Electrophysiological Evaluation of Sweeteners - American Chemical

Chapter 22

Electrophysiological Evaluation of Sweeteners Goran Hellekant , D. Eric Walters , J. Chris Culberson , Grant E . DuBois , Claude Nofre , and Jean-Marie Tinti 1

2

2

3

2

3

Department of Veterinary Science, University of Wisconsin, Madison, WI 53706 The NutraSweet Company, Mount Prospect, I L 60056 Faculté de Médecine Alexis Carrel, Université Claude Bernard, Rue Guillaume Paradin, 69008, Lyon, France 1

Downloaded by IOWA STATE UNIV on April 19, 2017 | http://pubs.acs.org Publication Date: December 31, 1991 | doi: 10.1021/bk-1991-0450.ch022

2

A method is described for the electrophysiological evaluation of the temporal profiles of sweeteners. Temporal profiles are difficult to quantitate in human taste panels because of the need for extensive panelist training and because time resolution is not adequate, particularly in the early portion of the profile. These problems can be circumvented by directly measuring nerve activity in the sensory nerves, particularly in the chorda tympani nerve. Results obtained from chorda tympani recordings in rhesus monkeys are in agreement with published human taste panel results. In contrast to salty taste, w h i c h i s elicited cleanly only b y N a C l a n d L i C l , there are n u m e r o u s s t r u c t u r a l classes of c o m p o u n d s w h i c h taste sweet. These i n c l u d e dipeptides (aspartame, alitame), a m i n o acids (D-tryptophan), k y n u r e n i n e s , aryl ureas (suosan), aryl g u a n i d i n e s , carbohydrates, halogenated carbohydrates (sucralose), N-sulfonylamides (saccharin, acesulfame), a n d proteins (thaumatin, monellin, pentadin). There are few areas of new product research w h i c h r e c e i v e m o r e i n d u s t r i a l effort t h a n h i g h - p o t e n c y sweeteners (i). A s a result, the n u m b e r of n e w sweeteners h a s grown s u b s t a n t i a l l y over the l a s t decade, a n d i t i s safe t o s a y t h a t a n even larger n u m b e r of sweeteners is currently u n d e r development. Three characteristics need to be evaluated p s y c h o p h y s i c a l ^ before a n e w c o m p o u n d c a n find u s e a s a sweetener: t h e flavor profile (taste q u a l i t y ) , t h e p o t e n c y profile (concentration/response function), a n d t h e t e m p o r a l profile (time/intensity function). T h e s t a n d a r d w a y of quantitating these characteristics i s to carry o u t p s y c h o p h y s i c a l evaluation w i t h a h u m a n taste panel. However, safety tests m u s t b e c a r r i e d o u t before h u m a n p a n e l s m a y evaluate a n e w c o m p o u n d , a n dextensive t r a i n i n g i s required i n order to get r e p r o d u c i b l e r e s u l t s (2). A m o n g t h e p r o p e r t i e s l i s t e d a b o v e , t h e 0097-6156/91/0450-0290$06.00A) © 1991 American Chemical Society

Walters et al.; Sweeteners ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

22.

HELLEKANT ET A L

Electrophysiological Evaluation of Sweeteners

291

t e m p o r a l profile i s p a r t i c u l a r l y difficult to a s s e s s . F i r s t w e define t h e t e m p o r a l profile, t h e n we review a p p r o a c h e s to t e m p o r a l p r o f i l e a n a l y s i s i n h u m a n s u b j e c t s , a n d finally w e d e s c r i b e a n electrophysiological a p p r o a c h i n w h i c h temporal characteristics are p r e c i s e l y q u a n t i t a t e d b y m e a s u r e m e n t of the c h o r d a t y m p a n i nerve activity i n anesthetized monkeys.


