Flavor Chemistry - ACS Publications - American Chemical Society

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Chapter 11

Temporal Aspects of Flavoring P. Overbosch and W. J. Soeting Unilever Research Laboratorium Vlaardingen, P.O. Box 114, 3130 AC Vlaardingen, Netherlands The aroma of a food product is often measured by a sensory technique called descriptive profiling, in which flavour experiences are described by a panelist as a set of component impressions or sensations of varying degrees (1). Profiles do not hold explicit information about the temporal characteristics of a flavour, its persistence and the times of appearance of the individual notes. Nevertheless, the rank order of the attributes sometimes reflects, to some extent, the order of appearance of the corresponding impressions. Some notes are then said to be released "early", others "late". However, there is little published experimental evidence that demonstrates a relationship between the temporal features of aroma perception and the stimulus concentration near the sensory receptors. In the following we describe some experiments that examine the issue directly and some theoretical ideas that appear to explain the results. Psychophysical Measurement When carrying out psychophysical measurements on a flavoured food we usually define the system as: flavour/matrix

> sensory response

where the flavour/matrix is e.g. diacetyl in margarine and the sensory response is a magnitude score representing perceived intensity. This view, however, is too simple. In reality we have to consider a stimulus-response system where the stimulus is defined as a concentration, not in the product but at the receptor sites and not as a single value but as a function of time. Likewise, the response should be measured as a function of time. c

0097-6156/89/0388-€138$06.00/0 1989 American Chemical Society

Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

11. The

Temporal Aspects of Flavoring

OVERBOSCHANDSOETING

system c a n t h e n be f o r m u l a t e d flavour/matrix > stimulus response ( t )

To be a b l e t o u n d e r s t a n d

139

as f o l l o w s :

( t ) [psychophysical function (t)] >

t h i s system we have

developed:


- a methodology t o measure t h e c o n c e n t r a t i o n o f f l a v o u r as r e l e a s e d from a m a t r i x , a t t h e nose, b r e a t h - b y - b r e a t h ; - a time-dependent form o f t h e p s y c h o p h y s i c a l f u n c t i o n r e l a t i n g stimulus to perceived i n t e n s i t y ; - an improved methodology t o measure p e r c e i v e d i n t e n s i t y as a f u n c t i o n o f time ( I / t ) . Mass-spectrometric

breath-by-breath

analysis

B r e a t h - b y - b r e a t h a n a l y s i s o f gases and v o l a t i l e s i s w e l l known i n m e d i c i n e ( 1 ) . The e x p e r i m e n t a l t e c h n i q u e s used, however, were n o t v e r y w e l l s u i t e d t o our needs. F o r o u r purpose we needed a s i m p l e , r e l i a b l e i n l e t system w i t h o u t e x t e n s i v e f i l t e r i n g and p r e s s u r e r e d u c t i o n , b u t w i t h a h i g h s e n s i t i v i t y and s h o r t r e s p o n s e t i m e s . T h e r e f o r e a (semi-) c o n t i n u o u s m e a s u r i n g methodology, l i k e MS was c o n s i d e r e d . T r a c e a n a l y s i s b y MS v i a a membrane s e p a r a t o r was known ( 2 ) , b u t t h e decay times o f t h e s i g n a l p r e c l u d e d breath-by-breath analysis. When t h e c o n s t r u c t i o n o f t h e s e p a r a t o r was s t u d i e d more c l o s e l y , i t apppeared t h a t t h e d e v i c e t r a d e d r e s p o n s e time f o r s e n s i t i v i t y . A f a s t r e s p o n s e r e q u i r e s a s m a l l i n t e r n a l volume, b u t a h i g h s e n s i t i v i t y r e q u i r e s a l a r g e membrane s u r f a c e . R e d u c i n g t h e s u r f a c e a r e a and t h e i n t e r n a l volume r e s u l t e d i n v e r y s h o r t r e s p o n s e times and s u f f i c i e n t s e n s i t i v i t y ( s e e F i g . 1 ) . The

setup

r e s p o n s i b l e f o r these

improvements i s d e p i c t e d i n F i g . 2.

