n terms used i n the odor i n t e n s i t y c o r r e l a t i o n s were introduced as a d d i t i o n a l candidate terms Vapor pressures wer i n mm Hg. The r e s u l t s were as f o l l o w s : Experiment 1 Experiment 2 Simpler Same Plus Properties I n t e r a c t i o n Terms F-Ratio 200 190 Degrees of Freedom (15,310) (26,299) C o e f f i c i e n t of Determination 0.91 0.94 R e s i d u a l Standard D e v i a t i o n 0.52 0.41 Number of Terms i n Regression Equation 17 26 Apparently, the a d d i t i o n of i n t e r a c t i o n terms improved the c o r r e l a t i o n only somewhat. I t i s apparent that the vapor pressure data, not subject t o sensory v a r i a b i l i t y e f f e c t s , c o r r e l a t e d to the formula p r o p e r t i e s considerably b e t t e r (91 percent of v a r i a n c e accomodated) than the i s o - i n t e n s i t y data. However, the r e l a t i v e l y l a r g e standard d e v i a t i o n (0.52 l o g u n i t s , or by a f a c t o r of 3.3) i n d i c a t e s that the p r o p e r t i e s and t h e i r combinations used should be f u r t h e r refined. Halogen compounds were not represented i n the vapor pressure data. A l s o , f o r some substances the vapor pressure e x t r a p o l a t i o n s impermissibly extended downward through the f u s i o n p o i n t , without c o n s i d e r i n g the e f f e c t of the heat of f u s i o n on the vapor pressure. Larger d e v i a t i o n s occurred with s a l i c y l i c s t r u c t u r e s , musks, v a n i l l i n , l a c t o n e s , s k a t o l , i n d o l e , and compounds with s e v e r a l e s t e r groups. For some, such as musks, the l i t e r a t u r e data may a l s o be i n e x a c t , s i n c e t h e i r vapor pressures are very low and d i f f i c u l t to measure. On the whole, vapor pressures are p r e d i c a b l e u s u a l l y w i t h i n a f a c t o r of 3 (one standard d e v i a t i o n ) , and most u s u a l l y b e t t e r than 9 (two standard deviation).

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flavor quality: objective measurement

Slopes. Correlation of slopes η to the Wiswesser formula properties are yet to be developed. Summary The values of concentrations of odorants in a i r that would exhibit odors in a certain odor intensity ("easily noticeable") range can be approximated from data extracted from one-line Wiswesser notation formulas of odorants. Vapor pressures can be approximated considerably better. Thus, the potential exists for using Wiswesser notation formulas not only for a computerized information search, but also for calculations of approximate odor iso-intensity concentrations and of vapor pressures. Improvements in the approximations should be possible by review ing cases where significant deviations of the experimental calculated values occurred Acknowledgement. The assistance of Dr. F. C. Bock in treatment of the computerized data analysis is gratefully acknowledged. Literature Cited (1)

Laffort, P . , and Dravnieks, Α . , J. Theor. Biology (1973) 38, 335. (2) Dravnieks, Α . , and Laffort, P . , Physico-Chemical basis of quantitative and qualitative odor discrimination in humans, in "Olfaction & Taste IV", Schneider, ed., p. 142, Wissen Verlagsges, Stuttgart, Germany, 1972. (3) Dravnieks, Α . , Ann. N.Y. Acad. Sci. (1974) 237, 144. (4) ASTM E544, "Recommended Practice for Odor Suprathreshold Intensity Referencing", Am. Soc. Test. Materials, Philadelphia, Pa. 1975. (5) Moskowitz, H. R., Dravnieks, Α . , Cain, W., and Turk, Α . , Chem. Senses & Flavor (1974) 1, 235. (6) Patte, F., Etcheto, M . , and Laffort, P . , Chem. Senses & Flavor (1975) 1, 283 (7) Smith, E. G . , "The Wiswesser Line-Formula Chemical Notation", McGraw-Hill, New York, 1968. (8) ASTM DS48, "Compilation of Odor and Taste Threshold Values Data", Stahl, ed., Am. Soc. Test. Materials, Philadelphia, Pa. 1973. (9) Katz, S. H . , and Talbert, E. J., "Intensities of Odors and Irritating Effects of Warning Agents for Inflammable and Poisonous Gases", U.S. Dept. Commerce Bureau of Mines, Techn. Publ. 480 (1930). (10) Apell, L., Perf. Cosm. Savons (1965) 8, 255. (11) "Handbook of Chemistry & Physics", Weast, ed., 50th E d i t . , The Chemical Rubber Co., Cleveland, Ohio 1969.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3 Flavor Chemical Mixtures—A Psychophysical Analysis HOWARD R. MOSKOWITZ—MPI Sensory Testing, Inc., New York, NY 10021 CYNTHIA N. DUBOSE—Behavioral Sciences Division, U.S. Army Natick Development Command, Natick, MA 01760 MARY JO REUBEN—Wellesley College, Wellesley, MA 02181

Gas chromatographi many mixtures, and are by research and development chemists. Yet, despite the impressive evidence which has accumulated concerning the composition of aromas, little information i s available on how odors are perceived when presented in concert with each other. This paper concerns the psychophysical evaluation of odors evaluated in pairs. Odors can be assessed on at least three criteria: intensity, hedonics and quality. Intensity. Most studies using the method of magnitude estimation (1,2) suggest that odor intensity conforms to a decelerating function of concentration. The function can be approximated by a power equation of the form S = kC (n between 0.4 and 0.7 for a i r dilutions of an odorant, and much lower for liquid dilutions of the odorant; (3, 4, 5, 6)). Magnitude estimation yields numbers which possess ratio properties. A 20 on the magnitude estimation scale indicates an odorant which i s twice as strong (sensorically) as an odor rated 10. There are no highest nor lowest numbers on the scale, and only ratios convey information. n

Hedonics. Most pure chemicals are unpleasant (5^, 7). Even odorants which are reminiscent of actual food aromas are considered unpleasant, and less pleasing than are their natural counterparts, which comprise many components. Complexity of an odor tends to improve i t s acceptability in those cases. Hedonics is often assessed by means of a scale which recognizes a fixed point of neutrality (0 point), and allows for ratings of l i k i n g and d i s l i k i n g on separate parts of the scale (5^, 8). Sometimes experimenters force the panelist to use a single continuum of positive numbers, and thus, never know when an odorant becomes unpleasant (;9, 10).

29 In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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Q u a ! i t y . The q u a l i t y of an odor can best be captured by means of an a d j e c t i v e d e s c r i p t o r l i s t . Numerous l i s t s have been proposed. Recent l i s t s i n c l u d e the Crocker-Henderson system (11) Harper et_ a]_'s l i s t of 44 d e s c r i p t o r terms f o r f l a v o r of foods (12), and Dravnieks' l i s t of 136 d e s c r i p t o r terms. The des c r i p t o r l i s t i s meant as a p a r t i a l , and not a complete l i s t of nuances which can be p e r c e i v e d , and f o r s p e c i f i c foods, the l i s t must be augmented ( Γ 3 ) . Recent developments i n multidimensional s c a l i n g have added y e t another method f o r e v a l u a t i n g q u a l i t y . Multidimensional s c a l i n g i s a method which l o c a t e s s t i m u l i i n a geometrical space of low d i m e n s i o n a l i t y , w i t h the property t h a t s t i m u l i q u a l i t a t i v e l y s i m i l a r to each other are l o c a t e d c l o s e to each o t h e r . Numerous methods e x i s t f o r converting e v a l u a t i o n s of s u b j e c t i v e s i m i l a r i t y (obtained from p a n e l i s t s ) to l o c a t i o n s of p o i n t s i n space, w i t h the points corresponding to the s t i m u l i which the p a n e l i s t s ha Odor M i x t u r e s . Odor mixtures have been evaluated i n terms of i n t e n s i t y , hedonics and q u a l i t y . Intensity. I n t e n s i t y of mixtures i s u s u a l l y lower than the i n t e n s i t y sum of t h e i r components. The exact amount depends upon the two components (or more i n the m i x t u r e ) . Berglund et al_ (18) have suggested t h a t two component mixtures can be approximated by a vector model of a d d i t i v i t y . (Mixture I n t e n s i t y ) = ( A ) (105£*< 2

Where:

2

+ (Β) 130)

2

+ 2AB (cos)<X.

A = odor i n t e n s i t y of odorant 1, Β = odor i n t e n s i t y of odorant 2 , mixture = odorant 1 and 2 mixed i n a i r , a l l scaled by magnitude e s t i m a t i o n *

They evaluated mixtures of noxious odors, such as dimethyl s u l f i d e and dimethyl d i s u l f i d e . Berglund (19) suggested a method whereby mixtures of 3 , 4 and 5 components could be evaluated f o r i n t e n s i t y and p r e d i c t e d v i a the vector model. Cain (20) and Cain and D r e x l e r (21) discussed the nature of odor m i x t u r e s , and suggested t h a t f o r odor masking of a pleasant odor by an un pleasant odor (amyl butyrate masking propanol, l i n a l o o l and l i n a l y l acetate and l a v a n d i n , r e s p e c t i v e l y , masking p y r i d i n e ) , the vector model represents a good approximation o f the sensory effects for intensity. Hedonics. The hedonics of mixtures has not been as thoroughly s t u d i e d . An e a r l y study by Spence and G u i l f o r d (22) suggested intermediacy, so t h a t the mixture was n e i t h e r as pleasant as the more preferred component, nor as unpleasant as the l e s s preferred one. However, these r e s u l t s are at best p r e l i m i n a r y , and do not i l l u s t r a t e the large scope of hedonic m o d i f i c a t i o n s i n mixtures which u n d e r l i e odor masking and

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modification. Q u a l i t y . Odor q u a l i t y of mixtures i s the most d i f f i c u l t aspect to s t u d y , p r i m a r i l y because there are no adequate models of odor q u a l i t y w i t h which to i n v e s t i g a t e , f o r m a l i z e and evaluate q u a l i t y s h i f t s . Moskowitz (23) has suggested t h a t the method of multidimensional s c a l i n g be used to assess the r e l a t i v e p o s i t i o n s of odors and t h e i r mixtures i n space, which would p i c t o r i a l l y d i s p l a y the s h i f t s i n q u a l i t y , but not lend verbal d e s c r i p t i o n s to those q u a l i t i e s . Moskowitz (24) discussed the d i f f i c u l t i e s which could be encountered when e v a l u a t i n g the aroma of a f l a v o r m a t e r i a l by sensory e v a l u a t i o n as w e l l as when c o r r e l a t i n g the f l a v o r w i t h the array of chemicals which the aroma comprises. The Scope Of This Paper The present study two component m i x t u r e s , evaluated at d i f f e r e n t c o n c e n t r a t i o n s , f o r odor i n t e n s i t y , odor hedonics and odor q u a l i t y . The aim i s to develop a s e r i e s of mathematical (or a t l e a s t q u a n t i t a t i v e ) models which describe the perceptions of odor when unmixed, and r e l a t e those perceptions to behavior of the odorants i n b i n a r y mixtures of known composition. The assessment method of magnitude e s t i m a t i o n (2, 25) provides the optimum procedure f o r determining the r e l a t i v e odor i n t e n s i t i e s , hedonic v a l u e s , and q u a l i t y r a t i n g s as w e l l as f o r e v a l u a t i n g the percentage change i n sensory i n t e n s i t y , e t c . , i n m i x t u r e s . Magnitude e s t i m a t i o n was developed at Harvard U n i v e r s i t y to assess b r i g h t ness of l i g h t s and loudness of tones, w i t h the aim of r e l a t i n g these, through meaningful e q u a t i o n s , to measured p h y s i c a l q u a n t i t i e s . The method has found wide use i n the e v a l u a t i o n of t a s t e s , s m e l l s , appearance and c o l o r , e t c . Experimental

Section

S t i m u l i . The s t i m u l i were two reagent grade c h e m i c a l s , with the a p p r o p r i a t e and d i s t i n c t odor c h a r a c t e r s . The s t i m u l i were heptyl acetate (pear, r o s e ) , and e t h y l s a l i c y l a t e ( w i n t e r q r e e n ) . (See Table 1) The Apparatus. An a i r d i l u t i o n olfactometer was developed by A. Dravnieks of the I l l i n o i s I n s t i t u t e of Technology Research I n s t i t u t e (Chicago). The olfactometer presented p a n e l i s t s w i t h two odorants at four concentrations (saturated odorant d i l u t e d to four f i n a l l e v e l s ) . I t a l s o presented the 16 m i x t u r e s , by continuous a i r f l o w , so t h a t the p a n e l i s t had at her d i s p o s a l 24 d i f f e r e n t a i r channels, w i t h two sets of four channels presenting two unmixed s t i m u l i at four concentrations ( r e l a t i v e s a t u r a t i o n s = 1/5, 1/20, 1/80, 1/320). The flow system of the olfactometer was set up to d e l i v e r 320 cc/minute of odorous a i r . In both the

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unmixed flows and i n the m i x t u r e s , the two components were pre sented at s p e c i f i c concentrations (10%, 2.5%, 0.625%, and 0.153% s a t u r a t i o n ) , and makeup a i r was added to produce the f o l l o w i n g : a) b)

The components embedded i n a t o t a l a i r flow of 320 cc/min. With respect to the e n t i r e f l o w , the c o n c e n t r a t i o n of each component at i t s proper l e v e l .

Moskowitz, Dravnieks and Gerbers (10) discussed the design of a s i m i l a r o l f a c t o m e t e r , which presented p a n e l i s t s w i t h one odorant at 8 c o n c e n t r a t i o n s . That design was modified i n the present apparatus to accomodate two odorants, and t h e i r m i x t u r e s , but the b a s i c design of the system was maintained. A i r d i l u t i o n olfactometry has a d i s t i n c t advantage over standard s n i f f b o t t l e techniques, since a) b) c)

The odorants ar The mixtures are never i n l i q u i d , only i n a i r ; The c o n c e n t r a t i o n can be adjusted by a d j u s t i n g flow rates.

The Experimental Design. P a n e l i s t s were women r e s i d e n t s of the Framingham-Natick (Massachusetts) a r e a , who were t r a i n e d i n the method of magnitude e s t i m a t i o n . They were i n s t r u c t e d to a s s i g n numbers to odors, so t h a t the r a t i o s of the numbers r e f l e c t e d as c l o s e l y as p o s s i b l e the r a t i o s of odor i n t e n s i t y , odor hedonics, and odor q u a l i t i e s , r e s p e c t i v e l y . For example, an estimate of 30 was to imply an odor twice as strong as an odorant assigned a magnitude estimate of 15. The f o l l o w i n g p r o v i s i o n s were made i n the assignments: a) b)

c)

For i n t e n s i t y judgements, a 0 was to r e f l e c t no odor, and i n c r e a s i n g p o s i t i v e numbers were to r e f l e c t i n c r e a s i n g degrees of odor i n t e n s i t y . For hedonic judgements, a 0 was to r e f l e c t n e u t r a l i t y ( n e i t h e r l i k i n g nor d i s l i k i n g ) , p o s i t i v e numbers were to r e f l e c t i n c r e a s i n g degrees of l i k i n g , and negative numbers were to r e f l e c t i n c r e a s i n g degrees of d i s l i k i n g . Q u a l i t y judgements were t r e a t e d l i k e i n t e n s i t y judgements. Eight i n d i v i d u a l s p a r t i c i p a t e d i n the study. They evaluated every one of the 24 odors i n random o r d e r , a s s i g n i n g magnitude estimates to odor i n t e n s i t y , odor p l e a s a n t n e s s , and odor q u a l i t i e s . Table 1 shows the odor q u a l i t i e s evaluated i n each experiment. When p o s s i b l e , a d e s c r i p t i o n of the odor q u a l i t y was provided i n depth to assure the p a n e l i s t s of the meaning of t h a t q u a l i t y .

The p a n e l i s t s r e p l i c a t e d the experiment e i g h t t i m e s , to produce a t o t a l of 64 r a t i n g s per sample (8 p a n e l i s t s χ 8 r e p l i cates = 64 p a n e l i s t / r e p l i c a t e r a t i n g s ) .

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Results Table 1 contains the average r a t i n g s on a t t r i b u t e s f o r d i f f e r e n t concentrations of the two s t i m u l i . Odor I n t e n s i t y . Figures l a and l b show how the average perceived sensory i n t e n s i t y v a r i e s w i t h c o n c e n t r a t i o n , f o r each odorant, evaluated both a l o n e , (Figure l a ) and i n the presence of the other odorant at varying c o n c e n t r a t i o n of the second odorant (Figure l b ) . Both coordinates are l o g a r i t h m i c a l l y spaced i n both f i g u r e s . The major f i n d i n g regarding s u b j e c t i v e estimates of odor i n t e n s i t y can be summarized as f o l l o w s : a)

b) c)

Odor i n t e n s i t y grows approximately as a power f u n c t i o n of c o n c e n t r a t i o n , supporting previous r e s u l t s . However, the range of c o n c e n t r a t i o n exclude other candidate equations ( e . g . , l i n e a r , logarithmic, exponential). The exponents f o r the odorants are a l l lower than 1.0, so t h a t odor i n t e n s i t y grows as a d e c e l e r a t i n g f u n c t i o n of c o n c e n t r a t i o n . Representative power f u n c t i o n s a r e : Ethyl S a l i c y l a t e :

S= 8.26

(%C)

0-65

Heptyl A c e t a t e :

S=16.9

(%C)

0-53

Where:

S= magnitude estimate of odor i n t e n s i t y

The p r i n c i p a l f i n d i n g f o r odor i n t e n s i t y of mixtures (Figure l b ) i s t h a t p a i r s of odors suppress each o t h e r . The mixture i s weaker than would be expected on the b a s i s of a d d i t i v i t y of component odor i n t e n s i t y . For some c a s e s , the i n t e n s i t y of the mixture i s weaker than the weaker component i t s e l f , whereas f o r the m a j o r i t y of cases, the odor i n t e n s i t y l i e s between the stronger and the weaker component. À mathematical model of odor mixtures can be developed by appeal to the r u l e s governing vector summation. Berglund, Berglund, L i n d v a l l and Svensson (18) suggested t h a t mixtures o f odorants add together i n i n t e n s i t y as i f they were v e c t o r s , w i t h an estimated angle of 105O - 130cr separating the v e c t o r s . The model o f v e c t o r a d d i t i v i t y was used here, to p r e d i c t the angular separation between the p a i r s of odorants. The mean r a t i n g s f o r the components and f o r the mixtures were used i n the f o l l o w i n g formula, and an estimate of cosine x was o b t a i n e d : (MIX)2 = A2 + B2 + 2AB cos (

)

Figure 2 shows how the vector model behaves as a f u n c t i o n of the odor i n t e n s i t y of the components.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

34

FLAVOR QUALITY:

Table I. LEVEL ETHYL SALI CYLATE

OBJECTIVE M E A S U R E M E N T

Odor Concentrations and Average Ratings on A t t r i b u t e s LEVEL HEPTYL ACE- INTEN TAT Ε SITY

PLEAS ANTNESS

COM PLEXITY

FRUITY

FRA GRANT

MINTY

1

0

5.6

3.7

18.1

0.6

0.5

0.2

2

0

14.7

8.0

26.6

1.6

5.8

7.4

3

0

31.6

18.3

36.4

4.4

12.9

22.4

4

0

49.8

26.9

34.1

2.5

23.4

38.6

0

1

2.3

7.1

19.3

2.5

2.6

0.1

0

2

5.6

0

3

17.9

3.6

40.5

22.6

12.6

1.6

0

4

32.1

-2.5

45.9

29.7

15.8

4.4

1

1

3.3

3.2

16.5

3.8

3.0

0.0

2

1

6.2

8.1

26.3

1.9

2.2

1.8 26.7

3

1

20.9

17.2

27.2

1.7

15.3

4

1

41.6

26.6

33.5

3.1

26.4

44.0

1

2

11.3

6.6

32.9

7.7

1.8

2.6

2

2

13.7

8.3

38.0

13.1

7.2

2.3

3

2

19.2

10.0

40.7

16.7

7.9

7.1

4

2

30.0

29.6

35.8

3.9

22.5

38.4

1

3

32.0

4.8

37.3

25.0

10.9

3.8

2

3

24.1

6.6

29.6

19.1

8.2

2.3

3

3

25.5

11.1

32.8

16.4

13.1

8.6

4

3

34.2

25.6

34.6

14.4

22.6

30.6

1

4

43.6

0.2

40.3

28.2

12.1

5.6 4.3

2

4

43.8

-4.3

39.3

26.8

14.5

3

4

36.7

-0.5

36.9

23.6

10.9

3.2

4

4

49.9

2.4

42.3

27.0

17.7

13.9

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3. M O S K O W I T Z E T A L .

35

Flavor Chemical Mixtures

Table I (cont.)

AROBANANA SWEET MATIC PEAR

FLOWSPEARWINEY HERBAL ERY HEAVY MINT

0.0

2.7

1.3

0.5

0.3

2.6

0.3

0.0

0.3

1.0

4.0

8.8

4.7

0.8

2.4

5.2

1.3

1.0

1.6

10.6

19.9

2.2

1.8

6.7

16.1

3.9

5.2

1.7

14.5

27.0

3.3

2.7

7.9

20.5

2.5

6.9

0.8

3.8

6.4

3.6

9.1

13.0

6.6

11.4

16.1

21.6

4.1

19.7

4.1

5.4

7.2

10.5

10.6

20.3

24.5

8.2

28.8

6.6

7.2

9.4

1.9

4.5

4.2

4.3

1.8

2.0

0.6

0.6

0.0

0.7

2.7

9.9

7.6

0.8

3.3

2.4

0.9

1.3

1.1

9.7

19.2

2.7

2.0

8.8

14.4

2.0

5.8

27.9

3.7

3.2

26.5

3.9

6.0

2.7

18.7

11.0

5.9

7.3

12.1

12.1

2.1

6.5

2.7

2.3

3.8

5.3

10.9

15.1

16.6

5.5

8.8

3.7

5.8

3.1

4.0

11.8

11.8

12.0

6.3

4.1

4.8

2.2

14.2

27.8

23.1

3.4

4.9 6.4

8.0

15.2

12.0

5.6

4.0

6.4

5.5

11.4

11.3

5.3 20.2 16.9

2.5 5.0 4.1

12.2 7.8 17.5 19.4

4.5

4.2

8.3

6.8

8.0

7.5

5.5

7.8

6.1

14.1

13.5

17.3

5.5

14.6

5.2

16.1

25.3

8.1

5.8

13.6

8.7

17.8

15.5

25.3

5.7

29.5

6.7

6.3

11.0

17.0 11.4

23.9

5.7 7.2

23.3

7.5

27.2

5.4

7.7 7.8

11.7

7.0

21.1 15.6

8.3

22.9

20.2

6.4 KEY

31.8

7.7

13.5

10.0

21.1 20.3

21.0

10.0

LEVEL 1 = 0.153% SATURATION

LEVEL 3 = 2.5% SATURATION

LEVEL 2 = 0.625% SATURATION

LEVEL 4 = 10% SATURATION

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.9

FLAVOR

QUALITY: OBJECTIVE

>- 100b

Figure la. Dose-response (psy chophysical) function relating percentage saturation of single odorants to perceived odor in tensity assessed by magnitude estimation. The coordinates are log-log, in which a straight line implies that the function is a power function.

• Heptyl A Ethyl

MEASUREMENT

acetate salicylate

2

3

CONCENTRATION

M I I I

LEVEL 1 LEVEL 2

I I I

0 LEVEL OF HEPTYL ACETATE ADDED TO ETHYL SALICYLATE

LEVEL OF ETHYL SALICYLATE ADDED TO HEPTYL ACETATE

Figure lb. Dose-response (psychophysical) functions rehting percentage saturation of mixtures of odorants to per ceived odor intensity. The coordinates are log-log, in which straight lines imply that the function is a power function.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3.

MOSKOWITZ ET A L .

Flavor

Chemical

Mixtures

37

In Figure 2, a V represents the f a c t t h a t the mixture i n t e n s i t y can be f i t by the v e c t o r model. A l i m i t on cos was set so t h a t 105° < ~< ^ 140O (or - 0 . 7 6 ^ cos < -0.26). Α 'ν+' means t h a t the mixture was stronger than would be p r e d i c t e d by the vector model (i.e.,-^< 6. 105° or cos > 0.76). Α ' ν ' would mean t h a t the mixture was weaker than would be p r e d i c t e d by the vector model ( i . e . , 180° I > 140°). An ' s * r e f l e c t s the f a c t t h a t the mixture was weaker than would be p r e d i c t e d , even if = 180° (or cos «=K = 1 ) . Synergy r e f e r s to the f a c t t h a t the a r i t h m e t i c sum of the mixture odor i n t e n s i t i e s was g r e a t e r than the sum o f the mixture i n t e n s i t i e s . Figure 2 suggests t h a t there are three regions of m i x t u r e : a) An intermediate region of i n t e n s i t i e s , where the vector model h o l d s . T h i s region i s t h a t where the two odorants are s i m i l a r (although not n e c e s s a r i l y equal) i n intensity. b) A region of enhancement above the l e v e l which the v e c t o r model p r e d i c t s . T h i s region encompasses a high l e v e l of heptyl acetate and a very low l e v e l of e t h y l s a l i c y l a t e . c) A region of suppression (or diminished a d d i v i t y ) . This region comprises low l e v e l s of heptyl acetate plus varying l e v e l s of e t h y l s a l i c y l a t e . Hedonics. Figure 3 shows the hedonic r a t i n g s of the mixture and the components (vs. c o n c e n t r a t i o n ) . The layout of Figure 3 i s s i m i l a r to t h a t of Figure l b . An attempt was made to r e l a t e the hedonic r a t i n g s of mixtures (MH) to the hedonic r a t i n g s o f the components (AH & BH). The equation best f i t t i n g the r e s u l t s is: For mixtures of e t h y l s a l i c y l a t e (E)

and heptyl acetate

(H)

MH = - 0 . 0 8 ( E H ) -1.01(HH) = 14.24 R = 0.48 F(2,21) = 3.21 Where:

R = correlation coefficient F = F r a t i o , a n a l y s i s of variance

The important t h i n g about the hedonic tone of b i n a r y mixtures i s t h a t they cannot be e a s i l y p r e d i c t e d from the hedonic tones o f the components. Rules of intermediacy do not n e c e s s a r i l y hold f o r hedonics, p o s s i b l y because: a) b) c)

The mixture has changed i n c h a r a c t e r ; The hedonic tones o f mixtures do not obey a l g e b r a i c combination r u l e s ; The vector model i s i n a p p r o p r i a t e f o r p o s i t i v e v s . negative r a t i n g s .

Q u a l i t y S h i f t s . Q u a l i t y s h i f t s i n mixtures can be assessed by c o n t r a s t i n g the p r o f i l e of the components and of t h e i r binary

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

38

F L A V O R Q U A L I T Y : OBJECTIVE

Figure 2. The nature of additivity of odor intensities in mixtures vs. the component odor intensities. The axes indicate the component, unmixed odor intensities, (v) the mixture can be ade quately modeled by the vector model; ('ν-\-') the mixture intensity can also be modeled by the vector model, but the angular separation is less than 105°. A 'v—' icould mean that the intensity would also be modeled by the vector model but that the angular separation is greater than 140°. (Sup) suppression— the mixture odor intensity is less than the difference obtained by subtracting the weaker odor intensity from the stronger odor intensity. (Synergism)—the mixture odor intensity exceeds the arith metic sum of the component odor sities.

Figure 3. Dose-response functions rehting hedonic tone to odor concentra tion for mixtures. The abscissa reflects the rela tive level of one odorant added to a constant amount of a background odorant. The ordinate re flects the average liking (-\-) or disliking (—) mag nitude estimate assigned to the mixture.

sup

MEASUREMENT

additivity

L E V E L OF HEPTYL A C E T A T E ADDED TO E T H Y L S A L I C Y L A T E

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3.

MOSKOWITZ ET AL.

Flavor

Chemical

Mixtures

39

m i x t u r e s . Figures 4 and 5 show some of these m i x t u r e s , and t h e i r r e l a t i o n s to t h e i r components. A general r u l e which emerges from Figures 4 and 5 i s t h a t there i s no systematic r u l e that p r e d i c t s the q u a l i t y notes of a mixture from the q u a l i t y notes of i t s components. Other things which emerge a r e : a) b)

The presence of a q u a l i t y note i n a pure odorant can be completely masked by the a d d i t i o n of a second odorant. Rarely does an e n t i r e l y new q u a l i t y note emerge t h a t was not present i n the components evaluated alone. This c o n c l u s i o n must be tempered w i t h the r e a l i z a t i o n that i n the experiment an exhaustive l i s t of d e s c r i p t o r s was not used. Some d e s c r i p t o r s may have a p p l i e d to the m i x t u r e , but not to the components.