T h e T e m p o r a l Profile T h e sweetness of a sweetener c h a n g e s d u r i n g the t i m e it is o n the tongue, sometimes dramatically. The w a y this h a p p e n s c a n be very different for different s w e e t e n e r s . Sucrose a n d t h a u m a t i n provide a n i l l u s t r a t i v e contrast. A 1 0 % s o l u t i o n of s u c r o s e is as sweet as a 0 . 0 2 5 % s o l u t i o n of t h a u m a t i n , b u t t h i s is n o t evident d u r i n g the first s e c o n d s after the t h a u m a t i n is tasted. Sucrose reaches its m a x i m u m s w e e t n e s s w i t h i n a few s e c o n d s . T h a u m a t i n h a s n o t a s t e at a l l for t h e first s e c o n d s , t h e n its s w e e t n e s s i n t e n s i t y g r a d u a l l y b u i l d s to a m a x i m u m over a p e r i o d of a b o u t 10 seconds. D i s a p p e a r a n c e of the sweetness i s also v e r y different; the sweetness of s u c r o s e c l e a r s r a p i d l y , w h i l e the sweetness of t h a u m a t i n p e r s i s t s f o r s e v e r a l m i n u t e s a f t e r s w a l l o w i n g (3). Other sweeteners have t e m p o r a l p r o f i l e s i n t e r m e d i a t e b e t w e e n t h e s e e x t r e m e s (4). The t e m p o r a l profile of a sweetener is a n i m p o r t a n t parameter, since it h a s a s u b s t a n t i a l i m p a c t o n acceptability i n food s y s t e m s . P s y c h o p h y s i c a l E v a l u a t i o n of Sweeteners S e v e r a l m e t h o d s h a v e b e e n u s e d to r e c o r d t e m p o r a l profiles of sweeteners. E a r l y t i m e - i n t e n s i t y w o r k [5-8) was done w i t h panelists r a t i n g sweetness intensity at time intervals determined w i t h a clock or stopwatch. S t r i p c h a r t r e c o r d e r s ( 9 - J 2) a n d potentiometers (J3) h a v e a l s o b e e n u s e d to p e r m i t c o n t i n u o u s r e c o r d i n g of t i m e - i n t e n s i t y d a t a . However, there are several l i m i t a t i o n s to t e m p o r a l profile a n a l y s i s w i t h h u m a n p a n e l s . Even w i t h extensive t r a i n i n g , it i s d i f f i c u l t to get reproducible q u a n t i t a t i v e d a t a . V a r i a b l e s s u c h as rate of m i x i n g w i t h s a l i v a a n d t h e s a l i v a flow r a t e a r e h a r d to c o n t r o l . I n a d d i t i o n , t i m e r e s o l u t i o n i s l i m i t e d to s e v e r a l s e c o n d s , w h i c h m a y n o t b e a d e q u a t e for e a r l y portions of the time-intensity profile. There exists the c o m p l i c a t i o n of subjective i n t e r p r e t a t i o n b y the p a n e l i s t . In a d d i t i o n , p a n e l i s t fatigue l i m i t s the rate at w h i c h d a t a c a n be a c q u i r e d . Therefore, we d e s c r i b e a n a l t e r n a t i v e a p p r o a c h to d i r e c t m e a s u r e m e n t of t e m p o r a l profiles of sweeteners: electrophysiological recording from the taste nerves. T h i s m e t h o d is based o n several physiological a n d a n a t o m i c a l conditions. T h e first is t h a t a l l s e n s a t i o n s ( i n c l u d i n g taste) are c a r r i e d b y nerve i m p u l s e s f r o m p e r i p h e r a l s e n s e o r g a n s to t h e b r a i n . T h e s e n s e o r g a n s for t a s t e are called taste b u d s . Taste information is carried from the taste b u d s to the b r a i n p r i m a r i l y i n the c h o r d a t y m p a n i a n d glosso-


292

SWEETENERS:

DISCOVERY, M O L E C U L A R

DESIGN, A N D

CHEMORECEPTION

pharyngeal nerves. The c h o r d a t y m p a n i nerve carries signals from the anterior p a r t of the tongue. T h i s nerve i s r e l a t i v e l y e a s y to l o c a t e s u r g i c a l l y a n d to u t i l i z e for e l e c t r o p h y s i o l o g i c a l r e c o r d i n g from anesthetized animals.