V i a two s m a l l g l a s s p i p e s , one i n each n o s t r i l , a s m a l l pump sucks 550 ml/min o f a i r from t h e nose and p a s t t h e membrane. The MS takes 20 d a t a p o i n t s / s and t h e r e s u l t i s a f u l l b r e a t h - b y - b r e a t h quantific a t i o n o f v o l a t i l e s r e l e a s e d from t h e mouth d u r i n g m a s t i c a t i o n . A typical result

i s shown i n F i g . 3a.

One c a n see a v e r y sharp l e a d i n g edge, f o l l o w e d by an e x p o n e n t i a l decay as t h e f l a v o u r i s d e p l e t e d from t h e o i l . To o b t a i n p a n e l r e s u l t s , t h e i n d i v i d u a l c u r v e s a r e m o d e l l e d by f i t t i n g a f u n c t i o n c o n s i s t i n g o f two e x p o n e n t i a l s , one r e p r e s e n t i n g the r i s e and t h e o t h e r t h e decay o f t h e s i g n a l , t o t h e d a t a . T h i s procedure transforms the i n d i v i d u a l breath-by-breath results i n t o a smooth s t i m u l u s c u r v e , c h a r a c t e r i s e d by t h e parameter v a l u e s o f the e x p o n e n t i a l s (see F i g . 3b).



140

FLAVOR CHEMISTRY: TRENDS AND DEVELOPMENTS

•5ml headspace • 100mg 2-pentanône/kg water • direct injection in system lnt.M/Z86(M*) 10,

MEMBRANE SEPARATOR ORIGINAL

MODIFIED llOOr

50

20

Fig.

1

30

Τ 5^ 10 Retention time/mm

Peak shape o f h e a d s p a c e o f 2-pentanone

solution

i n water

TEMPERATURE PROGRAMMABLE OVENj MASS Teflon

Teflon

PUMP Fig.

2

^ F J B J " L i CONTROLLER HP 9825 Β HP 5970 MEMBRANE SEPARATOR

FLOW METER Lay-out o f breath

analyzer


11.

OVERBOSCHANDSOETING

Temporal Aspects ofFlavoring

141


The parameter v a l u e s a r e s u b s e q u e n t l y a v e r a g e d t o p r o d u c e a p a n e l s t i m u l u s c u r v e . A p p a r e n t l y , the pentanone i s d e p l e t e d from the l i q u i d l a y e r i n the mouth v e r y r a p i d l y . I t s h o u l d be borne i n mind t h a t t h i s i s n o t o n l y due t o r e l e a s e i n t o the gas phase, b u t must a l s o be a s c r i b e d t o uptake i n t o the mouth and u p p e r a i r w a y s ( 3 ) . F i g . 4 d e p i c t s the p a n e l c u r v e s o f the s i m u l t a n e o u s r e l e a s e o f butanone-2 and pentanone-2 from water. As pentanone-2 i s more hydrophobic i t i s r e l e a s e d f a s t e r . B o t h c u r v e s peak a t the same time b u t pentanone-2 peaks h i g h e r and i s s u b s e q u e n t l y d e p l e t e d f a s t e r . A f t e r about 50 s the r e l e a s e c u r v e s cross. I f the f l a v o u r c h a r a c t e r s o f t h e s e s u b s t a n c e s would have been s u f f i c i e n t l y d i f f e r e n t the p a n e l would p r o b a b l y have commented t h a t butanone-2 r e l e a s e d " l a t e " . A time-dependent form o f the p s y c h o p h y s i c a l f u n c t i o n I n o r d e r t o be a b l e to p r e d i c t the e f f e c t o f a l t e r a t i o n s t o the time c o u r s e o f s t i m u l a t i o n on p e r c e i v e d i n t e n s i t y o v e r time, the s t a t i c p s y c h o p h y s i c a l f u n c t i o n had t o be extended. I n the f o l l o w i n g s e c t i o n , t a s t e and s m e l l w i l l be t r e a t e d e q u a l l y . I n d e t a i l t h i s i s n o t c o r r e c t b u t f o r the l i n e o f thought t o be d e v e l o p e d h e r e the t r e a t m e n t i s the same. We s t a r t e d from S t e v e n s ' law (4) i n c l u d i n g the t h r e s h o l d correction: I-k (S - S o * ) n

