pH-responsive indicator films contained composite anthocyanins for monitoring meat freshness

The color changes at different pH (pH 6.0, 7.0 and 8.0) and intermolecular interactions of anthocyanins (purple cabbage (PC), mulberry fruit (MF) and purple sweet potato (PSP)) and their complex with different proportions (10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8 and 1:9 respectively) were investigated. When PC and MF anthocyanin solutions were mixed in a ratio of 9:1 (PC-MF (9:1)), the color change was most obvious distinguishable at different pH values. According to the fourier transform infrared spectroscopy (FTIR) results, the intermolecular interactions between PC and MF composite anthocyanins were stronger and formed hydrogen bonds. The PC-MF (9:1) indicator film exhibited a distinct color change when chicken was gradually spoiled for 8 d storage at 4 °C. Based on gas chromatography mass spectrometer (GC-MS), the key reason for the color change of indicator film was that the reaction between anthocyanins and gases such as trimethylamine, indole, ammonium carbamate, and butyric acid that can cause pH changes.