E l e c t r o p h y s i o l o g i c a l R e c o r d i n g s of T a s t e F i g u r e 1 s h o w s t y p i c a l r e c o r d i n g s of c h o r d a t y m p a n i nerve activity f r o m a r h e s u s m o n k e y o n s t i m u l a t i o n w i t h a series of sweeteners. T h e s e are n o t direct recordings of the i n d i v i d u a l nerve p u l s e s , as i n d i v i d u a l n e r v e p u l s e s are d i f f i c u l t to q u a n t i f y . Instead, the i m p u l s e activity is electrically s u m m a t e d a n d the nerve activity is d i s p l a y e d as a v o l t a g e i n s t e a d of a s a f r e q u e n c y . I n F i g u r e 1, r e s p o n s e s to x y l i t o l , s u c r o s e , a s p a r t a m e , a c e s u l f a m e - K , N a C l , a n d p r o t e i n sweeteners are recorded. In the first two series, native m o n e l l i n a n d t h a u m a t i n (both v e r y sweet) w e r e u s e d . I n the t h i r d series, the p r o t e i n sweetener is t h a u m a t i n i n w h i c h s i x of the l y s i n e r e s i d u e s a r e m e t h y l a t e d (14); t h i s c o m p o u n d i s s t i l l s w e e t , a n d it still gives a nerve response. In the f o u r t h series ( t h a u m a t i n w i t h i o d i n a t e d t y r o s i n e s , ref. 15) a n d t h e f i f t h s e r i e s ( t h a u m a t i n w i t h a c e t y l a t e d l y s i n e s , ref. 14), l o s s o f s w e e t t a s t e c o r r e l a t e s w i t h loss of nerve r e s p o n s e . S e v e r a l features of the nerve r e c o r d i n g s s h o u l d be n o t e d . F i r s t , the r e s p o n s e s are v e r y r e p r o d u c i b l e for a n y g i v e n s t i m u l u s . S e c o n d , tasteless c o m p o u n d s give n o nerve r e s p o n s e . T h i s r e s u l t i s supported b y behavioral experiments i n m o n k e y s a n d taste tests i n h u m a n s . T h i r d , cross-adaptation c a n be seen between the sweet proteins a n d the other sweeteners. T h e m a g n i t u d e of the s u c r o s e response following the protein sweetener is substantially reduced b e c a u s e of the prolonged s t i m u l a t i o n b y the p r o t e i n . F i n a l l y , the t e m p o r a l profiles of the p r o t e i n s w e e t e n e r s are considerably different f r o m t h o s e of the o t h e r sweeteners. The temporal profiles w i l l be further e x a m i n e d i n the following section. T h e T e m p o r a l Profile of t h e E l e c t r o p h y s i o l o g i c a l T a s t e R e s p o n s e T h e t e m p o r a l profile of a sweetener c a n r e a d i l y be observed i n these electrophysiological recordings, particularly if the recording is displayed w i t h a n expanded time scale. Several quantitative parameters c a n be obtained from s u c h recordings, as illustrated i n F i g u r e 2 . T h e maximum amplitude is the signal intensity attained, c o r r e s p o n d i n g to t h e m a x i m u m i n t e n s i t y o f s w e e t n e s s . The delay time is t h e t i m e f r o m i n i t i a l s t i m u l a t i o n to s i g n a l 1 0 % a b o v e b a s e l i n e , c o r r e s p o n d i n g to l a t e n c y b e t w e e n a p p l i c a t i o n a n d f i r s t t a s t e s e n s a t i o n . Rise time is the time between initial s t i m u l a t i o n a n d m a x i m a l r e s p o n s e a m p l i t u d e , i.e., t h e t i m e r e q u i r e d t o r e a c h maximal intensity. Slope [maximum amplitude/rise time) i s t h e c h a n g e i n m a g n i t u d e w i t h r e s p e c t to t i m e ; i t i s a n i n d i c a t o r of t h e r a t e o f c h a n g e o f i n t e n s i t y . Resume time i s t h e t i m e w h i c h e l a p s e s


HELLEKANT ET A L



22.

