Antioxidant activities of rice bran protein hydrolysates in bulk oil and oil-in-water emulsion

BACKGROUND: Recently, utilization of natural antioxidants in food processing has been of growing interest, owing to the concerns of health hazards of synthetic agents. Protein hydrolysates are a potent candidate for this purpose. In this work, rice bran protein hydrolysates (RBPH) with various degrees of hydrolysis (DH) were prepared, and their antioxidant activities in soybean oil and oil-in-water (O/W) emulsion were examined. RESULTS: With increasing DH, RBPH showed increasing antioxidant activities, as evidenced by the increases in DPPH radical scavenging activity, reducing power and ferrous chelating activity (P<0.05). The improved activity was associated with increasing surface hydrophobicity (SoANS). After hydrolysis for 60min, the content of hydrophobic amino acids was increased. When RBPH with various DH were incorporated into bulk soybean oil and O/W emulsion stored at 37°C for up to 15 days, lipid oxidation was successfully retarded, especially when DH increased. The efficiency in prevention of oxidation was dose dependent (0-10gL^-1), as indicated by the lower peroxide value and thiobarbituric reactive substances. CONCLUSION: The present work suggests that RBPH might be potently employed as a natural antioxidant in both bulk oil and emulsion models.