Enzymic preparation of acid-free-water-soluble chitosan

A chitinolytic enzyme complex produced by the Gram-positive bacterium Streptomyces kurssanovii was immobilized on macroporous cross-linked chitin by physical adsorption, and the biocatalyst obtained used for the preparation of acid-free-water soluble chitosan with a molecular weight of 2-9 kDa starting from commercial crab chitosan by two-step hydrolysis. The first hydrolysis at pH 4.6 lead to a 22-24 kDa chitosan of low solubility in water whereas the second hydrolysis at pH 6.2 allowed a 2-9 kDa acid-free-water soluble chitosan. Optimal conditions for the complex immobilization and chitinolytic hydrolysis are described. The method allows not less than 80-cyclic procedures of immobilized complex and chitin matrix utilization and is suitable for a large-scale production of the chitosan free of protein admixtures. (C) 2000 Elsevier Science Ltd. All rights reserved.