Abstract
Fish frame waste (FW) from threadfin breams ( Nemipterus japonicus ) was valorized into functional fish protein hydrolysates (FPH) using proteases from plant (ficin), microbial (neutrase), fungal and endogenous visceral sources for potential food and nutraceutical applications. A comparative enzymatic hydrolysis approach was adopted for evaluating influence of enzyme source and degree of hydrolysis (DH) on bioactivity and functionality of the resulting hydrolysates. Bioactivity increased with increasing DH, with plant protease derived FPH exhibiting the highest angiotensin I-converting enzyme (ACE) inhibitory potential. In contrast, antioxidant activity assessed using DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging and FRAP (ferric reducing antioxidant power) assays showed maximum activity in fungal protease-derived FPH. Functionality in terms of solubility, emulsifying activity index (EAI), emulsion stability index (ESI), foaming capacity, and fat absorption capacity were superior at lower DH with visceral enzyme–derived FPH showing enhanced interfacial functionality. The findings demonstrated that enzyme specificity and DH regulate the balance between bioactivity and functional performance, highlighting fish frame waste as a sustainable source of tailored bioactive ingredients for food and nutraceutical applications.