where I - p e r c e i v e d i n t e n s i t y as e x p r e s s e d S - p h y s i c a l stimulus strength So*- unadapted t h r e s h o l d l e v e l k and η a r e c o n s t a n t s I f p r o l o n g e d s t i m u l a t i o n , o f any t e m p o r a l form, i s t o have an e f f e c t on t h i s r e l a t i o n s h i p , i . e . i f I becomes I ( t ) , t h e n a t l e a s t one o f the o t h e r p a r a m e t e r s must a l s o become a f u n c t i o n o f time. The o n l y w e l l documented e f f e c t o f p r o l o n g e d s t i m u l a t i o n on the c h a r a c t e r i s t i c s o f t a s t e and s m e l l i s a d a p t a t i o n . F i g . 5a shows the e f f e c t s o f a d a p t a t i o n t o a c o n s t a n t s t i m u l u s p r i o r t o magnitude e s t i m a t i o n as measured by C a i n ( 5 ) ; the c u r v e s r e l a t i n g I n t e n s i t y t o S t i m u l u s s t r e n g t h drop o f f n e a r the c o n c e n t r a t i o n l e v e l o f the a d a p t i n g s t i m u l u s . A t h i g h e r s t i m u l u s l e v e l s , however, t h e y seem t o c o n v e r g e . I n F i g . 5b the a d a p t i n g l e v e l s have been d e d u c t e d from the a c t u a l s t i m u l a t i o n and r e s u l t s show s t r a i g h t l i n e s f o r p e r c e i v e d i n t e n s i t y a g a i n s t s t i m u l u s minus a d a p t i n g l e v e l . W i t h i n S t e v e n s ' e q u a t i o n , t h e r e f o r e , i t appears t h a t i t i s the t h r e s h o l d term t h a t i s a f f e c t e d by s t i m u l a t i o n . We had t o f i n d out how, however.


FLAVOR CHEMISTRY: TRENDS AND

DEVELOPMENTS

Ion current at m/z 86


I 0

Fig.

1 1

ι 2

. 3

. A

3a B r e a t h a n a l y s i s 100 mg 2-pentatone/kg MCT

. 5 Time/min

o i l i n the mouth

Ion current at m/z 59 • measuring point (mean of 15 consecutive data) ° after regression

B

•

fjSfifc^

/

N ,

ο

0

1

2

.3 Time/mm

3b S i n g l e r e l e a s e c u r v e o f b u t a n o l - 2 from water a f t e r smoothing and a f t e r r e g r e s s i o n . Each b l a c k square r e p r e s e n t s the mean o f 15 c o n s e c u t i v e d a t a p o i n t s i n a s i n g l e e x p e r i m e n t . The open c i r c l e s r e p r e s e n t the b e s t f i t t i n g curve.

ion current,arbitrary units

\

I

0

1

4 S i m u l t a n e o u s r e l e a s e o f butanone-2 water

ι 2 min

and pentanone-2


from

11.

OVERBOSCHANDSOETING


143

Rated perceived intensity • non-adapted

100


ο low"^ intensity • mid > of adapting • high J concentratTon

self-adaptation •

10

1

0.1

10 -1

Concentration/(mg

Fig.

I)

5a P e r c e i v e d i n t e n s i t y ( I ) v s s t i m u l u s c o n c e n t r a t i o n o f p e n t a n o l i n an o l f a c t o m e t e r e x p e r i m e n t , under v a r i o u s conditions o f pre-adaptation ( a f t e r W.S. C a i n , P e r c e p t . Psychophys. 7 (1970) 271) Rated perceived intensity 100r

10r o f

•^ [pentanol]

Ih

1

0.01

0.1

10

S-S^OngH) Fig.

5b P e r c e i v e d i n t e n s i t y ( I ) o f p e n t a n o l v s s t i m u l u s concen t r a t i o n ( d a t a from F i g . 5a) r e p l o t t e d a f t e r s u b t r a c t i o n o f t h e a d a p t i n g c o n c e n t r a t i o n from t h e s t i m u l u s concen t r a t i o n ( I v s . S-S*)


144


I n F i g . 6a d a t a by Hahn (6) a r e shown. Hahn d e t e r m i n e d the e f f e c t o f t h r e e l e v e l s o f s a l t c o n c e n t r a t i o n , as a f u n c t i o n o f time, on the threshold of perception. I f we

now

d e f i n e two

e x t r a parameters:

