Development of antioxidant and intelligent pH-sensing packaging films by incorporating purple-fleshed sweet potato extract into chitosan matrix

Antioxidant and intelligent pH-sensing films were prepared by incorporating anthocyanin-rich purple-fleshed sweet potato extract (PSPE) into chitosan matrix. Effect of PSPE incorporation on physical, structural, antioxidant and pH-sensing properties of chitosan-PSPE films was determined. Eight principal compounds in PSPE were identified as anthocyanins based on mass spectroscopic analysis. Due to abundant anthocyanin content, PSPE could change its colors with changing pH. The incorporation of PSPE could significantly increase the thickness, water solubility, UV–vis light barrier property and thermal stability of chitosan film. However, the incorporation of PSPE could decrease the moisture content, elongation at break and crystalline character of chitosan film. Water vapor barrier property and tensile strength of chitosan film were almost unchanged by PSPE incorporation. Microstructure observation showed a homogeneous state of chitosan-PSPE films. The existence of intermolecular interactions between PSPE and chitosan matrix was confirmed by infrared spectroscopy. Antioxidant assays showed chitosan-PSPE films could scavenge free radicals in dose- and time-dependent manners. Moreover, chitosan-PSPE films exhibited visible color changes along with the pH change. Therefore, chitosan-PSPE films can be used as antioxidant and intelligent pH-sensing films to extend the shelf-life and monitor the quality of food products.