293

1 min

met

tyros

. ,

a

c

e

.

«·Ρ ,,

e

u

c

acet

- L L U suc

ace

NaCI

asp

Figure 1. A series of s u m m a t e d c h o r d a t y m p a n i nerve recordings d u r i n g taste s t i m u l a t i o n i n a r h e s u s m o n k e y . Except for c h a n g e s i n t h e p r o t e i n sweetener, t h e s a m e s e q u e n c e o f stimuli w a s used i n a l l 5 recordings: xylitol, acesulfame-K, aspartame, s u c r o s e , protein sweetener (0.0296), sucrose, acesulfame-K, NaCI, aspartame. T h e protein sweeteners used w e r e : (a) m o n e l l i n ; (b) t h a u m a t i n ; (c) t h a u m a t i n i n w h i c h l y s i n e r e s i d u e s a r e m e t h y l a t e d [ s t i l l s w e e t ] ; (d) t h a u m a t i n i n w h i c h t y r o s i n e s a r e i o d i n a t e d [ t a s t e l e s s ] ; (e) t h a u m a t i n i n w h i c h l y s i n e s are acetylated [tasteless]. Walters et al.; Sweeteners ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

294

SWEETENERS:


DESIGN, A N D

CHEMORECEPTION

f r o m t h e c o n c l u s i o n of s t i m u l a t i o n u n t i l s i g n a l r e t u r n s to b a s e l i n e . Area is the integrated area u n d e r the recording.


