Eco-Safe Biopolymer Films for Controlled Release of Food Bioactives: pH-Responsive Anthocyanins and ZIF-8-Encapsulated Thyme Oil for Enhanced Blueberry Preservation

Abstract

Environmentally sustainable and functional food-packaging systems are increasingly being explored as platforms for the stabilization and controlled delivery of food bioactives. In this study, a multifunctional packaging film with pH-responsive properties was developed using poly(vinyl alcohol) and chitosan as the polymeric matrix. The film was enriched with thyme essential oil (TO) encapsulated in ZIF-8 nanostructures (ZIF-8@TO) and incorporated with red cabbage anthocyanin (RCA) to fabricate PCR/Z@T films for blueberry preservation. The incorporation of ZIF-8@TO and RCA imparted multiple functional properties to the developed films, including antibacterial, antioxidant, UV-blocking, and pH-responsive characteristics. The nanocomposite film effectively inhibited the growth of foodborne pathogens, including Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa, with the PCR/Z@T-1.6% film exhibiting the most pronounced antibacterial performance among the tested formulations. The incorporation of ZIF-8@TO and RCA into the polymer matrix significantly improved the mechanical properties of the films, achieving a tensile strength of 49 MPa and an elongation-at-break of 39%. In addition, the PCR/Z@T-1.6% film exhibited high antioxidant activity, with a free-radical scavenging activity of 79.84%, as well as desirable UV-blocking capability, pH-responsiveness color-changing properties, and soil-disintegration behavior. In the blueberry preservation study, the PCR/Z@T-1.6% film delayed visible deterioration and decay and helped maintain selected quality attributes of blueberries for up to 10 days at 25 °C. These findings demonstrate multifunctional performance combining active packaging properties with pH-responsive color-changing behavior, highlighting the potential of the developed film for postharvest preservation of fresh blueberries.