Flavor Precursors - ACS Publications - American Chemical Society

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Chapter 15

Peptides as Flavor Precursors in Model Maillard Reactions 1

1

1

2

Chi-Tang Ho , Yu-Chiang Oh , Yuangang Zhang, and Chi-Kuen Shu

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1

Department of Food Science, Rutgers University—The State University of New Jersey, New Brunswick, NJ 08903 Bowman Gray Technical Center, R. J. Reynolds Tobacco Company, Winston-Salem, NC 27102 2

Equimolar aqueous solutions of glycine, diglycine, triglycine and tetraglycine were heated separately with Dglucose at 180°C at pH 4-5 in a Hoke sample cylinder for 2 hr. The Maillard reactions of glucose with glycine and triglycine produced a significantly greater amount of pyrazines than either diglycine or tetraglycine. The similarity of the results of glycine with triglycine and diglycine with tetraglycine in the pyrazine formation also suggests that tripeptides or tetrapeptides could be degraded through diketopiperazines. Alkyl 2(1H)-pyrazinones were identified as peptidespecific Maillard reaction products. The volatile products generated from the Maillard reaction of glucose with glutathione and its constituent amino acids in an aqueous medium were also compared.

The M a i l l a r d r e a c t i o n i s a well-known r e a c t i o n t h a t o c c u r s i n food during cooking. Because o f t h e c o m p l e x i t i e s o f t h e M a i l l a r d r e a c t i o n , many i n v e s t i g a t i o n s have been aimed a t u n d e r s t a n d i n g the mechanisms o f t h e r e a c t i o n . The pathways f o r t h e M a i l l a r d r e a c t i o n o r g i n a l l y proposed by Hodge ( 1) have g a i n e d wide a c c e p t a n c e . Recent works on t h e g e n e r a t i o n o f aroma compounds from the M a i l l a r d r e a c t i o n were m o s t l y concerned w i t h model systems u s i n g amino a c i d s . Some o f t h e amino a c i d s used i n model systems were p r o l i n e ( 2 - 5 ) , h y d r o x y p r o l i n e (6), s e r i n e and t h r e o n i n e ( 7 ) , c y s t e i n e (8-9), l e u c i n e (10) and g l y c i n e (11-12). A l t h o u g h a wide range o f p e p t i d e s has been r e p o r t e d i n c o n s i d e r a b l e q u a n t i t y i n many food systems such as aged sake (13), meat (14) and h y d r o l y z e d v e g e t a b l e p r o t e i n (15), t h e r o l e o f p e p t i d e s as p r e c u r s o r s i n t h e g e n e r a t i o n o f f l a v o r compounds has n o t been i n v e s t i g a t e d t o an a p p r e c i a b l e e x t e n t . Chuyen e t a l . (16) s t u d i e d the r e a c t i o n o f v a r i o u s d e p e p t i d e s w i t h g l y o x a l and r e p o r t e d t h e i d e n t i f i c a t i o n o f 2 - ( 3 - a l k y l - 2 ' - o x o p y r a z i n - 1 ) a l k y l a c i d s as major 1

1

0097-6156/92/0490-0193S06.00/0 © 1992 American Chemical Society

In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

194

FLAVOR

PRECURSORS

products. Most r e c e n t l y , R i z z i (17) r e p o r t e d t h a t model M a i l l a r d r e a c t i o n s o f d i p e p t i d e s and t r i p e p t i d e s w i t h f r u c t o s e g e n e r a t e d S t r e c k e r d e g r a d a t i o n p r o d u c t s , such as S t r e c k e r aldehydes and a l k y l p y r a z i n e s , from amino a c i d s w i t h b l o c k e d amino and c a r b o x y l f u n c tionalities .

