Influence of the degree of hydrolysis (DH) on antioxidant properties and radical-scavenging activities of peanut peptides prepared from fermented peanut meal

To study the influence of degree of hydrolysis (DH) on antioxidant properties of peanut peptides, the peanut meal was fermented by Bacillus subtilis. The fermentation time was 48, 72, and 96 h, respectively, to prepare peanut peptides at different degree of hydrolysis. The peanut peptides (11.18, 16.20, and 21.41% of DH, respectively) were extracted from fermentation liquid. The antioxidant properties of these peanut peptides were evaluated based on DPPH^· radical (1,1-Diphenyl-2-picrylhydrazyl radical) scavenging activity, superoxide anion-scavenging activity, reducing power, metal-chelating activity, and inhibition of linoleic acid autooxidation. Peanut peptides (21.41% of DH) at 1 mg/mL exhibited 80.86 and 29.35% of scavenging concentration percent on DPPH^· and superoxide anion radical, respectively. In addition, the reducing power of peanut peptides was 0.368 at 2 mg/mL, and they possessed 76.32% of Fe²⁺-chelation ability at 2 mg/mL and 63.75% of inhibition of linoleic acid autooxidation at 0.8 mg/mL. The antioxidant activities of the peanut peptides (21.41% of DH) were stronger compared with others (11.18 and 16.20% of DH), and this indicated the antioxidant activities of peanut peptides increased with increasing DH (p < 0.05). To know much about the peanut peptides, they were subjected to amino acid analysis and determination of molecular weight distribution. Some acidic amino acids and essential amino acids were found, and the average molecular weight distributions were concentrated in <1,400 Da (86.96%). Combined with the results of the amino acid profiles, the peanut peptides were believed to have high nutritive value besides antioxidant activities.