Active chitosan/PVA films with anthocyanins from Brassica oleraceae (Red Cabbage) as Time–Temperature Indicators for application in intelligent food packaging

Food-packaging featuring Time-Temperature Indicators are among the so-called intelligent packages. They use a system that monitors a food's condition in real-time, thus indicating the overall influence of temperature on food product quality. This work aimed to develop and characterize a Time–Temperature Indicator (TTI) based on a PVA/Chitosan polymeric doped with anthocyanins in order to indirectly indicate food quality changes through the detection of changes in the pH of packaged food products when subjected to improper storage temperatures. The TTI was produced from chitosan, PVA and anthocyanins extracted from Brassica oleracea var. capitata (Red Cabbage). TG-DSC, FT-IR, UV–Vis, as well as Swelling Index (Si) techniques were used to characterize the TTI. The colour variation after activation by different pH values was measured through the CIELab scale. The mechanical properties of the TTI were established through stress/strain tests. Due to its physicochemical features, the developed TTI offers attractive features for application in intelligent food packaging, even though it presents a divergent modulus of elasticity in comparison to commercial polymers applied in food packaging. Application of the TTI presented here is supported by an activation test on pasteurized milk, with evident changes in the colouration of the film, which is important for indicating to consumers that the food has been subjected to changes in its chemical composition.