Chapter 14
Formation of Meatlike Flavor Compounds Werner Grosch and Gabriele Zeiler-Hilgart
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Deutsche Forschungsanstalt für Lebensmittelchemie, Lichtenbergstrasse 4, D-8046 Garching, Germany
The formation of 2-methyl-3-furanthiol (MF-SH), its oxidation product bis(2-methy13-furyl)disulfide (MF-S ) and 2-furfurylthiol (FF-SH) were determined in model systems containing the precursors in concentration levels approximated to those occurring in meat. The degradation of thiamine was more effective in the production of MF-SH than the reaction of ribose and cysteine. Addition of cysteine, and, to a lesser extent, of H S enhanced the formation of MF-SH from thiamine. In contrast to thiamine its pyrophosphate derivative was inactive as precursor of MF-SH. The amounts of FF-SH and MF-S formed were very low in a l l models investigated. 2
2
2
2-Methyl-3-furanthiol (MF-SH), its oxidation product bis(2-methyl-3-furyl)disulfide (MF-S ) and 2-furfurylthiol ( F F - S H ) h a v e been i d e n t i f i e d a s i m p a c t compounds of the "meaty" odor note of boiled beef, pork and c h i c k e n meat ( 1 - 3 ) . M o d e l e x p e r i m e n t s have i n d i c a t e d t h a t MF-SH a n d M F - S a r e f o r m e d by a d e g r a d a t i o n o f t h i a m i n e (4, 5) , b y a M a i l l a r d - t y p e r e a c t i o n o f r i b o s e and c y s t e i n e (6, 7) and r e c e n t l y by a r e a c t i o n o f i n o s i n e 5 - m o n o p h o s p h a t e with cysteine (8) . The l a t t e r two r e a c t i o n s h a v e a l s o been e s t a b l i s h e d as s o u r c e o f FF-SH (6-8). 4-Hydroxy-5-methyl-3(2H)-furanone (from r i b o s e ) and hydrogen s u l p h i d e (from c y s t e i n e ) have been suggested (6, 9) a s intermediates i n t h e Maillard reaction to M F - S H . F F - S H i s p r o b a b l y formed by t h e r e a c t i o n o f H S w i t h t h e s u g a r breakdown p r o d u c t f u r f u r a l (6, 10). 2
2
1
2
0097-6156/92/0490-0183$06.00/0 © 1992 American Chemical Society
Teranishi et al.; Flavor Precursors ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
184
FLAVOR
Table I.
PRECURSORS
Compounds D i s c u s s e d as Precursors of MF-SH, F F - S H and M F - S : C o n c e n t r a t i o n s i n Raw B e e f a n d P o r k (13-18) 2
Compound
Beef
Pork
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(mg/kg wet Ribose T o t a l SH Nonprotein SH GSH Thiamine
10-1300 690 (253Q) 11 (42) 71 0.9-2.3
C
a
Data not
D
Values
c
W i t h o u t GSH.
weight) _a
b
b
627 5
(2300) (19) 194 8-10
b
b
available.
in brackets:
SH-content e x p r e s s e d as
cysteine.
D u r i n g b o i l i n g o f meat, H S i s r e l e a s e d by t h e d e g r a d a t i o n o f c y s t e i n e o c c u r r i n g f r e e and b o u n d , e . g . in reduced g l u t a t h i o n e (GSH) and m u s c l e p r o t e i n s (11, 12). T a b l e I c o n t a i n s d a t a about the c o n c e n t r a t i o n l e v e l s i n both, raw b e e f and p o r k , o f f r e e and bound c y s t e i n e , GSH, t h i a m i n e and r i b o s e . In the f o l l o w i n g study the formation of MF-SH, M F - S and F F - S H was d e t e r m i n e d i n model systems containing t h e i r precursors i n concentration l e v e l s approximated to t h o s e o c c u r r i n g i n raw b e e f and p o r k meats ( T a b l e I ) . In t h e m o d e l s , t h e pH v a l u e was a d j u s t e d t o 5 . 7 , a s meat i s c h a r a c t e r i z e d by a pH r a n g i n g between 5 . 5 a n d 6 . 0 (19). A boiling period of 2 h which is usual for the p r e p a r a t i o n o f a b r o t h was c h o s e n . The a i m o f t h e p r e s e n t s t u d y was t o e s t i m a t e t h e a c t u a l c o n t r i b u t i o n of each of the p r e c u r s o r s d i s c u s s e d to the f o r m a t i o n of MF-SH, M F - S and F F - S H u n d e r t h e c o n d i t i o n s used f o r t h e b o i l i n g or meat. 2
2
2
Experimental The components o f t h e r e a c t i o n s y s t e m s d e t a i l e d i n T a b l e s I I - V I , and V I I I were d i s s o l v e d i n N a - p y r o p h o s p h a t e buffer (pH 5 . 7 , 0.2 mol/L, 500 mL) u n l e s s otherwise specified. Two d i f f e r e n t methods were u s e d t o b o i l the r e a c t i o n s y s t e m s and t o remove t h e v o l a t i l e compounds. Method I: the mixture was refluxed for 2 h and extracted after cooling. Method I I : the mixture was d i s t i l l e d and c o n t i n u o u s l y e x t r a c t e d (SDE) f o r 2 h i n t h e a p p a r a t u s a c c o r d i n g t o Nickerson and Likens. M F - S H , F F - S H and M F - S were q u a n t i f i e d i n t h e cooled reaction mixture (Method I) and i n t h e SDE extract (Method II) by mass chromatography using the corresponding deuterated flavor compounds (d-MF-SH, d - F F - S H , d - M F - S ) as i n t e r n a l s t a n d a r d s (20, 21). 2
2
Teranishi et al.; Flavor Precursors ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
14.
Table II.
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No.
1 2 3 4 5
7 8
Reaction
system
a
N
b
Amount (^g) C MF-S FF-SH MF-SH
2
