Synthesis, characterisation, antioxidant and antibacterial properties of p-hydroxybenzoic acid-grafted chitosan conjugates

In this study, p-hydroxybenzoic acid-grafted chitosan (PA-g-CS) conjugates with different grafting degrees were synthesised by free radical-regulated grafting approach. The obtained PA-g-CS conjugates were characterised by UV-Vis spectra, fourier transform infrared spectroscopy (FT-IR) spectra, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Results revealed that PA was successfully grafted onto the hydroxyl group and the amino group positions of CS. Compared with CS, PA-g-CS showed decreased crystallinity, thermal stability, as well as a loose and porous surface morphology. The antioxidant assays demonstrated that PA-g-CS exhibited remarkably enhanced 2,2-diphenyl-1-pyridohydrazino- and 2,2 '-azino-bis(3-ethylbenzothiazoline-6)-sulfonic acid-scavenging activities in vitro. Similarly, the synthesised PA-g-CS also significantly increased the antimicrobial activities towards gram negative and positive bacteria, such as Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus. Moreover, the products with a relatively higher grafting degree showed stronger biological activities. Our findings suggest that PA-g-CS conjugates have great potential application in the field of active packaging, antioxidants and preservatives.