Sustainability-oriented recovery of antioxidant and ACE-inhibitory low-molecular-weight peptide fractions from Thunnus albacares by-products via enzymatic hydrolysis and membrane ultrafiltration.

INTRODUCTION: Tuna by-products are an important and yet underutilized source of bioactive molecules, pointing out the need for innovative blue- and circular-economy-based approaches for their valorization. Fish protein hydrolysate, obtained through enzymatic hydrolysis, are a valuable source of biologically active peptides. Low-molecular-weight (low-MW) peptides derived from fish-byproducts, in addition to their nutritional value, exhibit remarkable health-promoting effects and have a broad potential for industrial applications, including nutraceutical, pharmaceutical, and cosmeceutical. METHODS: In the present study we optimized a valuable strategy that combines enzymatic hydrolysis of tuna mixed by-products including heads, bones, skin, connective tissues, viscera and dark muscle, using Alcalase and Savinase, with ultrafiltration through membranes with molecular weight cut-offs of 10, 5, and 3 kDa. The antioxidant and antihypertensive activities of the resulting peptide fractions were evaluated. The amino acid composition of the most biologically active fractions was subsequently analyzed, and their cytotoxicity was assessed using three in vitro cell lines. RESULTS: Our data identified the low-MW peptide fractions as those with the most prominent antioxidant capacity (AOC) and angiotensin-converting enzyme inhibitory (ACEi) activity, without any observed cytotoxic effect in vitro. Notably, the low-MW peptide fraction obtained from Alcalase digestion exhibited the highest bioactive potential (in terms of AOC and ACEi activity at the lowest tested concentration of 12.5 μg/mL) while Savinase-derived low-MW peptide fraction showed greater nutritional value due to its higher content of EAAs. Noteworthy, to the best of our knowledge, this study is among the few to report AOC activity in Savinase-digested tuna by-products. DISCUSSION: Our results demonstrate that enzymatic hydrolysis combined with membrane ultrafiltration is an effective and sustainability-oriented strategy for recovering bioactive peptide fractions from tuna by-products.