A comparative study on chitosan/gelatin composite films with conjugated or incorporated gallic acid

Gallic acid-grafted-chitosan (GA-g-CS) was synthesized in the presence of 1-ethyl-3-(3'-dimethylaminopropyl) carbodiimide and hydroxybenzotriazole under room temperature. To develop a kind of newly functional film, CS, gelatin, glycerol and Tween 20 were utilized to prepare CS-based composite films with incorporated GA (GA-CS) or conjugated GA (GA-g-CS), and the films were characterized in aspects of physical and functional properties, as well as microstructures. With the increasing of GA concentration, there was a reduction in transmittance, elongation at break and water vapor permeability (WVP) for GA-CS film. For GA-CS films, the higher tensile strength and lower WVP could be obtained when GA was evenly distributed across the films. Different from the GA-CS films, water solubility, swelling ratio, water vapor permeability and scavenging activities on 2,2-Diphenyl-1-picrylhydrazyl/2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) radicals were enhanced for GA-g-CS films, which could be ascribed to the rough surface morphology. The GA-g-CS films exhibited enhanced water vapor permeability when the substitution degree of GA increased. Also, the antimicrobial activities of GA-g-CS films were superior to those of GA-CS films. Our present work developed a way to prepare GA-g-CS films that owned many desirable properties and could be explored as promising biomaterials in food packaging.