Fermentation of soymilk by strains with high conversion ability to soy isoflavones: Strain screening, flavor characteristics, antioxidant properties, and in vitro digestion

Soy isoflavones are an important nutrient component in fermented soymilk. However, soy isoflavones in soymilk mostly exist as bound glycosides, which are not conducive to human absorption. Converting bound glycosides into free aglycones is beneficial for human absorption and has high biological activity. This study found through strain screening and response surface optimization that the content of soy isoflavone aglycones in fermented soymilk by Lacticaseibacillus paracasei JM053 can reach up to 78.62 ± 0.18 μg/mL. Compared with the content of isoflavone aglycone in unfermented soymilk (8.56 ± 0.15 μg/mL), it increased by 8.18 ± 0.16 times. After fermentation by Lacticaseibacillus paracasei JM053, the relative abundance of volatile flavor compounds such as 2-butanone, 2,3-pentanedione, acetoin, and butyl lactate in soymilk significantly increased, which can bring unique flavors to fermented soymilk. Fermented soymilk extract from Lacticaseibacillus paracasei JM053 can increase the activity of SOD and CAT antioxidant enzymes and has a protective effect on 2,2-Azobis (2-methylpropylimidazole) Dihydrochloride (AAPH) oxidative damage to HepG2 liver cancer cells. In addition, the fermentation of soymilk by Lacticaseibacillus paracasei JM053 can improve the bioavailability of soy isoflavones and promote the release of soluble proteins and small peptides with molecular weights below 10 kDa during simulated in vitro gastrointestinal digestion. Provide the experimental basis for the production of soymilk with flavor quality and functional activity.