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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:
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- 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).
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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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
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
11.
OVERBOSCHANDSOETING
Temporal Aspects ofFlavoring
141
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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.
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
FLAVOR CHEMISTRY: TRENDS AND
DEVELOPMENTS
Ion current at m/z 86
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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
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
from
11.
OVERBOSCHANDSOETING
Temporal Aspects ofFlavoring
143
Rated perceived intensity • non-adapted
100
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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*)
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
144
FLAVOR CHEMISTRY: TRENDS AND DEVELOPMENTS
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
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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 ) .
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
11.
Temporal Aspects ofFlavoring
OVERBOSCH AND SOBTTING
NaCl conc./% 20, Recovery curves
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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
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
146
FLAVOR CHEMISTRY: TRENDS AND DEVELOPMENTS
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
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- 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 .
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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11.
Temporal Aspects ofFlavoring
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.
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1155 15th St.,Chemistry M.W. Teranishi et al.; Flavor ACS Symposium Series; Washington, American Chemical Society: DC, 1989. D.C. 2003Washington, 6
FLAVOR CHEMISTRY: TRENDS AND DEVELOPMENTS
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Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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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 ) .
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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).
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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
Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
