Antioxidant Activity of Rice Bran Protein Extract, its Enzymatic Hydrolysates and its Combination with Commercial Antioxidants

Abstract: Rice bran protein extracted from defatted Khao Dawk Mali (KDML 105) rice bran using alkali extraction and isoelectric precipitation (RBPE) was prepared. RBPE was hydrolyzed with Alcalase 2.4 L and antioxidant activity of the hydrolysates were determined by 2,2-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and Ferric Reducing Ability Power (FRAP) assay at hydrolysis time of 0, 30, 60, 90 and 120 min. The DPPH free radicals scavenging activity and FRAP value of the alcalase RBPE hydrolysates were 32.1-35.5 % and 951-1,018 µmol FeSO4/mL of hydrolysate, respectively and were not significantly different (p>0.05) at different hydrolysis times. RBPE was freeze-dried (FD-RBPE) and it was found that freeze-drying did not affect antioxidant activity of RBPE. DPPH radical scavenging activity and FRAP of the FD-RBPE was 41.9 % and 92.6 µmol FeSO4/g protein, respectively. FD-RBPE was combined with butyrate hydroxyanisole (BHA) and their antioxidant activities were evaluated. It showed that FD-RBPE did not affect antioxidant activity of BHA. Based on DPPH radical-scavenging activity, 106 µg protein of FD-RBPE can replace 1 µg of BHA. It suggested that FD-RBPE can replace BHA or be combined with BHA as antioxidant in food products. Key words: Antioxidant activity, rice bran protein extract, combination effec