Antioxidant and tyrosinase inhibitory activities of a novel chitosan-phloroglucinol conjugate

A novel chitosanphloroglucinol conjugate was developed by conjugating phloroglucinol onto a chitosan backbone. The chitosanphloroglucinol conjugate was characterised by 1H nuclear magnetic resonance (NMR), and the NMR spectra confirmed the conjugation. Antioxidant and tyrosinase inhibitory activities of the chitosanphloroglucinol conjugate were investigated. The chitosanphloroglucinol conjugate showed strong 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydrogen peroxide and ABTS+ radical scavenging activities as well as reducing power compared with those of the unmodified chitosan (P<0.05). The formation of malondiadehyde (MDA) as an indicator of lipid peroxidation in a linoleic acid emulsion was 30.56M in the absence of the chitosanphloroglucinol conjugate after 4days incubation, whereas MDA was 4.14M in the presence of the chitosanphloroglucinol conjugate (P<0.05). The activity was higher than that of ascorbic acid, which is currently used as a food preservative. Moreover, the chitosanphloroglucinol conjugate inhibited 56.30% tyrosinase activity, which is responsible for browning of foods, and acted as non-competitive inhibitor. Taken together, the chitosanphloroglucinol conjugate may have potential for application in functional foods and/or as a food preservative.