Antioxidant activity of food proteins and food protein hydrolysates

The objective of this research was to study the antioxidant activity of soybean protein hydrolysates (SPH) and chickpea protein hydrolysates (CPH) at different concentrations, and to measure the antioxidant activity of fractions collected from the RP-HPLC analysis of SPH and CPH. Protein hydrolysates were prepared by the proteolytic enzyme trypsin. The hydrolysates obtained were subjected to DPPH (1, 1-diphenyl-2 picrylhydrazyl) radical scavenging assay. The SPH and CPH at concentration of 2.5-10 mg/ml showed antioxidant activity of 16.5-32 % and 3.4-26.8 %. SPH and CPH were fractionated by using RP-HPLC on C18 column. The antioxidant activity of four SPH and CPH fractions (F I, F II, F III, and F IV) was measured by using DPPH radical scavenging assay. For SPH, antioxidant activity of F III (47.7 %) was higher than other fractions at protein concentration of 1 mg/mL and for CPH; F II showed maximum antioxidant activity 27.9 % at protein concentration 1 mg/mL. The results from the SDS-PAGE confirmed the hydrolysis of protein samples.;The second part of the study was to measure the impact of high pressure processing (HPP) on the degree of hydrolysis and antioxidant activity of proteins. High pressure processing (HPP) of isolated soybean protein (ISP) and isolated chickpea protein (ICP) was done at 400 MPa and 600 MPa for 5 min and 10 min. The degree of hydrolysis of isolated soybean protein and isolated chickpea protein treated with high pressure processing and with trypsin hydrolysis showed continuous increase from 12.4 to 24.9 % for SPH and 13.6 to 26.2 % for CPH. The DPPH radical scavenging assay showed a more than two fold increase in antioxidant activity of SPH and CPH: 67 % as compared to the 32 % of SPH without HPP and 56.6 % as compared to the 26.8 % of CPH without HPP at concentration 10 mg/mL. These results show that HPP increased the degree of hydrolysis and antioxidant activity of protein hydrolysates.