Water-soluble chitosan-based indicator label membrane and its response behavior to carbon dioxide

In this work, two kinds of water-soluble chitosan derivatives (succinylated chitosan and hydroxypropyl chitosan) were used as substrates to prepare indicator label for detecting CO 2 concentration. The mixed-dyes of bromocresol blue and methyl red indicators were investigated and the results of SEM test revealed that the mixed indicator could be uniformly dispersed in the transparent membranes. The color differences of the indicator label under different environmental conditions (humidity and temperature) were highly correlated with the CO 2 concentration. The values of label membranes' color difference ( δ E ) showed a good linear relationship with the CO 2 content. Subsequently, these label membranes were successfully applied to reveal the evolution of the CO 2 content in fruit packaging to indicate the freshness of fruit. Therefore, these chitosan derivative-based indicator label membranes assume a promising application prospect in the future. • Chitosan derivative-based indicator label for detecting CO 2 concentration was fabricated. • The color difference ( δ E ) of label showed a good linear relationship with the CO 2 content. • The response to CO 2 level can be achieved under different conditions of humidity and temperature. • The freshness of fruits and vegetables can be revealed by the color change of this indicator label.