Effects of rice protein hydrolysates prepared by microbial proteases and ultrafiltration on free radicals and meat lipid oxidation

This study was to evaluate whether rice protein hydrolysates with strong antioxidant activity can be used to prevent lipid oxidation and improve shelf-life of meat products. Rice proteins were hydrolysed by three microbial proteases and further separated by sequential ultrafiltration to 12 hydrolysate fractions. The resulting hydrolysates were first evaluated for free radical scavenging capacity. The oxygen radical absorbance capacity (ORAC) of the fractions varied significantly ranging between 34.2 and 87.3 μmol Trolox equivalents (TE)/g dry weight with two small peptide fractions: Val-F3 produced by Validase from Aspergillus oryzae and AP-F3 produced by alkaline protease from Bacillus licheniformis possessing the highest values. The hydrolysate fractions at 100 mg/mL scavenged 31.2–49.7% of 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH•). The hydrolysates also exerted remarkable cation radical 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS+•) scavenging activity (10.8 and 28.3 μmol TE/g dry weight). Val-F3 and AP-F3 were incorporated into ground beef to determine their effect on lipid oxidation during a 15-day storage period. Val-F3 treatment at 500 μg/g inhibited lipid oxidation by 19% and 15% at storage day 8 and 15, suggesting that rice protein hydrolysates could be further developed and used to improve shelf-life of meat products.