Chitosan, as a natural polymer with a potential use in food packaging, exhibits only secondary antioxidant (AOX) activity. The primary AOX activity can be introduced by grafting of phenolic compounds to its amino and/or hydroxyl groups. Phenolic acids are efficient AOXs, acting by rapid donation of a hydrogen atom or electron terminating free radicals, and resulting in relatively stable phenoxy radicals. The objective of this study was to investigate the effect of solvent composition on efficiency of grafting gallic acid (GA) onto chitosan in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC)/N-hydroxysuccinimide (NHS). The activation of GA by EDC/NHS in different concentrations of d4-Methanol (CD3OD) /D2O was studied by nuclear magnetic resonance (NMR), which showed that higher methanol concentration inhibited successful grafting of GA by prohibiting the conversion of the intermediate O-acylisourea ester to a more stable NHS ester. In contrast, the grafting was successfully performed in 25%, 50% and 75% aq. ethanol (EtOH) as confirmed by FTIR. The efficiency of grafting was determined as Folin’s total phenolics and expressed as degree of substitution (DS). The AOX properties of grafted chitosans were assessed as DPPH scavenging activity and reducing power using K-ferricyanide. GA in 25% EtOH grafted to the largest extent, having DS=0.273. The DPPH activity and reducing power of GA-chitosan grafted in 25% EtOH were also higher than of chitosan grafted in 50% and 75% EtOH. The results suggested that the solvent conditions can be used to optimize the amidation/esterification between GA and chitosan via EDC/NHS.

Effect of solvent composition on grafting gallic acid onto chitosan via carbodiimides

249th National Meeting (2015)

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