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V o l a t i l e Compounds Formed from M a i l l a r d Reaction of Glucose with Gly, Gly-Gly, Gly-Gly-Gly and Gly-Gly-Gly-Gly E q u i m o l a r aqueous s o l u t i o n s o f g l y c i n e , d i g l y c i n e , t r i g l y c i n e and t e t r a g l y c i n e were heated s e p a r a t e l y w i t h D - g l u c o s e a t 180°C a t pH 4-5 i n a P a r r bomb f o r 2 h r . Each r e a c t i o n m i x t u r e was a d j u s t e d t o pH > 12 w i t h NaOH, then e x t r a c t e d w i t h methylene c h l o r i d e , c o n t a i n i n g an i n t e r n a l s t a n d a r d , i n a s e p a r a t o r y f u n n e l by m u l t i p l e ext r a c t i o n method (5X50 m l ) . The methylene c h l o r i d e e x t r a c t s were d r i e d o v e r anhydrous sodium s u l f a t e and c o n c e n t r a t e d by b l o w i n g w i t h n i t r o g e n gas t o a f i n a l volume o f 0.2 mL. The v o l a t i l e compounds were then a n a l y z e d by gas chromatography and gas chromatography-mass s p e c t r o m e t r y as d e s c r i b e d p r e v i o u s l y (18). T a b l e I l i s t s t h e v o l a t i l e compounds g e n e r a t e d i n these systems. From t h e q u a n t i t a t i v e d a t a , i t was o b s e r v e d t h a t g l y c i n e o r t r i g l y c i n e g e n e r a t e d a l a r g e r amount o f a l k y l p y r a z i n e s than e i t h e r d i g l y cine or t e t r a g l y c i n e . I t i s a l s o i n t e r e s t i n g t o note t h a t f u r f u r a l and 5-(hydroxym e t h y l ) f u r f u r a l were produced i n a g r e a t e r q u a n t i t y i n the r e a c t i o n o f d i g l y c i n e and t e t r a g l y c i n e w i t h g l u c o s e , as compared t o the g l y cine or t r i g l y c i n e . 2 - A c e t y l p y r r o l e and 2 - f o r m y l - 5 - m e t h y l - p y r r o l e were i d e n t i f i e d as t r a c e components i n t h e s e model r e a c t i o n s . The f o r m a t i o n o f d i k e t o p i p e r a z i n e s from the t h e r m a l d e g r a d a t i o n o f d r i e d p o l y g l y c i n e has been r e p o r t e d by Hayase e t a l . (19). From T a b l e I , t h e r e l a t i v e abundance o f p y r a z i n e s formed from g l y c i n e and t r i g l y c i n e are very close. However, the amount o f p y r a z i n e s formed from d i g l y c i n e o r t e t r a g l y c i n e was c o n s i d e r a b l y l e s s as compared t o either glycine or t r i g l y c i n e . The t r i g l y c i n e c o u l d be degraded i n t o g l y c i n e and d i g l y c i n e through d i k e t o p i p e r a z i n e . W h i l e t e t r a g l y c i n e was degraded p r i m a r i l y i n t o d i g l y c i n e , f u r t h e r d e g r a d a t i o n o f d i g l y c i n e i n t o g l y c i n e c o u l d r e q u i r e more energy. On t h e o t h e r hand, t h e d e g r a d a t i o n o f p e p t i d e s by d i r e c t h y d r o l y s i s w i t h o u t t h e i n t e r m e d i ate f o r m a t i o n o f d i k e t o p i p e r a z i n e cannot be r u l e d o u t . The r e a c t i v i t y o r d e r , t e t r a g l y c i n e > t r i g l y c i n e > d i g l y c i n e > g l y c i n e f o r t h e c o l o r f o r m a t i o n i n the browning r e a c t i o n r e p o r t e d by Chuyen e t a l . (16) d i f f e r s from o u r o b s e r v a t i o n f o r p y r a z i n e formation. T h i s c l e a r l y i n d i c a t e s t h a t f o r the M a i l l a r d r e a c t i o n t h e m e l a n o i d i n f o r m a t i o n i s d i f f e r e n t from aroma f o r m a t i o n i n mechanism and r e a c t i v i t y .