T h e C h o i c e o f a n A n i m a l M o d e l - P h y l o g e n e t i c Differences A very important consideration w h e n choosing a n a n i m a l model is t h a t the s e n s e of taste i n m a m m a l i a n s p e c i e s differs. Many c o m p o u n d s w h i c h are sweet to the h u m a n t o n g u e are n o t sweet to c o m m o n e x p e r i m e n t a l a n i m a l s s u c h a s r a t s o r d o g s (16). T h e r e i s a s t r o n g p h y l o g e n e t i c r e l a t i o n s h i p i n t a s t e (16-21), so that the more c l o s e l y r e l a t e d to h u m a n s t h e a n i m a l s p e c i e s w h i c h i s u s e d for t h e electrophysiological assay, the more s i m i l a r is its sense of sweet t a s t e to t h a t of h u m a n s . T a b l e I s u m m a r i z e s s o m e of t h e r e s u l t s found i n primates. F r o m Table I it c a n be c o n c l u d e d that the s q u i r r e l m o n k e y c a n n o t be u s e d for the e v a l u a t i o n of the s w e e t n e s s of a n a l o g s of aspartame or t h a u m a t i n , since these c o m p o u n d s do not taste sweet to N e w W o r l d m o n k e y s . O n the other h a n d , results i n Table I i n d i c a t e t h a t a n O l d W o r l d m o n k e y (e.g., r h e s u s ) i s a r e a s o n a b l e c h o i c e a s a n a n i m a l m o d e l for h u m a n taste. O n l y o n e difference (effect o f g y m n e m i c a c i d ) h a s b e e n f o u n d b e t w e e n t h e s e n s e o f sweet taste i n O l d W o r l d m o n k e y s a n d h u m a n s (22,23). C o m p a r i s o n B e t w e e n T e m p o r a l Profiles i n H u m a n s a n d M o n k e y s In order to evaluate t h i s m e t h o d of t e m p o r a l s c r e e n i n g , w e c h o s e sweeteners for w h i c h t e m p o r a l profiles h a v e b e e n s t u d i e d i n h u m a n s . A c e s u l f a m e - K (rapid onset) a n d m o n e l l i n (very s l o w o n s e t , lingering sweetness) represent the extremes i n t e m p o r a l profile. Sucrose, aspartame, a n d a n example of the h i g h l y potent g u a n i d i n e s ( c o m p o u n d 1) d i s c o v e r e d b y N o f r e a n d T i n t i (24) w e r e i n c l u d e d i n o r d e r to a s s e s s t h e u t i l i t y of t h i s m e t h o d i n r a n k i n g s w e e t e n e r s b y t e m p o r a l profile. In o r d e r to cover a range of c o n c e n t r a t i o n s , we selected for e a c h s w e e t e n e r a concentration equivalent in s w e e t n e s s to 1 0 % s u c r o s e (in h u m a n s ) ; w e t h e n u s e d s a m p l e s w i t h twice t h i s c o n c e n t r a t i o n a n d one-half of t h i s c o n c e n t r a t i o n . The data from the electrophysiological m e a s u r e m e n t s is s u m m a r i z e d i n T a b l e II a n d F i g u r e 3 . T h e d a t a f o r e a c h s w e e t e n e r c o n c e n t r a t i o n w e r e o b t a i n e d f r o m at least three s t i m u l a t i o n s of the m o n k e y ' s t o n g u e , a n d t h e n e u r a l r e c o r d i n g s w e r e d i g i t a l l y s u m m e d to enhance the signal-to-noise ratio. Temporal parameters were m e a s u r e d from the s u m m e d recordings. The data s h o w n i n Table II i s t a k e n f r o m a r e p r e s e n t a t i v e m o n k e y ; d a t a f r o m o t h e r m o n k e y s are comparable. A c e s u l f a m e - K s h o w e d the m o s t r a p i d onset followed, i n t u r n , b y s u c r o s e , c o m p o u n d 1, a s p a r t a m e , a n d m o n e l l i n . F i g u r e 3 s h o w s t h a t the taste of m o n e l l i n lingers after s t i m u l a t i o n is s t o p p e d . In t h i s respect, m o n e l l i n is quite different f r o m the other sweeteners, w h i c h r e t u r n to b a s e l i n e r a p i d l y after s t i m u l a t i o n .


22. H E L L E K A N T E T AL.


295


Rise Time

Baseline Activity

Delay Time Figure 2 . A representative s u m m a t e d recording from the c h o r d a t y m p a n i nerve of a r h e s u s m o n k e y d u r i n g a 1 0 sec stimulation w i t h a sweetener. T h e quantitative parameters maximum amplitude, delay time, rise time ( d t ) , resume time, a n d integrated area are indicated.

T a b l e I. primates

Effects

of some

Gymnemic a c i d effect on sweeteners H u m a n s , apes abolishes (Superfamilia sweetness Hominoidea) Old World n o effect monkeys (Superfamilia Cercopithecoidea) New World n o effect monkeys (Infraordo Platyrrhina) Half-monkeys n o effect (Ordo Prosimiae)

sweeteners

Thaumatin and aspartame taste sweet

taste

no

sweet

sweet taste

no

effect

a n dtaste

modifiers i n

Miraculin effect o n acid taste

Gymnemic a c i d effect on miraculin abolishes sweetness

induces sweetness

abolishes sweetness

induces sweetness

no

effect

no

effect

induces sweetness

no


effect

296

SWEETENERS:

DISCOVERY, M O L E C U L A R DESIGN, A N D

CHEMORECEPTION

T a b l e II. T e m p o r a l p a r a m e t e r s m e a s u r e d f o r a c e s u l f a m e - K , a s p a r t a m e , m o n e l l i n , g u a n i d i n e s w e e t e n e r 1, a n d s u c r o s e


