Chitosan-Enhanced pH-Sensitive Anthocyanin Indicator Film for the Accurate Monitoring of Mutton Freshness

Natural anthocyanin indicator films with an excellent pH response enable the visual assessment of meat freshness. In this investigation, chitosan was initially employed as a colorimetric enhancer, leading to the development of a pH-sensitive indicator film that was enhanced in colorimetry. The characteristics of this indicator film were thoroughly analyzed, and the mechanism responsible for the increased sensitivity of anthocyanin within the chitosan matrix, as indicated by the color response, was elucidated. The recrystallization of chitosan impeded the hydration of AH+ as the pH increased from 6.0 to 8.0, leading to distinct color changes. Moreover, the application of this indicator film was extended to the monitoring of mutton meat freshness. It facilitated the differentiation of mutton meat into three distinct stages, namely, fresh, sub-fresh, and spoiled, based on alterations in color. Additionally, a robust positive correlation was established between the color difference value of the indicator film and the total volatile basic nitrogen and bacterial count of the mutton meat, enabling quantitative analysis. The present study, therefore, demonstrated a novel function of chitosan, i.e., the enhancement of the color of anthocyanin, which could be useful in designing and fabricating indicator films with a high color response.