Metabolomics Analysis Of The Non-volatiles During Fresh Tea Leaves Withering And Green Tea Processing

Fresh tea leaves withering lays the foundation of tea quality.Withering time effect on the compounds of fresh tea leaves is an important basis to explain the formation of tea leaves.Green tea,with the longest history among the six categories of traditional tea,retain the greatest extent original taste of tea leaves in trait and taste.These manufacturing processes of green tea have biochemical reaction and thermal reaction.The different reactions in green tea processing are changed the compounds content to form the quality characteristics of green tea.Therefore,studying the non-volatiles changes in each step of green tea processing is a key basis for explaining the taste components and formation mechanism of green tea.In this study,we used the untargeted metabolomics analysis based on ultra-performance liquid chromatography-mass spectrometry data,and feature based molecular networking on the platform of Global Nature Product Social Molecular Networking to explored the influence of withering time and green tea processing steps on the chemical profile of tea,as well as the changes in structure and content of non-volatiles.The results of this research were obtained as follows: firstly,the content of many tea metabolites show a clear trend with time during the withering.We can divided the tea chemical profile of withering into three metabolic profiles: early period,middle period and later period.Secondly,we found that six unsaturated fatty acids signals increased significantly by 228%-446% with the later period,while lysophosphatidylcholines containing glyceride group will remove the glyceride group in the early and middle period of withering.The content of most catechins have decreased significantly in later period.Thirdly,withering,fixation,drying of green tea processing changed the composition and content of tea metabolites and made the green tea metabolic profile divide into four groups,while the processing of drying has the most dramatic influence on the chemical profile of tea.Finally,we found that amino acids and lysophosphatidylcholines were increased during the fixation.Most non-volatiles content are decreasing during the drying process and there is a correlation between the changes rate of the compound and its structure.The highlight of this study is the first comprehensive study on the changes of non-volatile metabolites in tea withering and green tea processing using the metabolomics technology of feature-based molecular networking combined with the tandem mass spectrometry calculation structural software.These techniques improves the efficiency of chemical profile analysis and metabolites identification analysis.This study not only provides theoretical basis for the research of compounds in tea withering and green tea processing,but also lays an important foundation for the formation of quality components in tea processing.