Control of phytic acid-zinic complexing by addition of chitosan

We examined the complexing of phytic acid with chitosan, and the effects of such complexing on the formation of phytic acid-zinc complexes. Chitosan is the main constituent of cell wall polysaccharides from Rhizopus acetoinus HUT 1219, and these polysaccharides decrease the inhibition by phytic acid of zinc absorption. Complexes of phytic acid and chitosan formed by the reaction of amino groups and phosphate ions in a mixture of these substances. The optimum pH for complex formation was from 1.7 to 3.2, and the stoichiometric ratio was 1 : 6 for phytic acid to glucosamine. When chitosan is added in a larger proportion than this, some complexes dissociate. Much more phytic acid-chitosan complexes formed than complexes of phytic acid with zinc, of chitosan with zinc, or of phytic acid, chitiosan, and zinc together. When the pH was greater than 3.2, dissociation of phytic acid-chitosan complexes was sometimes accompanied by the formation of chitosan-zinc complexes. The result suggested that the formation of stable phytic acid-chitosan complexes at lowpH values generated free Zn2+ leading to the diffusion of such ions or the formation of chitosan-zinc complexes. Both phenomena make the adsorption of Zn2+ ions easier than in the presence of stable phytic acid-zinc complexes. (Received December 12, 2001)