Multidimensional A n a l y s i s representations of odor q u a l i t y i n mixtures make an understanding of p o t e n t i a l sensory processes d i f f i c u l t to o b t a i n . However, p i c t o r i a l representations of odors and t h e i r mixtures i n a 'perceptual space' may i l l u s t r a t e h i t h e r t o undiscovered r e l a t i o n s between odors and mixtures i n a 'perceptual s p a c e . ' Such an approach was reported by Moskowitz (23) f o r f i v e component m i x t u r e s . Here, a s i m i l a r approach was t a k e n , i n order to v i s u a l i z e the r e l a t i o n s between components and m i x t u r e s . The method of f a c t o r a n a l y s i s (26) i s p a r t i c u l a r l y well s u i t e d to the a n a l y s i s of m i x t u r e s . Factor a n a l y s i s attempts to determine the number of independent f a c t o r s (or primaries) which, i n c o n c e r t , reproduce a set of s t i m u l i . The input f o r f a c t o r a n a l y s i s i s u s u a l l y a s e r i e s of d e s c r i p t o r terms that p e r t a i n to a set of s t i m u l i , and r a t i n g s of a number of s t i m u l i on these d e s c r i p t o r s . The output of the f a c t o r a n a l y s i s i s a set of c o r r e l a t i o n s between p a i r s of d i f f e r e n t d e s c r i p t o r s (computed across d i f f e r e n t s t i m u l i which were evaluated on the d e s c r i p t o r s ) , as w e l l as a set of axes. These axes or coordinates are perpend i c u l a r to each o t h e r , and represent the fundamental dimensions or p r i m a r i e s . Every d e s c r i p t o r comprises some percentage of each primary. Hence, by o b t a i n i n g a f a c t o r a n a l y s i s s o l u t i o n , the experimenter can see the o v e r l a p , communalities, e t c . , among d i f f e r e n t d e s c r i p t o r terms, as well as see how many underlying basic terms are r e a l l y needed. In t h i s experiment, the a n a l y s i s was turned around. The d i f f e r e n t odorants ( a l l 24) were t r e a t e d as odorants. Ratings f o r odor i n t e n s i t y were not included i n t h i s a n a l y s i s . The input to the f a c t o r a n a l y s i s was the set of odorants, and the outputs of the a n a l y s i s were: a) b)

The number of primary f a c t o r s (or underlying odors) that i n concert would reproduce the set of 24 odorants. The c o n t r i b u t i o n of each primary to each of the 24 odorants.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

40

FLAVOR

Έ çô 20

2

SWEET ODOR OF 0.153% . HEPTYL A C E T A T E

Q U A L I T Y : OBJECTIVE

MEASUREMENT

PEAR ODOR OF 10% HEPTYL A C E T A T E

SWEET ODOR OF 10% HEPTYL A C E T A T E

PEAR ODOR OF 0.153% HEPTYL A C E T A T E

10

Û

0 1 2 3 4

0 1 2 3 4

0 1 2 3 4

0 1 2 3 4

AMOUNT OF ETHYL SALICYLATE ADDED TO FIXED L E V E L OF HEPTYL A C E T A T E

Figure 4. Mixture quality profiles acetate. (Abscissa) the amount of (Ordinate) the mean magnitude estimates for sweetness and pear odor. There are two levels of heptyl acetate (0.153% and 10%) which serve as the base to which ethyl salicylate is added.

MINTINESS OF 10% ETHYL SALICYLATE

HEAVINESS OF 0.153% E T H Y L SALICYLATE

HEAVINESS OF 10% E T H Y L SALICYLATE 30

>

< 20

I—

MINTINESS OF 0.153% E T H Y L SALICYLATE

0 1 2 3 4

0 1 2 3 4

0 1 2 3 4

AMOUNT OF HEPTYL A C E T A T E ADDED TO FIXED L E V E L OF E T H Y L SALICYLATE

Figure 5. Mixture quality profiles for heptyl acetate added to fixed levels of ethyl salicylate. The attributes of ethyl salicylate are mintiness and heaviness. Those qualities change as different amounts of heptyl acetate are added to fixed levels of ethyl salicylate.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3.

MOSKOWITZ ET A L .

Flavor

Chemical

Mixtures

41

Figure 6 shows a two dimensional s o l u t i o n to the f a c t o r a n a l y s i s . The a n a l y s i s i n d i c a t e d that there were two b a s i c dimensions (corresponding to the two o d o r s ) . The pure odorants (unmixed) tend to l i e on or near axes, whereas the mixtures l i e i n between, showing t h a t they comprise some parts of each primary. Note t h a t the u n i t s i n Figure 6 are r e l a t i v e u n i t s o n l y . Figure 6 can be used to determine the nature of emergent q u a l i t i e s not present i n the mixture components evaluated alone. I f a l i n e i s drawn connecting the two components of a m i x t u r e , then i d e a l l y the mixtures should l i e on that l i n e . The mixture may l i e c l o s e r to one end or to another ( i n d i c a t i n g t h a t i t i s more h i g h l y c o r r e l a t e d w i t h , or s e n s o r i c a l l y r e l a t e d to one component, or to a n o t h e r ) . As the p o i n t s depart from the l i n e connecting the components i t becomes c l e a r t h a t the mixture c o r r e l a t e s l e s s w e l l w i t h the components, or even w i t h a l i n e a r combination of the components D i s c u s s i o n and Conclusions The present set of s t u d i e s shows that new techniques must be developed to assess the sensory c h a r a c t e r i s t i c s of m i x t u r e s . Thus f a r i t appears t h a t f o r e v a l u a t i n g mixture i n t e n s i t y , the vector model provides an i n i t i a l l y useful approach w i t h which to evaluate and compare d i f f e r e n t m i x t u r e s . F o r t u n a t e l y , the use of the vector model ( o r , i n f a c t , any combination r u l e f o r i n t e n s i t i e s ) allows the experimenter to formulate questions about pot e n t i a l mechanisms u n d e r l y i n g odor m i x t u r e s . With regard to hedonic tone of m i x t u r e s , the use of such simple mixture r u l e s as the vector model i s not e f f e c t i v e , e s p e c i a l l y when two odorants are mixed over l a r g e ranges of c o n c e n t r a t i o n , and a general r u l e f o r hedonics mixtures i s des i r e d . A s i m i l a r f a i l u r e to achieve a general r u l e of hedonic tone of mixtures occurs when t a s t e s are evaluated as w e l l ( 2 7 ) . They evaluated the pleasantness/unpleasantness of mixtures of glucose and a r t i f i c i a l sweeteners (cyclamate, s a c c h a r i n ) . They were unable to develop a model which would adequately p r e d i c t the o v e r a l l mixture hedonics from knowledge of the mixture concent r a t i o n s alone. I t may well turn out t h a t f o r a l a r g e range of mixtures of two components, of varying chemical s t r u c t u r e and smell q u a l i t y , there e x i s t s a simple averaging r u l e f o r hedonics, so t h a t , i n g e n e r a l , the hedonic tone of an odor mixture i s i n between the hedonic tones of the components. Spence and G u i l f o r d (22) found t h i s intermediacy f o r the e v a l u a t i o n of t h i r t e e n odorants. In the m i c r o - a n a l y s i s o f two odorants that intermediacy r u l e probably no longer holds,because of q u a l i t y s h i f t s i n the m i x t u r e s , the f i n e a t t e n t i o n paid to nuances when only two components are mixed i n various c o n c e n t r a t i o n s , and the o v e r a l l set or perceptual s t r a t e g y adopted by the respondent.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

42

F L A V O R Q U A L I T Y : OBJECTIVE

MEASUREMENT

1st = HEPTYL ACETATE (01,02,03,04) 2nd = ETHYL SALICYLATE (10,20,30,40)

02 .03?04

H

1

1

1

1

*3Ϊ·

(—

• 24 »32 23 »33

22·

®

• 12

• 44 34

• 43

•42

Figure 6. Two-dimensional factor space, obtained from factor analysis of the ratings. The odorants were factor-analyzed. The two-digit number reflects the concentrations of heptyl acetate and ethyl salicylate. The coordinate system is rehtive, so that the distances between the odorants are meaningful. The results suggest two primaries with projection of each odorant onto each primary shown in Figure 6. The primaries are orthogonal to each other.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3.

MOSKOWITZ E T A L .

Flavor Chemical Mixtures

43

Perhaps the most important thing about these studies is the types of quality shifts which are encountered in mixtures, and the difficulty of easily capturing the quality of a mixture, and relating that back to the qualities of the components. The present state-of-the-art requires appeal to one of two different approaches to evaluate quality: a) Descriptor checklists (_12, 28). b) Multidimensional scaling, in which mixtures are embedded in a geometrical space, alone with their components (23, 29). These two approaches only portray the quality shifts for the experimenter, and do not predict them. The picture which is developed may either be easy to understand, or so punctuated by minutiae of detail that the major quality shifts are hidden It is possible tha shifts by these scaling have no control over producing a mixture with a specific quality. That i s , given the data pertaining to two-component mixtures, we may not yet be able to produce a specific mixture (or determine that i t cannot be produced). In contrast, psychophysical analyses of odor intensity and odor hedonics produce descriptive functions, with the property that a curve can be f i t to the data, and an intermediate level of intensity or hedonic tone can be obtained by appeal to the curve (or to the descriptive equation). Abstract A study with chemicals mixed together pairwise in vapor phase and evaluated by panelists for odor intensity, odor hedonics and odor quality (character) reveals the following general rules: 1. Odor intensity is a power function of odorant concentration for unmixed odorants, with an exponent less than 1.0. 2. Odor hedonics is often a monotonic function of concentration, but cannot be modeled by a power function. 3. Odor quality can be captured by means of a profiling system, using magnitude estimation as the measuring system. 4. In binary mixtures, odor intensity is usually suppressed for more intense component, so that the final mixture intensity is somewhere in between the intensities of the components. 5. In binary mixtures, hedonics are often changed, so that the addition of a pleasing component to a displeasing one makes the mixture more pleasing. 6.

Mathematical equations can be developed to model some of the mixture effects.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

44

flavor quality: objective measurement 7.

The change in odor quality in mixture is a function of the type of odorants, their quality and their starting odor intensity.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

Moskowitz, H.R., Food Technology (1974), 28, 16. Stevens, S.S., "Psychophysics", John Wiley, New York, (1975). Berglund, B., Berglund, U., Ekman, G., and Engen, T . , Percept. and Psychophys., (1971), 9, 379. Cain, W.S., Percept. and Psychophys., (1969), 6, 349. Doty, R., Percept. and Psychophys., (1975), 17, 492. Moskowitz, H.R., Dravnieks, A . L . , and Klarman, L.A., Percept. and Psychophys., (1976), 19, 122. Moncrieff, R.W., "Odor Preferences" Leonard H i l l London (1966). Peryam, D.R., and Pilgrim Henion, K.E., J. Exp. Psychol., (1971), 99, 275. Moskowitz, H.R., Dravnieks, A.L. and Gerbers, C . , J. Experimental Psychology, (1974), 103, 216. Crocker, E . C . , and Henderson, L., Am. Perf. Ess. Oil Rev., (1927), 22, 325. Harper, R., Land, D.G., Griffiths, N.M., and Bate-Smith, E.C., Brit. J. Psychology, (1968), 59, 231. Von Sydow, E . , Moskowitz, H.R., Jacobs, H.L., Meiselman, H.L., Lebens. Wiss. U. Technol., (1974), 7, 18. Alabran, D., Moskowitz, H.R, and Mabrouk, A . F . , J. Ag. Food Chem., (1975), 23, 229. Green, P., and Rao, V., "Applied Multidimensional Scaling", Holt, Rinehart and Winston, New York, (1972). Schiffman, S.S., Ann. N.Y. Acad. S c i . , (1974), 237, 164. Shepard, R.N., Psychometrika, (1974), 39, 373. Berglund, B., Berglund, U., Lindvall, T . , and Svensson, L.T., J. Ëxptl. Psychol. (1973), 100, 29. Berglund, B., Ann. N.Y. Acad. S c i . , (1974), 237, 55. Cain, W.S., Chem. Senses Flavor, (1975), 1, 339. Cain, W.S., and Drexler, Μ., Αnn. N.Y. Acad. S c i . , (1974), 237, 427. Spence, W., and Guilford, J.P., Am. J. Psychol., (1933), 45, 495. Moskowitz, H.R., Lebens, Wiss. U. Technol., (1976), 9, 232. Moskowitz, H.R., Lebens. Wiss. U. Technol., (1975), 8, 237. Stevens, S.S., "Psychophysics", John Wiley, New York, (1975). Harman, H.Η. "Modern Factor Analysis", Univ. of Chicago Press (1966). Moskowitz, H.R., and Klarman, L., Chem. Senses Flav., (1975), 1, 411. Dravnieks, A . L . , Personal Communication. Engen, T. Ann. N.Y. Acad. S c i . , (1974), 237, 224.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4 Structural and Mechanical Indicators of Flavor Quality ZATA VICKERS Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108

Is the flavor of a and mechanical properties There is some literature on the subject but l i t t l e , i f any, attempts to explain how and why such relationships exist. Many of the newer foods on the market have their texture and flavor constructed or developed separately, making any general relationships between the two difficult to determine. At times it seems possible to combine almost any type and intensity of flavor with just about any texture. Assuming though, that there is some connection between flavor and texture, how does it occur or why does it exist? Is it due to an interaction between the sensory-systems perceiving flavor and those perceiving mechanical properties? In other words, does stimulating one set of sense organs affect the sensitivity of others? Or do changes in the structural and mechanical properties of a food affect the rate and extent of flavor formation and release? Both suggestions are valid. The first explanation is a phenomenon of an individual's sensory system. The latter is a result of changes occurring in the food. The sense organs involved in perceiving flavor are the taste buds, olfactory epithelium, and nerve endings responding to chemicals. Those involved in perceiving the structural and mechanical properties of foods are those responding to touch, pressure, position and sound. Periferally these senses are quite distinct. However, a l l sensory systems can interact together at higher levels in the brain. If one sense is stimulated it will affect to some degree the sensitivity of other senses. Therefore, if all or part of the sensory system perceiving mechanical properties was stimulated, one would expect some alteration in the perception of flavor. Stimulating one sense may enhance or depress sensations in another sense modality. Generally, a low level of an accessory stimulus will enhance perception, whereas higher levels of an accessory stimulus probably depress sensations. Little information is available on the enhancement or depression of odors or 45

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t a s t e s by t e x t u r e s or sounds (1), but expecting such e f f e c t s i s reasonable. A crunch reminiscent of the T i t a n i c h i t t i n g an i c e berg may leave the cruncher with l i t t l e i d e a o f whether the product was cheese or onion f l a v o r e d . The s t r u c t u r a l and mechanical p r o p e r t i e s of foods may a f f e c t f l a v o r by c o n t r o l l i n g both the r a t e o f f l a v o r r e l e a s e and the t o t a l amount of f l a v o r r e l e a s e d . T h i s i s f a i r l y easy to understand. A product that breaks down or melts q u i c k l y i n the mouth w i l l r e l e a s e i t s f l a v o r r e l a t i v e l y r a p i d l y . A product that d i s i n t e g r a t e s slowly gives up i t s f l a v o r l e s s r a p i d l y . I f two such products contained equal amounts of f l a v o r compounds, the one undergoing r a p i d breakdown would be p e r c e i v e d as being more intensely flavored. In many cases v i s c o s i t y modifying agents such as starches and gums appear t o change the t a s t e and odor i n t e n s i t i e s of s o l u t i o n s to which they ar be due t o the v i s c o s i t y odor compound and the h y d r o c o l l o i d i s probably r e s p o n s i b l e (2). For example, the f l a v o r compound acetaldehyde t a s t e s more intense i n a s o l u t i o n of sodium a l g i n a t e than i n p l a i n water. This i n t e n s i t y d i f f e r e n c e appears to be due to the i n t e r a c t i o n o f acetaldehyde with the a l g i n a t e . When acetaldehyde was mixed with other gums such as carboxymethyl c e l l u l o s e or hydroxypropyl c e l l u l o s e over e q u i v a l e n t ranges of v i s c o s i t y , there was no s i g n i f i c a n t change i n f l a v o r i n t e n s i t y (2). The same authors found s i m i l a r r e s u l t s with b a s i c t a s t e compounds and h y d r o c o l l o i d s . Enhancement or depression o f compounds, e.g., s a c c h a r i n and c a f f e i n e , a l s o appeared to r e s u l t from i n t e r a c t i o n s between the t a s t e compound and the v i s c o s i t y modifying agent. Some gums produced changes i n t a s t e i n t e n s i t y whereas others at equal v i s c o s i t i e s d i d not (3_) . The r e s u l t s o f these s t u d i e s provide evidence a g a i n s t any i n t e r a c t i o n between the p e r i p h e r a l sense organs f o r f l a v o r and those f o r v i s c o s i t y . From the consumer's p o i n t o f view, the most important way the s t r u c t u r a l and mechanical p r o p e r t i e s o f a food are r e l a t e d to f l a v o r i s through a s s o c i a t i o n . We a s s o c i a t e c e r t a i n t e x t u r e s and sounds with c e r t a i n f l a v o r s because through years o f e a t i n g experience we have learned they always occur together. Given two e q u a l l y red tomatoes, the s o f t e r one w i l l l i k e l y be r i c h e r i n f l a v o r . We expect a s o f t e r l o a f of bread t o be more f l a v o r f u l than a f i r m e r l o a f because the s t a l i n g process which makes i t firmer a l s o makes i t l e s s f l a v o r f u l . A c r i s p , j u i c y apple w i l l l i k e l y have more f l a v o r than a s o f t , mealy one. A curdy, rubbery Cheddar cheese has a m i l d e r , greener f l a v o r compared to the sharp nutty t a s t e of a more waxy aged cheese. Products where such a s s o c i a t i o n s can be made are g e n e r a l l y n a t u r a l or t r a d i t i o n a l l y processed meats, cheese, f r u i t s , e t c . , as opposed to f a b r i c a t e d foods. N a t u r a l or t r a d i t i o n a l foods are dynamic systems. Many r e a c t i o n s are o c c u r r i n g simultaneously and

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are producing changes i n both the s t r u c t u r a l and mechanical prop e r t i e s and the f l a v o r . These r e a c t i o n s are commonly caused by spontaneous chemical changes, enzyme systems, and h e a t i n g . Now, I would l i k e to look at some r e p r e s e n t a t i v e examples of such t e x t u r e - f l a v o r a s s o c i a t i o n s i n a few d i f f e r e n t commodities. R e l a t i o n s h i p s between the s t r u c t u r a l and mechanical propert i e s of meat and the f l a v o r of meat are commonly found. Probably the best known are those o c c u r r i n g during aging. Aging meat produces a more tender, f l a v o r f u l product, whereas imaged meat i s r e l a t i v e l y tough with a bland, m e t a l l i c and a s t r i n g e n t t a s t e . Why i s t h i s increase i n tenderness accompanied by an i n c r e a s e i n flavor? I f we look at one of the changes o c c u r r i n g i n a cut of meat as i t ages, we f i n d the cathepsins or p r o t e o l y t i c enzymes beginning to break up the m y o f i b r i l s f r a g i l i t y or tendernes bundles break more e a s i l y when subjected to t e n s i l e or shear stress. I f the m y o f i b r i l s are not e n z y m a t i c a l l y degraded, they s t r e t c h more when s t r e s s e d , producing a tougher muscle (4) (5). The p r o t e o l y t i c breakdown a l s o produces f r e e amino a c i d s . When meat i s heated or cooked, these f r e e amino a c i d s may p a r t i c i p a t e i n the non-enzymatic browning r e a c t i o n s which produce the lean meat f l a v o r (6). T h i s i s an example of an enzymatic process that produces both f l a v o r and texture changes. The p r o t e o l y t i c breakdown of m y o f i b r i l s c o n t r i b u t e s to both meat tenderness and flavor. Browning r e a c t i o n s are a l s o r e s p o n s i b l e f o r the formation of v o l a t i l e s that give f r e s h l y baked bread much of i t s f l a v o r . During s t a l i n g , t h i s f l a v o r p r o g r e s s i v e l y disappears. But the most pronounced change that takes place during s t a l i n g i s an i n c r e a s e i n firmness or hardness of the crumb. The extent of f i r m i n g can be used as an approximate index of f l a v o r l o s s or d e t e r i o r a t i o n duri n g s t a l i n g . T h i s i s why people shopping f o r bread judge i t s freshness and f l a v o r by squeezing the l o a f . Both firmness and f l a v o r l o s s are time and temperature dependent processes. Furthermore, the b a s i c molecular changes producing an increase i n firmness are l i k e l y the same ones producing the change or apparent l o s s of f l a v o r . Most of the increase i n firmness during s t a l i n g i s a t t r i b u t e d to changes i n the s t a r c h f r a c t i o n of the product. The s t a r c h i n bread increases i n c r y s t a l l i n i t y during aging. The exact nature of t h i s c r y s t a l l i n i t y i s not c l e a r (_7) . The l o s s of f l a v o r during s t a l i n g does not appear to be through v o l a t i l i z a t i o n or through chemical r e a c t i o n s (8). On reheating, when the process of s t a r c h rétrogradation or c r y s t a l l i z a t i o n i s temporarily reversed, the f l a v o r compounds are r e leased. T h i s suggests the f l a v o r compounds are probably trapped w i t h i n the c r y s t a l l i n e regions of the s t a r c h molecules. When trapped, they are prevented from v o l a t i l i z i n g or s o l u b i l i z i n g and, t h e r e f o r e , can make no c o n t r i b u t i o n to the t a s t e or aroma of the

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product. The molecular process r e s p o n s i b l e f o r the increase i n firmness during s t a l i n g i s a l s o the mechanism f o r trapping and r e l e a s i n g f l a v o r compounds. Experienced cheese graders can u s u a l l y guess the f l a v o r of a cheese by observing the t e x t u r e . The s t r u c t u r e and mechanical p r o p e r t i e s of a cheese depend p a r t l y on the b a c t e r i o l o g i c a l and/or enzymatic treatment of the milk, the processing techniques, any added p r o t e o l y t i c c u l t u r e s , and the aging process. These f a c t o r s are a l s o l a r g e l y r e s p o n s i b l e f o r the f l a v o r . For example, a f r e s h , unripe Cheddar cheese has a rubbery, curdy texture and a bland f l a v o r . T h i s texture i s due to the m i c r o s t r u c t u r e of c a s e i n m i c e l l e aggregates. As the cheese ages, the p r o t e i n s are broken down and the rubberiness changes i n t o a smooth, p l a s t i c texture. To a cheese grader t h i s smooth, s i l k y character i n d i c a t e s favorable f l a v o r development A dry texture i n Cheddar cheese woul a c i d f l a v o r , and a pasty fermented f l a v o r (9). Calves rennet i s c u r r e n t l y the most widely used p r o t e o l y t i c enzyme i n cheese making. The cheese i n d u s t r y has been engaged i n f i n d i n g a c l o t t i n g agent to s u b s t i t u t e f o r rennet. Problems a r i s e when other p r o t e o l y t i c enzymes are used because the p r o t e i n s break down i n a d i f f e r e n t manner. The way p r o t e o l y s i s occurs appears to a f f e c t how the c a s e i n m i c e l l e s a t t a c h to each other to form a g e l or curd. The m i c r o s t r u c t u r e of cheese made with proteases other than rennet tends to be more open (10). This a l t e r a t i o n i n b a s i c m i c r o s t r u c t u r e produces cheese with a l e s s p l a s t i c s t r u c t u r e . The p r o t e o l y s i s a l s o determines the peptides and amino a c i d s a v a i l a b l e . These not only c o n t r i b u t e to the t a s t e of the cheese but may undergo f u r t h e r enzymatic breakdown i n t o other f l a v o r compounds. In f r u i t s and vegetables, very important changes i n both texture and f l a v o r occur during r i p e n i n g . The texture of most f r u i t s becomes s o f t e r and l e s s c r i s p as i t matures. The f l a v o r becomes sweeter and more intense. The biochemical r e a c t i o n s that produce these changes occur independently. Changes i n f l a v o r are due to an increase i n the synthesis of sugars and an increase i n the r a t e at which v o l a t i l e s r e s p o n s i b l e f o r the aroma are synthesized. Changes i n the texture are l a r g e l y due to r e a c t i o n s taking place i n the p e c t i c substances of the middle l a m e l l a . In green f r u i t , the p e c t i c m a t e r i a l s have a high molecular weight and are i n s o l u b l e . They serve to cement the w a l l s of adjacent c e l l s together, thereby imparting considerable strength to the t i s s u e . During r i p e n i n g and senescence, enzymes i n the plant hydrolyze and otherwise a l t e r these p e c t i c substances, making them more s o l u b l e and l e s s e f f e c t i v e as cement. As a r e s u l t , the f r u i t becomes s o f t e r and e v e n t u a l l y mushy. Heat a l s o promotes the h y d r o l y s i s of p e c t i c m a t e r i a l s . This s o f t e n i n g i s r e a d i l y seen when f r u i t s or vegetables are cooked. The strength or cementing power of the middle l a m e l l a has important i m p l i c a t i o n s f o r both the f l a v o r and the texture of a

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product. I f the middle l a m e l l a i s stronger than the c e l l w a l l , which i s g e n e r a l l y the case with green and s l i g h t l y underripe f r u i t , the t i s s u e w i l l tend to f r a c t u r e or break across the c e l l w a l l s . I f the cementing power of the p e c t i c substances i s weakened, whether through enzymatic degradation or heating, the t i s s u e w i l l tend to f r a c t u r e between the c e l l w a l l s (11). From a sensory p e r s p e c t i v e , t h i s change i n f l u e n c e s both texture and f l a v o r . I f the c e l l s break across the c e l l w a l l s the c e l l contents w i l l run out, c r e a t i n g the sensation of j u i c i n e s s , and a l s o r e l e a s i n g the f l a v o r compounds i n s i d e the c e l l . The c e l l s of most f r e s h f r u i t s are t u r g i d , meaning there i s an i n t r a c e l l u l a r pressure d i r e c t e d outward against the c e l l w a l l . I f the product f r a c t u r e s across the c e l l w a l l , t h i s turgor p r e s sure i s r e l e a s e d r e s u l t i n g i n the r a p i d expansion of the c e l l ' s contents. T h i s sudden the product i s c r i s p . I f the product f r a c t u r e s between the c e l l s , they are not broken open. The product appears l e s s j u i c y , l e s s f l a v o r f u l , has a mushy or mealy texture, and l i t t l e , i f any, c r i s p n e s s . An example of such a system would be apples. A f r e s h , s l i g h t l y underr i p e or j u s t r i p e , c r i s p apple breaks across the c e l l w a l l s producing c r i s p , j u i c y , and f l a v o r f u l sensations. During prolonged storage or senescence, the middle l a m e l l a r p e c t i n s l o s e t h e i r cementing power. The same apple, i f stored f o r s e v e r a l months, would tend to l o s e i t s c r i s p n e s s and become mushy or mealy. The preceding examples i l l u s t r a t e that the processes genera t i n g changes i n f l a v o r are not n e c e s s a r i l y independent of those causing changes i n t e x t u r e . The s t r u c t u r a l and mechanical prop e r t i e s of foods are mainly due to l a r g e polymeric molecules. These molecules, e.g., s t a r c h , p r o t e i n s , c e l l u l o s e and p e c t i n s l i n k together or i n t e r a c t with each other to form the b a s i c s t r u c t u r e of the food. Such molecules themselves do not have any inherent f l a v o r p r o p e r t i e s . Molecules producing f l a v o r sensations are much smaller and g e n e r a l l y make no c o n t r i b u t i o n to t e x t u r e . When the s t r u c t u r a l molecules degrade or are broken down to smaller f l a v o r - p r o d u c i n g compounds, e.g., meat and cheese, or when changes i n the molecular s t r u c t u r e r e s p o n s i b l e f o r texture entrap or r e l e a s e f l a v o r compounds, e.g., s t a r c h systems and f r u i t s , the texture and f l a v o r changes w i l l take place c o n c u r r e n t l y .

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flavor quality: objective measurement Literature Cited

1.

2. 3. 4. 5. 6.

7. 8. 9. 10.

11.

