Rice bran is generally used as animal feed despite containing numerous nutritional compounds. Small peptides possessing high antioxidant activity can be obtained from rice bran protein via enzymatic hydrolysis. Immune-modulating and antioxidative activity of rice bran protein hydrolysates from crude rice bran protein and its fractions were studied. Albumin, globulin, glutelin, and prolamin proteins were fractionated based on solubility differences and hydrolyzed with two types of enzyme, namely pepsin and protease M. Albumin fraction showed a high degree of hydrolysis in both enzymes. Protease M differently digested rice bran protein fractions, in which it showed low digestion in glutelin and prolamin fractions. After 30 min of hydrolysis time, the reaction slowed down, and antioxidant activity remained constant in pepsin hydrolysis. Due to the high presence of lipopolysaccharide (LPS) in protease M digested fractions (caused by the enzyme), it could not be used to determine immune-modulating activity. THP-1 macrophages were simultaneously stimulated with 100 ng/mL LPS and rice bran protein hydrolysates from 4 h of pepsin digestion. Reduction of pro-inflammatory cytokine IL-1β and increase of anti-inflammatory cytokine IL-10 were observed from crude rice bran protein and albumin. In conclusion, pepsin-digested rice bran protein could be potentially used as antioxidative and anti-inflammatory agent.
Keywords: THP-1 macrophages; antioxidative activity; immune modulation; protein fractionation; protein hydrolysate.