Antioxidant and pH-sensitive films developed by incorporating purple and black rice extracts into chitosan matrix

Polyphenol-rich purple rice extract (PRE) or black rice extract (BRE) was incorporated into chitosan (CS) to develop antioxidant and pH-sensitive packaging films. Effect of extract content on the structural, physical and functional properties of CS-PRE and CS-BRE films was investigated. Results showed BRE had higher total phenol and anthocyanin contents than PRE. Scanning electron microscope showed that 1 wt% of PRE or BRE was compatible with film matrix, whereas 3 and 5 wt% of the extract significantly decreased the homogeneity of film matrix. Fourier transform infrared spectroscopy and X-ray diffraction further indicated that intermolecular hydrogen bonds formed between CS and the extract. Notably, the incorporation of PRE or BRE increased the thickness, light barrier property and antioxidant activity of CS film. Moreover, the water vapor barrier property and tensile strength of CS-PRE and CS-BRE films first increased and then decreased with the increase of extract content. Due to abundant anthocyanins in the extract, CS-PRE and CS-BRE films were pH-sensitive in different buffer solutions. When used to monitor pork spoilage, CS-PRE films showed more significant color changes than CS-BRE films. Our results suggested CS-PRE films could be used as antioxidant and intelligent packaging films in food industry.