Neuroprotection of fermented small black soybean (Rhynchosia nulubilis) on hippocampal neurons through antioxidant effect.

Rhynchosia nulubilis (RN), a small black soybean, is traditionally used in Korean oriental medicine. In this study, RN was fermented using a novel lactic acid bacterium, Pediococcus pentosaceus AOA2016 (AOA2016), which enhanced its antioxidant properties. Fermentation significantly increased total phenolic acid and procyanidin levels. Among phenolic acids, protocatechuic acid (PCA) increased the most (11.83 mg/100 g), while gentisic acid (GA) was newly produced (1.23 mg/100 g). Fermented RN extract, along with PCA and GA, significantly improved the viability of HT22 hippocampal neuronal cells and reduced intracellular reactive oxygen species (ROS), indicating protection against glutamate-induced oxidative stress. Co-treatment with PCA and GA, at proportions reflecting their levels in fermented RN, further enhanced neuronal protection. These findings suggest that RN extract fermented by AOA2016 has potential as a functional food ingredient. The enhanced antioxidative and neuroprotective effects of fermented RN highlight its potential in preventing neuronal damage and oxidative stress-related neurodegenerative conditions.