Response surface optimization and ultrasonic modification of soy protein isolate–gellan gum composite films

Abstract

Abstract Soy protein isolate (SPI)-based films are promising biodegradable packaging materials but often have limitations in mechanical strength and barrier performance. In this study, gellan gum (GG) was incorporated into SPI films, and response surface methodology (RSM) based on a Box–Behnken design was used to optimize the formulation. SPI concentration, GG content, glycerol content (w/w, based on SPI mass), and pH were selected as independent variables, with tensile strength (TS) as the response. The quadratic model was significant (R² = 0.93) with a nonsignificant lack of fit. The optimized formulation (5.00% SPI, 0.30% GG, 25.00% glycerol, pH 10.00) produced a TS of 25.45 ± 0.54 MPa, consistent with the predicted value. Ultrasonic modification significantly increased elongation at break while maintaining TS and reduced water vapor permeability (WVP) and oxygen permeability (OP) by 59.5% and 63.9%, respectively. It also improved dispersion stability, as indicated by decreased particle size and increased absolute zeta potential. FTIR analysis indicated subtle rearrangement of existing intermolecular interactions without the formation of new major chemical functional groups. These findings demonstrate that integrating RSM-based formulation optimization with ultrasonic modification effectively improves the functional performance of SPI–GG composite films and supports their development as biodegradable packaging materials.