Characterization of N,O-heterocycles in green tea during the drying process and unraveling the formation mechanism

Abstract

N,O-Heterocycles play an important role in the characteristic flavor of green tea owing to their strong odors and low odor thresholds. In this study, a rapid and sensitive method was developed to determine seven N,O-heterocycles in green tea by using headspace solid-phase microextraction Arrow (HS-SPME-Arrow) coupled with gas chromatography-triple quadrupole-tandem mass spectrometry. The HS-SPME-Arrow extraction was performed using a Carbon WR SPME Arrow fiber. Good linear ranges (5–1000 ng/mL) were obtained, with correlation coefficients (R2) higher than 0.99 for all target compounds. LODs and LOQs were in the range of 0.44–5.12 and 1.48–17.04 μg/kg, respectively. The recoveries of seven N,O-heterocycles were found to vary from 83.1% to 117.3%, with RSDs being lower than 10%. The dynamic changes of N,O-heterocycles during the drying process revealed that 25- and 40-min-long drying processes were key transition points. Furfural could be used as a key indicator compound for evaluating the extent of the drying. Moreover, furfural and 2-methylfuran revealed a significant positive correlation with proline (p < 0.05). The possible formation mechanisms of N,O-heterocycles were further elaborated by simulated Maillard reactions. Our results provide a theoretical foundation for the improvement and directional regulation of aroma quality of green tea during manufacturing.