Stone, H. and Pangborn, R. M. In "Basic Principles of Sensory Evaluation" p. 30-46. American Society for Testing and Materials. Philadelphia. 1968. Pangborn, R. M. and Szczesniak, A. S. J . Texture Studies (1974) 4 (4) 467-482. Pangborn, R. M . , Trabue, I. Μ., and Szczesniak, A. S. J . Texture Studies (1973) 4 (2) 224-241. Eino, M. F. and Stanley, D. W. J . Food S c i . (1973) 38 (1) 45-50. Eino, M. F. and Stanley, D. W. J . Food S c i . (1973) 38 (1) 51-55. Hornstein, I. In Price, J . F. and Schweigert, B. S. "The Science of Meat and Meat Products" W H Freeman and Co. San Francisco Willhoft, E. M. A Schoch, T. J. Baker's Dig. (1965) 39 40. Nelson, J . A. and Trout, G. M. "Judging Dairy Products" 4th ed. Olsen Publishing Co. Milwaukee. 1965. Stanley, D. W. and Tung, M. A. 1974. "Microstructure of food and its relation to texture." Presented at the symposium Advances in Food Texture, August 29, at Guelph, Ontario. Bourne, M. C. 1974. "Texture of fruits and vegetables." Presented at the symposium Advances in Food Texture, August 29, at Guelph, Ontario.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5 Relations between Sensory and Objective Measurements for Quality Evaluation of Green Beans JOHN J. POWERS and DAVID R. GODWIN Department of Food Science, University of Georgia, Athens, GA 30602 ROLF E. BARGMANN Department of Statistics and Computer Science, University of Georgia, Athens, GA 30602 For decades, substantia sound objective methods for quality evaluation of foods. Con siderable success has been achieved for color measurement; and for texture, moderate success. As was pointed out by Powers and Quinlan (1), part of this success has come about because some of the same forces or properties that cause us humans to respond to the food could be utilized in developing objective tests. Before the origin of gas-liquid chromatography (GLC) two decades ago, objective measurements of the numerous compounds that make up flavor was nigh impossible. Actually, not until a decade ago when Powers and Keith (2) and Dravnieks et al. (3) described practical means of analyzing GLC patterns could GLC measurements be efficiently correlated with flavor (4, 5). Quinlan et al. (6) and Powers (7) have reviewed most of the literature through early 1974. Recent papers are those of Galleto and Bednarczyk (8), Dravnieks et al. (9), Dravnieks (10), Gianturco et al. (11), Jobbágy and Holló (12), Severnants (13), and Powers (14). In spite of much progress, there are still major problems to be solved. Unlike color and texture, the relation between GLC peaks and flavor sensations is peripheral indeed. As Powers (7) pointed out, the properties that enable us to measure a substance chemically may often not be at all related to the properties that cause us to respond sensorially to that compound. In fact, in most cases, we don't know exactly the properties that do make us respond to a compound. Approximately two years ago, we turned to the sensory side to learn if better correlations could be obtained if one dealt with specific flavor or taste descriptions rather than the composite term, flavor. In the intervening years since GLC analysis became practical as a tool for flavor evaluation, others (9, 10, 12, 15, 16, 17, 18, 19, 20) have also endeavored to relate specific odor responses to GLC patterns. * Department of Statistics and Computer Science, University of Georgia. 51 In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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The problems i n t r y i n g to develop b e t t e r o b j e c t i v e methods for f l a v o r are: (A) We need to l e a r n the p r o p e r t i e s which make us respond s e n s o r i a l l y to t a s t e or odor substances; (B) We probably could use objective/sensory means more e f f i c i e n t l y , even though we are a long way from a t t a i n i n g the f i r s t o b j e c t i v e , i f we could r e l a t e s p e c i f i c terms on both sides of the o b j e c t i v e sensory equation rather than doing as we g e n e r a l l y do now, r e l a t e very s p e c i f i c e n t i t i e s (GLC peaks, f o r example) to a very broad term, f l a v o r ; and (C) No one of the sense m o d a l i t i e s operates i n a vacuum. Each one i s a f f e c t e d by the others. We have to l e a r n more about i n t e r r e l a t i o n s among the senses, e s p e c i a l l y as to sensations which encompass more than one sense modality. We have thus turned to the more general f i e l d of t r y i n g to r e l a t e nuances of sensory response to s p e c i f i c o b j e c t i v e measurements. Bargmann et a l . (21) a p p l i e d component a n a l y s i s to d e s c r i p t o r s f o r blueberry a t t r i b u t e s and q u a l i t y c a r r i e d on a f a c t o r a n a l y s i an o b j e c t i v e means of developing a s u i t a b l e terminology f o r t a s t e and odor sensations. In our laboratory, Hightower (23) has a p p l i e d a minimax approach (24) to component a n a l y s i s of potato chip f l a v o r s . This study i s a part of a continuing e f f o r t to broaden our base of knowledge and methodology so that objective/sensory measurements can be put upon an even f i r m e r foundation. Experimental A p r e l i m i n a r y t r i a l was c a r r i e d on i n mid-1975 f o r the purpose of s e t t i n g up a vocabulary of d e s c r i p t o r terms f o r appearance, c o l o r , mouthfeel, and f l a v o r of canned and frozen beans. Frozen or canned beans were heated f o r s e r v i n g and then sampled by approximately 40 i n d i v i d u a l s who were asked to w r i t e down every sensory response they thought p e r t i n e n t . This l i s t of 53 d e s c r i p t o r s was l a t e r e d i t e d to 27 terms thought to be p e r t i n e n t and not redundant. Sensory e v a l u a t i o n t r i a l s were then made using three commercial brands of canned beans and three of frozen beans, s e l e c t e d from a much l a r g e r group of brands to be sure that the brands a c t u a l l y used d i f f e r e d at l e a s t moderately i n q u a l i t y . The purpose of t h i s phase was to determine whether the terms which the l a r g e group of p a n e l i s t s s a i d were p e r t i n e n t were i n f a c t a c t u a l l y used and of a i d i n d i s c r i m i n a t i n g among the d i f f e r e n t l o t s of beans. A common problem i n a c c e p t a b i l i t y t r i a l s i s to be able to e x p l a i n the r e s u l t s . A p a n e l i s t may r a t e two products as being e q u a l l y acceptable; yet, say the products are d i f f e r e n t , simply because one a t t r i b u t e makes one product d e s i r a b l e whereas a d i f f e r e n t a t t r i b u t e makes the other product e q u a l l y acceptable. T h i s , of course, i s the reason f o r t r y i n g to go behind the general terms, f l a v o r or mouthfeel, f o r example, to seek out the s p e c i f i c sensory q u a l i t i e s which make the food d e s i r a b l e .

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F i r s t sensory t r i a l . The three frozen and canned products were evaluated s i m i l a r l y to the procedure described by Vuataz et a l . (25) and Wu et a l . (22). The p a n e l i s t s evaluated the products h e d o n i c a l l y f o r a c c e p t a b i l i t y , appearance, c o l o r , mouthfeel, and f l a v o r . Hereafter, these f i v e f a c t o r s w i l l be r e f e r r e d to as "general d e s c r i p t o r s " to save having to l i s t them each time. The hedonic terms f o r the general d e s c r i p t o r s were l a t e r t r a n s posed to a 9-point s c a l e . The p a n e l i s t s were a l s o asked to r a t e the degree to which each product was stronger or weaker as compared with a reference sample i n a p a r t i c u l a r a t t r i b u t e , using the 27 d e s c r i p t o r s chosen from the o r i g i n a l l i s t of 53 s p e c i f i c d e s c r i p t o r s . One of the brands of canned beans was the reference sample. The same product was a l s o included among the t e s t products as a coded sample to provide a check upon the p a n e l i s t s . The p a n e l i s t s were thu asked t (A) evaluat th q u a l i t f th beans, using hedonic term (B) compare each t e s t produc agains produc each of the 27 s p e c i f i c d e s c r i p t o r s , and then (C) re-evaluate the products, using the f i v e general d e s c r i p t o r s . There were 21 p a n e l i s t s and each product was evaluated four times. Before the t r i a l s s t a r t e d , a t a b l e of random numbers had been used to assign each product to a session so that e v e n t u a l l y each product was examined four times. At any one s e s s i o n , the p a n e l i s t s evaluated four samples plus the reference. Sampling was always between 10:30 to 11:30 AM. S t a t i s t i c a l a n a l y s i s . The sensory data were subjected to a n a l y s i s of variance to e l i m i n a t e i n e f f e c t u a l judges or d e s c r i p t o r s . By u n i v a r i a t e a n a l y s i s (MUDAID program) (26), the treatment/ e r r o r F values were computed. Judges or d e s c r i p t o r s , not s t a t i s t i c a l l y s i g n i f i c a n t , were dropped from f u r t h e r consideration, T h i s procedure i s r o u t i n e i n our l a b o r a t o r y (1, J5, 14, _21, 22, 23). The e d i t e d r e s u l t s were then analyzed by f a c t o r a n a l y s i s to detect d e s c r i p t o r s of major importance and to e f f e c t f u r t h e r e d i t i n g of the d e s c r i p t o r l i s t . The minimax program of Bargmann and Baker (24) was used f o r t h i s purpose, coupled with the f a c t o r a n a l y s i s by stepwise maximum l i k e l i h o o d s o l u t i o n and r o t a t e d (oblique r o t a t i o n ) by Thurstone's A n a l y t i c a l Method of Rotation (Harman) (27). A n a l y s i s of variance and Duncan's m u l t i p l e range t e s t s were used to t e s t f o r s i g n i f i c a n t d i f f e r e n c e s between the products, both f o r the general and 27 s p e c i f i c d e s c r i p t o r s . Main t r i a l s . The main experiment c o n s i s t e d of e v a l u a t i n g eight l o t s of beans, much as above. The t r i a l s were c a r r i e d on i n e a r l y summer 1976. There were 27 p a n e l i s t s , very few of whom were on the 1975 panel; there were 20 s p e c i f i c d e s c r i p t o r s (7 having been dropped as a r e s u l t of the 1975 t r i a l ) , and again the t r i a l s were r e p l i c a t e d four times. The beans consisted of four brands of canned beans, three of f r o z e n beans, and f r e s h beans.

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The f r e s h beans were used f o r the reference sample; as before, they were also included as a coded sample. The p a n e l i s t s were asked to evaluate f i v e or s i x products at each s e s s i o n . The products had p r e v i o u s l y been assigned to a p a r t i c u l a r session, using, as before, a t a b l e of random numbers. The judges evaluated the beans h e d o n i c a l l y f o r the f i v e general d e s c r i p t o r s , rated them against the reference sample f o r the 20 s p e c i f i c d e s c r i p t o r s , then re-evaluated the beans again f o r general a t t r i b u t e s . The f r e s h beans were cooked by simmering them f o r 25 minutes, an equal weight of beans with an equal weight of 1% s a l i n e s o l u t i o n . The frozen product was prepared by cooking 510 g of beans i n 700 ml of 1% s a l i n e s o l u t i o n f o r 15 minutes. The canned beans were heated f o r 15 minutes i n t h e i r own packing l i q u o r . For each product, a l l samples f o r sensory and o b j e c t i v e t e s t s were withdrawn fro th cookin l t th time. In other words, th were cooked e x a c t l y the trial. The organoleptic t e s t s were thus s t r i c t l y comparable to the o b j e c t i v e t e s t s i n terms of p r i o r treatment. The p a n e l i s t s were given 15-20 g of sample i n a t r a n s l u c e n t p l a s t i c s o u f l e cup. The cups were c o l o r coded, a given c o l o r was not assigned to the same p o s i t i o n , but randomly changed from session to session. Sensory evaluation was done e i t h e r at 9:30 to 10:30 AM or 3:30 to 4:30 PM. At the end of the t a s t e - t e s t i n g sessions, u n i v a r i a t e a n a l y s i s was used, as described above, to e l i m i n a t e p a n e l i s t s or d e s c r i p t ors not s t a t i s t i c a l l y s i g n i f i c a n t as judged by the treatment/error F value. GLC procedure. The GLC procedure was e s s e n t i a l l y the same as described i n e a r l i e r p u b l i c a t i o n s (28, 29). F i f t y grams of beans were placed i n a 2 l i t e r f l a s k with 1 l i t e r of water f o r the combined s t e a m - d i s t i l l a t i o n - s o l v e n t - e x t r a c t i o n procedure of Likens and Nickerson (30). D i e t h y l ether was the solvent. After e x t r a c t i o n , d i s s o l v e d and e m u l s i f i e d water was frozen out at -28 C. The e x t r a c t was decanted from the i c e c r y s t a l s i n t o a KudernaDanish assembly and the volume reduced to 0.5 ml. For GLC a n a l y s i s , a s i n g l e column chromatograph with a 3.66 m, 6.4mm s t a i n l e s s s t e e l column packed with 5% SP-1000 on Chromosorb W-HP, AW, DMCS, 60/80 mesh, was used. Programming was at 6.4 C/min from 25 to 200 C. A 5 y l sample was i n j e c t e d . Inspection of the chromatograms showed 45 d i s t i n c t peaks. Several other peaks were a l s o d i s c e r n i b l e , but only those which were w e l l resolved were used. The 45 peaks were converted to percent area (4). L i q u i d - s o l i d chromatography. N o n - v o l a t i l e and pigment components were analyzed f o r by a LC method. The products were prepared f o r a n a l y s i s by e x t r a c t i n g 50 g of beans with 100 ml of an e x t r a c t i o n solvent composed of acetone, chloroform, and

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hexane (1/1/1). The beans and the e x t r a c t i n g s o l v e n t were placed i n a high speed blender f o r 5 min and then separated by two f i l t r a t i o n steps through No. 4 and No. 42 f i l t e r paper, r e s p e c t i v e l y . The e x t r a c t was evaporated at reduced pressure to a dry residue i n a r o t a r y evaporator p a r t i a l l y submerged i n a water bath at 50-60 C. The residue was then r e - e x t r a c t e d with 25 ml of hexane. Drying had a two-fold o b j e c t i v e ; f i r s t , to remove v o l a t i l e compounds which were already being analyzed f o r by GLC a n a l y s i s and, secondly, to remove the p o l a r s o l v e n t s , e s p e c i a l l y water. The p o l a r s o l v e n t s and the h i g h l y - p o l a r water had to be removed p r i o r to the LC a n a l y s i s . The components are c a r r i e d by the i n j e c t e d sample i n i t i a l l y , but when s e p a r a t i o n occurs along the column, p a r t i t i o n i n g between the s t a t i o n a r y phase and the c a r r i e r produces such a high a f f i n i t y f o r the s t a t i o n a r y phase that p o l a r components become non-mobile bands on the column. For LC a n a l y s i s , a syste compose a Model UGK, U n i v e r s a l L i q u i d Chromatography I n j e c t o r and a Model 6000A solvent d e l i v e r y system with a model 440 absorbance d e t e c t or was used. The flow r a t e was 1.0 ml/min with d e t e c t i o n at 365 nm. The sample s i z e was 10 u l . The s o l v e n t , an adapted v e r s i o n of Pons (31) s o l v e n t , was 750 ml chloroform, 225 ml cyclohexane, 3 ml a c e t o n i t r i l e . and 2 ml 2-propanol. Inspection of the chromatograms y i e l d e d 11 peaks. These peaks were compared as absolute absorbance v a l u e s . 1

Color. The products were analyzed s p e c t r o p h o t o m e t r i c a l l y over the v i s i b l e region of the spectrum. The samples used f o r t h i s a n a l y s i s were a l i q u o t s taken from the hexane-extraction phase of the LC procedure described above. T h i s procedure was q u i t e e f f i c i e n t f o r the e x t r a c t i o n of p l a n t pigments. A Shimadzu Multipurpose Recording Spectrophotometer, Model MPS-50L, equipped with 1 cm c e l l s was used. A l l measurements were made i n the 0-1 absorbance range with necessary d i l u t i o n s to provide on-scale readings. (Just before the t r i a l s s t a r t e d , the instrument went s l i g h t l y out of adjustment so that switching from the 0-1 to the 1-2 range d i d not r e s u l t i n absolute coincidence; r a t h e r than delay the t r i a l s , the d i l u t i o n method was used w i t h backward c a l c u l a t i o n of the values to provide a continuous spectrum.) A f t e r a n a l y s i s , absorbance at 16 d i f f e r e n t wavelength was s e l e c t e d f o r comparisons. Mechanical measurements. Factor a n a l y s i s of the p r e l i m i n a r y t r i a l showed that there was a strong f a c t o r c o n s i s t i n g of "coarse, f i b r o u s , c r i s p , j u i c y , slimy, soggy, and tender." Thought was turned to u t i l i z i n g some mechanical t e s t which might correspond with t h i s sensory f a c t o r . I t was t h e r e f o r e decided to measure the c o e f f i c i e n t of f r i c t i o n between a moveable p l a t e (32) (sled) and the outer surface of the beans. The beans were o r i e n t e d i n two p o s i t i o n s : one was with the beans p a r a l l e d to the f o r c e

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and the second was with the beans perpendicular to the d i r e c t i o n of p u l l . The beans were t i g h t l y f i t t e d i n t o an area on the s t a t i o n a r y p l a t e of an Instron, Model 1130, apparatus equipped with a 1 lb. c e l l . The s t a t i c and dynamic surfaces were covered with aluminum f o i l . The s l e d was then p u l l e d on top of the beans u n t i l the |orce became constant. The p l a t e had a surface area of 39.69 cm . I t s dimensions were 6.3 χ 6.3 χ 1.2 cm and i t weighed 169.5 g. The f o r c e was c a l c u l a t e d as Newtons/cm . T e n s i l e strength. The t e n s i l e f o r c e required to p u l l beans apart l o n g i t u d i n a l l y was a l s o measured. The beans were clamped at each end between the jaws of two f i x t u r e s . The ends of the beans were wrapped once with cheesecloth so that the clamps could " b i t e " i n t o the beans s l i g h t l y ; otherwise, the beans tended to s l i p from between the jaws or e l s e the clamping f o r c e caused them to break f i r s t wher mediate between the tw 2 in/min. The t e n s i l e strength was taken as the maximum breakingp o i n t f o r c e d i v i d e d by the c r o s s - s e c t i o n a l area of the bean. As before, the t e n s i l e strength was u l t i m a t e l y expressed as Newtons/ cm . Shear f o r c e . The f o r c e required to cut the beans crosswise while i n a Warner-Bratzler type k n i f e assembly was a l s o measured. The crosshead speed was 2 in/min. The shear f o r c e was c a l c u l a t e d from the f o r c e r e s u l t i n g i n f a i l u r e of the bean d i v i d e d by the c r o s s - s e c t j o n a l area of the bean. The values were recorded as Newtons/cm . C l u s t e r a n a l y s i s . The procedure of T r i v e d i (33) was used to carry on " v i r t u a l " c l u s t e r a n a l y s i s . Bargmann and Grainey (34) and T r i v e d i (33) have defined " v i r t u a l . " B a s i c a l l y , the r e l a t i o n may be l i k e n e d to the c l u s t e r of s t a r s one sees when one gazes at the Pleiades against the v a u l t of the heavens and the a c t u a l p o s i t i o n s of the s t a r s . I f one were i n the midst of the P l e i a d e s , the s t a r s would not appear to be c l u s t e r e d at a l l . The c l u s t e r i s i l l u s o r y . We see t h e i r p o s i t i o n s i n three dimensions p r o j e c t e d against the surface of the c e l e s t i a l sphere i n two dimensions. S i m i l a r l y , i t i s w e l l known that random v a r i a b l e s can be regarded as spectors embedded i n the E u c l i d i a n space of i n f i n i t e dimensions. I f the s p h e r i c a l cap which r e s u l t s from the p r o j e c t i o n of the c l u s t e r i s compared with the e n t i r e surface area, one then has a measure of the density of the c l u s t e r . The computer program forms a c l u s t e r when the surface area of a s p h e r i c a l cap i n k dimension extending to the f a r t h e s t p o i n t i n s i d e the c l u s t e r i s compared with the surface area of the k dimension when one a d d i t i o n a l point or a t t r i b u t e i s added to i t . When t h i s r a t i o s u f f e r s a severe drop, a c l u s t e r core i s considered terminated. Those a t t r i b u t e s that have once been included i n a c l u s t e r core are not used again to form another c l u s t e r core. New c l u s t e r s are formed

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from the r e s i d u a l a t t r i b u t e s of prior-formed c l u s t e r s . In e f f e c t , the v e c t o r s are p r o j e c t e d onto a Unisphere where the p o i n t s on the Unisphere are connected by great c i r c l e s . The cosine of each of the great c i r c l e s represents the c o r r e l a t i o n between each p a i r of random v a r i a b l e s . The r e p r e s e n t a t i o n of c o r r e l a t i o n s as cosines of angles between v e c t o r s was f i r s t introduced by K a r l Pearson (35) i n 1901. To organize the data f o r c l u s t e r a n a l y s i s , the 27 sensory values that e x i s t e d f o r each product and r e p l i c a t i o n had to be reduced to one experimental u n i t to correspond with the one u n i t which e x i s t e d f o r each of the o b j e c t i v e measurements. The gen e r a l d e s c r i p t o r s were weighted by the f o l l o w i n g formula

1 +

w

|x

x

I

where χ was the score the judge gave knowingly to the reference sample and χ was the score he gave when he d i d not know he was judging the reference product. I f x^ equals χ , the weight attached to t h i s judgment on t h i s p a r t i c u l a r a t t r i b u t e w i l l be one. I f he makes a r a t h e r extreme misjudgment, the d i f f e r e n c e x^ minus could be, say, 4 p o i n t s . In t h i s case, h i s weight would be only 1/5 of that attached to a judge whose r a t i n g of the reference product was c o n s i s t e n t r e g a r d l e s s of whether he evaluated i t knowingly or unknowingly. For the 20 s p e c i f i c d e s c r i p t o r s , the weighting a t t r i b u t e d to each judge was somewhat d i f f e r e n t .

w

-

1 + jx -5l * u 1

In t h i s formula, χ i s the score the judge gave to the coded reference sample. Since he was comparing i t against the known reference sample and the "no d i f f e r e n c e " score was 5, he should have assigned a 5. I f he assigned any other score, he was being i n c o n s i s t e n t and the weight of h i s score was decreased accord i n g l y . By weighting the general and s p e c i f i c d e s c r i p t o r scores i n the f a s h i o n above, we then had 32 experimental u n i t s (8 products χ 4 r e p l i c a t i o n s ) on which we had a l l the o b j e c t i v e determinations and the composite judgment on each of the 30 d e s c r i p t o r s . A c o r r e l a t i o n matrix was then formed between the 58 v a r i a b l e s on the b a s i s of the 32 experimental u n i t s . The 28 o b j e c t i v e a t t r i b u t e s included 17 GLC peaks, 3 s p e c t r a l r a t i o s , 4 LC peaks, and 4 mechanical measurements. Results

1975

Factor a n a l y s i s . E d i t i n g of the 27 d e s c r i p t o r s used i n the p r e l i m i n a r y t r i a l s r e s u l t e d i n seven being dropped because

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they e i t h e r were not used or they d i d not d i s c r i m i n a t e among the products. Factor a n a l y s i s y i e l d e d the eight f a c t o r s l i s t e d below: Factor 1

Factor 4

Off-flavor 0.52 Persistent 0.42 aftertaste Bland f l a v o r 0.31 Pleasant -0.44 aftertaste

Coarse Fibrous Crisp Slimy Juicy Soggy Tender

Factor 7 0.57 0.57 0.53 -0.53 -0.55 -0.63 -0.66

Factor 2 Color-1 0.69 Color-2 0.64 Appearance-1 0.61 Appearance-2 0.58 Bright c o l o r 0.33 Pale c o l o r -0.38 Color o f f -0.43 shade Factor 3 Fibrous Coarse Buttery

0.47 0.46 0.34

Factor 5

aftertaste Hay-like taste Coarse Fibrous Bland Juicy

0.42 0.41 0.38 0.36 0.29

Factor 6 Coarse Fibrous Off-flavor Persistent aftertaste Hay-like taste Slimy

0.50 0.49 0.44 0.43

Soggy Slimy Juicy Buttery Tender

0.50 0.47 0.43 0.41 0.34

Factor 8 Color-1 Appearance-•1

0.55 0.51

Coarseness Fibrous Crisp Bright color Juicy Slimy Pale c o l o r Color o f f shade Tender

0.36 0.36 0.33 0.31 -0.32 -0.34 -0.39 -0.46 -0.50

0.33 0.31

Comment w i l l be reserved u n t i l we come to the c l u s t e r a n a l y s i s of the main experiment because the f a c t o r a n a l y s i s and the c l u s t e r a n a l y s i s corroborated each other, except to point out some of the major observations. Factor 7, f o r example, r e l a t e s e s s e n t i a l l y to mouthfeel except the f l a v o r note of "buttery" was a part of that f a c t o r . The same thing may be seen f o r f a c t o r 3; buttery again accompanies the mouthfeel sensations. Factor 4 shows the two sets of terms combined except b u t t e r y i s not s u f f i c i e n t l y w e l l c o r r e l a t e d to come w i t h i n the f a c t o r . Sensory c o n t r i b u t i o n s to a c c e p t a b i l i t y . One of the problems i n d e v i s i n g o b j e c t i v e t e s t s to s u b s t i t u t e f o r or to complement sensory evaluations i s to know how to weight the o b j e c t i v e t e s t so that i t w i l l c o n t r i b u t e i n the same manner to a c c e p t a b i l i t y as does each sense modality. L i s t e d below are the simple and

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

POWERS E T AL.

Quality

Evaluation

of Green

59

Beans

m u l t i p l e c o r r e l a t i o n c o e f f i c i e n t s f o r the 1975 and 1976 e x p e r i ments . Multiple

correlations

Acceptability Acceptability

Acceptability Simple

1975 T r i a l s

1976 T r i a l s

f l a v o r , mouthfeel, appearance & c o l o r vs. f l a v o r , mouthfeel & appearance

0.917

0.917

0.915

0.916

vs.

0.906

0.912

0.884 0.801

0.891 0.794

vs.

f l a v o r and mouthfeel

correlations

Acceptability Acceptability Acceptability Acceptability

vs. f l a v o r vs. mouthfeel vs. appearanc vs. c o l o

It i s q u i t e obvious that f l a v o r and mouthfeel e s s e n t i a l l y determine a c c e p t a b i l i t y and that appearance and c o l o r are of l e s s e r importance. This does not mean that appearance and c o l o r are unimportant. Rather, w i t h i n the commercial range, remaining v a r i a t i o n s i n c o l o r or appearance are apparently of l e s s e r importance i n determining a c c e p t a b i l i t y than the v a r i a t i o n s that occur i n t e x t u r a l and f l a v o r q u a l i t i e s . Emotional vs. a n a l y t i c a l judgments. One of the aspects we have been i n t e r e s t e d i n i s the e f f e c t of a n a l y t i c a l thought such as has to go i n t o the r a t i n g of each d e s c r i p t o r r e l a t i v e to the reference sample versus the rather low-key thought o r emotion i n v o l v e d i n r a t i n g foods h e d o n i c a l l y . Should the samples be judged f o r general c h a r a c t e r i s t i c s p r i o r to or a f t e r the a n a l y t i c a l phase? They cannot be judged apart without a great d e a l of e x t r a r e p l i c a t i o n to overcome the v a r i a t i o n r e s u l t i n g from using d i f f e r e n t l o t s and cooking batches. Immediately below are the c o r r e l a t i o n c o e f f i c i e n t s between corresponding general d e s c r i p t ors evaluated before and a f t e r the a n a l y t i c a l comparison phase. Factor Acceptability Appearance Color Mouthfeel Flavor

1 1 1 1 1

vs. vs. vs. vs. vs.

2 2 2 2 2

1975 Experiment

1976 Experiment

0.841 0.833 0.849 0.798 0.859

0.863 0.837 0.850 0.847 0.834

There was some evidence that a f t e r a n a l y t i c a l thought the paneli s t s rated the general q u a l i t i e s of the beans somewhat d i f f e r e n t l y than they had when they were merely expressing l i k i n g - d i s l i k i n g without a l o t of thought as to why. Cluster

analysis.