S* = t h r e s h o l d l e v e l as a f u n c t i o n o f time A «* a d a p t a t i o n c o n s t a n t


the c o n c l u s i o n s drawn from t h e s e d a t a can be u s e d t o c o n s t r u c t a d i f f e r e n t i a l e q u a t i o n r e l a t i n g t h r e s h o l d l e v e l t o s t i m u l a t i o n . The c o n c l u s i o n s from the measurements by C a i n and Hahn a r e : - A f t e r p r o l o n g e d s t i m u l a t i o n the t h r e s h o l d r i s e s t o a l e v e l which l i e s above the l e v e l o f s t i m u l a t i o n , the d i f f e r e n c e b e i n g r o u g h l y e q u a l t o the o r i g i n a l unadapted t h r e s h o l d l e v e l ( f o r t -»· «, S* S + So*). - The a d a p t a t i o n p r o c e e d s f a s t e r when the d i f f e r e n c e between t h r e s h o l d and stimulus

i s bigger;

S-S* dt

- The time i t t a k e s longer

f o r the t h r e s h o l d t o r e a c h the s t i m u l u s

A

for a stronger stimulus; dt

P u t t i n g these dS* « A dt S

w h i c h can be

arrive

at:

S*)

S o

i n t e g r a t e d to give _JAdt

S* - So* + e i n case

S

c o n c l u s i o n s t o g e t h e r , we

( * + s -

level is

of constant

s

JAdt . A

/

e

s

d X

L

t

1

s t i m u l a t i o n t h i s reduces to

_ At S* - So* + S (1 - e

S )

F i g . 6b shows the b e s t f i t o f t h i s e q u a t i o n t o Hahn's d a t a . Assuming t h a t t h i s r e l a t i o n s h i p would a l s o be v a l i d f o r n o n - c o n s t a n t stimul a t i o n , we can t r y t o p r e d i c t what would happen i f we would use a s t i m u l u s l i k e the one we measured w i t h the MS/breath method, a f t e r smoothing, a t two l e v e l s o f c o n c e n t r a t i o n (See F i g . 7 ) .


11.


OVERBOSCH AND SOBTTING

NaCl conc./% 20, Recovery curves


Adaptation curves

j.o-°-°JOT

15

10 . —A- - •j.p-ooo-o—ο

u

•ί^ρο-οο-ο—ο·· ί»5

0±

Fig.

10

20

30

10 20 Time Is

30

6a P e r c e p t i o n o f t h r e s h o l d s v s . time under s t i m u l a t i o n o f 5, 10 and 15% sodium c h l o r i d e s o l u t i o n s [ a f t e r H. Hahn, Z. S i n n e p h y s i o l . 65 (1934) 105] NaCl conc./%

,o 15

Ο . · . Δ . after Hahn (1934)

10

10

best fitting lines a c c o r d i n g to 5*= 0.24* . -2.46t/5) 5 ( 1

e

ft kys£=o.24% 10

20

30

Adaptation time Is

Fig.

6b P e r c e p t i o n t h r e s h o l d s v s . time under s t i m u l a t i o n o f 5, 10 and 15% sodium c h l o r i d e s o l u t i o n s


146


The t h e o r y p r e d i c t s t h a t i n b o t h c a s e s t h e t h r e s h o l d l e v e l r i s e s l i n e a r l y w i t h s t i m u l a t i o n i n t h e f i r s t p a r t o f t h e c u r v e and keeps r i s i n g u n t i l the t h r e s h o l d l e v e l equals the l e v e l o f s t i m u l a t i o n . S i n c e we s t i l l use S t e v e n s ' law which has now t a k e n a time-dependent form: I - k ( S - S * ) , we may p r e d i c t t h a t t h e h i g h e r c o n c e n t r a t i o n w i l l be p e r c e i v e d n


- more i n t e n s e l y - a t t h e same time o f maximum - f o r a longer duration

intensity

Now t h a t we have measured t h e a c t u a l s t i m u l u s shape and have p r e d i c t e d i t s p e r c e p t u a l r e s u l t , we e v i d e n t l y have t o measure p e r c e i v e d i n t e n s i t y as a f u n c t i o n o f t i m e . Measuring

p e r c e i v e d i n t e n s i t y o v e r time (I/t)

