Antioxidant properties of Salmon (Salmo salar) protein hydrolysate and peptide fractions isolated by reverse-phase HPLC

- Salmon peptides were separated by HPLC into fractions that differ in hydrophobicity.
- HPLC fractionation improved the free radical scavenging properties of Salmon peptides.
- DPPH radical scavenging was directly related to content of hydrophobic amino acids.
- Iron chelation was directly related to content of glutamic acid and histidine.
- Inhibition of linoleic acid oxidation was dose-dependent only for SF1 and SF4 fractions.

Deboned salmon flesh proteins were digested with three proteases (pepsin, trypsin and chymotrypsin) and the digest passed through a < 1 kDa equipped tangential flow filtration system; the permeate was collected as the salmon protein hydrolysate (SPH). SPH was separated by reverse-phase HPLC into four peptide fractions (SF1-SF4) and their in vitro antioxidant properties investigated using different assays. The results showed that most of the peptide fractions (SF2-SF4) displayed significantly higher (p < 0.05) oxygen radical absorbing capacity values (1315-1541 μM TE/g) than the SPH (819.3 μM TE/g). Most of the peptide fractions also significantly (p < 0.05) scavenged 2,2-diphenyl-1-picrylhydrazyl and superoxide free radicals when compared to the non-fractionated SPH. However, metal chelating activity of the SPH was significantly higher (p < 0.05) than that of the peptide fractions. Overall, the free radical scavenging capacity of the peptides increased with hydrophobicity, except for hydroxyl radicals. Glutathione exhibited superior antioxidant abilities in most assays except for chelating and reducing of metal ions, where SPH and its purified fractions showed better activities. SPH and the peptide fractions strongly inhibited linoleic acid oxidation in the following order SPH = SF2 = SF3 > SF1 > SF4, especially at 0.1 and 0.5 mg/mL peptide concentrations. Therefore, salmon peptides may serve as useful ingredients to improve shelf life of lipid-containing foods and also for the formulation of nutritional products aimed at oxidative stress reduction.