Sweetener Acesulfame 0.35 g/L 0.70 g/L 1.40 g / L Aspartame 0.35 g/L 0.70 g/L 1.40 g / L Monellin 13 m g / m L 26 mg/mL 52 mg/mL Guanidine 1 7.1 m g / m L 14.2 m g / m L 28.4 mg/mL Sucrose 0.15 M 0.30 M 0.60 M a

b

Max Amp

Area

3

a

Delay Time

Slope

3

Rise Tlme

b

b

Resume Time b

122 172 206

1192 1608 1580

250 190 270

21.8 41.0 54.2

560 420 380

1520 1920 4980

42 51 89

492 717 809

330 340 280

8.2 9.4 22.3

510 540 400

1580 1440 1440

24 33 37

446 1085 837

410 360 470

0.5 0.6 3.5

5270 5300 1070

12500 19520 19520

29 69 65

447 773 816

350 320 340

3.8 14.7 11.8

770 470 550

920 1480 1740

89 121 113

1481 2237 1837

300 300 300

16.8 25.2 27.6

530 480 410

2060 5440 8100

U n i t s of m e a s u r e are a r b i t r a r y . Milliseconds.

1ice-K

1.40

g/L

Figure 3. S u m m a t e d chorda tympani nerve recordings for a c e s u l f a m e - K ( 1 . 4 g / L ) , s u c r o s e ( 0 . 6 0 M ) , a s p a r t a m e (1.4 g / L ) , c o m p o u n d 1 ( 2 8 . 4 m g / L ) , a n d m o n e l l i n (52 m g / L ) . T h e b a r a t the b o t t o m of e a c h r e c o r d i n g i n d i c a t e s the 10 sec t i m e d u r i n g w h i c h s w e e t e n e r s o l u t i o n flowed o v e r t h e t o n g u e . Spikes in n e u r a l activity o c c u r i n g at the e n d of the s t i m u l a t i o n w i t h sucrose a n d acesulfame i n the figures above do not o c c u r i n a l l r e c o r d i n g s ; t h e y a p p e a r to be o c c a s i o n a l a r t i f a c t s of t h e magnetic valve switching.


HELLEKANT ET A L



Sucrose

0.60

As p a r t a m e 1.40

M

g/L

{ Guanidine

1 28.4

mg/L

Figure 3. Continued.


298

SWEETENERS:


