Development of Dual Enzymatic–Ionic Crosslinked Alginate–Gelatin Films Enriched with Pelargonium sidoides Extract for Active Packaging and Anthocyanin Preservation in Flame Seedless Grapes

Active biodegradable packaging materials capable of preserving fruit quality and reducing oxidative processes are promising alternatives to conventional petroleum-based plastics. In this study, alginate–gelatin composite films were developed using a dual crosslinking strategy combining microbial transglutaminase-mediated enzymatic crosslinking with Ca2+-induced ionic gelation. The films were then enriched with Pelargonium sidoides root extract as a natural antioxidant. The combined crosslinking approach resulted in a more compact protein–polysaccharide network, which was reflected in increased film density and reduced swelling. The highest density was observed for film 1.0F (ρ = 1.2004 ± 0.0151 g/cm3), while films containing Ca2+ showed lower swelling values, with SI60 decreasing from 7655 ± 70 for 0F to 5853 ± 49 for 0Ca2+F. The addition of the extract promoted additional interactions within the polymer matrix and affected the swelling and barrier properties of the films. The WVTR values were 36.1 ± 0.9 g/m2·24 h for 1.0F and 49.8 ± 1.5 g/m2·24 h for 1.0Ca2+F. The incorporation of P. sidoides extract also significantly increased the antioxidant activity of the films, particularly at higher extract concentrations. Furthermore, films containing Ca2+ and the extract contributed to the preservation of anthocyanins in Flame Seedless grapes during 14 days of storage, with the anthocyanin content reaching 0.208% ± 0.019 for the 1.0Ca2+F treatment. Overall, the results indicate that dual-crosslinked alginate–gelatin films enriched with P. sidoides extract have favorable physicochemical and functional properties and may be suitable for the development of sustainable active packaging materials for anthocyanin-rich fruits.