Characterization of yellowfin tuna ( <i>Thunnus albacares</i> ) skin gelatin extracted by bromelain hydrolysis and ultrasound pre‐treatment

Yellowfin tuna skin waste is a potential collagen source for gelatin through hydrolysis. Enzymatic hydrolysis is eco-friendly but expensive, necessitating efficiency improvements. Ultrasound pre-treatment enhances efficiency via cavitation effects. This study evaluated the effects of ultrasound amplitude, pre-treatment duration, enzyme concentration, and hydrolysis duration on yield; determined optimal conditions for ultrasound-assisted enzymatic extraction on yield, viscosity, and gel strength; and assessed the gelatin's physicochemical and functional properties. This research consists of three stages, factor screening using one variable at a time, optimization using response surface methodology with Box-Behnken design, and gelatin characterization. The study included three replicates. Screening identified factor ranges for optimization: 5-25 min pre-treatment, 1%-3% enzyme concentration, and 1-5 h hydrolysis. Optimization involved 15 experimental runs, focusing on yield, viscosity, and gel strength. Optimal conditions were 25 min pre-treatment, 1% enzyme concentration, and 2.17 h hydrolysis, yielding 64.08%, 9.29 mPa·s viscosity, and 166.28 bloom gel strength. The optimized gelatin showed emulsifying properties with EAI 50.5 m²/g and ESI 23.80 min, water-oil holding capacities of 192% and 406%, respectively, antioxidant activity of 60.16%, and molecular weight range of 17-160 kDa. The amino acid composition was mainly glycine (29.26%) and proline (18.26%), with 76.95% digestibility. This innovative, environmentally friendly extraction method improved gelatin extraction efficiency from yellowfin tuna skin, supporting a sustainable industry.