Methods f o r s c o r i n g p e r c e i v e d i n t e n s i t y o v e r time a r e known i n t h e l i t e r a t u r e ( 7 ) . They make use o f a p e n r e c o r d e r , a d i a l p o t e n t i o m e t e r o r a "mouse" d e v i c e c o u p l e d t o a p e r s o n a l computer. The p a n e l l i s t s move t h e p e n o r d i a l up when p e r c e i v e d i n t e n s i t y i n c r e a s e s and down when i t drops o f f . The d a t a a r e p o o l e d b y c a l c u l a t i n g mean I n t e n s i t y v a l u e s . The p r o c e d u r e c o n t r a s t s w i t h t h e above d e s c r i b e d MS/breath d a t a p o o l i n g method. I n b o t h c a s e s we s t a r t w i t h i n d i v i d u a l I / t c u r v e s . I n t h e MS/breath c a s e t h e s e a r e p a r a m e t r i z e d , so t h a t a f t e r p o o l i n g the p a r a m e t e r v a l u e s o f t h e p a n e l c u r v e a r e t h e mean v a l u e s o f t h e i n d i v i d u a l parameters. The l i t e r a t u r e method f o r p e r c e i v e d i n t e n s i t y o v e r time does n o t produce such p a n e l c u r v e s . Du B o i s and Lee (8) d e s c r i b e a method w h i c h does produce p a n e l a v e r a g e s f o r t h e t h r e e main p a r a m e t e r s : maximum p e r c e i v e d i n t e n s i t y (I max) as s c o r e d by t h e i n d i v i d u a l p a n e l l i s t s , t h e time a t which t h i s o c c u r s ( t max) and t h e e x t i n c t i o n time ( t e n d ) . S i n c e t h e s e parameters do n o t produce a complete c u r v e , we have d e v e l o p e d a method w h i c h produces complete c u r v e s w h i c h c a n be c o n s i d e r e d t o be r e a l p a n e l a v e r a g e s . T h i s method i s c a r r i e d o u t as f o l l o w s : A l l i n d i v i d u a l curves a r e n o r m a l i s e d i n the I n t e n s i t y d i r e c t i o n by c a l c u l a t i n g t h e g e o m e t r i c mean o f a l l i n d i v i d u a l Imax v a l u e s and m u l t i p l y i n g each i n d i v i d u a l c u r v e by IlHâx (geom) I^max S u b s e q u e n t l y a l l h a l f c u r v e s b e f o r e and a f t e r t^max a r e a v e r a g e d i n the time d i r e c t i o n . A g a i n t h e g e o m e t r i c mean i s t a k e n because a check on t h e d i s t r i b u t i o n o f t^max and t ^ - e n d v a l u e s (ATCS i n F i g . 8) showed a l o g normal d i s t r i b u t i o n . The r e s u l t i n g c u r v e c a n be c o n s i d e r e d t o be a r e a l p a n e l a v e r a g e .



11.


OVERBOSCHANDSOETING

Fig.

7

Dependence o f t h r e s h o l d o f p e r c e p t i o n S* (···) on an a r b i t r a r y time c o u r s e o f s t i m u l a t i o n ( ) a t two l e v e l s

Rated perceived intensity (I) tmaxl -

V

Imaxl tmax2

ATCS,

Fig.

ATCS

time

2

8a Schematic r e p r e s e n t a t i o n o f t h e e x i s t i n g p r o c e d u r e . The f i n a l curve i s obtained a f t e r averaging the i n d i v i d u a l c u r v e s i n the i n t e n s i t y d i r e c t i o n o n l y Rated perceived intensity (I)

Rated perceived intensity (I)

tmax! l

*max1 max2

^-Imaxl tmax2

" "^^r^^i~Imax

I max 2 time NORMALISATION IN THE I-DIRECTION

time ATC52

ATCSi

Rated perceived intensity (I)

Rated perceived intensity (I) tmaxl tmax2:^x1 *max2

Imax 1

l

max · max AND

\

A

%

A T C S

\

1ÀTC5

,time ATCS

.time A T C S

2

CALCULATION OF THE AVERAGES IN ΓΗΕ t-DIRECTION BEFORE AND AFTER I j

m a x

Fig.

FINAL CURVE

8b Schematic r e p r e s e n t a t i o n o f t h e new p r o c e d u r e . The f i n a l c u r v e i s o b t a i n e d a f t e r a v e r a g i n g the i n d i v i d u a l c u r v e s i n b o t h t h e iptens Lty_ a n ^ t h e t^me^ d i r e c t i o n

American r

emtcal society Library

1155 15th St.,Chemistry M.W. Teranishi et al.; Flavor ACS Symposium Series; Washington, American Chemical Society: DC, 1989. D.C. 2003Washington, 6



148


11.

