The seafood processing industry generates significant amounts of solid waste, including boiled tuna skin, a major byproduct with limited commercial use. Antioxidant activities of Flavourzyme hydrolysate derived from boiled Skipjack tuna (Katsuwonus pelamis) skin byproduct were assessed for their ability to reduce AAPH-induced oxidative stress in In Vitro and In Vivo. The functional properties were improved by enzymatic hydrolysis with Flavourzyme at pH 7.0 to produce an antioxidant hydrolysate. Antioxidant activity was evaluated for boiled tuna skin Flavourzyme hydrolysate (BTSFH) using Hydrogen Peroxide Scavenging activity and ABTS radical scavenging activity. The IC₅₀ values for H₂O₂ and ABTS radical-scavenging activities were 2.91 mg/mL and 7.52 mg/mL. BTSFH treatment increased cell viability, significantly reduced ROS production under AAPH-induced oxidative stress, and protected against AAPH-induced apoptotic DNA damage. BTSFH exhibited potent antioxidant activity by upregulating endogenous antioxidant enzymes (SOD and Catalase) in AAPH- stimulated Vero cells. An in vivo zebrafish assay demonstrated its antioxidant potential effects by reducing ROS generation, lipid peroxidation, and cell death, thereby supporting its potential as a bioactive compound. These in vitro and in vivo studies’ findings showed that the BTSFH sample represented strong antioxidant activity, making it preliminary evidence for use in pharmaceuticals and health supplements. Marine byproducts as a source of functional ingredients help reduce waste and promote better resource management, aligning with broader goals for a more sustainable circular bioeconomy.

Hairtail (Trichiurus lepturus) is a popular fish species in South Korea that generates substantial quantities of processing byproducts. This study investigated the potential functional properties of hairtail byproducts to enhance their utilization. Proximate composition analysis showed that crude protein was the most abundant component, accounting for approximately half of the total composition. Therefore, protein hydrolysates were prepared from hairtail byproducts using Protamex-assisted enzymatic hydrolysis. The yield of Protamex-assisted enzymatic hydrolysate (HBP) produced based on the raw material drying weight was 42.8%. Amino acid analysis revealed high levels of Aspartic acid and glutamic acid, which can provide instrumental help in muscle synthesis and growth, and free amino acids showed high L-leucine content. HBP also exhibited considerable antioxidant activity. In a dexamethasone-induced C2C12 cell atrophy model, HBP increased cell viability in a concentration-dependent manner, reaching 120.58% at 300 µg/mL. Cell proliferation also increased in a concentration-dependent manner, reaching 125.54% at the same concentration. Immunofluorescence analysis of myosin heavy chain (MyHC) and DAPI staining further indicated concentration-dependent enhancement of muscle cell differentiation. These findings suggest that hairtail byproducts may provide a sustainable source of functional protein hydrolysates with potential protective effects against muscle atrophy in a dexamethasone-induced C2C12 model.