Circular Valorization of Yellowfin Tuna (Thunnus albacares) Bone By-Products into Bioactive Hydrolysates Using Endogenous Visceral Proteases Compared with Commercial Trypsin

Yellowfin tuna (Thunnus albacares) processing by-products are underutilized resources rich in high-quality proteins that can be valorized into bioactive ingredients. In this study, proteins from yellowfin tuna tail bones were hydrolyzed using either an endogenous protease extract recovered from tuna viscera or commercial trypsin. The endogenous extract was characterized and exhibited optimal proteolytic activity at pH 8 and 40 °C. Comparative bioactivity assessment showed that trypsin-derived hydrolysates exhibited significantly higher antioxidant capacity, with ABTS and DPPH values of 11.8 ± 0.04 and 13.3 ± 0.40 mg Trolox/g, respectively, compared with 10.1 ± 0.12 and 7.3 ± 0.21 mg Trolox/g for hydrolysates produced with endogenous enzymes. Trypsin hydrolysates also showed stronger dipeptidyl peptidase-IV (DPP-IV) inhibition (IC50 = 0.83 ± 0.37 mg/mL) than endogenous-enzyme hydrolysates (IC50 = 1.60 ± 0.47 mg/mL). Remarkably, hydrolysates generated with the endogenous enzymatic consortium exhibited exceptionally potent angiotensin-converting enzyme (ACE) inhibitory activity (IC50 = 0.008 ± 0.004 mg/mL), outperforming trypsin hydrolysates (IC50 = 0.01 ± 0.007 mg/mL). Neither hydrolysate showed evidence of acute toxicity in the Artemia salina model at the tested concentrations, supporting their favorable performance in this preliminary toxicity screening assay. Considering that nearly two-thirds of total fish biomass is discarded during processing, this integrated bioprocess demonstrates a sustainable strategy for the simultaneous valorization of skeletal and visceral waste streams. By employing endogenous enzymes as biocatalysts, this approach reduces dependence on commercial proteases, mitigates environmental burdens, and supports the development of a circular marine bioeconomy through the production of highly potent, peptide-rich functional ingredients with promising cardiovascular health applications. Further toxicological evaluation is required to confirm their safety for food and nutraceutical applications.