Formation Priority of Pyrazines and 2-Acetylthiazole Dependent on the Added Cysteine and Fragments of Deoxyosones during the Thermal Process of the Glycine-Ribose Amadori Compound.

In this study, it was found that extra-added cysteine (Cys) became involved in volatile compound formation during the Maillard reaction of the glycine-ribose Amadori rearrangement product (GR-ARP). The priority of the Cys reaction with different α-dicarbonyls and its dependence on the Cys dosage were investigated. At the same concentrations of methylglyoxal (MGO) and glyoxal (GO), it was found that 2-acetylthiazole was the dominant product when the molar ratio of Cys to MGO was 1:1, while formation of pyrazines was improved when the Cys percentage increased. Cys preferentially reacted with MGO first rather than GO to exclusively generate 2-acetylthiazole at a high yield. The concentration of 2-acetylthiazole quickly increased up to a plateau and remained stable during further heat treatment. When MGO was totally consumed, remaining Cys began to react with GO through the predominant pathway where the keto form of carbonylcysteimine derived from Cys and GO was hydrolyzed to recover GO with cysteamine formation, whereas the hydrolysis reactivity of enolized carbonylcysteimine as the Strecker pathway for generation of pyrazines was relatively low. During the heat treatment of GR-ARP, the constantly lower ratios of α-dicarbonyls to Cys led to inhibited formation of 2-aminopropanal, which accounted for the decreased methylpyrazine yields.