The three strongest c l u s t e r s

included

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

60

FLAVOR QUALITY:

f a c t o r s f o r texture, below:

f l a v o r , and

appearance,

OBJECTIVE

MEASUREMENT

They are

Cluster 1—Texture

Cluster 2 — F l a v o r

Cluster

Coarse Fibrous Tender Juicy Crisp Buttery Hay-like f l a v o r Bright c o l o r Slimy Soggy

Flavor-1 Flavor-2 Acceptability-1 Acceptability-2 Mouthfeel-2 Mouthfeel-1 Pleasant a f t e r t a s t e Off-flavor Sweet

Color-1 Color-2 Appearance-1 Appearance-2

listed

3—Appearance

The program was set t i f the c o r r e l a t i o n c o e f f i c i e n t was above 0.70. Terms not used then went i n t o a r e s i d u a l group of f a c t o r s , from which a secon dary core set could be extracted and i n turn a t h i r d core and subsequent cores, denominated " v i r t u a l c l u s t e r s . " A c t u a l l y , 17 d i f f e r e n t c l u s t e r s were generated. The f i r s t three c l u s t e r s included only sensory f a c t o r s ; the l a t e r c l u s t e r s consisted predominantly of o b j e c t i v e measurements. The 58 χ 58 c o r r e l a t i o n matrix i s too massive to reproduce. From Tables I, I I , and I I I , one can observe some of the sensory-objective c o r r e l a t i o n s . As was true f o r the f a c t o r a n a l y s i s , a t t r i b u t e s which we tend to think of as being texture, f l a v o r , or appearance f a c t o r s are so w e l l c o r r e l a t e d with each other that they sometimes appear i n a d i f f e r e n t c l u s t e r than one would expect. Note that "buttery," " h a y - l i k e f l a v o r , " and " b r i g h t c o l o r " show up i n a c l u s t e r otherwise r e l a t i n g to texture. To i l l u s t r a t e the numerous sensory-objective c o r r e l a t i o n s that d i d appear i n the 58 χ 58 matrix, three l i s t s are given as f o l l o w s : C o r r e l a t i o n of absorbance r a t i o 525/610 nm Color-1 Color-2 Color, off-shade Bright c o l o r GC 24 GC 32 Ratio 467/525 Ratio 525/665

-0.67 -0.64 0.69 -0.77 0.64 0.67 -0.74 0.66

Green veg. t a s t e -0.87 0.76 Buttery f l a v o r Hay-like t a s t e -0.65 0.71 Process f l a v o r

with -0.81 Crisp Coarse -0.75 0.70 Juicy Slimy 0.64 0.71 Soggy Fibrous -0.75 0.78 Tender

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Coarse Fibrous Tender Juicy Crisp Buttery Hay-like taste Green veg. t a s t e Bright c o l o r Slimy Soggy Process f l a v o r Color, o f f shade 525/610 Shear f o r c e Sweet Flavor Mouthfeel Acceptability Pleasant a f t e r t a s t e j T e n s i l e strength LC09 Off-flavor GC-24 GC-32 Color Pale c o l o r 525/665

Table I

Buttery -.90 -.94 .94 .89 -.88

Crisp .94 .92 .93 .91

Juicy .95 .92 .95

Tender

-.96 -.97

Fibrous

.97

C l u s t e r No. 1 Bright Color .82 .87 .87 .74 .83 .82 .82 .91

Green Veg. taste .90 .91 .90 .83 .92 .86 .84

Hay-like taste .91 .93 -.94 -.87 .89 -.92

.87 .86 .84 .88 .81 .77 .76 .78 .65

Slimy

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Coarse Fibrous Tender Juicy Crisp Buttery Hay«like t a s t e Green Veg. t a s t e Bright c o l o r Slimy Soggy Process f l a v o r Color, o f f shade 525/610 Shear f o r c e Sweet Flavor Mouthfeel Acceptability Pleasant a f t e r t a s t e T e n s i l e strength LC09 Off-flavor GC-24 GC-32 Color Pale c o l o r 525/664

Table I (continued)

.77 .79 .80 .75 .79 .67 .67 .83 .77 .71 .75

Process flavor t

.74 .78 .81 .77 .73 .71 .71 .75 .76 .75 .70 .87

Color off-shade

C l u s t e r No. 1

.75 .75 .78 .70 .81 .76 .65 .87 .77 .64 .71 .71 .69

;

Sweet

.77 j -.74 .79 ! -.79 .76 -.76 .67 -.71 -.61 .68 .84 -.76 -.82 .78 -.60 .68 -.61 .75 .58 -.58 .49 -.53 .44 -.58 .46 -.62 .43 -.57 -.73

j Shear 525/610 f o r c e -.70 -.74 .76 .67 -.61 .84 -.85 -.67 -.71 .50 .43 .40 .48 .50 -.62 .76

Flavor .64 .65 .68 .62 .55 .73 .73 .60 .60 .39 .37 .38 .36 .51 .55 .65 .88

Mouthfeel .64 .65 .65 .59 .51 .74 .77 .59 .59 .42 .36 .31 .31 .42 .57 .69 .95 .90

Acceptability -.60 -.64 .65 .56 -.56 .78 -.74 -.57 -.60 .39 .35 .24 .30 .46 -.49 .74 .84 .74 .82

Pleasant aftertaste

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Coarse Fibrous Tender Juicy Crisp Buttery Hay-like taste Green Veg. t a s t e Bright c o l o r Slimy Soggy Process f l a v o r Color, o f f shade 525/607 Shear f o r c e Sweet Flavor Mouthfeel Acceptability Pleasant a f t e r t a s t e T e n s i l e strength LC09 Off-flavor GC-24 GC-32 Color Pale c o l o r 525/665

Table I (continued)

.68 .70 -.66 -.71 .58 -.64 .66 .52 .51 -.58 -.54 -.47 -.45 -.37 .71 -.67 -.51 -.56 -.47 -.31

Tensile strength

1

! ; J ι

!

·

.61 .63 -.72 -.61 .57 -.67 .64 .63 .69 -.56 -.45 -.55 -.67 -.63 .47 -.46 -.56 -.39 -.43 -.48 .33

LC09

C l u s t e r No. 1

1

.54 .55 -.57 -.49 .50 -.67 .67 .50 .48 -.33 -.31 -.10 -.17 -.41 .35 -.63 -.78 -.65 -.76 -.90 .26 .48

Off-flavor

1

-.55 -.54 .62 .60 -.54 .57 -.44 -.55 -.57 .53 .47 .52 .60 .64 -.44 .37 .38 .41 .28 .33 -.34 -.55 -.23

GC-24 -.58 -.54 .62 .61 -.54 .52 -.48 -.60 -.48 .61 .59 .55 .58 .67 -.33 .32 .34 .35 .32 .32 -.25 -.57 -.30 .74

GC-32 .57 .60 -.65 -.56 .60 -.50 .55 .63 .67 -.55 -.53 -.74 -.82 -.67 .53 -.28 -.24 -.17 -.06 -.06 .40 .65 .01 -.51 -.49

Color -.54 -.57 .53 .47 -.50 .44 -.52 -.57 -.60 .59 .55 .56 .53 .40 -.55 .37 .31 .08 .27 .19 -.33 -.42 -.17 .25 .49 -.50

Pale color -.52 -.53 .51 .49 -.51 .55 -.39 -.56 -.43 .50 .50 .48 .45 .66 -.44 .33 .34 .29 .30 .24 -.43 -.40 -.25 .27 .42 -.31 .32

525/665

j

!

.37 .45 -.43 -.26 .29 -.50 .54 .48 .64 -.26 -.16 -.19 -.29 -.35 .53 -.46 -.60 -.37 -.54 -.62 .22 .56 .60 -.24 -.14 .22 -.44 -.24

GC-20

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Color Appearance Color, o f f shade Process f l a v o r 525/610 LC 09 GC-24 GC-32 Shear f o r c e Pale c o l o r GC-37

Table I I I

.83

Appearance -.82 -.52

-.74 -.51 .87

-.67 -.48 .69 .71

.65 .43 -.67 -.55 -.63

-.51 -.39 .60 .52 .64 -.55 -.49 -.31 .58 .55 .67 -.57 .74

.53 .18 -.62 -.58 -.57 .47 -.44 -.33

-.50 -.21 .53 .56 .40 -.42 .25 .49 -.55

.38 .27 -.50 -.58 -.40 .49 -.38 -.37 .34 -.33

.52 .42 -.42 -.48 -.41 .32 -.30 -.07 .47 -.27 .34

Color, Process Shear P a l e 525/610 LC 09 GC 24 GC 32 f o r c e c o l o r GC 37 GC 47 o f f shade f l a v o r

C l u s t e r No. 3

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

!

.88 .90

.84 .82 .74

-.78 -.76 -.65 -.90

.76 .69 .65 .74 -.63

-.62 -.57 -.54 -.49 .35 -.73

-.60 -.54 -.37 -.62 .60 -.46 .53

-.61 -.47 -.57 -.46 .43 -.69 .42 .25

-.51 -.47 -.56 -.31 .26 -.67 .71 .22 .54

C l u s t e r No. 2. i Pleas Ac Off ant ceptTensile Shear a b i l Mouth a f t e r f l a strength Bland GC-20 force Sweet vor t a s t e feel ity

.95 Flavor Acceptability Mouthfeel Pleasant a f t e r t a s t e Off-flavor Sweet Shear f o r c e GC-20 Bland T e n s i l e strength GC-33 Uniform LC09 LC02

Table I I

-.60 -.59 -.46 -.51 .54 -.32 .22 .63 .39 .25

ι

-

525/ 610

.50 ! .50 -.56 -.50 1 .43 -.43 .44 .42 ! .36 -.39 .55 .51 1 .33 -.48! .42 .46 i .48 -.38 -.41 S-.30 .45 .43 S .64 -.46 57 1-.44 .47 -.18 — .32 .56 -.20!-.35 -.72 .30 -.58 j-.22 -.42 .33 -.42 ,-.37 -.30 ! .27 ί-.41 -.12 -.25 ! .24 .04 I-.41 -.63 ! .26

1

1 'UniGC-33 form;LC09 LC02

1

66

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

C o r r e l a t i o n s of shear f o r c e w i t h Soggy Coarse Crisp Mouthfeel-1 Slimy Juicy Tender

0.79 0.77 0.68 -0.55 -0.58 -0.71 -0.76

Hay-like f l a v o r Green veg. t a s t e Acceptability-1 Process t a s t e Flavor-1 Sweet Buttery f l a v o r

0.78 0.68 -0.57 -0.58 -0.62 -0.73 -0.76

Bright color 0.75 Pale d o l o r -0.55 Ratio 525/610 -0.57 Color, off-shade -0.62

C o r r e l a t i o n s with LC Peak No. Color-1 0.65 Color, o f f -shade --0.67 Bright c o l o r 0.69 525/610 nm r a t i o --0.6

-0.67 Buttery Green veg. t a s t e 0.63 0.64 Hay-like taste

9 0. 61 Coarse Juicy -0. 61 F i b r o u s 0. 63 Tende 2

Discussion Some of the observations and r e l a t i o n s have been commented on above. One of the s t r i k i n g things with regard to the GLC measurements was that most of the GLC peaks were n e g a t i v e l y r e l a t e d to f l a v o r i n d i c a t i n g that the compounds being measured were detrimental to f l a v o r . Some of the r e l a t i o n s with regard to a b r i g h t c o l o r were a l s o noteworthy. The c o r r e l a t i o n s are l i s t e d below: C o r r e l a t i o n s of b r i g h t c o l o r w i t h Color-1 Green veg. taste Hay-like flavor Crisp Coarse Fibrous GC 20

0.67 0.91 0.82 0.83 0.82 0.87 0.64

Acceptability-1 Flavor-1 Sweet Buttery Process f l a v o r Pleasant a f t e r taste Juicy

-0.59 -0.71 -0.61 -0.82 -0.77 -0.60

Slimy Soggy Tender Pale c o l o r Color, off-shade

-0.65 -0.67 -0.87 -0.60 -0.76

-0.74

The c o r r e l a t i o n s i n d i c a t e the r i s k s involved i f one confines oneself to one sense modality (as many of us have done i n the past). The i n t e r r e l a t i o n s between the sense m o d a l i t i e s i s so strong that p r e f e r a b l y a l l should be evaluated at the same time, e s p e c i a l l y i f one hopes to make informed judgments as to the o b j e c t i v e t e s t s which w i l l n e a r l y r e f l e c t o v e r a l l a c c e p t a b i l i t y . Within the past few years, increased emphasis has been placed on r e l a t i n g d e s c r i p t o r terms to q u a l i t y or s p e c i f i c chemicals (9-13, 15-23, 36-48). The procedures depend on a r t i c u l a t i n g a l i s t of d e s c r i p t o r s based upon " s n i f f i n g " or sampling the food with considerable deep and mature thought as to the sensations being perceived. Objective means of e v a l u a t i n g the

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

POWERS E T A L .

Quality

Evaluation

of

Green

Beans

67

d e s c r i p t o r s a r r i v e d at should be used to seek out main d i s c r i m i nators (49, 50, 51) because our s u b j e c t i v e impressions do not always c o i n c i d e with the way we a c t u a l l y use words (45), as demonstrated by Lehrer (45), Wu et a l . (22) and i n t h i s study. The u l t i m a t e goal, of course, i s to be able to develop a general equation s u i t a b l e f o r p r e d i c t i n g the q u a l i t y of the food from o b j e c t i v e measurements or a mixture of sensory-objective terms. There are s e v e r a l s t u d i e s where covariance or m u l t i r e g r e s s i o n procedures have been used (13, 52, 53, 54) to e s t a b l i s h r e l a t i o n s between response to one or a few sense m o d a l i t i e s and o b j e c t i v e measurements. This study shows that a l l of the senses should be taken i n t o account because one component o f t e n i n f l u e n c e s one's response to the food i n ways not suspected (or at l e a s t f u l l y understood) unless the data are evaluated objectively. The road to a genera any given commodity w i l l be long and tortuous. Cluster analysis i s but one of the methods a p p l i c a b l e i n moving along that road. I t permits r e l a t i o n s among components to be e s t a b l i s h e d . Component a n a l y s i s should have value, too, i n demonstrating the strength of the a s s o c i a t i o n between p a r t i c u l a r o b j e c t i v e measurements and sensory components. From these analyses, one should be able to reduce the number of v a r i a b l e s which have to be t e s t e d i n the f u t u r e . Sometimes a t e s t can be eliminated because another t e s t measures the same thing or e l s e the t e s t i s of so l i t t l e value i t should be e l i m i n a t e d . Once one has s e t t l e d upon appropriate and p r e c i s e t e s t s , then d e c i s i o n s w i l l have to be made as to how the o b j e c t i v e t e s t s are to be weighed so as to make the p r e d i c t i o n match that which would have been s a i d about the a c c e p t a b i l i t y of the food i f i t had been evaluated s e n s o r i a l l y f o r a l l of the major sense f a c t o r s . M u l t i p l e and simple c o r r e l a t i o n s c a l c u l a t e d between the d i f f e r e n t sense m o d a l i t i e s and a c c e p t a b i l i t y , as we d i d i n t h i s study and i n p r i o r s t u d i e s ÇL, 6^, _7. 14), provides information h e l p f u l f o r that phase of the task. To c a l c u l a t e these c o r r e l a t i o n s i s q u i t e simple. As was pointed out i n the beginning, we w i l l be handicapped as long as we have to use words to describe sensations, because d e s c r i p t o r s are so s u b j e c t i v e , r a t h e r than being able to measure the p a r t i c u l a r property that generates the sensation i n the f i r s t p l a c e . The day when we w i l l be able to measure p r o p e r t i e s i n s t e a d of having to use words f o r most sense responses i s a long way o f f . In the meantime, we can be o b j e c t i v e i n determining the r e l a t i o n s among d e s c r i p t o r s f o r sensations by such methods as f a c t o r a n a l y s i s , which procedure should permit us to p i c k those d e s c r i p t o r s most appropriate and p e r t i n e n t . In turn c l u s t e r a n a l y s i s , component and m u l t i - r e g r e s s i o n techniques should enable us to q u a n t i f y the r e l a t i o n s between sensory and o b j e c t i v e measurements.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

68

FLAVOR QUALITY: OBJECTIVE MEASUREMENT

Acknowledgements The authors thank Messrs, Tommy Mundy and Davis Staser, NSF Highschool Summer Participants, who conducted the 1975 sensory t r i a l s and carried on the preliminary s t a t i s t i c a l analyses. Mrs, Louise Wu made the factor analysis. Appreciation i s expressed to Mrs. Wu and Messrs. José Novo, Randall Evans, and Ronald Cox whose efforts permitted the carrying on of the sensory and objective tests simultaneously for the 1976 t r i a l s , Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

11. 12. 13. 14.

15. 16.

Powers, J. J. and Quinlan, M. C., J. Agr. Fd. Chem. (1974) 22, 744-749. Powers, J. J. and Keith, E. S., Abstracts of Papers, 2nd Intern'l. Congres p. 439, Warsaw Dravnieks, A . , Krotoszynski, B. K . , Abstracts, 154th meeting, Am. Chem. Soc. (1967). Powers, J. J. and Keith, E. S., J. Food Sci. (1968) 33, 207213. Dravnieks, A. and Krotoszynski, Β. K . , J. Gas Chromatography (1968) 6, 144-149. Quinlan, M. C., Bargmann, R. E., E l - G a l a l l i , Υ. Μ., and Powers, J. J., J. Food Sci. (1974) 39, 794-799. Powers, J. J., Proceedings, IV Int. Congress of Food Science and Technology (1974) vol. I I , 173-182, Madrid, Spain. Galleto, W. G. and Bednarczyk, A. A . , J. Food Sci. (1975) 40, 1165-1167. Dravnieks, Α . , Krotoszynski, B. K . , and Shah, J., J. Pharmaceutical Sci. (1974) 63, 36-40. Dravnieks, Α . , i n , Correlating Sensory/Objective Measurements --New Methods for Answering Old Problems, edited by Powers, J. J. and Moskowitz, H. W., Pub. STP 594, Am. Soc. for Testing and Materials (1976), 5-25, Philadelphia. Gianturco, Μ. Α . , Biggers, R. E., and Ridling, Β. H., J. Agr. Fd. Chem. (1974) 22, 758-764. Jobbágy, A. and Holló, J., Nahrung (1976) 20, 295-305. Sevenants, M. R., Abstracts, 168th meeting, Am. Chem. Soc. (1974). Powers, J. J., in, Correlating Sensory/Objective Measurements --New Methods for Answering Old Problems, edited by Powers, J. J. and Moskowitz, H. W., Pub. STP 594, Am. Soc, for Testing and Materials (1976), 111-122, Philadelphia. von Sydow, E. and Karlsson, G . , Lebens.-Wiss. u. Technol. (1974) 4, 152-155. Karlsson-Ekström, G. and von Sydow, E., Lebens.-Wiss. u. Technol. (1973) 6, 86-89.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5. powers et al. 17. 18. 19. 20. 21.

22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38.

Quality Evaluation of Green Beans

69

Persson, T . , von Sydow, E., and Åkesson, C . , J. Food Sci. (1973) 38, 386-392. Persson, T . , von Sydow, E., and Åkesson, C . , J. Food Sci. (1973) 38, 682-689. Dravnieks, Α., Reilich, H. G., Whitfield, J., and Watson, C. Α., J. Food Sci. (1973) 38, 34-39. Tanaka, T . , Saito, N., and Yokotsuda, T . , J. Ferment. Technol. (1970) 48, 56-62. Bargmann, R. E., Wu, L., and Powers, J. J., in, Correlating Sensory/Objective Measurements--New Methods for Answering Old Problems, edited by Powers, J. J. and Moskowitz, H. W., Pub. STP 594, Am. Soc. for Testing and Materials (1976), 56-72, Philadelphia. Wu, L., Bargmann, R. E., and Powers, J. J., J. Food Sci. (submitted) Hightower, J. Α. Ga. Bargmann, R. E. and Baker, F . , Proc., Symp. Applications of Statistics (1976), Dayton, Ohio. Vuataz, L., Sotek, J., and Rahim, Η. Μ., Proceedings Fourth Intnl. Congress of Food Sci, and Technol., Madrid, Spain, Sept. 1974. Applebaum, M. and Bargmann, R. E., Tech. Rept. NONR 1834(39), Univ. of Illinois, Urbana, Ill. (1976). Harman, J. J., Modern Factor Analysis, 2nd Ed., (1968), University of Chicago Press. Young, L. L., Bargmann, R. E., and Powers, J. J., J. Food Sci. (1970) 35, 219-223. Milutinovic, L., Bargmann, R. Ε . , Chang, Κ. Y . , Chastain, M., and Powers, J. J., J. Food Sci. (1970) 35, 224-228. Likens, S. T. and Nickerson, G. B., Proc., Am. Soc. Brewing Chemists, Annual Meeting (1964), 5-13. Pons, W. Α., J r . , Assoc. Off. Anal. Chemists (1976) 59, 101-105. Rao, V. Ν. Μ., Unpublished Rept, Dept. of Food Science, Univ. of Ga., Athens, Ga. 30602. Trivedi, S. J., Themis Report No. 17, Technical Report No. 75 Department of Statistics and Computer Science, Univ. of Georgia, Athens, Ga. 30602. Bargmann, R. E. and Grainey, R. W., Themis Report No. 1, University of Georgia, Oct. 1969. Pearson, Κ., Philosophical Magazine (1901) 6, 559-572. Dravnieks, Α., Krotoszynski, Β. Κ., Keith, L., and Bush, I. M., J. Pharmaceut. Sci. (1970) 59, 495-501. von Sydow, Ε . , Andersson, J., Anjou, Κ., Karlsson, G., Land, D., and Griffiths, N., Lebensmittel-Wissenschaft u. Technol. (1970) 3, 11Meilgaard, Μ., Elizondo, Α., and Mackinney, Α., Wallerstein Laboratories Communications XXXIV (1971) 114, 95-110.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

70 39. 40. 41. 42. 43. 44.

45. 46. 47. 48. 49. 50. 51. 52. 53. 54.

FLAVOR QUALITY: OBJECTIVE MEASUREMENT Clapperton, J. F . , J. Inst. Brew. (1973) 79, 495-508. Persson, T. and von Sydow, Ε., J. Food Sci. (1973) 38, 377385. Mccredy, J. Μ., Sonnemann, J. C., and Lehmann, S. J., Food Technol. (1974) 28, 36-41. Palmer, D. Η., J. Sci. Fd. Agr. (1974) 25, 153-164. Schiffman, S. S., Science (1974) 185, 112-117. McDaniel, M. R. and Sawyer, F. Μ., Paper presented at the annual meeting, Canadian Institute of Food Science and Technology, Halifax, Nova Scotia, June 1975 (Abstract in Newsletter of Sensory Evaluation Div., Institute of Food Technologists). Lehrer, Α., Language (1975) 51, 901-923. Williams, Α. Α., J. Sci. Fd. Agr. (1975) 26, 567-580. Dravnieks, Α., J. Brower, K. R. and 538-540. Harper, R., Applied Statistics (1956) 5, 32-48. Harries, J. Μ., J. Sci. Fd. Agr. (1973) 24, 1571-1581. Frijters, J. E. R., Poultry Sci. (1976) 55, 229-234. Kosaric, Ν., Duong, T. B. and Svrcek, W. Υ., J. Food Sci. (1973) 38, 369-373. Biswas, Α. Κ., Biswas, Α. Κ., and Sarkar, A. R., J. Sci. Fd. Agr. (1971) 22, 196-204. Andersson, Y., Drake, B., Granquist, Α., Halldin, L., Johansson, B., Pangborn, R. Μ., and Åkesson, C., J. Texture Studies (1973) 4, 119-144.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6 Measurement of Flavor Quality i n Apples, A p p l e Juices, and Fermented Ciders A. A. WILLIAMS, A. G. H. LEA, and C. F. TIMBERLAKE University of Bristol, Research Station, Long Ashton, Bristol, ΒS18 9AF, England

Quality may be understoo bility in a product and consumer acceptance, something which is important to any producer, whether of fruit products or foods in general, because without it he will soon be out of business. The consumer, whether he buys directly or has his opinion reflected in the eyes of a buyer for a processing industry, is therefore the final key to what constitutes quality. One function of the scientist interested in flavour is to translate this consumer opinion into tangible information, such as the chemical and physical composition of the product, so that eventually he has a better understanding of what the consumer considers as constituting quality and can then devise logical scientific methods for its improvement. When considering the produce of the apple industry, although it is the sensory responses evoked in the consumer and the pleasure and satisfaction they give, that have the greatest influence on quality, other factors are also important. The keeping quality of the fruit or beverage, its nutritional value, the variety of uses to which it can be put in the home, the ease and convenience of eating and, of course, the price, are some of the more tangible attributes which are also important to the consumer. The fact that man made fertilisers and insecticides may have been used during the growing of the fruit, the image created by the varietal name, advertising and preconceived ideas of the product also have subtle effects on the acceptability of a fruit. Such phrases as an apple a day keeps the doctor away have l i t t l e scientific backing but may well subconsciously influence the housewife when she shops for apples and apple products. Other factors besides the sensory quality of the fruit are also important to the apple producer and processor. Crop yields, resistance of the tree to disease, length and uniformity of harvest, ability to transport and storage potential play a major role in the growers choice of orchard practices and selection of varieties. For apples destined for juice and cider production, f

1

1

71 In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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a b i l i t y to r e a d i l y produce a h i g h y i e l d of j u i c e i s another factor i n defining quality. During the l a s t twenty years i t i s s u c h c o n s i d e r a t i o n s as t h e s e w h i c h have a l m o s t e n t i r e l y g o v e r n e d the type of f r u i t produced. T h i s h a s b e e n p a r t i c u l a r l y so i n the case of e a t i n g a p p l e s , where the o n l y t a n g i b l e c r i t e r i a b e i n g i m p o s e d b y t h e r e t a i l e r a p p e a r t o be t h o s e o f c o l o u r , s i z e , shape and l a c k o f d i s o r d e r s . When t r a d i t i o n a l m e t h o d s w e r e b e i n g u s e d to grow and market f r u i t such c r i t e r i a p o s s i b l y proved q u i t e adequate. However, as a r e s u l t of modern t e c h n o l o g y , greater y i e l d s o f a p p l e s a n d a l o n g e r s t o r a g e l i f e a r e now p o s s i b l e a n d c r i t e r i a , s u c h as f l a v o u r , w h i c h a r e not d i r e c t l y a s s e s s e d , are beginning to suffer. I n t h e a p p l e j u i c e and c i d e r i n d u s t r i e s i n c r e a s e d c l e a n l i n e s s , the use of a s c o r b i c a c i d , s u l p h u r d i o x i d e and pure y e a s t c u l t u r e s have g i v e n t h e m a n u f a c t u r e r s more c o n t r o l o v e r t h e i r p r o d u c t s . T h i s has mean unacceptable beverages i s becoming l e s s frequent and, here again, t h e m a n u f a c t u r e r i s b e c o m i n g more c o n c e r n e d w i t h m a i n t a i n i n g those f l a v o u r aspects of h i s product which the customer considers t o be d e s i r a b l e . Measurement

of

Flavour

Quality

S e v e r a l a t t e m p t s h a v e b e e n made t o f o r m u l a t e sensory, p h y s i c a l and a n a l y t i c a l c r i t e r i a by which q u a l i t y o f b o t h a p p l e s a n d t h e i r p r o d u c t s c a n be a s s e s s e d a n d c o m p a r e d . Sensory assessments are mainly of the type i n which general attributes s u c h as c l a r i t y , aroma and f l a v o u r a r e s c o r e d and combined, w i t h e i t h e r the r e s u l t s of simple chemical analyses, or estimabes of c o m m e r c i a l v a l u e t o g i v e a n i n d i c a t i o n o f q u a l i t y (.1,2.). Over r e c e n t y e a r s , h o w e v e r , a number o f more o b j e c t i v e approaches have been developed i n c o n n e c t i o n w i t h s p e c i f i c r e s e a r c h p r o grammes 6), b u t , a p a r t from the v o c a b u l a r y u s e d by V G n S y d o w e t a l . (5) a n d M o s k o w i t z a n d V a n S y d o w (6) to describe apple j u i c e s , these are s t i l l of a r a t h e r general n a t u r e . From the p o i n t o f v i e w of p h y s i c a l measurements r e l a t i o n s h i p s a r e c l a i m e d t o e x i s t b e t w e e n b o t h t h e c o l o u r CZ.,8,.2.) a n d l i g h t t r a n s m i t t a n c e ( 1_0,ll) o f a p p l e s a n d t h e i r e a t i n g q u a l i t y a n d u s e h a s b e e n made o f t h e s e i n d e v e l o p i n g i n s t r u m e n t s f o r g r a d i n g p u r p o s e s ( U l g _ , Y%_, H ) . A n a l y t i c a l l y , measurements of the sugar and a c i d c o n t e n t s have been u s e d f o r e s t i m a t i n g q u a l i t y o f a p p l e s (± V2. 16) a n d j u i c e s (2., Vj), although i n the case of the l a t t e r i t i s claimed that the polyphenol content should also f a l l w i t h i n s p e c i f i c l i m i t s (ijO . I n England i t has l o n g been t h e custom to c l a s s i f y c i d e r s , c i d e r a p p l e s and t h e i r j u i c e s o n t h e i r a c i d and p o l y p h e n o l c o n t e n t as a means o f i n d i c a t i n g t h e i r f l a v o u r p r o p e r t i e s and s u i t a b i l i t y f o r c i d e r m a k i n g . Whether i t i s an apple, j u i c e or c i d e r , s i m p l e , a n a l y t i c a l and p h y s i c a l measurements o f t h i s n a t u r e are o n l y v e r y crude i n d i c a t o r s of q u a l i t y , g i v i n g very l i t t l e i n d i c a t i o n of the true 9

9

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and

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f l a v o u r e f f e c t s of i n d i v i d u a l compounds. For example, s c i e n t i s t s are unable to t e l l from the r e s u l t s of permanganate t i t r a t i o n s whether the polyphenols are c o n t r i b u t i n g to b i t t e r ness or a s t r i n g e n c y or whether they are soapy or hard . Also, e x c e p t b y a s s o c i a t i o n , s u c h m e a s u r e m e n t s do n o t t a k e i n t o a c c o u n t t h e more s u b t l e e f f e c t s o f t h e v o l a t i l e components on aroma and f l a v o u r , the i n t e r a c t i o n of b o t h v o l a t i l e and n o n - v o l a t i l e f l a v o u r components and the e f f e c t o f f r u i t s t r u c t u r e on the r e l e a s e of the f l a v o u r i m p a r t i n g compounds. 1

1

!

