Antioxidant Properties of Peptides from Soybean Meal Protein Hydrolysates Evaluated by Electron Spin Resonance Spectrometry

Peptides from soybean meal were subjected to extrusion and the effects of extrusion conditions, such as moisture of the materials, barrel temperature, screw speed and nozzle diameter, on the antioxidant properties were studied. The extrusion conditions that had the highest free radical-scavenging activity were further separated into three peptide fractions (using ultra filtration); hydrolysis of isolation of soybean meal protein (ISMP)-I (>3 kDa), ISMP-II (3 kDa 1 kDa) and ISMP-III (<1 kDa). The barrel temperature has the most influence on the antioxidant properties of the peptide, with a radical-scavenging activity (RSA) of 91.7%. Under the same extrusion conditions (moisture 10%; barrel temperature 105°C; screw speed, 100 r/min; and nozzle diameter, 18 mm), ISMP-III had the highest scavenging effects on hydroxyl radicals with an RSA of 99%. The antioxidant properties of the peptide from soybean meal protein hydrolysates could be enhanced by ultra-filtration.