金萱炒青绿茶中挥发性对映异构体分析方法的优化及应用OA北大核心CSTPCD

To investigate the changes in volatile enantiomers during the drying of'Jinxuan'roasted green tea,an optimized method using headspace solid-phase microextraction-enantioselective-gas chromatography-mass spectrometry(HS-SPME-Es-GC-MS)was applied for qualitative and quantitative enantiomer analysis.The chemometric evaluation was also performed on four roasted green tea samples dried at 120℃for different durations(30 min,60 min,90 min and 120 min).The optimal HS-SPME conditions were found to be:addition of NaCl(3 mL,3 mol·L-1,solid-to-liquid ratio of 1∶6,extraction temperature of 60℃,and extraction time of 25 min.The optimal temperature program for Es-GC-MS was as follows:initial temperature at 35℃held for 2 min,then ramped up to 110℃at 4℃min-1 and held for 10 min,followed by a further increase to 210℃at 4℃min-1.Using an optimized method to analyze four'Jinxuan'roasted green tea samples,a total of 8 enantiomers were detected,with no change in the types as drying time increased.Among them,the contents of R-(-)-linalool and S-(+)-linalool increased with the drying process,while the contents of the other 6 enantiomers began to decline after 60 min or 90 min.Hierarchical cluster analysis and partial least squares discrimination analysis show that the samples with different drying times were obviously classified into four groups.Based on variable importance in projection(VIP)>1 and significance analysis,four different enantiomers were screened,and their VIP values were ranked in descending order as R-(-)-linalool,(2R,5S)-theaspirane B,(2R,5R)-theaspirane A,and S-(+)-linalool.This study provided a reference for improving aroma quality and selecting drying processes during the roasting of green tea.