Model studies on the formation of 2-vinylpyrazine and 2-vinyl-6-methylpyrazine in Maillard-type reactions.

Vinylpyrazine compounds are widely present in foods, especially in hot-processed foods, as a class of flavor compounds; however, their formation mechanism in food systems is still unclear. Therefore, in this study, 2-vinylpyrazine and 2-vinyl-6-methylpyrazine were identified in the Maillard model reaction of d-glucose and glycine. The Maillard model reaction of glucose-glycine was constructed to explore the effects of reaction parameters on vinylpyrazines and the related products. The Maillard reaction of [U-13C6] glucose and glycine was established, and alkylpyrazines and formaldehyde were determined via isotope tracing technique as the precursors of vinylpyrazines. The formation of vinylpyrazines was verified by building a model reaction between alkylpyrazines and formaldehyde. The H/D exchange experiment confirmed that the active site of alkylpyrazines was on the methyl group, which was the reaction site for the condensation reaction of alkylpyrazines with formaldehyde. Results suggest that vinylpyrazines are formed by the condensation reaction of alkylpyrazines and formaldehyde.