Ohmic Heating Assisted Fabrication of Antioxidant Edible Films from Shark Gelatin Functionalized with Opuntia stricta Pulp Extract

This study evaluated the effects of ohmic heating (OH) and Opuntia stricta pulp (OSP) incorporation on the physicochemical, structural, optical, and antioxidant properties of white cheek shark skin gelatin films developed for active food packaging. Films containing 0, 15, and 30% OSP were prepared using conventional water bath heating or OH. OSP incorporation significantly affected film performance in a concentration-dependent manner. Tensile strength decreased with increasing OSP content, whereas films produced by OH showed consistently higher tensile strength than conventionally heated films, indicating improved protein network organization. Elongation at break increased at 15% OSP but decreased at 30%, suggesting a transition from plasticizing to rigidifying effects at higher pulp levels. OSP addition also increased water vapor permeability and opacity, particularly in OH-treated films. FTIR and SEM analyses confirmed protein–polyphenol and protein–polysaccharide interactions, while OH promoted more ordered β-sheet-rich structures and greater surface heterogeneity. In addition, OSP significantly enhanced betalain content, total phenolic content, and DPPH radical scavenging activity, with OH-treated films showing superior phytochemical retention and antioxidant capacity. Overall, the combination of OH and OSP provides a green strategy to produce bioactive gelatin films with enhanced antioxidant functionality and tunable physical properties for sustainable active packaging applications requiring controlled moisture transfer. Further work on composite systems, scalable processing, and real food packaging trials is recommended to support the industrial adoption of OH-assisted bioactive gelatin films.