Antioxidant peptides from goat milk protein fractions hydrolysed by two commercial proteases

Goats' milk microfiltration fractions were hydrolysed with subtilisin or trypsin, or both, and tested for 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging capacity, iron chelation capacity, and inhibition of secondary oxidation products formation in liposomes. The retentate treated with subtilisin was most active regarding radical scavenging capacity (SC50 ≈ 4 μg mL−1), while the permeate treated with subtilisin exhibited the best iron chelation capacity (IC50 ≈ 65 μg mL−1) and prevention of secondary lipid oxidation products formation (33% inhibition at 25 μg mL−1). In the retentate hydrolysate various active peptides were identified. Tyrosine seemed fundamental in the ABTS radical scavenging capacity of the peptides, and also to play a role in the inhibition of formation of secondary lipid oxidation products, in which phenylalanine seemed to play the key role. Non-protein compounds in the permeate hydrolysate seemed more important than peptides for the antioxidant activities detected.