Development of a freshness indicator packaging system using cold atmospheric plasma on LLDPE–PVA with Laponite–anthocyanin biohybrid

This study developed a freshness indicator based on poly(vinyl alcohol) (PVA) and a biohybrid (BH) of Laponite® and anthocyanins adhered to linear low-density polyethylene (LLDPE) using cold atmospheric plasma (CAP). LLDPE was treated with CAP for 0 to 300 s, which resulted in an increased surface energy, characterized by an important increase in its polar component up to 120 s of treatment, due to the formation of polar groups on the surface of LLDPE. No changes in mechanical properties and water vapor permeability of LLDPE were observed. LLDPE–PVA–BH films were more homogeneous if BH was added before the acidification of the film-forming solution due to more negative zeta potential and lower particle size of BH in basic medium. Indicators made with BH were able to maintain color after 8 weeks of exposure to light, while those made with anthocyanin extract had fully degraded after 3 weeks. The freshness indicator's color changed from purple to blue and finally to green when exposed to ammonia hydroxide (30% NH₃) and from purple to blue when exposed to a simulant liquid of spoiled meat (0.03% NH₃). Similar color variance was observed when the indicator was applied to monitor shrimp freshness, changing from purple to blue when the shrimp pH reached pH 7.6. Thus, bilayer films of LLDPE–PVA and natural BH produced using CAP have potential food packaging applications. © 2024 Society of Chemical Industry.