Production of chitosan oligosaccharides by chitosanase directly immobilized on an agar gel-coated multidisk impeller

Abstract

An immobilized enzyme bioreactor consisting of an agar gel-coated multidisk impeller was developed for the hydrolysis of highly viscous chitosan solutions, and the operating conditions for the production of physiologically active chitosan oligosaccharides (pentamers and hexamers) were investigated. Chitosanase was directly immobilized on the agar gel-coated multidisk impeller by a multipoint attachment method. The high stability of the immobilized enzyme was confirmed by means of five repetitions of a batch hydrolysis reaction. When the enzyme activity at the support surface was relatively high, the yield of the target products was higher at an impeller speed of 2 s −1 than at a speed of 1 s −1. However, no significant increase in yield was observed at impeller speeds higher than 2 s −1 in reactions at either of the two substrate concentrations tested (5 and 20 kg/m 3). When the surface enzyme activity was low, the impeller speed did not affect the yield of the target products. The maximum yield of pentamers and hexamers increased as the surface enzyme activity decreased, and high yields (>30%) were obtained at activities below 160 U/m 2. From the viewpoint of productivity, the optimal surface-enzyme activity was about 340 U/m 2, and at that activity, the yield of target products was 22%. This yield was higher than that reported for conventional acid hydrolysis. To maximize both the productivity and the yield of the target products, the surface area for the immobilized enzyme should be increased. Our results suggest that it may be possible to obtain high yields of pentamers and hexamers of chitosan oligosaccharides from highly viscous chitosan solutions with this reactor.