Antioxidant properties of peptide fractions from tuna dark muscle protein by-product hydrolysate produced by membrane fractionation process

• Tuna dark muscle by-products could be considered as source of bioactive compounds.
• Effect of membrane fractionation on antioxidant properties of peptides was underlined.
• Antioxidant activity was related to peptide molecular weight.
• Low MW peptides (< 1 kDa) were more effective radical scavenging than peptides > 1 kDa.
• Inhibition of linoleic acid autoxidation was related to content of hydrophobic AA.

Tuna dark muscle by-product was hydrolyzed using Alcalase and fractionated by ultrafiltration (UF) and nanofiltration (NF) membrane processes into three fractions. The antioxidant activities of tuna dark muscle by-product hydrolysate (TPH) and its peptide fractions were evaluated. The TPH showed the highest iron chelating activity (75%) compared to other peptide fraction hydrolysates. The NF permeate showed the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radical scavenging activities (75% and 65% respectively). The NF retentate (1–4 kDa) that contained antioxidant amino acids such as Tyr, Phe, Pro, Ala, His, and Leu, which accounted 30.3% of the total amino acids showed the highest superoxide radical and reducing power activities. The effect of the membrane fractionation on the molecular weight distribution of the peptide fractions and their bioactivities was underlined. In conclusion, the TPH and their peptide fractions may serve as useful ingredients in food industry for various applications and for the formulation of nutritional products.