Evaluation of the in vitro antioxidant properties of a cod (Gadus morhua) protein hydrolysate and peptide fractions

Mechanically-deboned cod muscle proteins were sequentially hydrolysed using pepsin and a trypsin + chymotrypsin combination, which was followed by passing the digest through a 1 kDa equipped tangential flow filtration system; the permeate (<1 kDa peptides) was collected as the cod protein hydrolysate (CPH). Reversed-phase high performance liquid chromatography (RP-HPLC) was used to separate the CPH into four peptide fractions (CF1–CF4) and their in vitro antioxidant properties investigated. Results showed that most of the peptide fractions (CF2–CF4) displayed significantly higher (p < 0.05) oxygen radical absorbance capacity values (698–942 μM Trolox equivalents, TE/g) and 2,2-diphenyl-1-picrylhydrazyl scavenging activities (17–32%) than those of CPH (613 μM TE/g and 19%, respectively). However, the unfractionated CPH displayed improved capability to scavenge superoxide and hydroxyl radicals as well as significantly higher (p < 0.05) ferric iron reduction and chelation of iron than the RP-HPLC peptides. The CPH and peptide fractions displayed a dose-dependent inhibition of linoleic acid oxidation.