Preparation, isolation and identification of novel antioxidant peptides from extruded-expanded tuna bone meal

Tuna bone, a by-product of fish processing, is rich in protein but often underutilized. This study aimed to enhance its bioavailability by preparing nanoscale tuna bone meal through extruded-expanded technology and subsequently hydrolyzing it with proteases to produce antioxidant peptides. The extruded-expanded tuna bone meal (EE-FB) exhibited a significantly reduced average particle size (296.45 nm) compared to non-extruded-expanded samples (982.85 nm). This indicates that extruded-expanded treatment has a significant effect on the particle size change of tuna bone meal, which helps to ensure sufficient contact between tuna bone meal and protease during the enzymatic hydrolysis and improve the enzymatic hydrolysis rate. Optimal enzymatic hydrolysis conditions were determined using response surface methodology: dual-enzyme (trypsin and alcalase) dosage of 4600 U·g -1 , solid-liquid ratio of 1:6.90 (w/v), and hydrolysis time of 4.10 hours, achieving a degree of hydrolysis (DH) of 45.06%. The hydrolysate was fractionated by ultrafiltration, further purified by Sephadex G-15 gel chromatography, and identified six novel peptides: VQQPL, VTDLN, AGPQGP, APDPFR, GDRAFLI, and SGPAGPA by LC-ESI-MS/MS. Six novel peptides have shown the ability to scavenge free radicals (DPPH, superoxide, hydroxyl). The molecular weight of the six new peptides was < 1000 Da and they exhibited antioxidant activity. This may be attributed to the hydrophobic and alkaline amino acids contained in the peptide. This study provides a rapid and efficient method for producing bioactive peptides from tuna bone, with potential applications in functional food and pharmaceutical production. • Extruded-expanded treatment (EET) significantly improved the porosity of tuna bone. • EET increased the accessibility of protease and utilization of tuna bone. • Obtain small molecule peptides under optimal dual enzyme hydrolysis conditions. • Tuna bone-derived antioxidant peptides have excellent biological activity.