Influence of ascorbic acid on the stability of chitosan solutions

The chitosan solution stability in 2% acetic acid in the presence of different amounts of ascorbic acid (AA) was investigated. It has been shown that already low concentrations of ascorbic acid induce a rapid destruction of the polymer with the formation of water-soluble chitosan fragments at definite stages of the reaction. The elimination of air oxygen from the system considerably inhibits the chitosan destruction. On the other hand, the experiments demonstrate an accelerated oxidation of ascorbic acid in the presence of chitosan. For the initial stages of reactions first order reaction rate constants for the AA destruction can be calculated. It is suggested, that the polymer destruction induce hydroperoxyl radicals, which are formed at reaction of AA with air oxygen. Hydroperoxyl radicals abstract hydrogen from the chitosan or form unstable hydroperoxydes decomposition of which induce splitting of the glycosidic bond in the polymer.