A Visual Ratio PVA/curcumin/indigo Nanofibre Membrane Based on Natural Pigments for Detecting Mutton Freshness

In the storage process, meat is susceptible to external factors that produce corruption and deterioration, affecting consumers' health. Therefore, preparing an indicator membrane that can detect freshness in real time, non-destructively, and visually is significant. Herein, an indicator membrane was prepared by electrostatic spinning technology using polyvinyl alcohol (PVA) as the substrate and curcumin (CUR) and indigo (IND) as the mixed indicator for freshness detection. When curcumin and indigo were mixed at 3:1 (w/w), CUR was transformed from ketone type to enol type with the gradual increase of pH, and IND underwent electron leaps, which resulted in green, brown, and reddish-brown colour changes in the solution, and the colour development effect was effectively improved. The characterisation results showed that the average fibre diameter of the PVA/0.8 indicator membrane was 252 nm, the hybrid indicator was successfully loaded in the nanofibres, and the water contact angle was 103.6 degrees, which was hydrophobic. In addition, the indicator membrane was sensitive to trimethylamine (limit of detection 17.38 ppm) and triethylamine (limit of detection 27.77 ppm) but insensitive to saline, ethanol, ethyl acetate, and other contaminants with detection specificity. Finally, the colour of the indicating membrane changes from green to brown during the storage of mutton in the mutton was rotten, indicating that the naked eye can judge the freshness of the mutton. Therefore, the PVA/CUR/IND indicator membrane has excellent potential for application in real-time and non-destructive detection of mutton freshness.