Preparation and characterization of antioxidant and pH-sensitive films based on chitosan and black soybean seed coat extract

Antioxidant and pH-sensitive chitosan based films were developed by incorporating different amounts of black soybean seed coat extract (BSSCE). Spectroscopic analysis showed the main anthocyanins in BSSCE were cyanidin-3-O-galactoside (21.38%), cyanidin-3-O-glucoside (63.30%) and peonidin-3-O-glucoside (11.92%). Incorporation of BSSCE could greatly alter the barrier, optical and mechanical properties of chitosan film. Notably, chitosan-BSSCE films presented better water vapor and UV–vis light barrier properties and higher mechanical strength than chitosan film. However, chitosan-BSSCE films exhibited lower moisture content and transparency than chitosan film. Among all films tested, chitosan-BSSCE film containing 15 wt% of BSSCE on chitosan basis exhibited the best performance. Scanning electron microscopy showed BSSCE was uniformly distributed in chitosan-BSSCE films. Fourier transform infrared spectra of chitosan-BSSCE films further revealed chitosan could interact with BSSCE through non-covalent bonds. Importantly, chitosan-BSSCE films showed dose- and time-dependent 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity. Moreover, color variations were observed in chitosan-BSSCE films by changing pH. Results suggested chitosan-BSSCE films could be used as promising antioxidant and visible pH-sensing food packing materials.