Application of kombucha combined with fructo-oligosaccharides in soy milk: Colony composition, antioxidant capacity, and flavor relationship

Plant-based milk is considered a healthy and environmentally sustainable option. In order to solve the physical and chemical instability problem of most plant milk and increase the chance of consumer acceptance of the flavor, this experiment used soybean as raw material, fructo-oligosaccharides (FOS) as prebiotics, and added kombucha for fermentation. The microbial composition, functional components, antioxidant capacity, physico-chemical properties and flavor relationship of fermented soy milk at different fermentation times (up to 96 h) were studied by high-throughput sequencing, laser confocal scanning imaging, and gas chromatography-mass spectrometry. According to the results, the synbiotic interaction of FOS and kombucha consortium promoted the growth of yeast and lactic acid bacteria in soy milk. The ideal fermentation time was 84 h. At this time, fer-mented soy milk added with FOS displayed increased beta-glucosidase activity (by 68.10 mU/mL), isoflavones mainly represented by genistein content (by 612.41%), and DPPH radical scavenging activity (by 25.02%). Furthermore, the addition of FOS intensified the sour taste of the 84 h-fermented soy milk. The content of hexanal was reduced, while favorable flavor substances, such as citric acid and linalool, were also produced. Soymilk fermented with kombucha and FOS provides an opportunity to explore the physical and chemical characteristics and the mechanism of flavor formation in multi-strain co-fermentation systems and to develop commercial plant-based fermentation products.