Intelligent Chitosan/PVA nanocomposite films containing black carrot anthocyanin and bentonite nanoclays with improved mechanical, thermal and antibacterial properties

This study investigated the potential of chitosan/PVA films containing black carrot anthocyanins as a natural pH indicator and bentonite as a nano-filler, for intelligent packaging applications. Two series of chitosan/PVA (CP) films, with different concentrations of bentonite (CPB3%, CPB5%) and with a constant concentration of anthocyanin (CPA, CPAB3%, CPAB5%) were prepared by solution casting method. The colorimetric parameter b* showed an increase from 1.0 +/- 0.2 for CP films to 2.7 +/- 0.2 and 8.8 +/- 1.1 for CPB3% and CPB5% films, respectively which indicates that addition of bentonite increases the intensity of yellow color in the nano composite films. The presence of anthocyanins caused to shifting of a* values from negative to positive values which indicated the color change of films from greenness to redness. Addition of bentonite reduced the tensile strength from 100.6 for CP film to 86.5 and 67.2 for CPB3% and CPB5% films which was related to the solution intercalation method used for preparation of nanocomposite films. In contrast, addition of anthocyanins increased the tensile strength for CPA, CPAB3% and CPAB5% due to the hydrogen bonding interactions between its OH groups and PVA and chitosan chains. Water vapor permeability (WVP) of the films was decreased from 1.140 (mg.mm/m(2).kPa.h) for CP film to 0.5620 and 0.3515 for CPB3% and CPB5% films, respectively. In contrast, anthocyanins caused to increase WVP of the samples compared to the anthocyanin free films. Thermo-gravimetric analysis showed that the films containing bentonite and anthocyanins have a better thermal stability. Finally, CPAB5% showed the highest bacterial growth inhibition against Escherichia colt, Pseudomonas aeruginosa and Staphylococcus aureus, respectively 75.20%, 69.95% and 44.38%.