Antioxidant activity and functional properties of peptides derived from egg white proteins by two-step enzymatic hydrolysis

Abstract

The objective of this study was to investigate the effect of ultrasound pretreatment on two-step enzymatic hydrolysis of egg white proteins (EWPs) using commercial food-grade proteases as well as evaluating some functional properties of obtained hydrolysates. Three commercially available proteases used in this work were: alcalase from Bacillus licheniformis, neutrase from Bacillus amyloliquefaciens and flavourzyme from Aspergillus oryzae. Thus obtained hydrolysates were further separated by sequential ultrafiltration into three peptide fraction viz. Fraction I (< 1kDa), II (1 - 10 kDa), III (10 - 30 kDa) which were investigated in terms of their antioxidant activity. The antioxidant activity of hydrolysates and peptide fractions were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. Comparing the hydrolytic curves of two-step enzymatic process, the highest equilibrium degree of hydrolysis (DH) was achieved by a combination of alcalase and neutrase. The order of addition of these two proteolytic enzymes didn't lead to significant differences in the initial rate of reaction, but significantly affected the equilibrium DH (32.25 ± 2.08%). The two-step hydrolysis, in which flavourzyme is followed by alcalase, seemed to perform with the same initial rate, but DH was considerably lower (28.23 ± 0.91%). Two-step enzymatic hydrolysis appeared to increase solubility and substantially improved the foam stability while the foam capacity didn't change significantly vs. control. The high yield of peptides soluble at pH 6 and pH 8 were obtained by combination of alcalase and flavourzyme while more voluminous foams were obtained with alcalase and neutrase. The most abundant fraction in terms of antioxidant activity was the Fraction II, which indicates that the combination of alcalase and flavourzyme was efficient at reducing the pretreated into low molecular weight peptides. This study showed that by combining ultrasound pretreatment under controlled conditions with careful proteases selection, hydrolysates with improved functional and antioxidant properties can be produced enhancing utilization of egg white in food products.