Unraveling the dynamic variations of volatile and non-volatile metabolites in green tea during the yellow-light irradiation spreading process by targeted and untargeted metabolomics

Spreading, the initial process of green tea manufacturing, plays a pivotal role in shaping the quality of green tea. Herein, a comprehensive study was conducted employing targeted and untargeted metabolomics to explore the dynamic variations of volatile metabolites (VMs) and non-volatile metabolites (NVMs) throughout the yellowlight irradiation spreading procedure. Findings indicated that both VMs and NVMs exhibited continuous variations during the spreading process, with the most significant alterations observed at 2-h spreading. A total of 74 VMs were successfully identified, with esters (29.73%), aldehydes (25.68%), and alcohols (17.57%) being the predominant compounds. Moreover, 19 VMs such as (E, Z)-2,6-nonadienal and phenylethyl alcohol were regarded as crucial odorants during the yellow-light irradiation spreading process. These key odorants primarily stemmed from the lipid degradation and glycoside hydrolysis during the spreading process. Additionally, a total of 124 NVMs belonging to 10 subcategories were identified, and 29 pivotal NVMs were identified as important differential metabolites throughout the spreading process as per variable importance in projection >1.0 and p < 0.05. These findings provide a robust theoretical framework for the strategic processing of green tea with respect to regulating its quality.