Optimized Protamex Digested Oat Bran Proteins: Antioxidant Properties and Identification of New Peptides

The aim of this study was to determine the radical scavenging properties and spectroscopic characteristics of hydrolysates produced from oat bran proteins digested for 1-4h and 1:10 to 1:40 enzyme (Protamex)/substrate (E/S) ratios. Four complementary bioassays were used to determine the activity of the twelve hydrolyzed proteins. The oxygen radical absorbance capacity assay showed that digestion for 3h produced hydrolysates with higher peroxyl radical scavenging activities (521-695 μM TE/g) while digestion for 2h with either 1:20 or 1:30 E/S ratio resulted in greater inhibition of superoxide radical anions 57.4±5.1% and 57.7±1.6%, respectively. The hydroxyl radical scavenging activity of all hydrolysates decreased overtime while there was little time dependent change in ferrous ion chelating activity.Overall, hydrolysis with 1:30 E/S for 2 or 3h produced hydrolysates with greater antioxidant capacity due to their relative higher content of hydrophobic (Leu+Ile+Val) and aromatic (Tyr+Phe) amino acids as indicated by 1H-NMR data. The sequence of nine novel peptides was determined by LC-MS/MS in these two most active samples.