Isolation of an endophytic yeast for improving the antibacterial activity of water chestnut Jiaosu: Focus on variation of microbial communities

Recent years have seen an increase in the development of functional Jiaosu products, including eco-friendly Jiaosu and antimicrobial healthcare fermentation products. As a result, research on the antibacterial activity of Jiaosu has attracted attention. In the present study, the endophytic yeast WCF016, which exhibits antibacterial activity against Escherichia coli and Staphylococcus aureus, was isolated from the peel of water chestnut and identified as Candida sake via morphological and phylogenetic analyses based on 26S rDNA D1/D2 region sequencing. Water chestnut Jiaosu with or without WCF016 inoculation exhibited similar flavor and physicochemical properties. However, inoculation significantly enhanced the antibacterial activity of water chestnut Jiaosu, especially in group D (inoculate of both fruit and vegetable enzyme starter and WCF016), which showed the largest diameter in its inhibition zone for both E. coli and S. aureus, reaching 25 ± 0 mm and 24 ± 1.0 mm. Moreover, inoculation with WCF016 influenced the abundance of the microbial community, especially Lactiplantibacillus and Zygoascus, which reached 51.76 % and 24.46 %, respectively, in group B (inoculated WCF016), thereby improving the antibacterial activity and flavor quality of the water chestnut Jiaosu. Notably, final pH, total sugar, and all organic acids effectively promoted fungal diversity and exhibited a positive correlation with most of the fungal genera. These results indicate that conditions conducive to the formation of organic acid-producing microbes and the synthesis of organic acids promote the antibacterial activity of Jiaosu.