Nutritional and flavor properties of grape juice as affected by fermentation with lactic acid bacteria

Two lactic acid bacteria (LAB) strains of Lactobacillus plantarum 21802 and Lactobacillus brevis 6239 were selected and combined for fermentation of grape juice. The changes of sugars, organic acids, volatiles, phenolic compounds as well as antioxidant capacity of the grape juice were characterized. Results showed that fermentation with LAB led to a slight decrease in sugar content and increased in organic acid content. The sugars were mainly consumed at the initial stage of fermentation, while the malic acid was consumed completely during the fermentation. The contents of total phenolics and flavonoids in grape juice decreased gradually during the fermentation process. As compared with the initial contents in unfermented grape juice, the contents of proanthocyanin B2, rutin, isoquercitrin, rhamnose-3-O-glucoside in the final fermented grape juice were increased by 26.83%, 249.24%, 138.48%, 139.60%, respectively, while the contents of gallic acid, proanthocyanin B1, catechin and epicatechin were decreased by 24.49%, 14.85%, 71.68%, 42.52%, respectively. The mice fed with the fermented grape juice showed higher activity of superoxide dismutase and lower level of malondialdehyde both in serum and liver tissue than those fed with the unfermented grape juice. Fermentation with LAB also enhanced the flavor profile by increasing the total number and content of volatile compounds, especially those of monoterpene alcohols, which are the main and characteristic aroma volatile compounds in Muscat aroma grapes. This research confirmed that fermentation with LAB might be a desirable option for improving the flavor and nutritional attributes of grape juice by altering the ratio of sugar to organic acid, improving the phenolic compounds, enhancing the antioxidant capacity, intensifying of the characteristic aroma and pleasant flavor of the grape juice.