pH-Responsive Gelatin/Diatomite/Rose Anthocyanin Composite Films by Melt Extrusion: Physicochemical Properties and Application in Monitoring Freshness of Litopenaeus vannamei

Smart packaging systems for real-time visual monitoring of food freshness play a crucial role in food safety. However, the intelligent packaging film is prepared by solution casting and extrusion moulding, the low efficacy limited the application. In this study, a pH colorimetric indicator film based on gelatin, anthocyanin and diatomite was fabricated via the industrial method of melt extrusion. The film exhibited good mechanical properties as well as excellent water resistance and antioxidant properties. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicated that the fish gelatin (FG) interaction with anthocyanin/diatomite ( AD ) reduced the crystallinity and influenced the microstructure and mechanical properties of the thin film. The film exhibited high sensitivity to volatile amines with visible colour changes. When used to monitor the freshness of Litopenaeus vannamei from day 0 to 10 , the colour of the film shifted from purplish-red to brownish-yellow. Pearson correlation analysis indicated that the colour changes on films are closely related to the variations in TVB-N ( r = 0.98, p < 0.001) and pH ( r = 0.93, p < 0.01) values of L. vannamei . Therefore, the film can be utilized to monitor the freshness of L. vannamei and holds significant potential for large-scale industrial production.