Pyrazinones as Peptide-specific M a i l l a r d Reaction Products As shown i n T a b l e I , t h r e e n o v e l p y r a z i n o n e s were i d e n t i f i e d i n the r e a c t i o n o f g l u c o s e w i t h d i g l y c i n e , t r i g l y c i n e o r t e t r a g l y c i n e . The p y r a z i n o n e s i d e n t i f i e d were 1 , 6 - d i m e t h y l - 2 ( 1 H ) - p y r a z i n o n e , 1,5-dimethyl-2(1H)-pyrazinone and 1 , 5 , 6 - t r i m e t h y l - 2 ( 1 H ) - p y r a z i n o n e . The mass spectrum o f 1 , 6 - d i m e t h y l - 2 ( 1 H ) - p y r a z i n o n e i s shown i n F i g u r e 1.

In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

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15. HO ET A L

Peptides as Flavor Precursors in Model Maillard Reactions 195

T a b l e I . Amount o f V o l a t i l e Compounds G e n e r a t e d by G l y c i n e , D i g l y c i n e , T r i g l y c i n e and T e t r a g l y c i n e w i t h G l u c o s e a t 180°C f o r 2 Hours ik Compounds pyrazine methylpyrazine furfural 2,5-dimethylpyrazine 2,6-dimethylpyrazine trimethylpyrazine 2-acetylpyrrole tetramethy1pyrazine 5-(hydroxylmethyl)furfural 1,6-dimethyl2(lH)-pyrazinone 1,5-dimethyl2(1H)-pyrazinone 1,5,6-trimethyl2(lH)-pyrazinone a

*

a

Gly

di-Gly

tri-Gly

tetra-Gly

mg/mole amino compound 738 798 808 887

12.18 257.80 14.14 360.86

894

198.76

980

486.77

1058 1065

1.36 71.44

1208

125.61

100.44

-

-

186.81 3.87 266.57

3.17 16.93 46.88

-

139.50

17.41

8.11

375.98

54.52

10.28

797.04

1315

-

1379

-

t

1476

-

t

323.00

-

1.59 55.63

127.41

119.35

422.35

1.37

t

2.85

Linear retention indices calculated according (1974) on an HP-1 column. t = trace

to M a j l a t

In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

0.57

et a l .

FLAVOR PRECURSORS

196

The s t r u c t u r e o f the p y r a z i n o n e s were c o n f i r m e d by comparing t h e i r mass s p e c t r a and GC r e t e n t i o n times w i t h the a u t h e n t i c com­ pounds s y n t h e s i z e d by the r e a c t i o n o f d i g l y c i n e w i t h p y r u v a l d e h y d e . These t h r e e p y r a z i n o n e s were formed by the r e a c t i o n o f d i g l y c i n e w i t h p y r u v a l d e h y d e i n y i e l d s o f 25.56%, 9.39% and 20.16% f o r 1 , 6 - d i methyl-2(1H)-pyrazinone, 1,5-dimethyl-2(1H)-pyrazinone and 1,5,6trimethyl-2(1H)-pyrazinone, respectively. The t o t a l p y r a z i n o n e s amounted t o 55.11%. A c c o r d i n g t o the mechanism proposed by Chuyen et a l . (16), v a r i o u s d i p e p t i d e s would r e a c t w i t h α-dicarbonyl com­ pounds t o y i e l d the p y r a z i n o n e d e r i v a t i v e s , 2 - ( 3 ' - a l k y l - 2 - o x o p y r a z i n - 1 - y D a l k y l a c i d s . On t h e o t h e r hand, t h e d e g r a d a t i o n o f g l u c o s e would produce v a r i o u s α-dicarbonyl compounds such as g l y o x a l , py­ r u v a l d e h y d e and d i a c e t y l . As shown i n F i g u r e 2, i n the case o f py­ r u v a l d e h y d e , t h e amino end o f t h e d i p e p t i d e would p r e f e r t o r e a c t w i t h t h e a l d e h y d i c c a r b o n y l group than t h e o t h e r ketone c a r b o n y l carbon because o f a s t e r i c e f f e c t . A f t e r Amadori rearrangement, t h e i n t e r m e d i a t e o f d i p e p t i d e - p y r u v a l d e h y d e was c y c l i s i z e d t o form 2( 3 - a l k y l - 2 - o x o p y r a z i n - 1 ' - y D a l k y l a c i d s . A t t h e e l e v a t e d tempera­ t u r e (180°C) used i n o u r model experiment, t h e 2-(3 alkyl-2'-oxo­ p y r a z i n - 1 - y D a l k y l a c i d s would undergo d e c a r b o x y l a t i o n t o y i e l d 2pyrazinones. I t i s worth n o t i n g t h a t these p y r a z i n o n e s were o n l y i d e n t i f i e d i n t h e d i g l y c i n e , t r i g l y c i n e and t e t r a g l y c i n e , but n o t i n the f r e e g l y c i n e system.

