Heterocyclic compounds formation in large-leaf yellow tea induced by the Maillard reaction at different roasting temperatures

Abstract

Maillard reactions occurred during the roasting process of large-leaf yellow tea (LYT) were the main reason for the formation of their unique flavor. However, the contribution of different amino acids and soluble sugars to the formation of heterocyclic compounds in the Maillard reaction is still unclear. First, this study found that trimethylpyrazine, 2-ethyl-3,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine and 2,5-diethylpyrazine, which had higher odor activity values (OAV), were significantly increased with the increase of roasting temperature. In contrast, only five amino acids (l-theanine, glutamic acid, lysine, glutamine, histidine) and three monosaccharides (d-glucose, d-fructose, and l-fucose) decreased significantly with increasing roasting temperature, which were significantly and positively correlated with each other. This indicates that these five amino acids and three monosaccharides were involved in the Maillard reaction during the roasting process. In addition, the model thermal reaction results showed that lysine contributed significantly to the formation of pyrazine especially with d-glucose to methylpyrazine, 2,5-dimethylpyrazine, trimethylpyrazine and 3-ethyl-2,5-dimethylpyrazine, while l-theanine contributed significantly to the formation of 1-ethylpyrrole-2-carbaldehyde. The d-glucose and d-fructose were the main contributors to the Maillard reaction among soluble sugars. This study lays the foundation for future studies on the relationship between volatile compounds and Maillard reactions.