Dynamic Changes of Metabolites during Grape Jiaosu Fermentation

The objective of this work was to analyze the changes in metabolites during the inoculated fermentation of grape Jiaosu. The changes of total acids, organic acids, ethanol, total phenolic compounds, major enzymes (SOD and β-glucosidase) and aroma components during the sequential fermentation process of yeast, acetic acid bacteria and lactic acid bacteria were analyzed. The results showed that the total acid concentration increased first and then decreased during the fermentation process, reaching a maximum value of 19.37 g/L on the 34^th day. The organic acids produced during yeast fermentation (0-6 days) were mainly citric acid, malic acid and tartaric acid. Ethanol was also mainly produced at this stage. During fermentation with acetic acid bacteria (6-27 days), acetic acid was produced. During fermentation with lactic acid bacteria (27-41 days), lactic acid and citric acid gradually increased to a maximum value of 102.09 and 67.70 mg/L, respectively, while malic acid decreased. Moreover, ethanol content decreased to a minimum value of 0.47% and then tended to be stable. The trends of total phenol content and β-glucosidase activity were consistent, both of which were mainly produced during yeast and at the late stage of lactic acid bacterial fermentation (34-41 days). The activity of SOD showed a fluctuating increase. The volatile compounds produced during grape Jiaosu fermentation were mainly alcohols, acids and esters. These results can provide a theoretical basis for precise preparation and quality optimization of grape Jiaosu.