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1

1

1

1

1

1

T a b l e I I shows the p y r a z i n o n e s i d e n t i f i e d i n t h e r e a c t i o n o f glucose with e i t h e r g l y - l e u or leu-gly. I t was found t h a t the d i ­ p e p t i d e s , g l y - l e u and l e u - g l y , produced t h e same type o f p y r a z i n o n e s . Q u a n t i t a t i v e l y , both d i p e p t i d e s produced s i m i l a r amounts o f p y r a z i ­ nones. The o n l y p o s s i b l e e x p l a n a t i o n f o r t h i s phenomenon i s t h a t t h e g l y - l e u d i p e p t i d e i s i n e q u i l i b r i u m w i t h the l e u - g l y d i p e p t i d e .

Comparison of the M a i l l a r d Reaction of Glucose with Glutathione and a Mixture of t h e i r Constituent Amino Acids (glu, cys and gly) I t i s known from o u r p r e v i o u s study (20) t h a t t h e r e l e a s e o f hydrogen s u l f i d e was much f a s t e r than ammonia d u r i n g t h e thermal d e g r a d a t i o n o f g l u t a t h i o n e (γ-Glu-Cys-Gly) i n an aqueous s o l u t i o n . However, t h e r e l e a s e o f both hydrogen s u l f i d e and ammonia from c y s t e i n e was f a s t and produced f o u r times as many v o l a t i l e s as g l u t a t h i o n e under t h e same c o n d i t i o n s (20). On t h e o t h e r hand, when c y s t e i n e and g l u t a ­ thione reacted with 2,4-decadienal, r e s p e c t i v e l y , the y i e l d o f v o l a ­ t i l e g e n e r a t i o n became almost i d e n t i c a l . T h i s phenomena was a t t r i b ­ u t e d t o t h e f a c t t h a t c a r b o n y l s , such as 2 , 4 - d e c a d i e n a l and t h e i r r e t r o a l d o l i z a t i o n p r o d u c t s , c a t a l y z e d the ammonia r e l e a s e d from g l u ­ t a t h i o n e v i a the f o r m a t i o n o f t h e S c h i f f - b a s e (21). We compared the M a i l l a r d r e a c t i o n o f e q u i m o l a r s o l u t i o n s o f g l u c o s e w i t h g l u t a t h i o n e (G-G) and i t s c o n s t i t u e n t amino a c i d s (GGCG) i n an aqueous medium. Each r e a c t i o n s o l u t i o n was a d j u s t e d t o pH 7.5 and heated f o r one hour a t 180°C. The r e a c t i o n mass was s i m u l t a n e o u s l y s o l v e n t - e x t r a c t e d and s t e a m - d i s t i l l e d by u s i n g d i ­ e t h y l ether with a Likens-Nickerson apparatus. The d i s t i l l a t e s were d r i e d over anhydrous sodium s u l f a t e and c o n c e n t r a t e d w i t h a KudernaD a n i s h a p p a r a t u s t o a f i n a l volume o f 0.5 mL. The c o n c e n t r a t e d sam­ p l e s were a n a l y z e d by GC/MS as d e s c r i b e d p r e v i o u s l y (22). A more r o a s t e d and n u t t y aroma was observed i n the G-GCG system than i n t h e