DESIGN, A N D

CHEMORECEPTION


1 I n s t u d i e s w i t h h u m a n p a n e l i s t s , D u B o i s a n d L e e (J J) c h a r a c t e r i z e d t h e t e m p o r a l p r o f i l e o f s w e e t e n e r s i n t e r m s o f appearance time (time r e q u i r e d to a t t a i n m a x i m u m s w e e t n e s s i n t e n s i t y ) a n d extinction time (time r e q u i r e d for s w e e t n e s s i n t e n s i t y to r e t u r n to a d e f i n e d l o w l e v e l ) . T h e y f o u n d s u c r o s e (10%) a n d a s p a r t a m e ( 7 5 0 p p m ) t o h a v e s i m i l a r a p p e a r a n c e t i m e s (4 a n d 5 s e c , r e s p e c t i v e l y ) , w h i l e a s p a r t a m e s h o w e d a l o n g e r e x t i n c t i o n t i m e (13 a n d 19 sec, respectively). O t t a n d c o w o r k e r s (12) h a v e m e a s u r e d t i m e - i n t e n s i t y p r o f i l e s o f sucrose, aspartame, alitame, a n d acesulfame-K w i t h a h u m a n panel. T h e y d e r i v e d a n u m b e r of q u a n t i t a t i v e p a r a m e t e r s f r o m t h e i r recordings. T h e y f o u n d a m o r e r a p i d r e s p o n s e to a c e s u l f a m e - K t h a n to s u c r o s e o r a s p a r t a m e ( T M A X , t i m e to m a x i m u m i n t e n s i t y , = 7 . 9 , 9 . 7 , 9 . 6 s e c , r e s p e c t i v e l y ; RATEMAX, m a x i m u m intensity divided b y T M A X , = 8.4, 7.1, 7.8, respectively). They also found t h a t the sweetness of a s p a r t a m e p e r s i s t s longer t h a n t h a t of s u c r o s e o r a c e s u l f a m e - K (RT, recording time, = 53.0, 3 6 . 3 , 3 4 . 7 sec, respectively). Q u a n t i t a t i v e t e m p o r a l profiles h a v e n o t b e e n r e p o r t e d for m o n e l l i n , b u t i t s sweetness i s r e p o r t e d to p e r s i s t for a n u n u s u a l p e r i o d of t i m e (25). Discussion Overall, results w i t h h u m a n panelists correlate well w i t h o u r e l e c t r o p h y s i o l o g i c a l f i n d i n g s . It w a s o f i n t e r e s t t o d e t e r m i n e i f a n y of the m e a s u r e d t e m p o r a l p a r a m e t e r s m i g h t be i n d e p e n d e n t of concentration, t h u s allowing a j u d g m e n t of a c o m p o u n d ' s t e m p o r a l a c c e p t a b i l i t y ( s i m i l a r i t y to s u c r o s e a n d aspartame) f r o m d a t a o n a single c o n c e n t r a t i o n of m a t e r i a l . T h e effect of sweetener c o n c e n t r a t i o n o n t e m p o r a l p r o f i l e i s i l l u s t r a t e d i n T a b l e II. An i n c r e a s e i n sweetener c o n c e n t r a t i o n l e a d s to a n i n c r e a s e i n the m a x i m u m point reached, slope, a n d the r e s u m e time. In other words, a more concentrated solution results i n a more intense response w h i c h is realized more q u i c k l y a n d w h i c h lasts longer. O u r electrophysiological findings are i n good agreement w i t h the h u m a n t a s t e p a n e l r e s u l t s o f O t t et al (12) w i t h r e s p e c t t o t h e r a p i d o n s e t (short r i s e t i m e , large slope) of a c e s u l f a m e r e l a t i v e to s u c r o s e and aspartame.



22. H E L L E K A N T ET XL

Electrophysiologiccd Evaluation of Sweeteners

299

A t this point i n o u r development of this methodology, the best method for the judgment of temporal acceptability i s visual i n s p e c t i o n of t h e response profiles. R e s p o n s e s characterized b y a r a p i d o n s e t (large s l o p e , s m a l l delay) a n d a r a p i d r e t u r n t o b a s e l i n e (short r e s u m e time) after s t i m u l a t i o n a r e acceptable t o c o n s u m e r s , since they are characteristic of sucrose. Figure 3 shows response p r o f i l e s f o r t h e five s w e e t e n e r s u s e d f o r t h i s s t u d y . A l l of the sweeteners except m o n e l l i n show sucrose-like s u m m a t e d nerve responses. S i n c e t h e temporal profile s h o w s some c o n c e n t r a t i o n dependence, it i s probably necessary to make measurements at s e v e r a l c o n c e n t r a t i o n s (or a t a c o n c e n t r a t i o n w h i c h g i v e s a response i n t e n s i t y i n t h e desired range). W o r k i s c o n t i n u i n g i n t h e q u a n t i t a t i o n of more subtle t e m p o r a l differences. Conclusion The method outlined provides a technique for evaluating t h e temporal properties of sweeteners. This technique h a s the advantage that i t provides quantitative d a t a o n t h e entire temporal profile (both onset a n d lingering) w i t h o u t t h e c o m p l i c a t i o n of subjective interpretation w h i c h occurs i n h u m a n psychophysical experiments.

Literature Cited 1.

