Improvement of Antioxidant Activity of Defatted Selenium-Enriched Rice Bran by Lactic Acid Bacteria Fermentation

Selenium-enriched rice bran is a major by-product in the production of selenium-enriched polished rice, which is rich in selenium, dietary fiber, and active substances such as phenolic compounds. However, the high-value utilization of selenium-enriched rice bran has not been fully explored. In this study, four strains of lactic acid bacteria (Lactobacillus acidophilus, Streptococcus thermophilus, L. plantarum, and L. delbrueckii subsp.) were used to ferment defatted selenium-enriched rice bran. The physicochemical properties, nutritional characteristics, microstructure, physicochemical properties and antioxidant activity of selenium-enriched rice bran were compared before and after fermentation. The results showed that lactic acid bacteria fermentation increased the insoluble dietary fiber/water-soluble dietary fiber ratio in selenium-enriched rice bran by 20%–45%, the contents of total phenols and total flavonoids by 5%–6% and 16%–31%, respectively, and the conversion efficiency of inorganic selenium to SeCys₂ by 42%–49%. Moreover, the fermentation reduced the particle size of selenium-enriched rice bran, made the surface more loose and porous, and enhanced the hydration properties, cholesterol adsorption capacity and antioxidant activity. The decreasing order of the comprehensive scores of fermented selenium-enriched rice bran in principal component analysis (PCA) was L. plantarum > L. delbrueckii subsp. > S. thermophilus > L. acidophilus. Among these samples, the sample fermented with L. plantarum exhibited the strongest antioxidant activity in vitro, as well as the highest contents of total acid, SeCys₂, total phenols and total flavonoids. This study provides a theoretical basis for the intensive development and utilization of selenium-enriched rice bran.