Influence of cysteine, glutathione, and thiamin oxidation on Maillard or thermally generated volatile compounds

Cysteic acid and cysteinesulfinic acid, the oxidized forms of reduced cysteine, were heated separately with glucose in an aqueous system of pH 6.0 at ;Glutathione is a cysteine containing tripeptide. The Maillard compounds obtained from the reaction of glutathione and glucose were mainly furans, carbonyl compounds, and sulfur compounds. The reaction between glutathionesulfonic acid, an oxidized form of glutathione, and glucose produced primarily furans, carbonyl compounds, pyrazines, and pyrroles. The pH also played a determining factor in the reaction product. The yields of sulfur compounds, pyrazines, carbonyl compounds increased the reaction pH increased. Furans dominated the products obtained from the reactions at pH 6.0 and 3.0 of the glutathionesulfonic acid/glucose reaction system.;The disappearance of sulfur compounds indicated that cysteic acid, cysteinesulfinic acid, and glutathionesulfonic acid could not provide sulfur source for reaction as the reduced cysteine and glutathione.;Thiamin was considered as a potential precursor for meat flavor. Thiamin can be oxidized to thiochrome in an oxidizing condition. Hydrogen peroxide effectively converted thiamin to thiochrome pH 7.0 and 9.5, but not at pH 1.5. The formation of thiochrome considerably reduced the yield of the thermal degradation compounds of thiamin. Even though hydrogen peroxide did not convert thiamin to thiochrome at pH 1.5, it transformed the chemical structure of thiamin.;The result of this study suggested oxidation of cysteine, glutathione, and thiamin could significantly change the profile of Maillard compounds and reduce the intensity of volatile compounds derived from thiamin degradation. As a consequence, oxidation could affect the flavor quality of foods.