In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

Peptides as Flavor Precursors in Model Maillard Reactions 197

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15. HO ET AL

F i g u r e 2. Mechanism f o r the f o r m a t i o n o f 1 , 6 - d i m e t h y l - 2 ( 1 H ) p y r a z i n o n e from p y r u v a l d e h y d e and d i g l y c i n e .

In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

198

FLAVOR PRECURSORS

T a b l e I I . The Amount o f P y r a z i n o n e s Generated Reaction o f Glucose with E i t h e r G l y - l e u or Leu-gly

from t h e

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tS 3 R 1-- m e t h y l - 3 - i s o b u t y l 2(1H)-pyrazinone 1- i s o p e n t y l - 2 ( l H ) pyrazinone 1,6-dimethyl-3-isobutyl2(1H)-pyrazinone 1,5,6-trimethyl-3isobutyl-2(lH)pyrazinone

lie

LG

166

GL mg/mole p e p t i d e 351.41 1397

433.59

166

1432

185.58

129.95

180

1562

1629.69

1234.09

194

1638

84.17

83.54

MW

G-G system. The i d e n t i f i c a t i o n and q u a n t i f i c a t i o n o f v o l a t i l e s gene r a t e d i n these two systems a r e l i s t e d i n T a b l e I I I a c c o r d i n g t o t h e i r chemical c l a s s i f i c a t i o n s . I t i s i n t e r e s t i n g t o note t h a t about t h e same q u a n t i t y o f f u rans were produced by the G-G and G-GCG systems, however, t h e amino a c i d s m i x t u r e y i e l d e d 5.6 times the amount o f c a r b o n y l compounds than t h e g l u t a t h i o n e system. Furans a r e t h e c y c l i z a t i o n p r o d u c t s o f the s u g a r - d e r i v e d M a i l l a r d i n t e r m e d i a t e s and the c a r b o n y l compounds are g e n e r a l l y d e r i v e d from t h e f r a g m e n t a t i o n o f sugar. The h i g h e r c o n t e n t s o f the f r e e amino groups i n the G-GCG system may f a v o r the sugar d e g r a d a t i o n r e a c t i o n t o y i e l d c a r b o n y l compounds such as 3hydroxy-2-pentanone and 2-hydroxy-3-pentanone. The g e n e r a t i o n o f h e t e r o c y c l i c compounds such as p y r a z i n e s , t h i a z o l e s and t h i o p h e n e s from t h e G-GCG system had a much h i g h e r y i e l d than from t h e G-G system. The amino a c i d s m i x t u r e produced 14 times more p y r a z i n e s than t h e g l u t a t h i o n e when r e a c t e d w i t h glucose. The t r i t h i o l a n e s and t e t r a t h i a n e s i d e n t i f i e d a r e well-known i n t e r a c t i o n p r o d u c t s o f hydrogen s u l f i d e and a c e t a l d e h y d e , b o t h o f which a r e t h e d e c o m p o s i t i o n p r o d u c t s o f c y s t e i n e . The G-GCG system produced 32 times more o f these c y c l i c p o l y s u l f i d e s . Although g l u t a t h i o n e i s e f f i c i e n t i n r e l e a s i n g hydrogen s u l f i d e , i t may n o t be a good p r e c u r s o r f o r the g e n e r a t i o n o f a c e t a l d e h y d e .