f

Modern a n a l y t i c a l techniques have, of course, been a p p l i e d t o most a s p e c t s of a p p l e p r o d u c t s . F o r example, gas c h r o m a t o g r a p h y h a s e n a b l e d o v e r 2 5 0 v o l a t i l e c o m p o n e n t s ( 1 8 , 1 9 , 2 θ ) t o be i d e n t i f i e d and o t h e r c h r o m a t o g r a p h i c t e c h n i q u e s have g i v e n i n f o r m a t i o n on the n o n - v o l a t i l e s . Some o f t h e s e obviously c o n t r i b u t e more t o t h e one c a n s t a t e w h i c h a r t i c s , s u c h i n f o r m a t i o n c a n n o t be u s e d as a g u i d e t o q u a l i t y . As s t a t e d e a r l i e r , t h e c u s t o m e r i s t h e f i n a l k e y t o u n d e r standing quality. H o w e v e r , a l t h o u g h t h e a v e r a g e c o n s u m e r , when p r e s e n t e d w i t h a number o f p r o d u c t s , c a n r e a d i l y t e l l you w h i c h he p r e f e r s , he i s o f t e n much l e s s p r e c i s e i n s a y i n g why he l i k e s t h e one he h a s c h o s e n . I n e v a l u a t i n g f l a v o u r q u a l i t y i t was t h e r e f o r e c o n s i d e r e d u n w i s e t o t r y , e i t h e r t o get t o o much i n f o r m a t i o n from the consumer or to i n t e r p r e t h i s p r e f e r e n c e i n f o r m a t i o n d i r e c t l y , p a r t i c u l a r l y i n terms of a n a l y t i c a l d a t a . The a p p r o a c h a d o p t e d t h e r e f o r e was t o u s e a t r a i n e d p a n e l a n d w e l l defined terminology to assess o b j e c t i v e l y the c h a r a c t e r i s t i c s p r e s e n t i n the p r o d u c t , t h u s o b t a i n i n g a d e t a i l e d measiire b o t h q u a l i t a t i v e l y and q u a n t i t a t i v e l y , of t h e v a r i o u s s e n s o r y c h a r a c t e r i s t i c s c o n t r i b u t i n g to the o v e r a l l a p p r e c i a t i o n of the f r u i t , juice or c i d e r . C o r r e l a t i n g t h i s i n f o r m a t i o n on t h e one hand w i t h the consumer s assessment or p r e f e r e n c e r a t i n g s would give an i n d i c a t i o n of the r e l a t i v e importance of the c h a r a c t e r i s t i c s f o r a c c e p t a n c e and q u a l i t y , w h i l s t c o m p a r i n g i t w i t h t h e c h e m i c a l and p h y s i c a l d a t a w o u l d e n a b l e the a n a l y t i c a l parameters which give r i s e to these various a t t r i b u t e s t o be d e t e r m i n e d . 1

This three d i r e c t i o n a l approach i n v o l v i n g preference r a t i n g s , o b j e c t i v e s e n s o r y assessment and a n a l y t i c a l d a t a has formed t h e b a s i s of our t h i n k i n g w i t h r e g a r d t o q u a l i t y and f l a v o u r e v a l u a t i o n o v e r t h e p a s t two y e a r s and two e x a m p l e s i l l u s t r a t i n g a s p e c t s o f t h i s a p p r o a c h , one i n v o l v i n g t h e aroma c o m p o n e n t s of a p p l e s a n d a n o t h e r t h e p h e n o l i c s o f f e r m e n t e d c i d e r w i l l now b e discussed. Annies From the p o i n t o f v i e w of e a t i n g q u a l i t y , the c u l t i v a r C o x s Orange P i p p i n , i s c o n s i d e r e d by the 1

apple majority

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E n g l i s h g r o w e r s , r e t a i l e r s a n d c o n s u m e r s t o be a m o n g s t t h e m o s t d e s i r a b l e o f a p p l e s , p a r t i c u l a r l y when c o n s i d e r i n g c u l t i v a r s w h i c h c a n be k e p t f o r any l e n g t h o f t i m e a f t e r h a r v e s t i n g . Preference r a t i n g s , comparing i t with three other v a r i e t i e s , Red D e l i c i o u s , S p a r t a n and I d a r e d ( T a b l e i ) , even t h o u g h t a k e n i n A p r i l when t h e C o x was n e a r i n g t h e end o f i t s s t o r a g e life, serve to i l l u s t r a t e the overwhelming s u p e r i o r i t y of t h i s cultivar. For economical reasons i t i s becoming d e s i r a b l e to TABLE Mean r a n k i n g o f

four

I varieties

of

apples

* Cultivar

C o x s Orange P i p p i n Spartan Idared Red D e l i c i o u s 1

* 1 β most

preferred

External

aroma

* Overall

2

1.25

2.6

3 2.5

2.3 2.6

4 =

2.9 least preferred

s t o r e Cox f o r l o n g p e r i o d s b e f o r e m a r k e t i n g . Although these l a t e s t o r e d Cox a p p l e s are f r e e o f d i s o r d e r s and have excellent t e x t u r e and a p p e a r a n c e , t h e i r f l a v o u r i s not a t t r a c t i v e and t h e consumer i s b e g i n n i n g to c o m p l a i n . The i n d u s t r y i s n a t u r a l l y w o r r i e d b e c a u s e i t b e l i e v e s t h a t much o f t h e s a l e s o f t h i s c u l t i v a r depends on f l a v o u r . The t h r e e d i r e c t i o n a l a p p r o a c h d e s c r i b e d i s b e i n g a d o p t e d t o t r y a n d d i s c o v e r w h a t i s s o d e s i r a b l e i n t h e C o x a p p l e a n d how t h e i m p o r t a n t a t t r i b u t e s from t h e s e n s o r y and a n a l y t i c a l p o i n t o f v i e w change b o t h d u r i n g C o n t r o l l e d Atmosphere s t o r a g e and i t s shelf l i f e afterwards. The development of an o b j e c t i v e language for d e s c r i b i n g the v a r i o u s sensory a t t r i b u t e s of the f r u i t was t h e f i r s t s t e p i n t h e p r o g r a m m e . To a c c o m p l i s h t h i s , t e r m s a n d i d e a s w e r e c o l l e c t e d f r o m a p a n e l o f 21 t a s t e r s who a s s e s s e d a p p l e s d u r i n g t h e 1 9 7 3 - 7 4 s e a s o n b o t h a s t h e y came f r o m the t r e e and a f t e r r e m o v a l from s t o r a g e . A p p r o x i m a t e l y 200 a d j e c t i v e s and p h r a s e s were s u g g e s t e d f o r d e s c r i b i n g the v a r i o u s a s p e c t s o f Cox f l a v o u r . The most f r e q u e n t l y u s e d , t o g e t h e r w i t h a number of the o t h e r terms w h i c h the p a n e l c o n s i d e r e d s i g n i f i c a n t , were d i s c u s s e d and, where p o s s i b l e , s t a n d a r d s i n the form of essences, c h e m i c a l s and n a t u r a l m a t e r i a l s , p r o d u c e d . The t e r m s d e r i v e d were g r o u p e d i n t o v a r i o u s c l a s s e s w h i c h u l t i m a t e l y formed the b a s i s of an assessment sheet f o r s c o r i n g

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WILLIAMS ET

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75

Ciders

v a r i a t i o n s i n t h e f l a v o u r c h a r a c t e r s f r o m one b a t c h o f a p p l e s t o another. The sheet c o n s i s t e d o f e i g h t s e c t i o n s d e a l i n g w i t h the e x t e r n a l and i n t e r n a l appearance o f the a p p l e , i t s f e e l to the hand, i t s e x t e r n a l and i n t e r n a l aroma, t a s t e and t e x t u r e and finally its aftertaste (Table II). Each s e c t i o n contained the TABLE Segregation

of

flavour

II

attributes

1.

Appearance

2. 3.

Feel Aroma

4. 5. 6.

Taste Texture Aftertaste

for

sensory

G ι) 0 D)

external internal

0 i)

external

evaluation

a p p r o p r i a t e d e r i v e d a d j e c t i v e s a n d p h r a s e s and was s c o r e d o n t h e amount o f a p a r t i c u l a r a t t r i b u t e p r e s e n t i n t h e a p p l e u s i n g a 0-5 s c a l e . I n s c o r i n g these a t t r i b u t e s p a n e l i s t s were i n s t r u c t e d t o be o b j e c t i v e a n d n o t t o be i n f l u e n c e d b y p e r s o n a l preferences, these being i n d i c a t e d separately. In order to reduce e r r o r s apples were assessed i n a p r e - s e t manner. Examination of c o r r e l a t i o n co-efficients between o v e r a l l r a t i n g s and the v a r i o u s i n d i v i d u a l s e c t i o n r a t i n g s (Table III) based on t w e l v e months t a s t i n g s i n d i c a t e d t h a t the t a s t e and texture sensations r e f l e c t e d the o v e r a l l r a t i n g s best, i n t e r n a l aroma and e x t e r n a l aroma as s u c h o n l y g i v i n g r e l a t i v e l y low correlation co-efficients. The r e s u l t s o f m u l t i p l e r e g r e s s i o n 1

TABLE Correlation

of

III

individual section

rating with

overall

Correlation co-efficients with overall rating

External External Internal Internal External External Internal Taste Texture

appearance colour appearance colour feel aroma aroma

0.80 0.43 0.74 0.77 0.75 0.56 0.69 0.87 0.84

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OBJECTIVE

MEASUREMENT

a n a l y s i s , however, i n d i c a t e d t h a t the r a t i n g f o r t a s t e c o u l d not be i n t e r p r e t e d e n t i r e l y i n t e r m s o f s w e e t n e s s , s o u r n e s s and b i t t e r n e s s , b u t , as e x p e c t e d , was a f f e c t e d b y o t h e r factors s u c h as t h e m i n o r c h a r a c t e r i m p a r t i n g , v o l a t i l e f l a v o u r components not d i r e c t l y defined i n t h i s s e c t i o n . A n a l y t i c a l m e t h o d s w e r e d e v e l o p e d a t t h e same t i m e t o g i v e i n f o r m a t i o n on t h e c h e m i c a l components i n the a p p l e . In connection with t h i s i t i s worth noting that differing q u a l i t a t i v e and q u a n t i t a t i v e p i c t u r e s were o b t a i n e d from the v o l a t i l e s d e p e n d i n g on t h e c o l l e c t i o n method u s e d and the d e g r e e o f enzyme a c t i o n a l l o w e d t o t a k e p l a c e d u r i n g p r e p a r a t i o n . As t h e a i m o f t h e w o r k was t o i n t e r p r e t r e s u l t s i n t e r m s o f a s e n s o r y e f f e c t the problem e x i s t s as to w h i c h method gave r e s u l t s c l o s e s t t o t h e c o m p o s i t i o n o f t h e aroma when t h e f r u i t was b e i n g c h e w e d w h e n , a f t e r a l l , some enzyme a c t i o n a n d o x i d a t i o n must o c c u r . Afte was f i n a l l y d e c i d e d t o a d o p t two p r o c e d u r e s f o r collecting volatiles. Headspace c o l l e c t i o n from i n t a c t f r u i t u s i n g a s i m p l e s y r i n g e t e c h n i q u e , supplemented by c o l l e c t i o n on P o r a p a k Q, w a s u s e d t o o b t a i n i n f o r m a t i o n f o r c o m p a r i s o n w i t h the e x t e r n a l aroma comments. To c o r r e l a t e w i t h t h e altogether different i n t e r n a l a r o m a a n d t a s t e s c o r e s i n f o r m a t i o n was o b t a i n e d by an e x t r a c t i o n p r o c e d u r e , based on c h i p p i n g t h e f r u i t f o l l o w e d by m e t h a n o l i n h i b i t i o n o f enzymes a f t e r 10-15 s e c . E x a m i n a t i o n of the aroma p r o f i l e s o f the Cox a p p l e s ( F i g u r e 1) s h o w e d t h a t t h e p a n e l i s t s h a d s e l e c t e d a n d w e r e s c o r i n g c h a r a c t e r s w h i c h were not the normal f r u i t y , e s t e r y ones usually associated with apples. Two o f t h e s e w e r e t h e d r i e d l e a f and s p i c y aromas, t h e former of w h i c h o f t e n d o m i n a t e d t h e e x t e r n a l aroma p a t t e r n . As y e t t h e c a u s e o f t h e d r i e d l e a f c h a r a c t e r has not been determined, but e x a m i n a t i o n of other a p p l e c u l t i v a r s showed t h a t t h e s p i c e - l i k e c h a r a c t e r was p r e s e n t i n a number o f t h e s e ( F i g u r e 1 ) , i n p a r t i c u l a r one known as E l l i s o n s O r a n g e , w h e r e i t was b e i n g d e s c r i b e d n o t j u s t as s p i c e l i k e b u t b y some t a s t e r s a s s p e c i f i c a l l y aniseed-like. 1

C o l l e c t i o n of the v o l a t i l e s from t h i s v a r i e t y u s i n g the P o r a p a k t e c h n i q u e (22) f o l l o w e d by gas c h r o m a t o g r a p h i c e x a m i n a t i o n n a t u r a l l y gave a v e r y complex p a t t e r n ( F i g u r e 2 ) . Odour e v a l u a t i o n of t h e s e p a r a t e d components i n d i c a t e d most o f them t o have f r u i t y and e s t e r y o d o u r s . One h i g h b o i l i n g p e a k h o w e v e r had a s s o c i a t e d w i t h i t the s p i c y aniseed aroma. Gas c h r o m a t o graphy-mass s p e c t r o m e t r y , p r e p a r a t i v e gas l i q u i d chromatography and i n f r a r e d s p e c t r o s c o p y gave i n f o r m a t i o n w h i c h e n a b l e d t h i s compound t o be i d e n t i f i e d as 4 - m e t h o x y a l l y l b e n z e n e , a compound with a d i s t i n c t aniseed smell. E x a m i n a t i o n of v o l a t i l e components from o t h e r c u l t i v a r s by t h i s and o t h e r methods showed 4 - m e t h o x y a l l y l b e n z e n e t o be p r e s e n t i n a l l c u l t i v a r s examined, t h e amounts d e t e c t e d , however, corresponding approximately to the l e v e l of s c o r i n g of the s p i c y c h a r a c t e r by the p a n e l ( F i g u r e 3)·

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

Apples,

WILLIAMS E T A L .

Apple

Juices,

ADJECTIVE SCORE 1

Dried leaves

2

Green

and Fermented

d

(i)Cox

3

Sharp Alcoholic/Winey

5

Scented

6

Estery

7

Banana like

8

Sugary

9

Spicy

10

Estery (wax like)

11

Fatty/Greasy

12

Rancid

(iii) Ellison's Orange

At

M

4

77

Ciders

4

_9.

(iv)Bramley

(ii)Egremont Russett

10

mmn ADJECTIVE Figure

1.

External

Sugary Pineapple

Peardrops

aroma profiles of apples

Cooked apple

F r u i t

η ,

π

E

Apple l p e e

v/ ,

\ I ,stery I / Fruity ^ r r y \ » Apple I ^ Sharp! / Α

0

E

β

tiim Μ

-

in

/

η

χ

T /* V

\

μ

2r

/

οι Aniseed

î

Mv

Green

Green apple

\

VjU Time/ Momp

„

Column :150m * 0 76mm Carbowax Figure

2.

Chromatogram

mins °C

50 165

30 105

20M; programmed from 65*-210*C at 2-4'C/min

of vohtiles Aroma

from apples comments.

(Cultivar

Ellisons

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Orange)

78

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

T h r e s h o l d measurements i n aqueous s o l u t i o n based on t r i a n g u l a r assessments i n wine glasses i n d i c a t e d 4 - m e t h o x y a l l y l b e n z e n e t o h a v e a t h r e s h o l d o f 0.035 ppm ( s i g n i f i c a n t P=0.01) w h i c h p u t s i t on a p a r w i t h compounds l i k e h e x y l a c e t a t e and hexyl 2-methylbutyrate ( 2 4 * 2 5 ) , two compounds o f i m p o r t a n c e i n apples (Table IV). I t i s h o w e v e r a f a c t o r o f 100higher t h a n ethyl 2-methylbutyrate, t h e s i g n i f i c a n t compound i n A m e r i c a n Delicious apples (24). TABLE Threshold

values

(ppm)

compounds Our

in

IV of

significant

figures

Flath

et

(24) Hexanal 2-Hexenal Ethyl 2-methyl butyrate Hexyl 2-methyl butyrate Hexyl acetate 4-methoxyallylbenzene

aroma

apples

0.017 0.0001 0.08

0.002

a l . Jakob

et

al.

(2£)

0.00008 0.06 0.085

0.035

D i s t r i b u t i o n measurements between an aqueous s o l u t i o n of 4m e t h o x y a l l y l b e n z e n e and i t s v a p o u r i n d i c a t e t h a t an aqueous c o n c e n t r a t i o n o f 0.035 ppm g i v e s r i s e t o a v a p o u r c o n c e n t r a t i o n o f 2.1 χ 10"-^ ppm. Q u a n t i t a t i v e f i g u r e s from the c o l l e c t i o n of a p p l e v o l a t i l e s on Porapak Q i n d i c a t e d t h a t the gas stream from E l l i s o n s O r a n g e c o n t a i n e d i n t h e r e g i o n o f 1 χ 10~4 ppm o f 4methoxyallylbenzene, approximately f i v e times greater than t h i s threshold concentration. 1

Fermented

Cider

Odour e v a l u a t i o n of the gas c h r o m a t o g r a p h i c e f f l u e n t (26). t h e u s e o f t h r e s h o l d v a l u e s a n d o d o u r u n i t s (20) and c o r r e l a t i o n of gas chromatographic d a t a w i t h s e n s o r y d e s c r i p t i o n of the a r o m a (27»28) h a s y i e l d e d m u c h u s e f u l i n f o r m a t i o n o n t h e c o n t r i b u t i o n i n d i v i d u a l v o l a t i l e c o m p o n e n t s make t o t h e a r o m a o f ciders. Although important to the o v e r a l l f l a v o u r of the b e v e r a g e t h e s e compounds w i l l n o t be d i s c u s s e d f u r t h e r i n t h i s paper. In the E n g l i s h c i d e r i n d u s t r y the p r a c t i c e of fermenting c o m p l e t e l y and a d j u s t i n g t h e s u g a r and a c i d c o n t e n t b e f o r e b o t t l i n g has meant t h a t t h e a b i l i t y o f t h e o r i g i n a l j u i c e t o i m p a r t sweetness and a c i d i t y i s becoming l e s s and l e s s i m p o r t a n t . T h i s i s not so w i t h t h e compounds r e s p o n s i b l e f o r b i t t e r n e s s and a s t r i n g e n c y , two e s s e n t i a l f l a v o u r c h a r a c t e r i s t i c s o f E n g l i s h c i d e r s w h i c h c a n o n l y be d e r i v e d f r o m t h e f r u i t . Unfortunately, there i s a c o n t i n u i n g shortage of apples which can impart these

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

WILLIAMS ET AL.

Apples,

Apple

Juices,

and

Fermented

Ciders

79

c h a r a c t e r s , p a r t i c u l a r l y i n r e l a t i o n t o demands t o increase cider production. T h e i n d u s t r y c a n make u p some o f i t s f r u i t d e f i c i e n c i e s by u s i n g s u r p l u s d e s s e r t a p p l e s , but t h i s can o n l y go so f a r , a s c i d e r made e n t i r e l y f r o m t h e s e v a r i e t i e s l a c k s t h e true cider flavour. B e f o r e s a l e s u c h c i d e r s must be b l e n d e d w i t h a c e r t a i n amount o f m a t e r i a l made f r o m b i t t e r s w e e t or bittersharp cider fruit. From the p o i n t o f v i e w o f the i n d u s t r y a n d c o n s u m e r s i t i s t h e r e f o r e i m p o r t a n t t h a t we o b t a i n m o r e knowledge on t h e compounds r e s p o n s i b l e f o r t h i s d e s i r a b l e b i t t e r n e s s and a s t r i n g e n c y and d i s c o v e r means o f i n c r e a s i n g them b o t h i n t h e c i d e r a p p l e s a n d t h e c i d e r s made f r o m t h e m . The i n v o l v e m e n t o f p h e n o l i c m a t e r i a l i n t h e b i t t e r n e s s a n d a s t r i n g e n c y o f E n g l i s h c i d e r s and p e r r i e s has been recognised s i n c e 1801 ( 2 9 ) . b u t n o t u n t i l c o m p a r a t i v e l y r e c e n t l y h a s i t been p o s s i b l e to separat general 'tannin' mixture b u t e t o t h e c h a r a c t e r s o f b i t t e r n e s s and a s t r i n g e n c y so d e s i r a b l e i n true English cider. In the mid 1950 s paper chromatography r e v e a l e d t h a t t h e p h e n o l i c s o f c i d e r c o u l d be b r o k e n down i n t o a number o f g r o u p s ( F i g u r e 4). C i r c u m s t a n t i a l evidence d e r i v e d from t a s t i n g pure commercial c o m p o u n d s i n d i c a t e d t h a t i t was o n l y t h e p r o c y a n i d i n s w h i c h made any d i r e c t c o n t r i b u t i o n to b i t t e r n e s s and a s t r i n g e n c y . C o n f i r m a t i o n o f t h i s w a s o b t a i n e d w h e n new p r e p a r a t i v e scale s e p a r a t i o n t e c h n i q u e s , u s i n g Sephadex g e l as an a d s o r p t i o n medium,allowed l a r g e enough q u a n t i t i e s of the p h e n o l i c fractions t o be i s o l a t e d f r o m c i d e r f o r t a s t i n g t r i a l s t o be c a r r i e d o u t . !

Although a t o t a l p r o c y a n i d i n f r a c t i o n , free from other p h e n o l i c s , c o u l d e a s i l y be i s o l a t e d o n S e p h a d e x , t h e p r o b l e m o f s e p a r a t i n g i n d i v i d u a l p r o c y a n i d i n s p e c i e s f r o m one a n o t h e r s t i l l remained. The r e a d i n e s s o f t h e s e compounds t o b o t h h y d r o g e n bond w i t h or to H a n almost any s u r f a c e or c h r o m a t o g r a p h i c s u p p o r t , a n d t o be c o n v e r t e d t o a m o r p h o u s b r o w n p o l y m e r s u n d e r t h e i n f l u e n c e o f h e a t , l i g h t a n d o x y g e n made t h i s v e r y d i f f i c u l t . 1

The t e c h n i q u e w h i c h p r o v e d more s u c c e s s f u l t h a n any o t h e r i n s e p a r a t i n g b u l k q u a n t i t i e s o f p r o c y a n i d i n s was t h a t o f c o u n t e r - c u r r e n t d i s t r i b u t i o n between e t h y l a c e t a t e and w a t e r . By u s i n g a m o d e r n a u t o m a t e d m a c h i n e w h i c h moved b o t h t o p and b o t t o m p h a s e s i n o p p o s i t e d i r e c t i o n s , i t was p o s s i b l e t o s e p a r a t e t h e p r o c y a n i d i n s o f c i d e r i n t o s i x f r a c t i o n s ( T a b l e V), gram q u a n t i t i e s s u f f i c i e n t f o r b o t h s e n s o r y and s t r u c t u r a l studies thereby easily being obtained.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

80

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

1 St.Edmund's Russett 4-Methoxy allyl benzene

2 Idared 3 Discovery 4 Cox's Orange Pippin 5 Beauty of 6 Golden

Bath

Delicious

7 Bramley 8 Worcester Pearmain 9 Egremont 10 Laxton's

Russett Superb

11 Kidd's Late Orange 12 Ellison's

Figure

3.

Orange

Rehtionship

.

of spicy scores to amounts

of

4-methoxyallylbenzene

H O ^

phenolic acids eg

Chlorogenic acid

H=CHCOO

/H\COOH J/OH

HO\|

phloretin derivatives eg

Phloridzin H

V \

0

H

^ y ^ C O C H ^ H ^ OGI

Vc \ = /

simple catechins

procyanidins eg H°

Figure

4. Paper chromatographic ration of cider phenolics

sepa-

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

WILLIAMS ET

AL.

Apples, Apple Juices, and Fermented Ciders

TABLE Counter

current

Component

V

separation

procyanidins

Tetrameric procyanidin Trimeric procyanidins Dimeric procyanidins Epi-catechin

of

cider

Partition co-efficient (Ethyl acetate/ water)

P o l y m e r i c and o x i d i s e d procyanidins Pentameric

81

phenolics Taste

) 0 0.05

-

0.10

i

Most

astringent

)

0.37 0.67 4.0

S t r u c t u r a l s t u d i e s , based on techniques developed by Weinges e t a l . i n H e i d e l b e r g (^0.) a n d H a s l a m e t a l . i n S h e f f i e l d (31 ), i n v o l v e d p u r i f i c a t i o n o f t h e p r o c y a n i d i n s on Sephadex g e l s , mass s p e c t r o m e t r y o f t h e m e t h y l e t h e r s t o o b t a i n m o l e c u l a r w e i g h t s and n u c l e a r magnetic resonance s p e c t r o s c o p y of b o t h the n a t i v e and a c e t y l a t e d compounds t o g i v e s t e r e o c h e m i c a l information. Cleavage of the procyanidins w i t h a c i d t o l u e n e t h i o l followed by paper chromatography and n u c l e a r magnetic r e s o n a n c e spectroscopy o f the fragments a l s o gave v a l u a b l e i n f o r m a t i o n on the c o n s t i t u t i o n o f u n i t s m a k i n g up the p r o c y a n i d i n s . By p r e s e n t i n g the i s o l a t e d f r a c t i o n s i n aqueous s o l u t i o n to a t a s t i n g p a n e l , i t was p o s s i b l e t o d e m o n s t r a t e t h a t o n l y t h e materials of p a r t i t i o n co-efficient <0.2 were e f f e c t i v e l y bitter o r a s t r i n g e n t at n a t u r a l l y o c c u r r i n g s t r e n g t h s and t h a t , o f these, t h e t e t r a m e r i c p r o c y a n i d i n was d e c i d e d l y t h e most b i t t e r a n d t h e more p o l y m e r i c m a t e r i a l s the most a s t r i n g e n t . However, a l l the p r o c y a n i d i n s c o n t r i b u t e t o t h e t o t a l b i t t e r n e s s and a s t r i n g e n c y , a n d i t i s i m p o s s i b l e t o i d e n t i f y any one component as b e i n g s o l e l y responsible for these c h a r a c t e r i s t i c s . I t was a l s o apparent that a l l procyanidins possessed both the c h a r a c t e r i s t i c s o f b i t t e r n e s s and a s t r i n g e n c y s i m u l t a n e o u s l y r a t h e r t h a n t h e r e b e i n g t w o c l a s s e s o f compounds e a c h r e s p o n s i b l e f o r one o r o t h e r sensation. I t i s p o s s i b l e t h a t t h i s d u a l e f f e c t a r i s e s from the different a c t i o n o f the p r o c y a n i d i n m o l e c u l e on d i f f e r e n t areas o f t h e t a s t e p a p i l l a e membrane. Current theories imply that a s t r i n g e n c y i s caused by hydrogen-bonding of p h e n o l i c groups to p r o t e i n i n the tongue, whereas b i t t e r n e s s r e s u l t s from the i n t e r a c t i o n of p o l a r molecules w i t h a l i p i d p o r t i o n of p a p i l l a e membranes ( 3 2 ) . A l a r g e p r o c y a n i d i n m o l e c u l e (as l o n g as i t r e m a i n s w a t e r s o l u b l e ) w o u l d t h e r e f o r e be more a s t r i n g e n t t h a n

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

82

FLAVOR

QUALITY:

OBJECTIVE

MEASUREMENT

a s m a l l one, whereas f o r b i t t e r n e s s , i n c r e a s i n g the m o l e c u l a r s i z e c o u l d w e l l reduce l i p i d s o l u b i l i t y and hence i t s a b i l i t y react

with

the

appropriate

to

receptor.

Unlike the p r o f i l e procedures described i n connection with a p p l e s t h e s e n s o r y a s s e s s m e n t o f b i t t e r n e s s a n d a s t r i n g e n c y was relatively simple. As o n l y two a t t r i b u t e s were b e i n g a s s e s s e d , and as r e a s o n a b l y a p p r o p r i a t e s t a n d a r d samples were a v a i l a b l e , l i t t l e t r a i n i n g was n e c e s s a r y . However, a number o f s p e c i a l problems did e x i s t . Unlike other organoleptic sensations which are g e n e r a l l y subject to fatigue e f f e c t s , the intense p h y s i c a l t a n n i n g e f f e c t o f t h e s e compounds c a u s e s r e p e a t e d samples t o have a c u m u l a t i v e e f f e c t on the p a l a t e . When two i d e n t i c a l s a m p l e s are presented i n sequence i t w i l l thus always appear t h a t the s e c o n d i s t h e most a s t r i n g e n t . F o r t h i s r e a s o n , o n l y two s a m p l e s c o u l d be h a n d l e p r e s e n t e d i n random o r d e r c i d e r s were m e r e l y compared f o r b i t t e r n e s s and a s t r i n g e n c y u s i n g a f i v e p o i n t c e n t r e z e r o s c a l e ( F i g u r e 5) a l o n g s i m i l a r l i n e s t o the method o r i g i n a l l y d e v i s e d by S c h e f f e (33). A l t h o u g h c o u n t e r - c u r r e n t d i s t r i b u t i o n a l l o w e d one t o o b t a i n q u a l i t a t i v e i n f o r m a t i o n on the v a r i o u s p r o c y a n i d i n f r a c t i o n s it was n o t r e a l l y a m e t h o d w h i c h l e n t i t s e l f t o c o n t i n u o u s r o u t i n e a n a l y s i s w h i c h was n e c e s s a r y i f t h e e f f e c t o f m a n u f a c t u r i n g v a r i a b l e s and c u l t u r a l c o n d i t i o n s on b i t t e r n e s s and a s t r i n g e n c y w e r e t o be u n d e r s t o o d . The ' t o t a l t a n n i n methods w h i c h s u r v i v e from t h e p r e - 1 9 1 4 l i t e r a t u r e , s u c h as permanganate t i t r a t i o n , F o l i n - D e n i s and V a n i l l i n method, were a l s o not s e l e c t i v e enough 1

for the purpose. A m o d i f i e d a n a l y t i c a l v e r s i o n of the Sephadex column chromatographic technique, u s i n g a methanol-water g r a d i e n t , h a s so f a r g i v e n t h e b e s t i n f o r m a t i o n and t h i s h a s been used r o u t i n e l y over the past three y e a r s . Typical of results

obtained

are

i l l u s t r a t e d i n Figure

6.

