PLA-Based pH-Sensitive Food Packaging Films Incorporating Anthocyanins from Wine Byproducts

The growing demand for biodegradable and intelligent packaging materials has accelerated efforts to valorize agro-industrial byproducts. Wine industry byproducts (WB) are rich in anthocyanins, natural pigments with halochromic properties that can be exploited as freshness indicators. This study aimed to develop pH-sensitive PLA-based films by incorporating anthocyanin-rich WB extracts. As part of the valorization process, the drying kinetics of WB were also evaluated as a necessary pretreatment to find out the right drying technique and so facilitate anthocyanin recovery. Anthocyanin extracts (AE) were then incorporated into PLA matrice (10-70%) using solution casting, and the resulting films were characterized for mechanical, thermal, optical, and pH-responsive properties. The results showed that freeze-drying preserved higher anthocyanin activity than microwave drying. Mechanical strength decreased with AE addition, from 76 MPa in neat PLA to 7 MPa at 70% AE, while films with 10% AE retained 60 MPa. Opacity increased from 1.37 to 11.32, enhancing halochromic visibility. Thermal stability decreased slightly, with T-g shifting from 60 degrees C to 54 degrees C and T-m from 156 degrees C to similar to 150 degrees C. Importantly, the composite films exhibited distinct color changes with pH values, with more pronounced shifts under alkaline conditions. These findings highlight the feasibility of upcycling WB into PLA-based halochromic films, offering a sustainable alternative to conventional plastics for intelligent food packaging applications.