In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

15. HO ET A L

Peptides as Flavor Precursors in Model Maillard Reactions 199

T a b l e I I I . V o l a t i l e Compounds I d e n t i f i e d from the I n t e r a c t i o n of G l u c o s e w i t h G l u t a t h i o n e o r G l u t a t h i o n e ' s C o n s t i t u e n t Amino A C i d s ( G l u , Cys, G l y ) i n an Aqueous S o l u t i o n a t pH 7.5 and 180°C MW

I k

86 72 88 74 86 100 88 84 90 100 102 102 104 114 118 96

561 572 599

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Compounds Carbonyls diacetyl 2-butanone ethyl acetate hydroxyacetone 2-pentanone 2. 3-pentanedione acetoin 3-penten-2-one l-mercapto-2-propanone 2,4-pentanedione 3-hydroxy-2-pentanone 2-hydroxy-3-pentanone 3-mercapto-2-butanone 2,4-hexanedione 4-hydroxy-3-hexanone 2-cyclohexenone T o t a l Amount Furans 2-methylfuran 2,5-dihydrofuran 2,5-dimethylfuran 2,3-dihydro-4methylfuran 2-methyltetrahydrofuran-3-one furfural furfuryl alcohol 2-acetylfuran 2,5-dimethyl-3(2H)furanone 5-methylfurfural 5-methyl-2-acetylfuran l-(2-furyl)-l,2propanedione T o t a l Amount Thiophenes thiophene 2,3-dihydrothiophene 2-methylthiophene 3-methylthiophene 2-ethylthiophene 2,5-dimethylthiophene 2 ,3-dimethylthiophene tetrahydrothiophen3-one 5-methyltetrahydrothiophene-3-one

mg/mol. Glutathione Glu+Cys+Gly 1..83 4..34 15.,56

-

-

667 668 680 719 741 758 773 782 787 859 865 904

3..60 0..82 0..31

26..46 82 70 96 84

4.64 72.53 t t t

-

t 1.28 t 41.99 18.28 t 2.22 1.30 5.79 148.03

-

t t 0.54 t

699

-

100

776

9..26

17.08

96 98 110 112

809 835 882 922

9..95 0.88 23,.12

1.19 6.52 5.88 1.15

110 124 138

934 1019 1034

111,.01 2,.13 2,.61

111.46

158,.96

143.82

t

84 86 98 98 112 112 112 102

648 756 760 844 853 877 912

21 .71 1 .69 0 .61 0 .81 19 .43

19.38 t 64.96 17.08 0.35 t t 90.73

116

946

1 .52

5.50

-

Continued on next page In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

FLAVOR PRECURSORS

200

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Table I I I . MW Compounds Thiophenes C o n t i n u e d 2 - m e t h y l t e t r a h y d r o t h i o - 116 phene-3-one 112 thiophene-2-carboxyaldehyde 112 thiophene-3-carboxyaldehyde l-(2-thienyl)130 ethanethiol 2-acetylthiophene 125 126 methylformylthiophene 3-acetylthiophene 126 126 5-me t h y 1 - 2 - f o r m y l thiophene 3-methyl-2-formyl126 thiophene 5-me t h y 1 - 2 - a c e t y l 140 thiophene 3-methy1-2-acetyl140 thiophene 2-(1-propionyl)140 thiophene methylacetylthiophene 140 thenio-[3,2-B]140 thiophene 3 - m e t h y l - 2 - ( o x o p r o p y l ) - 154 thiophene 144 2,5-dimethyl-4hydroxy-3(2H)thiophene 135 thieno-[2,3-C]~ pyridine 154 5-methylthieno[2 ,3-B]-thiophene 168 5-ethylthieno[2,3-D]-thiophene T o t a l Amount Thiazoles thiazole 85 2-methylthiazole 99 4-methylthiazole 99 5-methylisothiazole 99 5-methylthiazole 99 2,5-dimethyl113 thiazole 113 5-ethylthiazole 113 3,5-dimethylisothiazole trimethy1thiazole 127 2-acetylthiazole 127 127 trimethylisothiazole

