Ilona Kołodziejska¹, Anna Wojtasz-Pająk², Gabriela Ogonowska¹ and Zdzisław E. Sikorski^1
1Technical University of Gdańsk, Gabriela Narutowicza 11/12, 80-952 Gdańsk, Poland
²Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland

Key words: chitin, chitosan, chitin deacetylase, chitosanolytic enzymes.

Abstract.
The two-stage chemical and enzymatic process may be used for preparing chitosans with different deacetylation degrees. The first, chemical stage of processing in a hot NaOH solution should only lead to ensure solubilization of chitin in slightly acid solutions. For further deacetylation of the substrate a chitin deacetylase preparation can be used. In case of crude deacetylase extracts from Mucor rouxii mycelium and 0.25% solution of the substrate with initial deacetylation degree of 68%, the enzymatic deacetylation reached 90% at optimum conditions after 6 h. In 1.2% solution of this substrate the highest degree of deacetylation was 85% after at least 10 h. The use of a crude enzyme preparation containing chitosanolytic and chitinolytic enzymes leads to partial hydrolysis of the polysaccharide. A substantial inhibition of the hydrolytic activity was achieved when the deacetylase extract was pre-purified by acidification to pH 4 and pre-incubated with 1 mM Zn²⁺ or by adding these ions to the reaction mixture. However, the viscosity of the products of enzymatic deacetylation was at least about 10 times lower than that of the substrates. This shows, that even in the most purified preparation the minute residual amounts of hydrolytic enzymes can effectively degrade the polysaccharide chains. For obtaining highly viscous chitosans the enzyme preparation should be purified in order to completely remove the chitino- and chitosanolytic enzymes.