Functional properties and preservative effect on Penaeus vannamei of chitosan films with conjugated or incorporated chlorogenic acid

The chlorogenic acid-grafted-chitosan conjugates (CA-g-CS) with three grafting ratios were synthesized. Then the CA-g-CS conjugated films (CA-g-CS I, CA-g-CS II, and CA-g-CS III) and the CA-CS incorporated films (CA-CS I, CA-CS II, and CA-CS III) with equivalent chlorogenic acid content were prepared, respectively. The physical, mechanical, and biological properties of CA-g-CS conjugated and CA-CS incorporated films were evaluated. Further, the CA-g-CS III and CA-CS III were chosen to evaluate their preservative effect on shrimp. Compared with CS film, CA-g-CS conjugated and CA-CS incorporated films showed enhanced opacity and water solubility, changed thickness and water vapor permeability, and reduced moisture content, tensile strength and elongation at break. Conjugation or incorporation of CA enhanced antioxidant and antibacterial activities of CS films, and these activities increased with the increasing of CA content. CA-g-CS III showed better preservative effect on shrimp than CA-CS III in terms of weight loss, pH value, total volatile basic nitrogen, total bacterial count and sensory score of shrimp during storage. Therefore, CA-g-CS conjugated films exhibited better bioactivities and preservative effect on shrimp than CA-CS incorporated films. Compared with incorporation, conjugation of CA with CS is a more efficient way to improve properties of CS film.