The metabolite changes of wolfberry (Lycium barbarum) tea in different processing stages

Wolfberry (Lycium barbarum) tea has a long history of consumption in China and is an important cash crop. Wolfberry tea is prepared through five processing stages: picking, withering, fixation, stir-firing, and fragrance enhancement, which correspond to the fresh wolfberry buds (FWB), withered wolfberry shoots (WWS), fixed wolfberry shoots (FWS), stir-fried wolfberry shoots (SFWS), and fragrance-enhanced wolfberry shoots (EFWS) groups, respectively. There remains a lack of in-depth research on the analysis of the overall metabolism and changes in metabolic pathways of wolfberry (Lycium barbarum) tea at different processing stages.

Thus, in this study, the dynamic changes of metabolites in wolfberry (Lycium barbarum) tea during processing were investigated through metabolomics.

The analysis of variability showed that the high temperature treatment in the frying procedure was the main reason for the differences between the groups. Compared with FWB, the metabolites that were up-regulated at different processing stages of wolfberry buds were mainly flavonoids, while the down-regulated metabolites were mainly lipids and amino acids and their derivatives. High-temperature treatment (SFWS/EFWS stage) induced significant changes in metabolites, with most of the differential compounds related to glycoside hydrolysis (e.g., quercetin-3-O-rutinoside). A class of furan derivatives unique to wolfberry tea (e.g., 2-pentylfuran) showed a significant correlation with the formation of a nutty flavor. Stir-frying at 220 °C (SFWS stage) triggered the Maillard reaction, resulting in a decrease in free amino acid content (such as L-tryptophan) and the production of Maillard reaction products specific to wolfberries (related to umami intensity). Thermosensitive β-glucosidase is activated at 80-120 °C (SFWS stage) and catalyzes the hydrolysis of flavonoid glycosides (e.g., isoquercitrin → quercetin), directly increasing the bitterness threshold. This study is the first to investigate the changes of metabolic components in the production process of wolfberry tea, which will provide valuable data support for the further development of wolfberry tea in the future.

At the different stages of wolfberry tea making process, the metabolites of wolfberry tea could change obviously. Our research on the metabolites of wolfberry tea is conducive to optimizing the tea making process of wolfberry tea, improving the quality and yield of wolfberry tea, in order to meet the requirements of more Chinese and foreign consumers.