Water‐soluble chlorogenic acid‐chitosan and polydatin‐chitosan conjugates: antibacterial activity and inhibition of lipid and protein oxidation

Abstract BACKGROUND Chitosan (CS), an abundant alkaline polysaccharide, is valued for its biocompatibility, non‐toxicity, and antibacterial properties. However, its limited solubility and modest antioxidant activity constrain its utility. Grafting polyphenols onto chitosan through the use of grafting reactions can enhance both the solubility and bioactivity of chitosan. Among the techniques employed, the free radical grafting method is favored for its simplicity, environmental sustainability, and its effectiveness in preserving biological activity. RESULTS In this study, chlorogenic acid (CGA) and polydatin (PLD) were conjugated successfully to chitosan by a Vc/H 2 O 2 redox system. Analytical techniques such as ultraviolet‐visible (UV‐visible) spectroscopy, fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), and proton nuclear magnetic resonance ( 1 H NMR) were employed to confirm the formation of covalent bonding between the polyphenol molecules and the chitosan backbone. The novel conjugates displayed superior antioxidant properties in comparison with pristine chitosan, as evidenced by their enhanced 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical, 2,2'‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) radical, and hydroxyl radical scavenging capacities, and Fe 2+ reducing power. Both CGA‐CS and PLA‐CS exhibited excellent lipid and protein oxidation inhibition capabilities. Furthermore, the conjugates were shown to have significant antibacterial effects against four common pathogenic bacteria: Pseudomonas fluorescens , Pseudomonas aeruginosa , Pseudomonas putida , and Staphylococcus aureus ( P < 0.05). CONCLUSION The newly synthesized water‐soluble polyphenol‐chitosan conjugates demonstrated remarkable biological activity, particularly CGA‐CS. This study offers new insights and a strong theoretical foundation for developing natural food preservation materials with potential applications in the food industry. © 2024 Society of Chemical Industry.