Novel trends and applications of natural pH-responsive indicator film in food packaging for improved quality monitoring

Natural pH-responsive indicator films usually used in smart packaging can real-time monitor the changes of food quality. The pH-responsive colorimetric indicator films based on natural ingredients show good pH-sensitivity and growing population, which safely and environmentally indicate food quality. Recently, the application of natural pigments and polymer carriers shows great potential in smart packaging based on pH-responsive indicator. This article mainly reviews the application and progress of natural pigments (e.g. anthocyanins, betalains, carotenoids, chlorophyll, curcumin) and natural polymer carriers (e.g. chitosan, gum, starch, plant protein, and milk-based protein) in pH-responsive colorimetric indicator films, and also further discusses the main problems and corresponding methods to improve performances of current pH-responsive colorimetric indicator films.