Processing-Dependent Incorporation of Food By-Product Extract into Zein-Based Active Packaging Films

The recovery of antioxidant compounds from agri-food by-products represents a sustainable strategy for active packaging production. However, the compatibility between natural extracts and film-forming techniques plays a key role in determining film formation and properties. In this work, antioxidant extracts obtained from spent coffee grounds and tomato waste were incorporated into zein-based films produced using two different techniques. The objective was to investigate how extract type and processing technique influence film morphology, wettability, thickness, and mechanical properties. The results demonstrated a strong processing-dependent compatibility between extract composition and production techniques. Spent coffee ground extract was successfully incorporated into compact cast films, while tomato waste extract did not allow the formation of homogeneous cast films and required electrospinning to obtain uniform fibrous structures. The incorporation of spent coffee ground extract significantly increased surface wettability and film stiffness, with Young's modulus reaching 695 MPa. In contrast, electrospun films containing tomato waste extract exhibited lower tensile strength due to their porous fibrous structure, although uniform fibers were obtained. These findings demonstrate that extract chemistry critically affects the suitability of the processing technique and provide useful guidelines for the design of sustainable zein-based active packaging systems derived from agri-food waste valorization.