Insight into the mechanism of roasting-induced characteristic aroma formation in Wuyi rock tea using an “in-leaf” model with isotopic labeling

Wuyi Rock Tea (WRT) undergoes complex chemical transformations during roasting that significantly influence its aroma. This study explores the mechanisms involved in the formation of key aroma compounds, specifically alkylpyrazines and furans. Using HS-SPME-GC-O-MS and aroma dilution analysis, we identified 15 odor-active compounds, including three alkylpyrazines (2,6-diethyl-pyrazine, 2-ethyl-3,5-dimethyl-pyrazine, and 2-methyl-3,5-diethyl-pyrazine) and two furans (furfural and 5-methyl-2-furancarboxaldehyde), with odor-active values exceeding 1. An “in-leaf” labeling approach utilizing isotopically labeled alanine ([ 15 N]-Ala) and glucose ([U 13 C 6 ]-Glc) was employed to explore the contributions of tea leaf matrix and soluble compounds. Results indicated that the incorporation of two nitrogen atoms from alanine was the predominant pathway for alkylpyrazine formation, while five or six carbon atoms from glucose were primarily responsible for furan formation. Additionally, the insoluble tea leaf matrix contributed 13 % to 32 % of alkylpyrazines and 12 % to 25 % of furans. These findings enhance our understanding of the Maillard reaction's role in WRT's flavor development.