Underlying substituted pyrazines formation in the glucose-alanine Maillard reaction: Carbon module labeling and...

The Maillard reaction between glucose and alanine plays a pivotal role in the formation of substituted pyrazines responsible for roasty aromas, yet the underlying formation mechanisms remain poorly elucidated. The carbon skeleton rearrangement patterns and formation mechanisms of substituted pyrazines were clarified in this work. The absorbance of glucose-alanine Maillard model significantly increased (p < 0.05) during heating, reaching its maximum value at 50 min. A total of 11 substituted pyrazines were identified, among which the concentrations of all pyrazines except 2-methylpyrazine substantially increased (p < 0.05) with heating duration. Irrespective of thermal reaction stages, the carbon skeletons of substituted pyrazines were primarily derived from the rearrangement of carbon chains in glucose. Except for formaldehyde, heptanal, octanal, and nonanal, the contents of carbonyls produced by glucose pyrolysis were significantly higher than those produced by alanine pyrolysis. It was hypothesized that the glucose-alanine reaction generated C₂-C₄ carbonyls, such as 1-hydroxy-2-butanone, glyoxal, and methylglyoxal. The products formed by the aldol reaction and keto-enol tautomerism of these carbonyls further reacted with alanine to produce aminocarbonyls. The combination of aminocarbonyls with different structures and substitution sites ultimately caused the formation of diverse substituted pyrazines. Additionally, carbonyls, namely 2-nonanone, decanal, and nonanoic acid, might be recognized as markers discriminating the different thermal reaction degrees of glucose-alanine model. These results provided new insights into the formation of roasty substituted pyrazines via the glucose-alanine Maillard reaction.