Identification and quantification of alkyloxazoles in roasted tea infusion (Camellia sinensis): Their thresholds, sensory impact, and related amino acids

Roasting significantly affects heterocyclic compound formation in tea. This study investigated and identified 9 rarely reported alkyloxazoles in tea infusion using SPME and SPE. Their concentrations increased with roasting temperature and time ranging from trace levels of a few μg/L to several tens of μg/L. Among these, 2,4,5-trimethyloxazole exhibited the highest concentration, reaching approximately 20 μg/L. Roasted tea leaves contained more alkyloxazoles than stems, particularly 2,4,5-trimethyl- and 4,5-dimethyloxazole. These compounds were widely detected in roasted teas. OAV analysis and addition tests confirmed the aroma contributions of 2,4,5-trimethyl-, 4,5-dimethyl-2-ethyl-, and 4,5-dimethyl-2-isopropyloxazole. Model reactions indicated their formation involved minor amino acids like glycine, alanine, threonine, valine, and leucine, while theanine played a minimal role. The findings expanded the chemical understanding of aroma compounds in tea, offering valuable insights into the complexity of roasted tea aroma and providing a theoretical foundation for optimizing aroma quality of roasted teas.