Higginbotham, J.D. In Developments in Sweeteners--2; Grenby, T.H.; Parker, K.J.; Lindley, M.G., Eds.; Applied Science: London, 1983; pp 119-155. 2. DuBois, G.E.; Walters, D.E.; Schiffman, S.S.; Warwick, Z.S.; Booth, B.J.; Pecore, S.D.; Gibes, K.; Carr, B.T.; Brands, L.M., this volume, Chapter 20. 3. Higginbotham, J.; Lindley, M.; Stephens, P. In The Quality of Foods and Beverages: Chemistry and Technology; Charalambous, G.; Inglett, G., Eds.; Academic: New York, 1981, Vol. 1; pp 91-111. 4. DuBois, G.E.; Crosby, G.A.; Stephenson, R.A. J. Med. Chem. 1981, 24, 408-428. 5. Neilson, A. In Flavor Research and Food Acceptance; Reinhold: New York, 1957; chapter 7. 6. Lawless, H.T.; Skinner, E.Z. Perception Psychophys. 1979, 25, 180-184. 7. Birch, G.G.; Latymer, Z.; Hollaway, M. Chem. Senses 1980, 5, 63-78. 8. Yamamoto, T.; Kato, T.; Matsuo, R.; Kawamura, Y.; Yoshida, M. Physiol. Behavior 1985, 35, 411-415. 9. Larson-Powers, N.; Pangborn, R.M. J. Food Sci. 1978, 43, 4146. 10. Swartz, M. J. Food Sci. 1980, 45, 577-581. 11. DuBois, G.E.; Lee, J.F. Chem. Senses 1983, 7, 237-247.



300

SWEETENERS: DISCOVERY, MOLECULAR DESIGN, AND CHEMORECEPTION

12. Ott, D.B.; Edwards, C.L.; Palmer, S.J. J. Food Sci., in press. 13. Overbosch, P.; van den Enden, J.C.; Keur, B.M. Chem. Senses 1986,11,331-338. 14. Van der Wel, H.; Bel, W.J. Chem. Senses Flavours 1976, 2, 221. 15. Van der Wel, H. In Olfaction and Taste VII; van der Starre, H., Ed.; IRL: London, 1980; pp 13-21. 16. Brouwer, J.N.; Hellekant, G.; Kasahara, Y.; van der Wel, H.; Zotterman, Y. ActaPhysiol.Scand. 1973, 89, 550-557. 17. Hellekant, G. Chem. Senses Flavours 1976, 2, 97-105. 18. Hellekant, G.; Glaser, D.; Brouwer, J.N.; van der Wel, H. Acta Physiol. Scand. 1976, 97, 241-250. 19. Glaser, D.; Hellekant, G.; Brouwer, J.N.; van der Wel, H. Folia Primatol. 1978, 29, 56-63. 20. Hellekant, G.; Glaser, D.; Brouwer, J.N.; van der Wel, H. In Olfaction and Taste VII; van der Starre, H., Ed.; IRL: London, 1980; pp 183-186. 21. Hellekant, G.; Glaser, D.; Brouwer, J.N.; van der Wel, H. Chem. Senses 1981, 6, 165-173. 22. Hellekant, G.; Hard af Segerstad, C.; Roberts, T.; van der Wel, H.; Brouwer, J.N.; Glaser, D.; Haynes, R.; Eichberg, J.W. Acta Physiol. Scand. 1985, 124, 399-408. 23. Hellekant, G.; van der Wel, H. In Neural Mechanisms of Taste; Cagan, R., Ed.; CRC Press: Boca Raton, FL, 1989; pp 85-96. 24. C. Nofre, C., J. -M. Tinti, and F. Chatzopoulos-Ouar, Eur. Pat. Appl. EP 241,395; Chem. Abstr. 109, 190047k (1988). 25. Morris, J.A.; Cagan, R.H. Biochim. Biophys. Acta 1972, 261, 114-122. RECEIVED September 5, 1990


Electrophysiological Evaluation of Sweeteners - American Chemical

Recommend Documents