Abstract: In order to clarify the effect of inoculated fermentation on the bioaccessibility of phenolic compounds and antioxidant activity in grape jiaosu (fermented grape juice), the changes in fermentation properties, phenolic composition and antioxidant activity during fermentation were studied, and the bioaccessibility of polyphenols was also evaluated by in vitro simulated gastrointestinal digestion. The results showed that the reducing sugar content decreased from 31.91 to 0.46 g/L and the pH decreased from 3.77 to 3.19 during fermentation. The ethanol content increased to 7.66% (V/V) on the sixth day, and then decreased to 0.47% on the 27th day. The release of phenolic compounds was promoted by inoculated fermentation. The contents of total phenols and flavonoids presented a fluctuant increasing trend during the fermentation process, and were increased by 2.16 and 1.83 folds at the end of fermentation. Compared with must, the contents of gallic acid, vanillic acid and myricetin were increased by 7.17, 5.18 folds and 60.29%, respectively. After in vitro gastrointestinal digestion, five phenolic acid showed higher bioaccessibility in the range from 39.11% to 57.77%. Among the tested flavonoids, myricetin and quercetin showed higher bioaccessibility of 35.78% and 42.34%, respectively. The antioxidant activity of grape jiaosu showed an overall increasing trend with fermentation time. Compared with must, the scavenging capacities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical increased by 51.45% and 82.23%, respectively at the end of fermentation. In conclusion, inoculated fermentation can increase the concentrations of specific phenolic compounds, improve the bioaccessibility of some polyphenols, and enhance the antioxidant activity of grape jiaosu. These results indicate that inoculated fermentation can be used as an effective way to prepare grape jiaosu, which can improve the nutrition and function of grape jiaosu and provide a basis for the development of other functional jiaosu products.

Key words: grape jiaosu; in vitro simulated digestion; polyphenol; bioaccessibility; antioxidant activity