Barbara Piotrowska1, Ilona Kołodziejska1
and Anna Wojtasz-Pająk2
1 Gdańsk University of Technology,
G. Narutowicza 11/12, 80-952 Gdansk, Poland
2 Sea Fisheries Institute, Kołłątaja
1, 81-332 Gdynia, Poland
Key words: chitin, chitosan, chitin deacetylase, deacetylation.
Abstract.
A two-stage, chemical and enzymatic process can be used to prepare chitosans
with desired degrees of deacetylation. However, it is not possible to obtain
products with a higher degree of deacetylation than 84% from chitosan with an
initial degree of deacetylation of 68% when a 1.2% solution is used as a substrate
for the pre-purified deacetylase from Mucor rouxii mycelium. The objective
of this study was to investigate the reasons behind this phenomenon. The incomplete
deacetylation of chitosan under the applied conditions of enzymatic reactions
was not the result of the thermal denaturation of deacetylase during the relatively
long enzymatic reaction. The amount of acetic acid released and the degree of
deacetylation did not increase as a result of adding a fresh portion of the
enzyme to the reaction mixture after 10, 16, and 24 h of the reaction. It was
shown that enzymatic deacetylation could be partially inhibited by acetic acid
released during deacetylation. The main product of deacetylation - chitosans
deacetylated to about 82-84%, also decreases the rate of deacetylation. Only
35% of the total possible acetic acid released from chitosan with a degree of
deacetylation of 82% was detected after 24 h of enzymatic deacetylation. The
total inhibitory effect of both products of deacetylation on chitin deacetylase
activity was investigated by conducting enzymatic deacetylation of chitosan
with a degree of deacetylation of 82% in the presence of added acetic acid at
a concentration of 12 mmoles/ml of the reaction mixture. After 24 h, the amount
of acetic acid formed was so low that the degree of deacetylation of the product
was almost unchanged.