Impact of a novel probiotic Lactobacillus strain isolated from the bee gut on GABA content, antioxidant activity, and potential cytotoxic activity against HT-29 cell line of rice bran

Rice bran was fermented with Lactobacillus apis, isolated from the bee gut as a novel probiotic strain, and Saccharomyces cerevisiae to investigate the relationship between its metabolites and antioxidant activity, nutraceutical value, and cytotoxic activity against the HT-29 cell line. The findings showed that L. apis improved the antioxidant activity (DPPH of 37.73%) and antioxidant capacity (ABTS of 37.62 mg Trolox/g,), as well as, hydroxyl radical-scavenging activity (91.55%) of rice bran compared to S. cerevisiae. The metabolic analysis of volatile compounds revealed an increase of alcohols and lactones in the samples fermented with S. cerevisiae. While the samples fermented with L. apis displayed an increase of ketones, esters, and thiazoles. On the other hand, L. apis and S. cerevisiae exhibited a significant ability to increase γ-aminobutyric acid during different fermentation times. Compared with non-fermented samples (18.54%), L. apis increased the cytotoxic activity of rice bran against the HT-29 cell line to 34.17%, and S. cerevisiae to 31.34%. These results suggest that the fermentation of rice bran with S. cerevisiae and L. apis provides a promising strategy to improve the antioxidant activity and nutraceuticals of rice bran, and a potential source for plant-based pharmaceutical products.