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

Summary 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.