Antioxidant potential of peptide fractions from tuna dark muscle protein isolate: A green enzymatic approach

Abstract Tuna dark muscle protein isolate (TDMPI) derived from yellowfin tuna ( Thunnus albacares ) represents a sustainable by-product for bioactive peptide production. In this study, TDMPI was hydrolysed using alcalase, an eco-friendly enzymatic approach, to generate antioxidant-rich hydrolysates. These hydrolysates contained a diverse profile of hydrophobic and negatively charged amino acids, which contributed to their antioxidant properties. Ultrafiltration was employed to fractionate the hydrolysates into three peptide fractions, which were tested for 2,2-diphenyl-1-picrylhydrazyl free radical scavenging (DPPH-RSA), lipid peroxidation inhibition (LPIA), and total reducing power (TRPA). Results showed that peptides <10 kDa exhibited higher antioxidant activity than the unfractionated hydrolysates, with peptides <3 kDa exhibiting the highest DPPH-RSA and TRPA. However, LPIA was higher in peptides >10 kDa. Hydrolysis time significantly affected antioxidant activity: DPPH-RSA increased up to 9 h, while LPIA peaked at 6 h and TRPA at 3 h before declining. This study demonstrated that TDMPI hydrolysates and their peptide fractions exhibited significant antioxidant activities, making them promising natural alternatives to synthetic preservatives. Their utilisation potentially supports functional food applications and aligns with green processing strategies for valorising fishery by-products.