L*k

Continued mg/mol. Glu+Cys+Gly Glutathione

953

9.74

55.64

958

4.40

38.42

967

9.95

12.05

1035

-

6.13

1049 1054

11.20 2.16

150.09 30.56

1058 1086

24.31 11.49

177.93 27.54

1089

5.20

65.73

1128

8.85

31.37

1135

3.34

3.51

1153

1.31

-

-

34.70 60.67

1192

2.59

-

1195

-

2.98

1213

-

2.75

1282

1.45

20.11

1380

-

6.58

1174 1185

-

141.76

924.76

707 783 795 820 827 860

9.53 1.29 2.57 1.09

95.97 t 2.00 t 3.09 4.44

-

-

t t

977 988

0.45 21.68

-

-

9.35 39.56 t

-

In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

15. HO ET A L

Peptides as Flavor Precursors in Model Maillard Reactions 201 Table

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MW

III.

*

mg/molT

I*k

Compounds T h i a z o l e s Continued 4-methy1-2-acetyl141 1083 thiazole T o t a l Amount Pyrazine pyrazine 80 710 methylpyraz ine 94 799 2,5-dimethyl108 888 pyrazine 2-ethylpyrazine 108 893 2,3-dimethypyrazine 108 897 2-methy1-5-ethyl122 977 pyrazine 122 trimethylpyrazine 979 2-methyl-6-ethyl122 984 pyrazine 3,6-dimethyl-2136 1059 ethylpyrazine 5,6-dimethyl-2136 1065 ethylpyrazine T o t a l Amount Pyridines pyridine 79 2-methylpyridine 93 798 T o t a l Amount Other S u l f u r - c o n t a i n i n g Compounds 2-pentanethiol 104 838 4H-tetrahydrothio116 1011 pyran-4-one 152 3,5-dimethyl-l,2,41103 trithiolane 3,5-dimethyl-l,2,4152 1110 trithiolane 184 1345 3,6-dimethyl-l,2,4, 5-tetrathiane 184 1352 3,6-dimethyl-l,2,4, 5-tetrathiane 4,6-dimethyl-l,2,3, 184 1368 5-tetrathiane 4,6-dimethyl-l,2,3, 184 1396 5-tetrathiane T o t a l Amount a

Continued

Glutathione

Glu+Cys+Gly

0.88

6.94

37.49

161.35

-

113.46 73.44 107.41

13.09 8.19 1.06 2.52

3.91

-

15.31 16.65 5.68 47.06 7.82

-

10.01

t

1.68

28.77

398.52

-

t 5.20 5.20

0.44

1.69 2.71

1.49

89.93

4.40

101.23

-

-

10.12

-

5.69

0.70

3.79

-

0.38

7.03

215.54

t = trace Iir = l i n e a r r e t e n t i o n i n d i c e s were o b t a i n e d by u s i n g p a r a f f i n s t a n d a r d s on a n o n p o l ar fused s i l i c a c a p i l l a r y column (60 m χ 0.25 mm [ i . d . ] ) ; 0.25 ym t h i c k n e s s ; DB- l ; J&W S c i e n t i f i c )

In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

202

FLAVOR

PRECURSORS

Acknowledgement s New J e r s e y A g r i c u l t u r a l E x p e r i m e n t S t a t i o n P u b l i c a t i o n No. D-1054414-91 s u p p o r t e d by S t a t e f u n d s , and t h e C e n t e r f o r Advanced Food Technology. The C e n t e r f o r Advanced Food T e c h n o l o g y i s a member o f the New J e r s e y Commission f o r S c i e n c e and T e c h n o l o g y . We thank Mrs. Joan B. Shumsky f o r h e r s e c r e t a r i a l a i d .

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In Flavor Precursors; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.