Caseinate–guar gum films enriched with tomato by-product oleoresins as potential active food packaging materials

The development of functional biopolymer films incorporating compounds recovered from agro-industrial by-products is of increasing interest for potential food-packaging applications. This study evaluated the effect of partially replacing beeswax (BW) with tomato by-product oleoresins (TBO) on the structure, physical properties, and antioxidant activity of sodium caseinate–guar gum (SC–GG) films cross-linked with microbial transglutaminase. TBO incorporation significantly modified the colloidal organization of film-forming emulsions, resulting in a narrower particle-size distribution, higher apparent viscosity (0.02–0.13 Pa s), and improved physical stability. In the resulting films, increasing TBO content enhanced surface hydrophobicity, with water contact angle increasing from 54.5° to 93.8°, and improved thermal stability, while decreasing tensile strength and increasing water solubility. FT-IR results supported good compatibility between TBO and the SC–GG matrix and suggested the occurrence of non-covalent lipid–polymer interactions. TBO also conferred antioxidant activity, which increased with oleoresin concentration and reached approximately 36 % and 62 % radical inhibition in the DPPH and ABTS assays, respectively. Overall, the results demonstrate that lipid-phase composition can be used to modulate the colloidal organization and functional properties of TGase-cross-linked SC–GG films. The incorporation of tomato by-product oleoresins provided antioxidant functionality while enhancing thermal stability and surface hydrophobicity, supporting the potential of these films as active packaging materials. Further studies addressing real-food performance, migration and safety, biodegradability, storage stability, and scale-up are required before practical food-contact application.