Ultrasound-Assisted Extraction of Gelatin from Asian Sea Bass (Lates calcarifer) Swim Bladder: Physicochemical Characteristics and Film-Forming Properties Compared with Commercial Gelatins

This study investigated the ultrasound-assisted extraction (UAE) of gelatin from the swim bladder (SB) of Asian sea bass (Lates calcarifer) and evaluated its physicochemical and film-forming properties in comparison to commercial bovine and fish skin gelatins. UAE significantly enhanced the extraction efficiency, achieving a yield of 85.26–91.62% (dry weight) within 1–2 h, compared to 78.81% obtained through a 6 h conventional hot-water method. The SB gelatin optimally extracted via UAE for 1 h showed the presence of high-molecular-weight protein cross-links (β- and γ-chains). Consequently, it exhibited a gel strength of 258.64 g, which was higher than that of commercial fish skin gelatin (233.35 g), despite possessing a lower hydroxyproline content (47.30 mg/g). Furthermore, the SB gelatin demonstrated viable film-forming capabilities when incorporated with 25% (w/w) of hydrophilic plasticizers (glycerol, PEG-400 and a 1:1 mixture). The resultant SB films displayed higher tensile strength (60.93–71.56 MPa) and lower elongation at break compared to films derived from both commercial marine and bovine gelatins (p < 0.05). Among the evaluated plasticizers, glycerol yielded films with higher initial mechanical flexibility (indicated by the lowest elastic modulus), while the binary mixture of glycerol and PEG-400 provided the most effective water vapor barrier for the SB gelatin films. Overall, UAE-extracted Asian sea bass swim bladder represents a potential alternative source of gelatin that exhibits preliminary potential for bio-based packaging applications.