Isolation, identification, and formation conditions of a novel Maillard yellowish pigment, pyrrolothiazolate.

We isolated a novel yellow pigment from a model Maillard reaction system containing l-cysteine, l-lysine, and glucose and identified it as 6-hydroxy-3[R],7a[S]-dimethyl-7-oxo-2,3-dihydropyrrolo[2,1-b]thiazole-3-calboxylic acid. This compound was a novel pyrrolothiazole derivative carrying a carboxy group and was named pyrrolothiazolate. This compound showed the absorption maxima at 300 and 360 nm under acidic and neutral conditions, while 320 and 400 nm did under alkaline conditions. Pyrrolothiazolate formed from cysteine and glucose was the major low-molecular-weight Maillard pigment in the reaction mixture, and its formation was stimulated by adding lysine to the reaction cocktail. After heating at 110 °C for 2 h, 1-2 mg/mL of pyrrolothiazolate was formed in a reaction mixture containing 100 mM cysteine, 200 mM lysine, and 300 mM glucose dissolved in 0.5 m acetate buffer (pH 6.0) or 0.5 m phosphate buffer (pH 6.5).