Development of real-time intelligent films from red pitaya peel and its application in monitoring the freshness of pork

Red pitaya peel (RPP) is a good source of polysaccharides, which can be used in the production of biodegradable material. Betacyanins in it possess antioxidant and pH-sensitive properties. However, RPP is commonly discarded during fruit processing. This study aimed to develop real-time intelligent film using RPP to evaluate pork freshness.Real-time intelligent films were developed with film-forming substrates (FFS) composed of 60-100% (w/w) RPP and 0-4% (v/w) glycerol in pH 4.3 ~ 8.0. Rheology tests revealed that the FFS exhibited shear-thinning behavior. Fourier-transform infrared (FTIR) analysis showed that molecules in the RPP interacted with glycerol and formed hydrogen bonds. It showed that the film developed with FFS of 80% RPP and 2% (v/w) glycerol had strong molecular interaction, dense structure, and optimal tensile strength and elongation at break. Film with pH adjusted to 7.0 had greater sensitivity to ammonia than film that was prepared at an original pH of 4.3, so this film was used to monitor freshness of pork. A visible change in the color of the film was observed during the spoiling process of pork, which correlated with the accumulated total volatile base nitrogen.Based on its sensitivity to ammonia, the film made of 80% (w/w) RPP and 2% (v/w) glycerol at pH 7.0 was recommended for use in monitoring the freshness of protein-rich food. Our findings are of great significance for ensuring meat quality and safety and for reducing food waste. © 2022 Society of Chemical Industry.