OVERBOSCH AND SOETING

149

Temporal Aspects of Flavoring

F i g s . 8a/b show a s l i g h t l y s i m p l i f i e d v e r s i o n o f b o t h t y p e s o f d a t a t r e a t m e n t mentioned. Our approach may be i l l u s t r a t e d t h r o u g h t h e c o m b i n a t i o n o f two e x p e r i m e n t s . The f i r s t i n v o l v e s I / t measurements o f two c o n c e n t r a t i o n s o f p e n t a n o n i n i n v e g e t a b l e o i l . The p r e d i c t e d r e s u l t s a r e o b t a i n e d : a h i g h e r maximum and a t t h e same time a l o n g e r d u r a t i o n f o r t h e h i g h e r c o n c e n t r a t i o n (see F i g . 9 ) .


When t h e s e r e s u l t s a r e compared w i t h those o f t h e measurement o f t h e r e a l s t i m u l u s ( F i g . 3a) t h e a d a p t a t i o n e f f e c t i s e v i d e n t ; p e r c e p t i o n a l r e a d y ends when t h e a c t u a l s t i m u l u s h a s dropped o n l y t o a r o u n d h a l f o f i t s highest value. Summing up, we have d e f i n e d o u r system as f o l l o w s : flavour/matrix response ( t )

> stimulus

( t ) (psychophysical

function (t)

>

We have measured b o t h time-dependent v a r i a b l e s : the a c t u a l s t i m u l u s and t h e r e s p o n s e , and i t h a s been shown t h a t a s u i t a b l e time-dependent v e r s i o n o f S t e v e n s ' law c o u l d be c o n s t r u c t e d from m a t e r i a l a v a i l a b l e i n t h e l i t e r a t u r e ( 9 , 1 0 ) . F o r s t i m u l i c o n t a i n i n g more t h a n one component i t was shown t h a t d i f f e r e n t p h y s i c a l r e l e a s e r a t e s , s t a r t i n g a t t h e same time, c o u l d very w e l l give r i s e to p e r c e i v e d d i f f e r e n c e s i n r e l e a s e times.

References 1. R.M. Pangborne, Flavour 81 3-32, P. Schreier ed., 1981. 2. F.M. Benoit, W.R. Davidson, A.M. Lovett, S. Nacson, A. Ngo, Breat analysis by atmospheric pressure ionization mass spectrometry, Anal. Chem. 55, 805-807 (1983) and references therein. 3. H.K. Wilson and T.W. Ottley, The use of a transportable mass spectrometer for the direct measurements of industrial solvents in Breath, Biomedical Mass Spectrometry, 8 (12) (1981). 4. M. Stupfel and M. Mordelet-Dambrine, Penetration of pollutants in the airways. Bull. Physiopath. resp. 10, 481-509 (1974). A.H. Beckett and R.D. Hossie, Buccal absorption of drugs, Handbook of experimental Pharmacology, 28, 24-26 (1971). 5. S.S. Stevens, The surprising simplicity of sensory metrics. Am. Psychol., 17, 29-39, (1962). 6. W.S. Cain, Odor intensity after adaptation and cross adaptation, Percept. Psychophys. 7, 271-275 (1970). 7. H. Hahn, Die Adaptation des Geschmacksinnes. Z. Sinnesphysiol. 65, 105-145 (1934).


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8. P. Overbosch, J.C. van den Enden and B.M. Keur, An improved method for measuring perceived intensity/time relationships in human taste and smell, Chemical Senses, 11, (3) pp. 331-338 (1986). 9. G.E. DuBois and J.F. Lee, A simple technique for the evaluation of temporal taste properties, Chem. Senses, 7, 237-247 (1983).


10. P. Overbosch, A theoretical model for perceived intensity in human taste and smell as a function of time, Chemical Senses, 11, (3) pp. 315-329 (1986). 11. W.J. Soeting and J. Heidema: A mass spectrometric method for measuring flavour concentration/time profiles in human breath. To be submitted for publication. RECEIVED September 23, 1988


Flavor Chemistry - ACS Publications - American Chemical Society

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