Effects of anthocyanin-rich purple and black eggplant extracts on the physical, antioxidant and pH-sensitive properties of chitosan film

Active and intelligent food packaging films were developed by mixing chitosan (CS) with anthocyanin-rich purple eggplant extract (PEE) or black eggplant extract (BEE). Results showed the anthocyanin contents in PEE and BEE were 93.10 and 173.17 mg/g, respectively. Besides, the anthocyanin compositions of PEE and BEE were totally different. PEE and BEE increased the blueness, thickness, UV-vis light barrier and mechanical properties of CS film. Nevertheless, PEE did not change the moisture content of CS film and BEE did not change the water vapor permeability of CS film. Microstructure observation showed low contents (1 and 2 wt%) of PEE and BEE were well distributed in CS matrix. Fourier transform infrared spectroscopy revealed the existence of intermolecular interactions between CS and extracts. X-ray diffraction indicated PEE and BEE somewhat increased the crystallinity of CS film. The antioxidant ability of CS film was remarkably enhanced by PEE and BEE. Moreover, CS-PEE and CS-BEE films were pH-sensitive and showed remarkable color changes in different buffer solutions, which could be used to monitor milk spoilage. Our results suggested CS-PEE and CS-BEE films could be applied as active and intelligent food packaging materials.