Relationship between the physico-chemical Property of Xanthan and its Antioxidative Activity in Emulsion.

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Xanthan have been considered as stabilizing an oil/water (O/W) emulsion by increasing the viscosity of the aqueous phase and inhibiting its coalescence. Xanthan chelated such as a metal ion as Fe^<2+> between two side chains with a pyruvate residue and thereby inhibited the oxidation of soybean oil in the emulsion. The effects of emulsion viscosity and oil-droplet size on the oxidation of soybean oil in O/W emulsions containing xanthan or other polysaccharides were investigated. The antioxidative effects were evaluated by measuring the Fe^<2+>-induced consumption of oxygen dissolved in the O/W emulsion. The degree of oxygen consumption was, from the lowest, in the order of xanthan<pectin<guar gum<Tragacanth gum, and was closely related to the Fe^<2+>-binding ability of the polysaccharides. The oxygen consumption was also affected by the viscosity of the aqueous solution in the emulsion, but not by the oil-droplet size.The viscosities of xanthan and deacetylated xanthan solutions were decreased by the treatment of cellulase (Trichoderma viride). The deacetylated and cellulase-treated xanthan was smaller in molecular size. Both low-molecular-weight xanthans retained the pyruvate residue, Fe^<2+>-binding and chelating abilities (dissociation constant and number of binding sites), and showed strong antioxidative activity.The antioxidative mechanism for xanthan can be accounted for primarily by its high metal-binding ability, and additionally by its viscous behavior.