Time Course Evaluation of Biochemical Contents and Biocatalytic Activities of Jiaosu from Fruit Wastes During One-Year Natural Fermentation

Jiaosu is a multifunctional solution derived from the fermentation of a mixture of fruit or vegetable wastes, sugar, and water for a typical period of three months. The present study evaluated the changes in pH, proteins, phenolics, carbohydrates, alcohols, and organic acids (oxalic, tartaric, malic, lactic, acetic, citric, and succinic) as well as amylase, protease, and lipase activities of different groups of jiaosu throughout one year of natural fermentation. Three jiaosu groups, each with different types of fruit peels, were prepared: orange-papaya-watermelon (OPW), grapefruit-mango-pineapple (GMP), and durian-jackfruit-passion fruit (DJP). A total of 18 jiaosu samples (days 0, 7, 14, 21, 28, 42, 56, 70, 84, 120, 150, 180, 210, 240, 270, 300, 330, and 360) were analyzed for each group. Using repeated measures multivariate analysis of variance (MANOVA) over the one-year fermentation period, the pH, the concentrations of proteins, phenolics, carbohydrates, alcohols, and lactic acid, and the amylase, protease, and lipase activities were significantly different (p < 0.05) between all three groups of jiaosu. Notably, GMP showed the highest total protein and phenolic concentrations and the lowest specific protease activity (p < 0.05) among the jiaosu groups. Meanwhile, DJP exhibited higher specific lipase activity and lactic acid concentration, but lower total alcohol concentration (p < 0.05) compared to OPW and GMP. The results indicated that the biochemical contents and enzyme activities of jiaosu were influenced by fermentation duration and the types of fruit peels used for the fermentation.