W i t h t h i s p r o c e d u r e a c i d e r sample c a n be a p p l i e d d i r e c t l y t o t h e c o l u m n , f r a c t i o n s c o l l e c t e d o n t h e b a s i s o f c o n t i n u o u s UV m o n i t o r i n g , and the c o n c e n t r a t i o n of p h e n o l i c s i n each f r a c t i o n calculated being time

f r o m t h e UV a b s o r b a n c e . consuming and not r e a l l y

Despite the disadvantage of g i v i n g adequate r e s o l u t i o n

i n t h e r e g i o n o f t h e o r g a n o l e p t i c a l l y s i g n i f i c a n t compounds (H t o J ) , t h i s m e t h o d g i v e s m o r e i n s i g h t t h a n d o t h e t r a d i t i o n a l analyses. Attempts to use high pressure l i q u i d chromatography t o s o l v e t h e s e p r o b l e m s have so f a r been l a r g e l y u n s u c c e s s f u l due t o l a c k o f s u i t a b l e p a c k i n g s , t h o u g h i n t i m e i t i s believed t h a t s u c h d e v e l o p m e n t w i l l be p o s s i b l e . In the meanwhile, the Sephadex column t e c h n i q u e has been used i n c o n j u n c t i o n w i t h the s e n s o r y p r o c e d u r e d e s c r i b e d , t o e n a b l e a number o f horticultural and m a n u f a c t u r i n g parameters a f f e c t i n g b i t t e r n e s s and a s t r i n g e n c y t o be investigated.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

WILLIAMS ET AL.

Apples,

Apple

Juices,

and

NAME

DATE .

SESSION NO

GROUP

Please

taste

Sample

Please Figure

Astringency

j

J Much more

J

j

Slightly

more

|

j

j

j

.. . h a s

state 5.

83

Ciders

... f i r s t

Bitterness

Sample

Fermented

t h a n sample

j

I

j

j Much l e s s

Slightly

i f you f i n d

Assessment

less

j

[

any o t h e r major

sheet

for

. ..

j

j taste

evaluating

difference:

bitterness

and

astringency

A

ρ Coumaroylquinic acid

Β

Chlorogenic acid

C

Phloretin xyloglucoside and caffeic acid

D

(-)Epicatechin

Ε

(+)Catechin and phloridzin

F

Procyanidin dimers

G

Minor procyanidins (including B5)

H

Procyanidin trimer

I

Procyanidin tetramer

J

Complex

B2 and B1

polymeric procyanidins

Figure

6.

Dabinett

Analysis cider

of

phenolics

on Sephadex

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

from LH20.

84

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

The e f f e c t o f g e l a t i n f i n i n g o n t h e b i t t e r n e s s , astringency and p o l y p h e n o l c o n t e n t of pure v a r i e t y c i d e r s i s t y p i c a l of t h e i n f o r m a t i o n w h i c h has been o b t a i n e d . This procedure i s used to b r i n g down h a z e s c a u s e d b y n o n - f l o c c u l a t i n g y e a s t s , b u t u n f o r t u n a t e l y i t a l s o r e d u c e s b i t t e r n e s s and a s t r i n g e n c y , as o u r t a s t i n g t e s t s showed. A n a l y t i c a l r e s u l t s confirmed the e a r l i e r r e s u l t s o n t h e i m p o r t a n c e o f some o f t h e p o l y m e r i c p r o c y a n i d i n s t o t h e t a s t e b e c a u s e i t was o n l y t h o s e w h i c h were e f f e c t i v e l y r e m o v e d b y t h e f i n i n g , t h e l o w e r m o l e c u l a r w e i g h t compounds b e i n g less affected (Figure 7). On r e f l e c t i o n t h i s i s h a r d l y s u r p r i s i n g s i n c e i f p r o c y a n i d i n s are able to hydrogen bond t o the tongue p r o t e i n t h e y w i l l c e r t a i n l y be a b l e t o do t h e same t o t h e g e l a t i n , and c o n v e r s e l y i f t h e y c a n n o t t a n t h e t o n g u e t h e n t h e y w i l l not react w i t h the g e l a t i n . I n p r a c t i c a l t e r m s we h a v e s h o w n t h a t g e l a t i n f i n i n g may r e m o v e u p t o 2 5 % o f t h e organol e p t i c a l l y important phenolic desperately t r y i n g to r e t a i n . I t i s i n t e r e s t i n g t o note t h a t t r a d i t i o n a l methods o f e s t i m a t i n g polyphenols, because they estimate ' t o t a l polyp h e n o l s , much o f w h i c h i s low m o l e c u l a r w e i g h t m a t e r i a l , showed no s i g n i f i c a n t d i f f e r e n c e due t o t h e t r e a t m e n t a n d h e n c e a p p e a r e d t o be a t v a r i a n c e w i t h t h e s e n s o r y d a t a . S i m i l a r e x p e r i m e n t s , some i n v o l v i n g 1 , 0 0 0 t r e e s i n f i e l d t r i a l s , have shown t h a t h i g h l e v e l s o f n i t r o g e n f e r t i l i s e r s i n g e n e r a l depress t o t a l p h e n o l i c s i n c i d e r a p p l e s and t h a t t h i s change i s d e t e c t a b l e i n the f i n i s h e d product (Table V l ) . f

TABLE

VI

E f f e c t of n i t r o g e n l e v e l s on p h e n o l i c s , astringency and b i t t e r n e s s i n pot-grown c i d e r apples (cultivar Dabinett)

Leaf

N

2

Organoleptically significant procyanid i n s i n c i d e r (mg/l00 Total in

Fed

Starved

Difference

2.34%

2.00%

-17%

133

155

+17%

350

410

+17%

ml)

phenolics

cider

(mg/l00 ml)

Bitterness/astringency of cider

Least

Most

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Apples,

WILLIAMS E T A L .

250

Apple

Juices,

and Fermented

Ciders

T

Tetramer & polymers

200+

mg/100 mis 150+

Phenoli

100+

Ο

B2

Ο

^Epicatechin Trimer

50+

^

Q

Minor dimers Phloretin xyloglucoside Phloridzin

Gelatin

0% Most

Figure

0 03%

0015%

Least

J Bitterness I j Astringency j

7. Effect of gehtin fining cultivar V

on phenolics liberie)

of cider

(Apple

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

86

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

It i s also clear that different c u l t i v a r s respond i n d i f f e r e n t ways t o t h e f e r t i l i s e r t r e a t m e n t s , and t h a t differences i n amounts o f p h e n o l i c s , whether r e g i s t e r e d by c h r o m a t o g r a p h i c o r o r g a n o l e p t i c means, i s f a r g r e a t e r between c u l t i v a r s t h a n w i t h i n any g i v e n c u l t i v a r s u b j e c t e d to v a r i o u s n i t r o g e n levels. T o t a l f r u i t y i e l d s a l s o a p p e a r t o be d e p r e s s e d by l o w n i t r o g e n l e v e l s , so i t i s u n l i k e l y t h a t n i t r o g e n - d e f i c i e n t orchards w i l l be s e r i o u s l y c o n s i d e r e d a s a means o f i n c r e a s i n g b i t t e r n e s s , although i n t r a d i t i o n a l grazed cider orchards t h i s i s exactly what u s e d to h a p p e n . The amount o f o r g a n o l e p t i c a l l y s i g n i f i c a n t p o l y p h e n o l s i n the c i d e r i s a l s o a f f e c t e d by the degree of o x i d a t i o n at the juice pressing stage. I t has been shown t h a t u s e o f s u l p h u r d i o x i d e at t h i s stage v i r t u a l l y doubles the q u a n t i t y of such compounds, s i m i l a r improvement by hot water d i f f u s i o n m i l l and p r e s s procedure. !

1

E x p e r i m e n t s i n v o l v i n g b i t t e r n e s s and a s t r i n g e n c y are s t i l l , h o w e v e r , i n t h e i r i n f a n c y and a g r e a t d e a l more n e e d s t o be done b e f o r e we c a n s p e c i f y t o t h e c i d e r m a k e r h o w t o o b t a i n t h e taste s e n s a t i o n he d e s i r e s , b u t w i t h a n a l y t i c a l and t a s t i n g t o o l s i m p r o v i n g a l l t h e t i m e i t c a n o n l y be a m a t t e r o f t i m e b e f o r e this objective i s accomplished. Conclusions The combined u s e o f s e n s o r y and a n a l y t i c a l p r o c e d u r e s h a s e n a b l e d i n f o r m a t i o n t o be o b t a i n e d o n t h r e e i m p o r t a n t flavour c h a r a c t e r i s t i c s , the s p i c y note i n a p p l e s and b i t t e r n e s s and astringency i n cider. I t m u s t be s t r e s s e d , h o w e v e r , t h a t these are o n l y t h r e e , a l b e i t i m p o r t a n t , f l a v o u r c h a r a c t e r s and t h a t the f u l l f l a v o u r q u a l i t y of e i t h e r of these products i s the r e s u l t o f a l a r g e number o f s e n s a t i o n s a l l a c t i n g s i m u l t a n e o u s l y on the b r a i n . To i n t e r p r e t t h e t r u e s i g n i f i c a n c e o f c h a r a c t e r s s u c h as t h e s e and t h e i r i n t e r - r e l a t i o n s h i p w i t h o t h e r aspects of q u a l i t y r e q u i r e s the i n t e g r a t i o n of such information w i t h consumer o p i n i o n . T h i s may be o b t a i n e d d i r e c t l y a s i n t h e c a s e of f r e s h apples or r e f l e c t e d i n the eyes of a manufacturing i n d u s t r y as i n t h e c a s e o f c i d e r . O n l y a minimum u s e has been made o f t h e c o n s u m e r i n t h e i n v e s t i g a t i o n s r e p o r t e d i n t h e p r e s e n t paper and a l t h o u g h a g r e a t d e a l of work, b o t h sensory and a n a l y t i c a l , i s s t i l l r e q u i r e d b e f o r e q u a l i t y o f e i t h e r a p p l e s , j u i c e s o r c i d e r s c a n be d e f i n e d , t h e c o n s u m e r i s i n e v i t a b l y bound t o p l a y a b i g g e r and more i m p o r t a n t r o l e i n any f u t u r e investigations.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6. WILLIAMS ET AL.

Apples, Apple Juices, and Fermented Ciders

87

Abstract In order that quality can be defined more precisely use i s being made of a three-directional approach i n which sensory assessment by panelists i s integrated with preference information on the one hand and analytical data on the other. The paper discusses the application of this approach to aspects of the flavour quality of apples and ciders. Illustrations are given i n which sensory procedures combined with gas l i q u i d chromatography, gas liquid chromatography-mass spectrometry have enabled the cause of an important spicy character i n certain types of apples to be determined, and counter-current and liquid chromatographic techniques again coupled with sensory appraisal methods have been used to give information on the contribution of the procyanidins to the bitterness and astringency of cider Literature Cited (1) (2)

Daep, H . U . , Schweiz. Z. Obst-Weinbau. (1966) 102, 695. Daep, H . U . , Dissertation Fed. Res. Stn. Arboric. V i t i c . Hortic., Wädenswil, Switz. (1970). (3) Lüthi, H.R., Techn. Rept. Federal Res. Sta. Arbori. V i t i c . Hortic. Wädenswil, Switz. [ 1970 ]. (4) Gorin, N., J. S c i . Food. Agric. (1975) 26, 599. (5) Von Sydow, E., Moskowitz, H.R., Jacobs, H . L . , Meiselman, H.L. Lebensm-Wiss. Technol. (1974) 7, 18. (6) Moskowitz, H.R., Von Sydow, E., J. Food S c i . (1975) 40, 788. (7) Lott, R . V . , Proc. Am. Soc. Hortic. S c i . (1943) 43, 59. (8) Brearley, Ν . , Breeze, J.E., Cuthbert, R.M., Food Technol. (1964) 18, 231. (9) Brearley, Ν . , Breeze, J.E., J. S c i . Food Agric. (1966) 17, 62. (10) Olsen, K . L . , Schomer, H . A . , Bartram, R . D . , Proc. Am. Soc. Hortic. S c i . (1967) 91, 821. (11) Aulenbach, B . B . , Yeatmann, J.N., Worthington, J.T., Report 936, U.S.D. Agric. Washington, D.C. (1972). (12) Collosie, S.S., Breeze, J.E., J. Food S c i . (1973) 38, 965. (13) Rosenthal, R.D., Webster, D.R., Food Technol. (1973) 27, 52. (14) Massie, D.R., Norris, K . H . , Trans. Am. Soc. Agric. Eng., (1975) 18, 173. (15) Thiault., C . , B u l l . Tech. Inf. (1970) 248, 191. (16) Gorin, Ν . , J. Agr. Food Chem. (1973) 21, 670. (17) Schobinger, U . , Müller, W., Fluess. Obst, (1975) 10, 414. (18) Drawert, F., Heimann, W., Emberger, R., Tressl, R . , Chromatographia (1969) 2, 57, 77. (19) Van Strating, S., de V r i j e r , F., List of Volatile Compounds i n Foods, Cent. Inst. Nutr. Food Res., Zeist, Neth. 1973. (20) Williams, Α . Α . , J. Inst. Brew. (London) (1974) 80, 455.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

88

FLAVOR QUALITY: OBJECTIVE MEASUREMENT

(21) Paillard, Ν., Lebensm-Wiss. Technol. (1975) 8, 34. (22) Williams, Α.Α., Tucknott, O.G., Lewis, M.J., Submitted to J. Sci. Food Agric. (1976). (23) Williams, Α.Α., Tucknott, O.G., Lewis, M.J., Manuscript in preparation (1976). (24) Flath, R.A., Black, D.R. Guadagni, D.G., McFadden, W.H. and Schultz, T.R., J. Agric. Food Chem. (1967) 15, 29. (25) Jakob, M.A., Hippler, R., Lüthi, H.R., Mitt. Geb. Lebensmittelunters Hyg. (1969) 60, 223. (26) Williams, Α.Α., Tucknott, O.G., J. Sci. Food Agric. (1971) 22, 264. (27) Williams, Α.Α., J. Sci. Food Agric. (1975) 26, 567. (28) Williams, Α.Α., The aroma components of cider apples and fermented cider In "Geruch-und Geschmackstoffe" (ed. Drawert) 141 (29) Knight, T.A. "A appl pea and the manufacture of cider and perry", London, 1801. (30) Weinges, K., Kaltenhauser, W., Marx, H.D., Nader, E., Nader, F . , Perner, J., Seiler, D., Liebigs Ann. Chem. (1968) 711, 184. (31) Haslam, E., Thompson, R.S., Jacques, D., Tanner, R.J.N., J. Chem. Soc. (Perkin 1) (1972) 11, 1387. (32) Koyama, N., Kurihara, K., Biochim. Biophys. Acta (1972) 288, 22. (33) Scheffé, Η., J. Am. Stat. Assoc. (1952) 47, 381.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7 Objective Measurements of the Flavor Quality of Beer R. C. LINDSAY Department of Food Science, University of Wisconsin, Madison, WI 53706

Beer is consumed fying sensory effects type world vary quite dramatically in sensory characteristics, but within populations consumers select their products on the basis of a general acceptance of beer flavor, subtle distinctive flavor notes, and an absence of unusual or off-flavors. The key role that flavor plays in product advertising and the fact that beer is a reasonably homogeneous liquid system have made the nature of beer flavor the subject of numerous investigations. Flavor Chemistry of Beer Most of the flavor chemistry literature describing beer flavor per se and the brewing parameters affecting flavors of finished products resides in the journals and publications that directly serve the brewing industry. Literature surveys confined to the usual sources of flavor chemistry articles will indicate a deceptive lack of information on the subject. While an extensive review of the flavor chemistry of beer is beyond the scope of this paper, excellent summaries have been published by Palamand and Hardwick (1) and Meilgaard (2,3). Collective considerations of the beer flavor literature indicate that well over 250 compounds have been characterized and reported for beer. These volatile compounds are derived from ingredients (grains, hops), brewing practices (wort boiling), fermentations (yeast, occasionally bacterial infections), and equilibrium reactions (esterifications, staling processes). As with other food flavors, some difficulties and disagreements have occurred in the assignment of roles for individual compounds in the flavor of beer. Undoubtedly many compounds of significance in beer flavor, particularly flavor defects, remain unrecognized at this time. S t i l l , much progress has been made, and attempts are being made to standardize beer flavor terminology (4). Based on extensive evaluations of quantitative data for 89 In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

FLAVOR QUALITY:

90

OBJECTIVE

MEASUREMENT

f l a v o r compounds i n beer and f l a v o r thresholds of i n d i v i d u a l and mixtures of compounds, Meilgaard (2) has proposed a tent a t i v e scheme f o r the r o l e of various beer c o n s t i t u e n t s i n determining the perceived f l a v o r of beer (Table I ) . This c l a s s i f i c a t i o n considers those compounds which g e n e r a l l y cont r i b u t e to aroma, t a s t e , and t a c t u a l sensations, and i t can be concluded that as f u r t h e r information accumulates m o d i f i c a t i o n s w i l l be necessary. The b a s i s f o r c l a s s i f i c a t i o n i n the scheme shown i n Table I i s that of Flavor Units (F.U. = Constant X Concentration/Threshold) or as i t i s sometimes r e f e r r e d to, Odor Units (5) . Compounds placed i n the category of primary f l a v o r constituents are present i n concentrations exceeding 2 F.U., and the removal of any one would cause a d e c i s i v e change i n the character of the product. I t can be noted that only s p e c i a l t y beers i n r e l a t i o n to the usual domestic adequate minor v o l a t i l t i o n i n the primary category. Secondary f l a v o r c o n s t i t u e n t s are those that are present between 0.5 and 2.0 F.U., and c o l l e c t i v e l y these c o n t r i b u t e much of the c h a r a c t e r i s t i c f l a v o r to beer. However, removal of any one would r e s u l t i n only a small change i n f l a v o r . T e r t i a r y f l a v o r c o n s t i t u e n t s are present i n l e v e l s equivalent to between 0.1 and 0.5 F.U., and add subs i d i a r y notes to the f l a v o r of beer. For these compounds, the removal of any one would not produce a p e r c e p t i b l e f l a v o r change. The remaining f l a v o r compounds would f a l l i n t o the category of background f l a v o r c o n s t i t u e n t s (below 0.1 F.U.), and even though a great number of compounds f a l l i n t o t h i s category, Meilgaard (2) estimates that the group accounts f o r l e s s than 30 percent of the o v e r a l l f l a v o r of beer. A n a l y s i s of Beer V o l a t i l e s Most of the c l a s s i c a l procedures f o r the a n a l y s i s of v o l a t i l e s i n foods and beverages have been employed with varying degrees of success f o r the determination of beer f l a v o r compounds (6). More complete recoveries of the e n t i r e spectrum of compounds are achieved by d i s t i l l a t i o n s (7,8), f r e e z e - d r y i n g followed by ether e x t r a c t i o n (9), and continuous l i q u i d - l i q u i d solvent e x t r a c t i o n s (10), but these methods are complex and can e a s i l y lead to the formation of a r t i f a c t s . More r e c e n t l y porous polymer entrainment procedures have been adapted f o r use i n the a n a l y s i s of beer v o l a t i l e s (11,12, 13>14,15), but as yet these techniques have not been g e n e r a l l y a p p l i e d f o r r o u t i n e monitoring of beer f l a v o r s . Wohleb (14) used Poropak Q f o r the entrainment of v o l a t i l e s from beer samples held under s e v e r a l storage c o n d i t i o n s , and subsequently analyzed the i s o l a t e s with glass c a p i l l a r y column gas chromatography. Computer a n a l y s i s of q u a n t i t a t i v e data f o r 54 beer f l a v o r compounds i n d i c a t e d that 11 peaks (mainly esters and alcohols)

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Table I.

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91

T e n t a t i v e Scheme f o r Role of Constituents i n Determining the F l a v o r of Beer.

a

PRIMARY FLAVOR CONSTITUENTS (Above 2 F.U. ) Ethanol Hop B i t t e r Compounds (e.g., Isohumulone) Carbon Dioxide S p e c i a l t y Beers Hop Aroma Compounds (e.g., Humuladienone) Caramel Flavored Compounds Several E s t e r s & A l c o h o l s (High-Gravity Beers) Short-Chain Acids D e f e c t i v e Beer 2- trans-Nonenal (Oxidized, Stale) D i a c e t y l & 2,3-Pentanedione (Fermentation) Hydrogen S u l f i d e , Dimethyl S u l f i d e and Other S u l f u r Compounds (Fermentation) A c e t i c A c i d (Fermentation) 3- M e t h y l b u t - 2 - e n y l t h i o l (Light-Struck-Hops) Others ( M i c r o b i a l I n f e c t i o n , e t c . )

2.

SECONDARY FLAVOR CONSTITUENTS (Between 0.5 - 2.0 F.U.) Volatiles Banana E s t e r s (e.g., Isoamyl Acetate) Apple E s t e r s (e.g., E t h y l Hexanoate) F u s e l A l c o h o l s (e.g., Isoamyl Alcohol) C , C , C- A l i p h a t i c Acids E£hyl Acefate B u t y r i c and I s o v a l e r i c Acids Phenylacetic Acid Non-Volatiles Polyphenols Various A c i d s , Sugars, Hop Compounds fi

ft

n

B

3.

TERTIARY FLAVOR CONSTITUENTS (Between 0.1 - 0.5 F.U.) 2-Phenethyl Acetate, £-Aminoacetophenone Isovaleraldehyde, Methional, A c e t o i n 4- E t h y l g u a i a c o l , gamma-Valerolactone

4.

BACKGROUND FLAVOR CONSTITUENTS (Below 0.1 F.U.) Remaining F l a v o r Compounds

F l a v o r Units (F.U.) = Constant X From Meilgaard (3) .

Concentration/Threshold.

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v a r i e d s i g n i f i c a n t l y w i t h the temperature of storage. Dravnieks (15) u t i l i z e d Apiezon L on Chromosorb Τ f o r the q u a n t i t a t i v e entrainment of beer aroma c o n s t i t u e n t s and u t i l i z e d these data for demonstrating the u t i l i t y of methods f o r c o r r e l a t i n g sub j e c t i v e and o b j e c t i v e f l a v o r data. However, i n f o r m a t i o n on i d e n t i f i e d samples i n a c t u a l experimental designs was not r e ported. To date l i m i t a t i o n s , i n c l u d i n g polymer s t a b i l i t y , ana l y t i c a l r e p r o d u c i b i l i t y , and a n a l y s i s time, have c o n t r i b u t e d to the l a c k of acceptance of porous polymer entrainment procedures f o r the r o u t i n e a n a l y s i s of beer headspace v o l a t i l e s . Most of the r o u t i n e monitoring of beer aroma c o n s t i t u e n t s i s accomplished through the use of e i t h e r s t a t i c headspace sampling procedures (16,17) or d i r e c t carbon d i s u l f i d e e x t r a c t i o n (18), although d i r e c t beer i n j e c t i o n s have been used to some extent (19). These method raphy, and the number l i m i t e d (Table I I ) . I t i s p o s s i b l e to observe l a r g e r numbers

Table I I .

V o l a t i l e Compounds i n Beer Determined by Q u a n t i t a t i v e S t a t i c Headspace Sampling and Carbon D i s u l f i d e E x t r a c t i o n Procedures.

Determined By Method Compound

Acetaldehyde E t h y l Acetate Ethanol n-Propanol Isobutanol 2-Methylbutene-2 Isopropyl Acetate E t h y l Propanoate 2-Methyl and 3-Methylbutanol m-Xylene ( I n t e r n a l Standard) Isoamyl Acetate E t h y l Hexanoate E t h y l Octanoate 1-Octanol ( I n t e r n a l Standard) Hexanoic A c i d 2-Phenethanol Octanoic A c i d Decanoic A c i d

S t a t i c Headspace

+ + + + + + + + + + +

-

Carbon

Disulfide

-

+ + + +

+ + + + + + + + +

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of peaks during a n a l y t i c a l runs by simply operating the gas chromatograph at higher s e n s i t i v i t i e s , but t h i s i s u s u a l l y not done because of greater a n a l y t i c a l v a r i a b i l i t i e s observed under these c o n d i t i o n s . Under usual c o n d i t i o n s from 10 to 18 peaks are observed i n a given run f o r the s t a t i c headspace or the carbon d i s u l f i d e e x t r a c t i o n procedures (17>1§)> ~ cepted that some peaks are not i d e n t i f i e d and that others may c o n t a i n more than one compound. S t i l l the data are u s e f u l , and many breweries are equipped f o r automated gas chromatographic a n a l y s i s of production samples of beer. I t can be noted that most v o l a t i l e s detected by the carbon d i s u l f i d e e x t r a c t i o n and headspace sampling techniques are d e r i v e d e i t h e r d i r e c t l y or i n d i r e c t l y from the fermentation (and aging) process (Table I I ) . Therefore, many f l a v o r c o n t r i b u t i o n s a r i s i n g from p r o c e s s i n g steps, i n g r e d i e n t s , and c o n s t i t u e n t i n t e r a c t i o n s ( i . e . staling) go undetected by these a

n

d

i t :

i s

a c

Sensory A n a l y s i s of Beer F l a v o r s T r a d i t i o n a l l y , the brewmaster has been delegated n e a r l y absolute a u t h o r i t y f o r the determination and maintenance of f l a v o r q u a l i t y of beer i s s u i n g from the brewery. However, as breweries grew i n s i z e and d i s t r i b u t i o n areas i n c r e a s e d , s h i f t s i n r e s p o n s i b i l i t i e s have occurred to the p o i n t that the brewmaster u s u a l l y r e c e i v e s sensory data from expert corporate panels (20,21) and t r a i n e d or s e l e c t e d panels composed of brewery workers (17,21). Expert panels o f t e n perform some type of d e s c r i p t i v e t e s t f u n c t i o n , but the p r i n c i p a l concern i s q u a l i t y c o n t r o l f o r products r e l e a s e d from the brewery. As a r e s u l t , d i f f e r e n c e t e s t i n g i s u s e f u l f o r monitoring u n i f o r m i t y , and the t r i a n g l e t e s t apparently i s the most widely used type of t a s t e t e s t used by expert and t r a i n e d groups i n the brewing i n d u s t r y (17). Some breweries u t i l i z e q u a n t i t a t i v e d e s c r i p t i v e a n a l y s i s procedures f o r c h a r a c t e r i z i n g beer f l a v o r p r o p e r t i e s , and t h i s approach has been reported to a s s i s t i n determining the degree to which consumers can recognize v a r i a t i o n s i n beer f l a v o r s (21). Since i t has been reported that under l a b o r a t o r y c o n d i t i o n s beer consumption r a t e s i n c r e a s e with hedonic r a t i n g s (22), there i s an increased i n t e r e s t i n r e l a t i n g beer f l a v o r a t t r i b u t e s to consumer preferences f o r products (23). Objective A n a l y s i s of Beer Q u a l i t y In a d d i t i o n to the compounds which comprise the v o l a t i l e aroma f r a c t i o n of beer, there are a great number of p h y s i c a l and chemical parameters which can be measured and u l t i m a t e l y u t i l i z e d i n describing or e v a l u a t i n g beer q u a l i t y (15,24,25,26,27). Included are c l a r i t y , foam head r e t e n t i o n , carbon d i o x i d e , and a i r which r e l a t e d i r e c t l y to q u a l i t y appearance f a c t o r s or which

