Extrusion and fungal fermentation change the profile and antioxidant activity of free and bound phenolics in rice bran together with the phenolic bioaccessibility

The effects of extrusion and fermentation on the free and bound phenolic distribution in grains and related products remain controversial. The phenolic bioaccessibility have not been comprehensively studied. Therefore, the effects of extrusion and fermentation on phenolic profiles and bioaccessibility, together with the antioxidant activity in defatted rice bran (DRB) were investigated in this study. Our results revealed extrusion and fermentation not only facilitate the release of phenolics, improve the extractability of bound phenolics in DRB. The free, bound and total phenolic content increased by 23.0%, 50.7% and 36.3% after extrusion, and by 99.4%, 40% and 71.6% after fermentation, respectively. Extrusion and fermentation changed the content and distribution of 8 detected phenolic compounds but not composition in DRB. Fermentation enhanced ORAC and CAA antioxidant activity with 1.8 and 4.1 folds increases, respectively, while extrusion had no effect on CAA. Bioaccessibile phenolics increased by 40.5 and 64.4% in extruded and fermented DRB after in vitro digestion compared with raw DRB, respectively. Scanning electron microscope analysis showed extrusion and fermentation changed the compact microstructure of DRB to loose and porous structure. Our research indicates fermented and extruded DRB (especially the former) represent potentially promising materials for developing health foods and nutraceuticals.