Extraction and Processing Strategies Enhance the Structural Characteristics and Bioactivities of Soybean-Derived Kefir Polysaccharides

Kefir is a probiotic beverage produced by symbiotic bacteria and yeasts. Polysaccharides from yellow and black soybeans (S, B) were extracted, fermented to obtain S-F and B-F, and further oxidatively degraded using ascorbic acid and hydrogen peroxide to produce S-FD and B-FD. Compositional analyses revealed distinct differences in sugar content, protein, phenolics, monosaccharide composition, molecular weight, and Fourier transform infrared spectra among S-F, S-FD, B-F, and B-FD. Fermentation enhanced angiotensin converting enzyme inhibitory activity, and subsequent degradation further improved this effect. Both fermented and degraded polysaccharides exhibited strong antioxidant activities, including radical scavenging capacity, ferrous ion chelation, and reducing power, with degraded samples showing superior performance. Neuroprotective effects were evaluated using SH-SY5Y cells. No cytotoxicity was observed at concentrations up to 400 μg/mL. Treatment at 200 μg/mL significantly increased cell viability and reduced apoptosis in rotenone-induced cells. However, multivariate analysis indicated that oxidative degradation, while enhancing antioxidant and ACE inhibitory activities, may attenuate neuroprotective effects. Overall, soybean derived kefir polysaccharides show potential for applications in blood pressure regulation, antioxidant defense, and neuroprotection.