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can i n f l u e n c e appearance i n time. Percent a l c o h o l , r e a l e x t r a c t , pH, t i t r a t a b l e a c i d s , f r e e amino a c i d s , headspace v o l a t i l e s , formol n i t r o g e n , and t r a c e metals are measured and r e f l e c t on the s t a t u s or success of the fermentation. Since the b i t t e r n e s s c o n t r i b u t i o n to the f l a v o r of beer i s p r i n c i p a l l y due to the hop r e s i n components, a s p e c i a l a t t e n t i o n i s paid to the measurement and c o n t r o l of these compounds, p a r t i c u l a r l y humulone and i s o humulone (α-acids) which are r e s p o n s i b l e f o r the major p o r t i o n of the b i t t e r f l a v o r i n beer (28). The l i s t of other analyses i s r a t h e r extensive, and depending upon the requirements of breweries v a r i o u s t e s t s are used to provide information f o r production and q u a l i t y c o n t r o l . Objective Measurements of Beer F l a v o r Q u a l i t y Objective assessment establishing a basis fo standards defined by measurements are only roughly r e l a t e d to q u a l i t y (29). Since aroma ( i . e . , f l a v o r ) c o n s t i t u t e s a major p o r t i o n of the o v e r a l l apparent q u a l i t y of foods, considerable e f f o r t has been expended f o r developing means f o r meaningfully using gas chromatographic data i n p r e d i c t i n g sensory q u a l i t y (30,31,32). Although c l a s s i f i c a t i o n of foods based on o b j e c t i v e f l a v o r data appears promising f o r a wide range of commodities (33,34,35,36,37), few a c t u a l instances of a p p l i c a t i o n of t h i s approach are apparent. Several a l t e r n a t i v e s f o r the o b j e c t i v e measurement of beer f l a v o r s and c l a s s i f i c a t i o n of beers have emerged from research i n the brewing i n d u s t r y . The PTPA Method. Hoff and Herwig (17) have reported a method f o r the c o r r e l a t i o n of s t a t i s t i c a l d i f f e r e n c e s or l a c k of s t a t i s t i c a l d i f f e r e n c e s between headspace v o l a t i l e p r o f i l e s of beer samples and the r e s u l t s of the widely-used t r i a n g l e t a s t e t e s t s f o r the same beers. A s t a t i c headspace a n a l y s i s technique employing a Poropak Q column f o r s e p a r a t i o n was used f o r c o l l e c t ing q u a n t i t a t i v e data f o r 12 peaks i n the v o l a t i l e fraction' ( e x c l u s i v e of the peaks f o r ethanol and the i n t e r n a l standard). Data from r e p l i c a t e GC analyses were processed by d i v i d i n g each i n d i v i d u a l raw peak area by the sum of a l l raw peak areas, and then s t a t i s t i c a l l y a n a l y z i n g these data between samples. Thus, the procedure was named the "Percent of the T o t a l Peak Area" (PTPA) method. In the PTPA method, a c h r o n o l o g i c a l l y updated database was used to c a l c u l a t e pooled standard d e v i a t i o n s f o r peak area values to overcome problems a s s o c i a t e d with aberrant values sometimes encountered f o r unexplained reasons or f o r those instances where the GC column c h a r a c t e r i s t i c s change with usage. The database c o n s i s t e d of standard d e v i a t i o n s f o r each peak of 24 previous r e p l i c a t e determinations plus the r e p l i c a t e deter-

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initiation under i n v e s t i g a t i o n . The standard d e v i a t i o n s of the o l d e s t of the 25 former r e p l i c a t e s were e l i m i n a t e d from the database each time a new e n t r y was made. When two beers were compared, the procedure was repeated f o r each. Then a t w o - t a i l e d t - t e s t was performed u s i n g the most recent of the pooled standard d e v i a t i o n s obtained from the database and the mean peak area values obtained from the r e p l i c a t e headspace determinations of the two beers. I f none of the peaks i n the v o l a t i l e p r o f i l e s of the two beers were s i g n i f i c a n t l y d i f f e r e n t at the 0.005 l e v e l , the r e s u l t s of a t r i a n g l e t a s t e panel of the beers were p r e d i c t e d to be i n s i g n i f i c a n t at the 0.05 l e v e l . On the other hand, i f one or more of the peaks i n the v o l a t i l e p r o f i l e s were found s i g n i f i c a n t l y d i f f e r e n t between samples at 0.001 l e v e l , the t r i a n g l e panel were p r e d i c t e d to be s i g n i f i c a n or more peaks were s i g n i f i c a n t l the 0.005 l e v e l , but were i n s i g n i f i c a n t at the 0.001 l e v e l , no p r e d i c t i o n was made and more analyses were r e q u i r e d to r e s o l v e the s i t u a t i o n . In a t e s t of the c o r r e l a t i o n of the PTPA method with t r i a n g l e t a s t e panel r e s u l t s (Table I I I ) , i t was found that the beers i n 32 of 69 comparisons of f r e s h American l a g e r beers were p r e d i c t e d by the PTPA method to give s i g n i f i c a n t l y d i f f e r e n t t r i a n g l e t a s t e panel r e s u l t s . In a c t u a l t r i a n g l e t a s t e panel t e s t i n g , beer samples i n 27 of these comparisons were found to be s i g n i f i c a n t l y d i f f e r e n t while the beers i n 5 of the comparisons were found not s i g n i f i c a n t l y d i f f e r e n t . Conversely, the PTPA method p r e d i c t e d 37 of the 69 comparisons to be not s i g n i f i c a n t l y d i f f e r e n t , and a c t u a l t a s t e panels showed that 35 of these p r e d i c t i o n s were c o r r e c t . Table I I I .

E v a l u a t i o n of C o r r e l a t i o n o f PTPA P r e d i c t i o n s with T r i a n g l e Taste Panel Results f o r Lager Beers.

PTPA P r e d i c t e d T r i a n g l e Panel Results T r i a l s Sig. Different

T r i a l s Not Sig. Different

A c t u a l T r i a n g l e Panel Results (0.05) T r i a l s Sig. Different

T r i a l s Not Sig. Different

32

0

27

5

0

37

2

35

From Hoff and Herwig (17).

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Hoff and Herwig (17) suggested that r o u t i n e t r i a n g l e t a s t e panel t e s t i n g of normal, f r e s h American l a g e r beers could be reduced by e l i m i n a t i n g those samples which were found to be not d i f f e r e n t by the headspace a n a l y s i s procedure. However, i t was noted that the PTPA method would not recognize samples of beers c o n t a i n i n g o r g a n o l e p t i c a l l y detectable l e v e l s of s u l f u r , s t a l i n g , or c e r t a i n hop compounds. Therefore, i t appears that some type of small d e s c r i p t i v e panel should be employed to detect beers e x h i b i t i n g these s i g n i f i c a n t , but unusual l a g e r beer f l a v o r c h a r a c t e r i s t i c s . Discriminant A n a l y s i s of GC V o l a t i l e P r o f i l e Data. The computer i d e n t i f i c a t i o n and c l a s s i f i c a t i o n of some s e l e c t e d beer samples with the a i d of stepwise d i s c r i m i n a n t a n a l y s i s (38) of v o l a t i l e p r o f i l e s fro or headspace vapors ha Chicoye (39,40). In t h i s work the sensory c h a r a c t e r i s t i c s of i n d i v i d u a l beer samples were not determined, but rather i t was assumed that competitive American l a g e r beers, beers brewed with d i f f e r e n t adjuncts (carbohydrate sources), and beers from branch p l a n t s w i t h i n a company would e x h i b i t f l a v o r d i f f e r e n c e s i f t h e i r v o l a t i l e p r o f i l e s d i f f e r e d . To demonstrate the u t i l i t y of the technique, i n d i v i d u a l l o t s of beer from a given source were d i v i d e d and subsequently analyzed by e i t h e r headspace or carbon d i s u l f i d e e x t r a c t i o n procedures to provide both a "known database and "unknown" beer sample data. 11

In one i n s t a n c e , four competitive American l a g e r beers were c l a s s i f i e d on the b a s i s of the q u a n t i t a t i v e amounts of four peaks (isoamyl a l c o h o l s , i s o b u t a n o l , e t h y l a c e t a t e , and isoamyl acetate) from carbon d i s u l f i d e e x t r a c t a b l e s which were s e l e c t e d by the stepwise d i s c r i m i n a n t a n a l y s i s of the 12 a v a i l able v a r i a b l e s . A c a n o n i c a l p l o t of the beers showed t i g h t groupings of both known and unknown samples w i t h i n sample l o t s . The technique was shown (39) to be u s e f u l f o r c l a s s i f y i n g a l l s e l e c t e d samples i n the study on the b a s i s of headspace or carbon d i s u l f i d e e x t r a c t a b l e v o l a t i l e s , i n c l u d i n g beers brewed with d i f f e r e n t types and amounts of adjuncts. An i n t e r e s t i n g aspect which was a l s o demonstrated was that of s h i f t i n g an o r i g i n a l c l a s s i f i c a t i o n of a beer from a branch p l a n t to that of another p l a n t ' s c l a s s i f i c a t i o n a f t e r a brewing m o d i f i c a t i o n was made. U t i l i z a t i o n o f such techniques could be very u s e f u l i n a s s e s s i n g the u n i f o r m i t y of f l a v o r q u a l i t y , p a r t i c u l a r l y when f l a v o r compounds r e f l e c t i n g fermentation parameters are measured. Discriminant A n a l y s i s of Physicochemical V a r i a b l e s I n c l u d i n g GC V o l a t i l e P r o f i l e Data. Reiner and P i e n d l (41) have demonstrated how d i s c r i m i n a n t a n a l y s i s of 49 physicochemical v a r i a b l e s , i n c l u d i n g carbon d i s u l f i d e e x t r a c t a b l e s , could be used to d i f f e r e n t i a t e types of beer, e.g., l a g e r , p i l s e n e r ,

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export, e t c . A modified U n i v e r s i t y of C a l i f o r n i a at Los Angeles BMD07M stepwise d i s c r i m i n a n t a n a l y s i s program (38) was used to s e l e c t v a r i a b l e s from the t o t a l physicochemical data a v a i l a b l e which included q u a n t i t a t i v e information on 14 general beer or brewing parameters, 20 α-amino a c i d s , and 15 metabolic by products from the fermentation process. Selected v a r i a b l e s were then used to demonstrate groupings of beer types i n canoni c a l p l o t s , and attempts were made to determine which p r o p e r t i e s allowed c l e a r d i f f e r e n t i a t i o n of beer samples evaluated. Although v a r y i n g degrees of success i n d i f f e r e n t i a t i o n of beer types on the b a s i s of s e l e c t e d physicochemical v a r i a b l e s was achieved by Reiner and P i e n d l (41), c o r r e c t c l a s s i f i c a t i o n of a l l beers w i t h i n a type was r e a l i z e d only f o r a l t and p i l sener d i e t beers when a l l of the i n i t i a l v a r i a b l e s were u t i l i z e d (Table I V ) . With t h i s approach d i f f i c u l t i e s were s t i l l en countered i n the d i f f e r e n t i a t i o Table IV.

Actual Beer Type L i g h t Lager

C l a s s i f i c a t i o n of Beers on the B a s i s of 14 General Parameters, 20 α-Amino A c i d s , and 15 Metabolic By-Products of Fermentation.

Light Lager

Light Export

C l a s s i f i c a t i o n As Pilsener Alt Lager Beer

Pilsener Diet

30

1

4

0

0

L i g h t Export

0

24

4

0

0

P i l s e n e r Lager

3

4

14

0

0

Alt

0

0

0

17

0

0

0

0

0

12

Beer

P i l s e n e r Diet

From Reiner and P i e n d l (41). type beers ( l i g h t l a g e r , l i g h t export, and p i l s e n e r l a g e r ) . While the a l t beer and p i l s e n e r d i e t beer samples were c h a r a c t e r i z e d by d i s t i n c t p h y s i c a l p r o p e r t i e s , the f u l l , l i g h t beer samples e x h i b i t e d s i m i l a r p h y s i c a l c h a r a c t e r i s t i c s . In order to d i f f e r e n t i a t e the f u l l , l i g h t beer types, i t was necessary to expand the a v a i l a b l e data, and t h i s was done by a l s o u t i l i z i n g the sums of a l i p h a t i c e s t e r s , a l i p h a t i c a l c o h o l s , l a c t a t e s , and the v i c i n a l diketones which were c a l c u l a t e d from the o r i g i n a l physicochemical data. The success

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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of the f i n a l d i f f e r e n t i a t i o n i s shown i n Table V. A l l 35 l i g h t l a g e r beers were c o r r e c t l y c l a s s i f i e d , and only one beer i n each of the l i g h t export and p i l s e n e r l a g e r c a t e g o r i e s was m i s c l a s s i f i e d . However, i t was claimed that these samples were a c t u a l l y c o r r e c t l y c l a s s i f i e d , and that e r r o r s i n i n i t i a l l a b e l i n g or c l a s s i f i c a t i o n l e d to the apparent f a l s e c l a s s i f i c a t i o n s . Table V.

C l a s s i f i c a t i o n o f Three Types o f L i g h t , F u l l Beers with I n d i v i d u a l Physicochemical Parameters Plus the Sums o f A l i p h a t i c A l c o h o l s , E s t e r s , L a c t a t e , and V i c i n a l Diketones.

C l a s s i f i c a t i o n As Actual Beer Type L i g h t Lager

Ligh Lage 35

0

0

L i g h t Export

0

27

1

P i l s e n e r Lager

1

0

20

From Reiner and P i e n d l (41). Further a n a l y s i s o f the data showed that l i g h t l a g e r beers were d i f f e r e n t i a t e d from l i g h t export beers by higher o r i g i n a l g r a v i t i e s , s o l u b l e n i t r o g e n , anthocyanogens, malate, l a c t a t e , p r o l i n e , and α-amino-nitrogen contents. P i l s e n e r l a g e r beers contained more b i t t e r substances and anthocyanogens, but l e s s pyruvate and higher a l i p h a t i c a l c o h o l s than pale o r l i g h t l a g e r beers. A l t beers which are h e a v i e r and darker beers were shown to have deeper c o l o r s , more anthocyanogens, g l y c e r o l , malate, c i t r a t e , e s t e r s and higher a l i p h a t i c a l c o h o l s than l i g h t l a g e r beers. P i l s e n e r d i e t beers were c h a r a c t e r i z e d by t h e i r very high l e v e l s o f a t t e n u a t i o n , high ethanol contents, low pyruvate and c i t r a t e contents, and very low v i s c o s i t i e s . I t was suggested by these workers that i n c l u s i o n o f q u a n t i t a t i v e data f o r higher aromatic a l c o h o l s and s u l f u r - c o n t a i n i n g compounds would g r e a t l y f a c i l i t a t e d i f f e r e n t i a t i o n o f beer types. However, methods f o r r o u t i n e a n a l y s i s of these components have not been a v a i l a b l e . Discriminant A n a l y s i s o f F l a v o r P r o f i l e D e s c r i p t o r Data. Some workers have taken the p o s i t i o n that methods f o r developing r e l i a b l e q u a n t i t a t i v e sensory data must be a v a i l a b l e before the p o t e n t i a l usefulness of chemical and instrumental f l a v o r analy s i s data w i l l be r e a l i z e d . Along t h i s l i n e , Brown, Clapperton,

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

LINDSAY

Flavor

Quality

of

Beer

99

and D a l g l i e s h (42) have shown that beers from d i f f e r e n t geographi c a l l o c a t i o n s (Europe, B r i t a i n , and America) can be successf u l l y c l a s s i f i e d by d i s c r i m i n a n t ( c l u s t e r ) a n a l y s i s of q u a n t i t a t i v e f l a v o r p r o f i l e c h a r a c t e r i s t i c s detected by a q u a l i f i e d panel. In t h i s work approximately 40 d e s c r i p t o r s were b e l i e v e d to adequately d e f i n e the f l a v o r of a l l types of beer, but of these only 27 gave s i g n i f i c a n t scores f o r t y p i c a l , l i g h t l a g e r beers. Average p r o f i l e panel scores f o r the 27 s i g n i f i c a n t sensory c h a r a c t e r i s t i c s were obtained f o r 9 brands of E n g l i s h l a g e r beer, 11 brands of C o n t i n e n t a l European l a g e r beer, and 13 brands of North American beer. D i s c r i m i n a n t a n a l y s i s of these data gave c l u s t e r p l o t s showing very c l o s e groupings of the beers w i t h i n each geographical sampling, and the groups were w e l l - s e p a r a t e d i n space. Discriminan ables to 12 ( i . e . , burnt dimethyl s u l f i d e , cabbagy, h i g h - g r a v i t y f u l l n e s s , warming, t o f f e e - l i k e , and l i v e l i n e s s ) , and using these data much more d i f f u s e c l u s t e r p l o t s were obtained. However, a reasonable degree of c l a s s i f i c a t i o n was s t i l l achieved. Brown, Clapperton and D a l g l i e s h (42) a l s o d i s c u s s e d the p r a c t i c e of producing u s e f u l p r a c t i c a l c o r r e l a t i o n s between sensory and instrumental analyses i n the brewery l a b o r a t o r y without a computer. Examples were discussed where l e v e l s of measured dimethyl s u l f i d e c o r r e l a t e d with sensory scores f o r t h i s compound, and that the type of malt employed d i r e c t l y i n f l u e n c e d the l e v e l s of dimethyl s u l f i d e encountered. Similar simple c o r r e l a t i o n s have been u t i l i z e d f o r other compounds causing o f f - f l a v o r s i n beer, and included are d i a c e t y l ( b u t t e r m i l k - l i k e ) , t-2-nonenal (cardboardy, o x i d i z e d ) , and c e r t a i n short-chain f a t t y a c i d s (soapy). Discriminant A n a l y s i s of A n a l y t i c a l (Including GC) and Sensory Data. Research i n t h i s category involves the demonstrat i o n of d i f f e r e n t i a t i o n of beers on the b a s i s of e i t h e r analyt i c a l measurements or sensory data, and then subsequent c l a s s i f i c a t i o n of the beers in the other set of data whichever the case may be. D i s c r i m i n a n t a n a l y s i s can then be used to reduce the number of v a r i a b l e s to those e s s e n t i a l to e f f e c t c o r r e c t classifications. M o l l e_t a l . (43) have used t h i s approach to study the f e a s i b i l i t y of c l a s s i f y i n g beers i n t o c a t e g o r i e s of good, average, or poor as determined by expert t a s t e r s . The expert panel f i r s t scored 10 f l a v o r and aroma c h a r a c t e r i s t i c s and the o v e r a l l f l a v o r impression f o r 34 beers produced under d i f f e r i n g brewing c o n d i t i o n s i n a French brewery. The same experimental beers were then analyzed f o r 12 i n d i v i d u a l as w e l l as t o t a l carbon disulfide-extractable v o l a t i l e s , and four metal ions (K, Mg, Na, Ca). P r i n c i p a l component a n a l y s i s of each of the data sets (sensory and a n a l y t i c a l ) y i e l d e d c l a s s i f i c a t i o n s of the beers

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

100

FLAVOR

QUALITY:

OBJECTIVE

MEASUREMENT

i n each instance which were separated i n t o three d i s t i n c t groupings (assigned as good, average, or poor). While the groupings obtained f o r the sensory data e v a l u a t i o n were used as the b a s i s f o r q u a l i t y assignments, only two samples were m i s c l a s s i f i e d (changing from average to poor) when the a n a l y t i c a l data alone were used. Stepwise d i s c r i m i n a n t a n a l y s i s was then employed Table VI.

C l a s s i f i c a t i o n of Beers i n t o Q u a l i t y Groupings (Good, Average, Poor) with Stepwise D i s c r i m i n a n t A n a l y s i s o f Physicochemical Data.

T o t a l Number of V a r i a b l e s

Variables Include

% of Beers

13

11 V o l a t i l e s 2 Mineral Salts

94.2 (32/34)

11

9 Volatiles 2 Mineral Salts

91.2 (31/34)

7

5 Volatiles 2 Mineral Salts

82.4 (28/34)

From M o l l et a l .

(43).

to reduce the number of v a r i a b l e s r e q u i r e d to e f f e c t c l a s s i f i c a t i o n i n t o the q u a l i t y groupings (Table V I ) , and even when the data from only 5 v o l a t i l e s and 2 minerals were used, 82.4 percent of the beers were c o r r e c t l y c l a s s i f i e d i n t o the groups determined by sensory c h a r a c t e r i s t i c s . This degree of success f o r these samples i s s i m i l a r to that achieved by the same workers f o r 58 French and f o r e i g n beers using 8 physicochemical v a r i a b l e s s e l e c t e d from 38 i n i t i a l v a r i a b l e s , and c l a s s i f i c a t i o n i n t o good or passable c a t e g o r i e s . In t h i s study 80.5% of the samples were c o r r e c t l y c l a s s i f i e d by using data f o r 3 amino a c i d s , 3 v o l a t i l e s , 1 m i n e r a l , and the c o n c e n t r a t i o n of b i t t e r substances i n beer. An extension o f t h i s approach has been discussed by Dravnieks (15) where odor c h a r a c t e r i s t i c s of i n d i v i d u a l GC peaks from beers analyzed by an entrainment technique were q u a n t i f i e d and c o r r e l a t e d with some GC peak areas f o r c e r t a i n aroma types. While the report was l i m i t e d to d e s c r i p t i o n s of a few c o r r e l a t i o n s , the approach should prove u s e f u l i n the f u t u r e . In summary, evidence has been accumulated to show that beers can be d i f f e r e n t i a t e d and c l a s s i f i e d with the a i d of appropriate s t a t i s t i c a l a n a l y s i s of both physicochemical and sensory data.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

Lindsay

Flavor Quality of Beer

101

Initiation of routine analytical monitoring of flavor quality appears feasible with current gas chromatography and computer methodology, but with experience and refinements of procedures greater applications should follow soon. Literature Cited 1. 2. 3. 4. 5.

6.

7. 8. 9.

10.

11. 12. 13. 14.

15.

16. 17.

Palamand, S. R. and Hardwick, W. A. MBAA Technical Quarter l y , (1969), 6 (2), 117-128. Meilgaard, M. C. MBAA Technical Quarterly, (1975), 12 (2), 107-117. Meilgaard, M. C. MBAA Technical Quarterly, (1975), 12 (3), 151-168. Clapperton, J. F., Dalgliesh, C. E., and Meilgaard, M. C. MBAA Technical Quarterly Teranishi, R., Hornstein "Flavor Research: Principles and Techniques, 30, Marcel Dekker, New York, (1971). Lindsay, R. C . , Withycombe, D. Α . , and Micketts, R. J. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1972), 4-7. Ahrenst-Larsen, B. and Hansen, H. L . Wallerstein Labora tories Communications, (1964), 27 (92), 41-42. Morgan, K. Journal of the Institute of Brewing, (1965), 71, 71-74. Visser, Μ. Κ. and Lindsay, R. C. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1971), 230-237. Harold, F. V . , Hilderbrand, R. P . , Morieson, A. S., and Murray, P. J. Journal of the Institute of Brewing, (1961), 67, 161-164. Jennings, W. G . , Wohleb, R., and Lewis, M. J. Journal of Food Science, (1972), 37, 69-71. Withycombe, D. A. and Lindsay, R. C. MBAA Technical Quarter l y , (1972), 9 (3), x x v i i - x x v i i i . Micketts, R. J. and Lindsay, R. C. MBAA Technical Quarterly, (1974), 11 (3), xix-xx. Wohleb, R. Η . , J r . "GLC Studies of Some Headspace Volatiles During Storage of Beer," 1-84, Ph.D. Thesis, University of California, Davis, (1975). Dravnieks, A. In: "Correlating Sensory Objective Measure ments--New Methods for Answering Old Problems," (Powers, J. J. and Moskowitz, H. R., eds.), ASTM STP 594, 5-25, American Society for Testing and Materials, Philadelphia, (1976). Maule, D. R. Journal of the Institute of Brewing, (1967), 73, 351-354. Hoff, J. T. and Herwig, W. C. Journal of the American Society of Brewing Chemists, (1976), 34 (1), 1-3.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

102

FLAVOR QUALITY: OBJECTIVE MEASUREMENT

18.

Trachman, H. and Saletan, L. T. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1969), 19-28. Bavisotto, V. S., Roch, L. Α., and Heinisch, B. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1961), 16-20. Meilgaard, M. Elizondo, Α., and Mackinney, A. Wallerstein Laboratories Communications, (1971), 34 (114), 95-113. Mecredy, J . Μ., Sonnemann, J . C . , and Lehman, S. J . Food Technology, (1974), 28 (11), 36-41. Sidel, J . L., Stone, Η., Woolsey, Α., and Mecredy, J . M. Journal of Food Science, (1972), 37, 335. Einstein, M. A. Journal of Food Science, (1976), 41, 383-385. Kneen, E. (chr. ed. brd.). "Methods of Analysis of the American Society o American Society o Hudson, J . R. Journal of the Institute of Brewing, (1960), 66, 1-102. Bishop, L. R. In: "Modern Brewing Technology" (Findlay, W. P. Κ., ed.), 292-323, Macmillan Press, London, (1971). Hough, J . S., Briggs, D. Ε . , and Stevens, R. "Malting and Brewing Science," 599-648, Chapman and Hall, London, (1971). Ashurst, P. R. In: "Modern Brewing Technology" (Findlay, W. P. K., ed.), 31-59, Macmillan Press, London, (1971). Doty, D. M. In: "Objective Methods for Food Evaluations," 3, National Academy of Sciences, Washington, (1976). "Correlation of Subjective-Objective Methods in the Study of Odors and Taste," ASTM STP 440, 1-107, American Society for Testing and Materials, Philadelphia, (1968). Powers, J . J . and Moskowitz, H. R. "Correlating Sensory Objective Measurements--New Methods for Answering Old Problems, ASTM STP 594, 1-134, American Society for Testing and Materials, Philadelphia, (1976). Powers, J . J . Food Technology, (1968), 22 (4), 383-388. Powers, J . J . and Keith, E. S. Journal of Food Science, (1968), 33, 207-213. Young, L. L., Bargmann, R. Ε . , and Powers, J . J . Journal of Food Science, (1970), 35, 219-223. Milutinovic, L., Bargmann, R. Ε . , Chang, Κ. Y . , Chastain, Μ., and Powers, J . J . Journal of Food Science, (1970), 35, 224-227. Dravnieks, Α., Reilich, H. G., Whitfield, J., and Watson, C. A. Journal of Food Science, (1973), 38, 34-39. Dravnieks, A. and Watson, C. A. Journal of Food Science, (1973), 38, 1024-1027. Dixon, W. J . (ed.). "BMD: Biomedical Computer Programs," 411-452, University of California Press, Los Angeles, (1975). Hoff, J . T . , Helbert, J . R., and Chicoye, Ε. MBAA Technical Quarterly, (1975), 12 (4), 209-213.

19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.

32. 33. 34. 35. 36. 37. 38. 39.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7. Lindsay 40. 41. 42. 43.

Flavor Quality of Beer

Helbert, J . R. and Hoff, J . T. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1974), 43-46. Reiner, L. and Piendl, A. Brauwissenschaft, (1974), 27, 33-39. Brown, D. G. W., Clapperton, J . F . , and Dalgliesh, C. E. Proceedings of the Annual Meeting of the American Society of Brewing Chemists, (1974), 1-4. Moll, Μ., Flayeux, R., That, V . , and Noel, J . P. Bios, (1974), 9, 328-333.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8 Use of Regression Models i n Objective Flavor Evaluation of Processed Orange Juice during Four Seasons ROBERT D. CARTER Florida Department of Citrus, University of Florida, IFAS, Agricultural Research and Education Center, Lake Alfred, FL 33850 JOHN A. CORNELL University of Florida, IFAS, Department of Statistics, Gainesville, FL 32611 Multivariate analysi processing in quality area (1), selected prime size and texture processing tomatoes, while Rolle and Vandercook (2) used three objective analyses to predict natural citric acid content of lemon juices, a value useful in detecting citric acid adulterations. In 1966, Powers and Keith (3), and Miller (4) working with potato chips, first described application of stepwise discriminant analysis to correlate flavor with chemical analyses. This tool has been refined and applied to a broad range of processed foods (5). In 1971, Fellers and Buslig (6) and Attaway and Carter (7) applied multiple regression analysis to processed orange juice using a season's data from the Juice Definition Program (JDP), developing models for objective flavor prediction. Models for a second season's JDP data were developed in 1972 (8) and models for a third and fourth JDP season combined were found in 1975 (9). In 1974, Persson and von Sydow concluded a five-paper study of the aroma of canned beef by relating sensory and chemical data by application of regression models (10). A general model predicting flavor of processed orange juice produced from any variety during any season would find good application in rapid objective flavor determination during processing, by means of automatic on-stream analysis for a few constituents (variables). Such flavor prediction could indicate necessary processing technique changes instantaneously. The degree of these changes necessary when coupled with the capability of current techniques for adjustment, would optimize quality of the product continuously at the time of juice extraction. The rapid response and increased sampling frequency made possible by this tool would be a valuable supplement to the normal intermittent subjective organoleptic evaluations now a normal function of quality control in the industry. The purpose of this paper is to report on objective prediction of flavor scores of orange juice by models found by a "forward 104 In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

CARTER A N DCORNELL

Processed

Orange

105

Juice

11

s e l e c t i o n procedure of m u l t i p l e l i n e a r stepwise r e g r e s s i o n a n a l y s i s of JDP data f o r 4 annual seasons (1970-71, 1971-72, 1972-73, and 1973-74) u s i n g v a r i o u s data s e t s . Experimental

Procedure

Harvesting, sample p r e p a r a t i o n , e x t r a c t i o n treatments, p r o c e s s i n g , and sample a n a l y s i s f o r each of the 4 seasons data used here have been described (7, 8 , and 9)· 'Hamlin, 'Pineapple, and ' V a l e n c i a v a r i e t i e s were used each season w i t h s e v e r a l harvests of each v a r i e t y throughout i t s m a t u r i t y season . A t o t a l of 84 harvests were made. Each harvest was t r e a t e d w i t h both a s o f t and a hard e x t r a c t i o n (squeeze) method, w i t h i n the range used commercially. T h i s produced a t o t a l of 168 samples, 50 'Hamlin, 54 'Pineapple,' and 64 'Valencia,' f o r the 4 seasons studied. 1

1

1

1

1

Samples were analyze 24 i s t i c s , i n c l u d i n g o r g a n o l e p t i c f l a v o r score e v a l u a t i o n by a 12member experienced panel u s i n g a 9-point hedonic s c a l e . The data were analyzed by stepwise l i n e a r m u l t i p l e r e g r e s s i o n , always l e t t i n g f l a v o r score (F) be a dependent v a r i a b l e and u s i n g the "forward s e l e c t i o n procedure" judged s u p e r i o r t o the "backwards e l i m i n a t i o n method of a stepwise r e g r e s s i o n a n a l y s i s " (11) used i n s t u d i e s of the 1970-71 JDP data ( 7 ) . Models were l i m i t e d t o 5 v a r i a b l e s , according t o Dravnieks QL2). Ten models and r e s p e c t i v e c o e f f i c i e n t s of determination ( R ) were found. Three of the models p r e d i c t f l a v o r scores s p e c i f i c f o r each of the 3 v a r i e t i e s . Two models p r e d i c t f l a v o r scores of j u i c e s prepared by each of the 2 treatments, s o f t and hard e x t r a c t i o n . One model appears f o r each of the 4 seasons s t u d i e d , and a model found by combining data of a l l seasons i s i n c l u d e d . 2

Results and D i s c u s s i o n V a r i e t a l models. models l i s t e d below:

Fourteen v a r i a b l e s appear i n the 3 v a r i e t a l

'Hamlin' F = 3.249 + 0.381 CR - 0.183 CY + 1.433 Sucrose + 0 . 2 4 0 T o t a l Sugar - 0.148 P r o t e i n 'Pineapple' F = 2.949 - 0.052 Sinking Pulp + 0.072 B r i x / A c i d - 0.025 Glycosides - 0.026 Limonin

+ 1.01 Ash

η = 50 R

Z

= 0.835

η = 54

R

= 0.870

'Valencia' η = 64 F = -13.873 - 0.603 A c i d - 0.270 Serum V i s c o s i t y - 16.022 O i l - 0.0077 Glycosides + 0.575 C o l o r No.

