Production of pH indicators from starch and anthocyanins for use in smart packaging

In this research, natural pigments, anthocyanins, were used to produce bio-based films that can be used in smart packaging, as they serve as pH indicators to monitor the freshness of the packaged products. The aim of the research is to analyse the colorimetric and optical differences in the produced films before and after they are exposed to the environment with different pH values. In order to evaluate the possibility of using the produced films in printing processes, the adhesion of the produced pH indicators to packaging material was determined. This research has shown that it is possible to produce pH indicators from anthocyanins extracted from plant residues as well as from different types of starch. The influence of the anthocyanins immobilised in the starches on the colorimetric properties of the produced films and the adhesion of the films to the packaging material was evaluated. The research results showed that it is possible to produce a pH-responsive indicator based on the ingredients used. Different types of starch showed no significant difference in the visual appearance of the films, but a difference was found when different anthocyanins were used. It was proposed to use potato starch with anthocyanins from red cabbage and maize starch with anthocyanins from red onions to produce pH indicators. These polymer composites showed clear color shifts that are easy to recognise visually.