Characterization of citric acid crosslinked chitosan/gelatin composite film with enterocin CHQS and red cabbage pigment

A chitosan/gelatin composite packaging film with antioxidant activity, bacteriostatic activity and pH responsiveness was prepared. Red cabbage pigment (RC) and enterocin CHQS were added as actives. In addition, different concentrations of citric acid (CA) were selected as crosslinking agents. Before that, in order to improve the yield of enterocin CHQS and simplify the purification process, we cloned and expressed CHQS in E. coli BL21 (DE3), resulting in an approximately 10-fold increase in yield. The appearances of the films were uniform and transparent with some UV-blocking ability. The results of antioxidant experiments of the films showed that the antioxidant capacity of the films was significantly increased by the addition of RC. Ammonia sensitivity experiments showed that the films could respond to volatile ammonia. Cross-linking improved the thermal stability, water sensitivity and photosensitivity of the films. FTIR and XPS revealed the mode of interaction between CHQS, CA, RC and the composite film structure. FTIR, XPS and XRD confirmed the cross-linking effect of CA. Atomic force microscopy showed that the addition of CA significantly increased the roughness of the film surface. The release experiments of RC showed that the cross-linking of CA promoted the release of active substances from the film and avoided the excessive release due to the dissolution breakage of the film. In addition, bacteria inhibition experiments showed that the addition of CA increased the antimicrobial properties of the films The experiments demonstrated that CHQS was effectively released and the bacteriocins in the films were stably preserved.