Purification and characterization of antioxidative and antimicrobial peptides from lactic-fermented sheep milk

This study aims to identify antioxidant and antimicrobial peptides from sheep milk produced using Lactobacillus plantarum (KGL3A). It was inferred that antioxidative and antimicrobial activities increased with increasing incubation time, and antioxidative properties (ABTS assay, superoxide free radical & hydroxyl free radical scavenging activity were 34.5, 34.7, and 29.2% respectively) and antimicrobial properties against Escherichia coli, S. typhimurium , E. faecalis , & B. cereus were 11.3, 12.7, 13.3, & 12.3 mm. However, inoculation of culture at a level of 2.5% and 48 h fermentation give the highest proteolysis activities. Fermented sheep milk fractions of 3 & 10 kDa were analysed for antioxidative and antimicrobial activity, and the 10 kDa permeate showed the highest ABTS assay. The hydroxyl free radical scavenging activity was greatest in 10 kDa retentate and superoxide free radical scavenging activity was observed in 3 kDa permeate (34.7, 43.4, and 34.6%, respectively). Antimicrobial activity of 10 kDa retentate against B. cereus & E. coli (13.3 mm) was greater than 3 and 10 kDa retentate against S. typhimurium (13 mm) and 3 kDa retentate against E. faecalis (13.7 mm). The molecular weight of the protein was estimated using SDS-PAGE. On electrophoresis on a 2-D gel, 6 peptides were identified using RP-LC/MS. BIOPEP, a database for antioxidative and antimicrobial peptides, validated the antioxidative & antimicrobial activities of several peptides in sheep's milk that has been fermented. Sheep milk fermented using Lactobacillus could be considered a novel source of antioxidative and antimicrobial proteins.