Carbodiimide-mediated grafting of caffeic acid on chitosan to improve its physicochemical and biological properties: used for Pompano (Trachinotus ovatus) preservation

Summary Chitosan-grafted caffeic acid (CS-g-CA) was successfully prepared using carbodiimide-based chemical coupling method. The results of UV–vis and FT-MIR showed that caffeic acid (CA) was successfully grafted onto chitosan (CS). The grafting degree of CA in CS determined by Folin–Ciocalteu scheme was up to 91.26 ± 2.58 mg g −1 . Compared with CS solution, CS-g-CA solution has lower apparent viscosity and thermal stability. The results of SEM demonstrated that the grafting treatment changed the microstructure of CS. The grafting of the CA on CS enhanced its antioxidant activity. It can be seen that the clearance rate of DPPH (82.52% ± 0.7%), ABTS + free radicals (88.21% ± 0.26%), T-AOC (94.91% ± 0.21%) and FRAP (13.51 ± 0.52 mmol L −1 FeSO 4 ) of CS-g-CA was similar to ascorbic acid at 2.0 mg mL −1 . The results of antibacterial experiments demonstrated that CS-g-CA had better antibacterial ability in vitro , and the diameter of inhibition zone of 20.0 mg mL −1 CS-g-CA against Pseudomonas fluorescens and Staphylococcus saprophyticus was 16.88 ± 0.05 mm and 19.17 ± 0.09 mm, respectively, and it was significantly higher than CS (11.25 ± 0.04 mm and 13.09 ± 0.07 mm). The texture and freshness of Control group and CS rapidly declines post-mortem. CS-g-CA treatment could effectively retard the deterioration of texture and keep the better quality of Pompanos ( Trachinotus ovatus ). This study indicates that grafting CA onto CS alters the biological activity and physicochemical properties of CS.