Identification of peptide molecular weight from rice bran protein hydrolysate with high antioxidant activity

• Protease type influenced protein extraction ability and antioxidant activity of RBPH.
• Alcalase potentially produced RBPH with the highest protein yield.
• The optimal condition to produce RBPH was hydrolysis by Alcalase for 2 h.
• Molecular weight of fractionated hydrolysate with high antioxidant activity was 6 kDa.

The effects of the enzyme type (Alcalase, Flavourzyme and Neutrase) and hydrolysis time (2, 4 and 6 h) on properties of rice bran protein hydrolysate (RBPH) were studied. The enzyme type had significant effects on the protein yield and the properties of RBPH whereas the hydrolysis time was less influence. There were small differences in the total phenolic content and the ABTS radical scavenging activity between protease-hydrolyzed and unhydrolyzed rice bran protein, but enzymatic hydrolysis using Alcalase was the most effective providing hydrolysate with the highest protein yield and protein content. The optimal hydrolysis conditions was 2 h using an Alcalase-yielding protein content of 30.3%, a protein yield of 56.6%, TPC of 22.1 mg GAE/g, ABTS of 7.57 mg GAE/g and FRAP of 152 mM Fe2+/g. Fractionated peptides from this hydrolysate using anion exchange chromatography showed high antioxidant activity containing both positive and negative charge fractions with a low MW of 6 kDa. The RBPH using Alcalase could be a protein source and antioxidant in functional foods and beverages.