R l O n l y one 'Hamlin' harvest

2

1970-71.

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

= 0.842

106

FLAVOR

QUALITY:

OBJECTIVE

MEASUREMENT

Only one variable, glycosides, appears more than once and appears i n both the 'Pineapple and 'Valencia models. Six of these variables: protein, sinking pulp, glycosides, limonin, o i l , and serum viscosity were previously shown (8) to be highly positively correlated with extraction pressures and highly negatively correlated with flavor. The remaining 8 variables: CR, CY, color no. (derived color functions) (13), sucrose, total sugar, Brix to acid ratio, ash, and acid, were shown to be well correlated with maturity of citrus (9), and 6 of these exhibit positive coefficients. A negative coefficient appears for acid as this variable decreases with maturity and thus i s associated with a flavor improvement. CY appears with a negative coefficient which cannot be readily explained i n view of this variable's usual positive correlation with flavor (7). After studying the appearance of both the maturity-related and extraction-related variables i n the models i s influenced most by maturity-relate 'Pineapple' and 'Valencia' flavor are affected most by extractionrelated variables. This indicates that soft extraction pressures are more necessary for good flavor scores i n 'Pineapple' and 'Valencia' than 'Hamlin. The complete dissimilarity of the 3 models i l l u s t r a t e s a unique influence of variables on flavor for each variety. The R^ values of the 3 models are strikingly close. 1

1

1

Extraction treatment models. A model found using a l l seasons data for soft squeeze extraction treatment only, and also a model found using a l l seasons data for the hard treatment only, are l i s t e d below: Soft squeeze F = 4.409 + 0.130 Brix/Acid - 28.784 O i l - 0.070 Limonin - 0.021 Cloud + 5.104 Protein Hard squeeze F = 0.972 + 3.113 Acid + 0.326 Brix/Acid - 32.222 O i l - 0.020 Glycosides - 0.022 Limonin

η = 84 9

R

= 0.593

η = 84 2

R

= 0.725

Limonin, o i l , and Brix to acid ratio variables appear i n both these models. The soft squeeze model has the lowest R^ value. The positive coefficient for acid appearing i n the hard squeeze model requires explanation as acid appeared i n the 'Valencia' model above with a negative coefficient, and acid has always had a negative simple correlation coefficient with flavor i n other regression analyses (9) where data sets are composed of samples treated with both hard and soft squeeze. Hard squeeze orange juice samples always had lower flavor scores and lower acid values than soft squeeze samples (7, 8, and 9)· Lower acid may result from dilution of acid i n hard squeeze by more lower or non-acid

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CARTER AND CORNELL

8.

Processed

Orange

107

Juice

components originating i n the cytoplasm of the cells i n the juice vesicle (14). Some of these components may contribute off-flavors accounting for the lower flavor scores of hard squeeze juices. Therefore, the higher acid juices i n the hard squeeze set probably indicate less severe treatment and thus higher flavor scores than the lower acid juices i n the set. Season models. Five models were found, one for each season 1970-71 through 1973-74 and one for a l l 4 seasons combined as follows : 1970-71 η = 24 F = 2.749 - 0.045 Sinking Pulp - 0.098 Serum Viscosity - 0.039 Limonin + 0.172 Cloud - 0.099 Sucrose R = 0.956 2

36

1971-72 F - 1.603 + 0.414 Brix - 0.926 Seru

y η = 36 0.230 Limonin R = 0.887

1972- 73 F = 4.183 + 0.113 Brix/Acid - 50.315 O i l + 0.059 CR - 0.850 Sodium

72

1973- 74 2.256 + 0.098 Brix/Acid - 42.487 O i l +0.051 CY - 0.953 Sodium

F

s

0.042 Limonin = 0.711

R

A l l Seasons η = 168 5.482 + 0.125 Brix/Acid - 45.623 O i l +0.047 Aldehydes 0.724 - 0.018 Glycosides - 0.025 Limonin R Z

The latter 3 seasons models and the a l l seasons model each have 3 variables i n common: limonin, o i l , and Brix to acid ratio, and these same 3 variables also appeared i n both the treatment models discussed earlier. Two of these, limonin and o i l , appeared i n the 3-variable linear model (R « 0.958) reported by Attaway and Carter (7). This model was found by the backwards elimination method of a stepwise regression analysis" and contained only 3 variables, which may account for i t s difference from the 1970-71 season model l i s t e d above u t i l i z i n g the same data. The 9-variable model (equation no. 1 where R = 0.901) reported by Attaway et a l (8) was found by a "forward selection procedure" with data used to find the 1971-72 model l i s t e d above. These 2 models developed by the same techniques from the same 1971-72 data have 4 variables i n common: limonin, o i l , Brix, and serum viscosity. In a l l models containing limonin and o i l , these extraction-related variables appeared with negative coefficients indicating their adverse effects on flavor. Conversely, Brix to acid ratio, a maturityrelated variable, always appeared with a positive coefficient. The appearance of 3 common variables i n 3 of the season models i s an indication that flavor of orange juice for 3 seasons ,f

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

108

FLAVOR QUALITY:

OBJECTIVE

MEASUREMENT

can be estimated u s i n g the same 3 v a r i a b l e s . T h i s i n d i c a t e s a consistency among seasons which i s encouraging i n looking f o r a model a p p l i c a b l e t o orange j u i c e produced i n any season. ο The IT* value of the a l l seasons model times 100% i n d i c a t e s that 72.4% of the v a r i a t i o n i n f l a v o r i n a l l samples can be explained by the model. The authors f e l t t h i s model might be u s e f u l i n multi-season f l a v o r e s t i m a t i o n and sought t o t e s t the p r o v i n c i a l i t y (12) of the model. T h i s was done by t a k i n g 30 random samples throughout the 4 seasons which were not a part of the data set of any of the season models. These samples were prepared i n a commercial manner s i m i l a r t o , but not n e c e s s a r i l y the same as, treatments used f o r the samples included i n the models above. Each of the 30 samples values f o r the 5 v a r i a b l e s of the a l l seasons model were s u b s t i t u t e d i n the a l l seasons model and a c a l c u l a t e d the samples. The range observed scores and c a l c u l a t e d scores are compared below: 1

Range Mean Value Standard D e v i a t i o n

Observed 4.0 - 6.5 5.4 0.74

Calculated 4.2 - 6.4 5.5 0.61

The c o r r e l a t i o n c o e f f i c i e n t ( r ) of the scores was 0.741. Residuals of the observed scores l e s s the c a l c u l a t e d scores were determined, and ranged from - 1.2 t o + 0.9 f l a v o r score p o i n t s . The above i n f o r m a t i o n i n d i c a t e s that the a l l season model can be a u s e f u l t o o l i n o b j e c t i v e f l a v o r e v a l u a t i o n of orange j u i c e i n the processing p l a n t , although a model producing more p r e c i s i o n between observed and c a l c u l a t e d f l a v o r scores i s d e s i r a b l e . The scope of t h i s study precluded the search f o r c u r v i l i n e a r models and the use of r a t i o s of v a r i a b l e v a l u e s . Work i n these areas i s i n progress. Acknowledgment For considerable a n a l y t i c a l data used to f i n d the models, the authors thank the f o l l o w i n g c o l l e a g u e s : B. S. B u s l i g , R. W. Barron, M. H. Dougherty, P. J . F e l l e r s , J . F. F i s h e r , E. S. H i l l , R. W. Huggart, and S. V. T i n g . Abstract Ten models are discussed which were found by m u l t i p l e l i n e a r r e g r e s s i o n of data f o r 24 chemical or p h y s i c a l c h a r a c t e r i s t i c s of 168 samples of processed orange j u i c e produced by both s o f t and hard commercial j u i c e e x t r a c t i o n methods during 4 annual seasons (1970-71, 1971-72, 1972-73, and 1973-74) from 'Hamlin, 'Pineapple, and 'Valencia' oranges. F l a v o r was always the dependent v a r i a b l e . 1

1

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8. carter and Cornell

Processed Orange Juice

109

Models were found using the following data sets: Each season's data, all seasons data, a l l data from each oraige variety, and data from each juice extraction treatment. Coefficients of determination (R ) for a l l models varied from 0.593 to 0.956. Limonin, o i l , and Brix to acid ratio a l l appeared in 3 season models and the all season model. Literature Cited 2

(1) Mittler, Α., Food Technol. (1962) 16 (3) 22. (2) Rolle, Lawrence Α., and Vandercook, Carl Ε . , J. AOAC (1963) 46 (3) 362-365. (3) Powers, J. J., and Keith, E. S. "Abstracts of 2nd International Congress of Food Science and Technology," 439, Warsaw, Poland, 1966. (4) Miller, W. O. Ph.D thesis Univ of Ga Library Athens Ga 1966. (5) Powers, John J. Foo (1968) (4) (6) Fellers, P. J., and Buslig, B. S. (1971) 22nd Annual Citrus Processors' Meeting, Mimeo report AREC-LA 71-40 p. 14. AREC, Lake Alfred, Fla. 33850. (7) Attaway, John Α., and Carter, Robert D. (1971) Proc. Fla. State Hort. Soc. 84 201-205. (8) Attaway et al (1972). Proc. Fla. State Hort. Soc. 85 193-203. (9) Carter et al (1975). Proc. Fla. State Hort. Soc. 88 358-370. (10) Persson, Tyko, and von Sydow, Erik (1974). J. Food Sci. 39 537-541. (11) Draper, N. R., and H. Smith, "Applied Regression Analysis," p. 167-171, John Wiley & Sons. New York, London, and Sydney. 1968. (12) Dravnieks, Andrew, "Approaches to Subjective/Objective Correlations in Flavor," p. 21, in Powers, J. J., and Moskiwitz, H. R., "Correlating Sensory Objective Measurements." Amer. Soc. for Testing and Materials. Philadelphia, Pa. 19103. 1976. (13) Florida Department of Citrus, "Official Rules Affecting the Florida Citrus Industry Pursuant to Chapter 601, Florida Statutes." 20-65.01-.05, Lakeland, Fla. 33802. 1976. (14) Albrigo, L. G., and Carter, Robert D., "The Structure of Citrus Fruits in Relation to Processing," in Veldhuis, Μ. Κ., Nagy, S., and Shaw, P., "Citrus Processing Science and Technology," Vol. I, Avi Pub. Co., Westport, Conn. 06880. (In press.)

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

INDEX A Absorbance ratio 60 Acceptability, sensory contributions to 58 Acetaldehyde 46,92 Acetic acid 91 Acetoin 91 Acetone 18,54 Acetonitrile 18 Acetophenone 18,2 Acid ratio, brix-to10 Acidity, titratable 2 Additivity of odor intensities in mixtures 38 Additivity, vector model of 30 Adsorptivities at water/oil interfaces 16 Air dilution olfactometer 31 Alcohols, aliphatic 98 Aldehyde(s) 6 groups 20, 24 Ale tasters 1 Aliphatic acids 91 alcohols 97,98 aldehydes 6 esters 97 Allyalcohol 18,25 Amino acids 47 reaction mixture, sugar2 groups 20 α-Amino acids 97 α-Amino-nitrogen contents 98 o-Aminoacetophenone 91 Amyl butyrate 30 Analytical judgments 59 Aniseed-like 76 Antagonism 5 Anthocyanogens 98 Apple(s) 5,46,49 Cox's Orange Pippin 73 esters 91 external aroma profiles of 77 flavor quality in 71 juices,flavorquality in 71 mean ranking of four varieties of .... 74 phenolics, astringency, and bitterness in pot-grown cider 84 threshold values of significant aroma compounds in 78 volatiles from 77

Ar-curcumene Aroma(s) comments compounds in apples, threshold values of dried leaf and spicy metallic mushroom profiles of apples, external

Ascorbic acid Astringency Attributes, odor concentrations and average ratings on

6 77 78 76 5 5 77

72 81,83 34

Β Banana 35 esters 91 Beans, canned and frozen 52 Beans, quality evaluation of green .... 51 Beef boiling 2 canned 6,104 cooked sliced 6 Beer(s) classification of 97 into quality groupings 100 constituents in determining the flavor of 91 flavor chemistry of 89 flavor quality, objective measure ments of 89,93,94 flavors, sensory analysis of 93 lager 95 volatile compounds in 5,90,92 Benzaldehyde 18, 25 Benzene 18 rings 20,24 Binary mixtures, hedonic tone of 37 Bitter compounds, hop 91 Bitterness 81 assessment sheet for 83 in pot-grown cider apples 84 Bonds, double 20,24 Bread 46 starch in 47 Brewing practices 89 Brix-to-acid ratio 106 Browning reactions, nonenzymatic 47

111

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

112

FLAVOR QUALITY:

Building blocks of molecules Butanoic acid 1- Butanol odor intensity equivalent referenced values of intensity 2- Butanone Butylbutanoate Butylether Butyric acid

16 18 13 18 12,14 18 18 18 91

C Caffeine 46 Calves rennet 48 Caramel flavored compounds 91 Carbocyclic ring 24 Carbon dioxide 91,9 disulfide 92,9 tetrachloride 18,2 Carbonyl group 24 Carboxyl groups 20 Carboxylic acid group 24 Carboxymethyl cellulose 46 Catechins, simple 80 Category scaling 12 Cells of fresh fruits 49 Cheese, cheddar 46,48 Chemical mixtures, psychophysical analysis of flavor 29 Chemical notation formulas, Wiswesser one-line 16 Chlorine 24 Chlorobenzene 18 α-Chloroethylsulfide 25 Chloroform 18,54 Chromatogram of volatiles from apples 77 Chromatograph sniffing the outlet of a gas 2 Chromatographic analysis, problems in the gas 3 separation of cider phenolics, paper 80 separation, gas 7 Chromatography, gas-liquid 51 Chromatography, liquid-solid 54 Cider from Dabinett 83 fermented 78 flavor quality in fermented 71 industry, English 78 phenolics 84, 85 counter current separation of 81 paper chromatographic separation of 80 in pot-grown 84 Cineole 18 Citrals 6,18 Citrate 98

OBJECTIVE

MEASUREMENT

Citric acid content 104 Cluster analysis 56, 59 Color 55,60 Columns, W C O T 4 Components, hedonic ratings of the ... 37 Compositional changes 3 Concentration 3 Corn, odor of 6 Correlation coefficients 75 Correlation, method of 17 Counter-current distribution 82 Cox's Orange Pippin apple 73 Crocker-Henderson system 30 Cultivars 74 Cumin constitutents, odors of 6 Currants, black 6 Cyanide groups 24 Cyano groups 20

D

Dabinett cider 83 Data analysis, computerized 7 Data, analytical 5, 73 Decanoic acid 92 Descriptor data, flavor profile 98 list 43,53 terms, Dravineks' list of 30 terms, Harper et al/s list of 30 Determination, coefficients of 105 Diacetyl 91,99 1.2- Dichloroethane 18 Dilution on odor intensity, effect of 13 olfactometer, air 31 olfactometer, vapor 13 ratio for saturation vapor pressure 26 3,4-Dimenthythiophene 5 Dimethylbenzylcarbinol 18 Dimethylpentane 18,25 Dimethyl sulfide 6,30,91,99 2,4-Dimethylthiophene 5 1.3- Dioxalans 5 Dioxane 18,25 Dithioethylglycol 25 Dose response function 36,38 parameters 14 plots for various odorants 22 Dravineks' list of descriptor terms 30 f

Ε Electrical response of olfactory or taste cells Emotional judgments English cider industry Epi-catechin

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2 59 78 81

113

INDEX

Equilibrium reactions 89 Ester(s) 98 groups 20,27 linkage 24 Estimation methods, magnitude 13 Ethanol 18,91,92 Ether groups 20 Ethyl acetate 81,91,92,96 Ethylbutanoate 18 Ethylbutyrate 25 4-Ethylguaiacol 91 Ethyl hexanoate 91, 92 Ethyl 2-methyl butyrate 78 Ethyl octanoate 92 Ethyl propanoate 92 Ethyl salicylate 31,34,40,42 Eugenol 18 Experimental design 32 Extraction procedures, carbon disulfide 9 Extraction treatments models 106

F Factor analysis 39,53,57 Factor space, two dimensional 42 Fatty acids 99 Fermentation(s) 89 metabolic by-products of 97 Fertilizers, nitrogen 84 Fining, gelatin 84 Flavor attributes for sensory evaluation, segregation of 75 chemical mixtures, psychophysical analysis of 29 chemistry of beer 89,91,93 evaluation, regression models in objective 104 onion 6 profile descriptor data 98 quality in apples, apple juices, and fermented ciders 71 of beer, objective measurements of the 89,94 objective measurements of 1,72,94 structural and mechanical 45 release 46 and texture, connection between . 4 5 , 4 7 units 90 Flowery 35 Force, shear 56,66 Formol nitrogen 94 Forward selection procedure 105 Fragrant 34 Fruits, cells of fresh 49 Fruity 34 Functional groups, arrangement of 16 Fusel alcohols 91

G Gas-liquid chromatography analysis, problems in the procedure retention volumes separation volatile profile data Gases, dissolved Gelatin fining Ginger essential oil Glycerol Guaiacol Gums

51 3 54 16 7 96 2 84, 85 6 98 18,25 46

H Halogen atoms Halogen compounds

20 27

concentration of odorants quantitative static techniques Hedonic ratings of the components ratings of mixtures tone of binary mixtures Heptyl acetate Herbal Heterocyclic ring 2- 4-Hexadienal Hexanal Hexane Hexanoic acid 1- Hexanol 3- Hexanol 2- Hexanone 2-Hexenal Hexyl acetate Hexyl 2-methyl butyrate Histogram Hop bitter compounds Humulone Hydrocarbon chain Hydrocolloids Hydrogen-bonding Hydrogen sulfide Hydroxy 1 group Hydroxypropyl cellulose

11 92 6 29,30 37 37 37, 38 31,34,40,42 35 17,20,24 16 6,18,25,78 55 18,92 18 18 18 78 78 78 21 91 04 20 46 16 91 20, 24 46

I Imino groups Indole Industry, English cider Intensity 1-butanol referenced values of concentrations, isoof mixtures odor (see Odor intensity)

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

20 18,27 78 29 14 21 30

114

FLAVOR QUALITY:

Interfaces, adsorptivities at water/oil 16 Iodine Γ. 24 1-Iodobutane 18 Isoamyl acetate 91,92,96 Isoamyl alcohol 91,96 Isobutanol 92,96 Isocyanide groups 24 Isohumulone 94 Isointensity concentrations 21 correlation 22 regression equations for 23 and vapor pressures 25 Isopropyl acetate 92 Isopropylpropionate 19 Isothiocyanate groups 20 Isovaleraldehyde 91 Isovaleric acids, butyric 91

OBJECTIVE

MEASUREMENT

Mesitylene Metallic aroma Methional 4-Methoxyallylbenzene 2-Methylbutanol 2- Methylbutene-2 3- Methylbut-2-enylthiol Methyl isopentanoate Methyl group Methyl pentanoate 2-M ethyl propanol Methyl propyl disulfide Methyl propyl trisulfide Methyl salicylate Methylsulfide Middle lamella Mineral salts Minty

19 5 91 76, 78,80 92 92 91 19 17,24 19 6,19 6 6 19 25 48 100 34,40

J Judgments, emotional vs. analytical Juice(s) definition program ( J D P ) flavor quality in apple during four seasons, processed orange lemon

59 104 71 104 104

Κ Knife assembly, Warner-Bratzler type

56

L Lactates Lactones Lager beers Lamella, middle Lavandin Leaf aromas, dried Lemon juices Lemony attribute rf-Limonene Limonin oil Linalool Linalyl acetate Linkage, ester Liquid-solid chromatography

97,98 27 95 48 30 76 104 6 18,25 106 18,30 30 24 54

M Magnitude estimation 5,12,13,31,36 Malate 98 Meat, aging 47 Mechanical indicators of flavor quality 45 Mechanical measurements 55 3-p-Menthen-7-al 6 Menthol 19 Mercaptan 24

hedonic tone of intensity of odor quality of quality profiles quality, shifts in Molecular properties of odorants shapes and sizes structures, properties derivable from the volumes weight · Molecules, building blocks of Monoterpene hydrocarbons Multidimensional analysis Multidimensional scaling Multivariate analysis Mushroom aroma Musks

37,38 30 30 31 40 37 16 16 11 16 20,24 16 6 39 31,43 104 5 27

Ν -N= groups Nerolidol Nitrile groups Nitro groups Nitrobenzene Nitrogen contents, α-amino fertilizers formol levels, pot-grown cider apples, effect of 1-Nitropropane ί-2-Nonenal

20 6 20 20 19 98 84 94 84 19 91,99

Ο Objective measurements, relations between sensory and

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

51

115

INDEX

Octanoic acid 92 1-Octanol (internal standard) 92 1- Octene 19 2- Octene 19 l-Octen-3-ol 5 1- Octen-3-one 5 2- Octyne 19 Odor(s) concentrations and average ratings on attributes 34 concentration for mixtures 38 of corn 6 of cumin constituents 6 of fried onions 5 intensity 22,33 effect of dilution on 13 equivalent of 1-butanol 18 measurements 11 in mixtures, additivity of 3 perceived (S) 1 saturation of odorants perceived 36 scales 15 with structural properties of odorants, correlation of 11 suprathreshold 21 quality of an 30 quality of mixtures 30, 31 stimuli, electrical response of olfactory or taste cells elicited by 2 Odorant(s) coefficients for 11 concentration C 12 dose-response plots for 22 in headspace samples, concentration of 11 molecular properties of 16 perceived odor intensity, saturation of 36 structural properties of 11 Oil ginger essential 6 interfaces, adsorptivities at water/ 16 onion 5 Olfactometer, air dilution 31 Olfactometer, vapor dilution 13 Olfactory cells, electrical response of 2 Onion(s) flavor 6 odor of fried 5 oil 5 Orange juice, processed 104

Ρ Paper chromatographic separation of cider phenolics Partition coefficient Peanut butter

80 81 6

Pear Pectic materials 2,3-Pentanedione 3-Pentanone Percent of the total peak area ( P T P A ) method pH 2-Phenethanol 2-Phenethyl acetate Phenolics, cider counter current separation of from Dabinett cider effect of gelatin fining on effect of nitrogen levels on paper chromatographic separation of Phenylacetic acid Phenylethanol

31,35 48 91 19 94 2 92 91 81 83 85 84 80 91 19

Physicochemical variables 96 α-Pinene 19 Polyphenols 72,84,91 Potato chips 104 Predicting equation for quality 67 Preference ratings 73 Procyanidins 79, 80 Proline 98 Propanoic acid 19 Propanol 30 1- Propanol 19,92 2- Propanol 19 Propylbutanoate 19 Propylmercaptain 25 Proteolytic breakdown 47 Psychophysical analysis 29 Psychophysical-statistical approach 6 Pyridine 19,30 Q Quality flavor (see Flavor quality) evaluation of green beans groupings, classifications of beers into of mixtures, odor of an odor predicting equation for profiles, mixture shifts in mixtures Quantitative changes Quantitative static headspace sampling Quaternary atoms

51 100 31 30 67 40 37 3 92 20

R

Reference scale, 1-butanol ( n-butanol )

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12

116

FLAVOR QUALITY:

Referenced values of intensity, 1-butanol 14 Regression equation(s) for isointensity concentrations 23 symbols in 24 for vapor pressure 23 Regression models in objective flavor evaluation 104 Rennet, calves 48 Ring(s) benzene 24 carbocyclic 24 heterocyclic 20,24 substituents on 20 substituted position on 24 Rose 31 Rotation, Thurstone's analytical method of 53 f

OBJECTIVE

MEASUREMENT

Spicy scores to amounts of 4-methoxyallylbenzene, relation of Starch in bread Starches Statistical analysis Stimuli Stimulus flowrate from sniffing port.... Strength, tensile Structural indicators of flavor quality Structural properties of odorants Structures, properties derivable from the molecular Styrene Substituents on rings Sugar-amino acid reaction mixture .... Sugars Sulfur-containing compounds

80 47 46 53 31 15 56 45 11 11 19 20 2 91 98

S -S- groups 20 S (perceived odor intensity) 12 -value scales 14 Saccharin 46 Salicyclic structures 27 Sample analysis 4 Sample preparation 4 Season models 107 Seasons, processed orange juice during four 104 Segregation of flavor attributes for sensory evaluation 75 Sensory analysis 4 of beer flavors 93 assessment, objective 73 attributes, correlate analytical data with 5 contributions to acceptability 58 data, discriminant analysis of 99 evaluation, segregation of flavor attributes 75 and objective measurements, relations between 51 trial, first 53 Separation 3 gas chromatographic 7 jS-Sesquiphellandrene 6 Shapes and sizes, molecular 16 Shear force 56,66 Skatole 17,25,27 Sniffing 66 the outlet of a gas chromatograph 2 port, stimulus flowrate from 15 Soapy note 6 Sodium alginate, solution of 46 Spearmint 35 Spectral characteristics 16 Spicy aromas 76

Synergism

5 Τ

Tannin mixture 79 Taste cells, electrical response of 2 Taste triangle panel 95 Tensile strength 56 Ternary atoms 20 a-Terpineol 6 1,1,2,2-Tetrachloroethane 19 Texture-flavor associations 45,47 Thiocyanate groups 20 Thiol groups 20 Thiophene 19 Thiophenol 14 Threshold values of significant aroma compounds in apples 78 Thurstone's analytical method of rotation 53 Toluene 19 Tomatoes 3,46,104 Trace metals 94 Triangle, taste panel 95

U Univariate analysis

53 V

α-Valerolactone Vanillin Vapor(s) in air to produce odor intensity equivalent of 1-butanol, concentrations of dilution olfactometer pressure(s) dilution ratio for saturation isotensity concentrations and

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

91 19,27

18,19 13 26 25

117

INDEX

Vapor pressure (continued) regression equation with structural properties of odorants, correlation of Varietal models Vector model of additivity Vicinal diketones Viscosity modifying agents Volatile(s) from apples, chromatogram of in beer, aroma compounds in beer profile data, G C Volumes, gas-chromatographic retention

W 23 11 105 38 30 97,98 46

Warner-Bratzler type knife assembly 56 Water/oil interfaces, adsorptivities at 16 W C O T columns 7 4 Winey 35 Wintergreen 31 Wiswesser one-line chemical notation formulas 11,16 Woody note 6

77 5 92 96

m-Xtjlene (internal standard)

16

Yeast culture, pure

X

19,92

Y

In Flavor Quality: Objective Measurement; Scanlan, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

72