Gallic acid crosslinked peanut protein-corn starch composite edible films produced at alkaline pH with ultrasound application

Corn starch and peanut protein blend films were prepared with and without gallic acid addition (0.25%, w/v) at pH 7, 9, and 11 by casting. The ultrasound (160 W, 20 kHz, 10 min) treatment was applied to the film-forming solutions. This study aimed to develop biopolymer-based films with gallic acid and to determine the interactions of components at different pHs and with ultrasound. The barrier, optical, mechanical, and thermal properties of films were examined. Moreover, structural characterization of films was conducted by Fourier transform infrared (FTIR), x-ray diffraction, and trinitro benzenesulfonic acid assay to enlighten the crosslinking interactions of gallic acid with biopolymers at different pHs. At neutral pH, gallic acid behaved as plasticizer. By acting as a crosslinker at pH 9, gallic acid provided the lowest moisture content, darker and more opaque appearance, enhanced barrier performance and thermal stability. The crosslinking degrees of gallic acid-enriched films were 49.1% (pH 7), 77% (pH 9), and 67.4% (pH 11). Additionally, gallic acid increased antioxidant capacity. The ultrasonication adversely affected the film properties by breaking bonds in the film structure. Peanut protein-corn starch-gallic acid films under mild alkaline conditions exhibited outstanding thermal stability, mechanical durability, light, and water barrier characteristics, making them appropriate for sustainable food packaging applications.