Cysteine reaction with xylose

The OV-17 phase has been found to give improved separation of the diastereoisomerlc pertrimethylsilylated methyl 2-(polyhydroxy-alkyl)thiazolidine-(ilR)-carboxylates formed from enantiomeric pairs of nine aldoses after reaction with L-cysteine methyl ester (c.f. Vol.20, p.2il8). Although each pair of sugar enantiomers gave separate peaks, those from different sugars, e.g., D-xylose and L-arabinose, sometimes co-eluted, ... 

It is precisely to the production of meatlike flavors that the great majority of patents based on the Maillard reaction have been directed. Mos of them indicate cysteine or cystine as the essential sulfur-containing compound. Other patents claim alternative sources for sulfur, e.g., derivatives of mercaptoacetaldehyde (36), mercaptoalkylamines (37), S-acetylmercaptosuccinic acid (38), 2-thienvltetrasulfide (39), "a sulfide" (40), and hydrogen sulfide (heated with aqueous xylose without any amino acid) (41). 

In theory, a crude cysteine-sugar reaction product with a high content of Amadori compoimd can also be used as a flavor precursor system. However, to avoid off-flavor formation, the cysteine-xylose reaction has already to be discontinued before 75% of the maximum Amadori compound concentration has been achieved. Moreover, dilution with other precursors and/or a flavor carrier is necessary for acceptable stability. In some cases, the use of mixtures of cysteine with Amadori compounds of other amino acids (5) can also be a suitable alternative for the in situ generation of meat flavors. 

It was identified in the products of thermal degradation of glucose (Heyns et al., 1966a Walter and Fagerson, 1968), in the model reaction cysteine xylose (Ledl and Severin, 1973), and in model reactions of serine and threonine with sucrose (as well as in coffee) by Baltes and Bochmann... 

It has been found in the reaction of cysteine (not cystine) with pyruvaldehyde (Kato et al., 1973a), in a heated cysteine/glucose model system (Sheldon et al., 1986), in a cysteine/xylose model (Tressl, 1989), in a cysteine/ribose system, being one of the most important thiophene derivatives, the most important compounds being the two fur an derivatives, 2-furanmethanethiol (1.128) and 2-methyl-3-furanthiol (1.120) (Whitfield et al., 1988). 

Numerous publications have been dedicated to the genesis of alkylthiazoles. A model reaction based on a mixture of cysteine/xylose/tributyrin was studied by Ledl and Severin (1973), who proposed the decarboxylation of cysteine into cysteamine (2-aminoethanethiol), followed by a condensation with sugar degradation products and a subsequent oxidation. Mulders (1973c) also proposed a model based on a system of cysteine/cystine/carbohydrates, with the formation of thiazolidines subsequently oxidized into thiazoles. The same pathway has been proposed by Flament (Firmenich, 1973), thiazolidines easily being formed by the reaction of cysteamine with aldehydes. Kato et al. (1973a) also found thiazoles in the volatile compounds produced by the reaction of L-cystine with carbonyl compounds. Similarly,... 

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