Immobilization and Stabilization of Chitosanase by Multipoint Attachment to Agar Gel Support

Abstract

Highly stable chitosanase immobilized on an agar gel support was prepared by the multipoint attachment method. The optimum pH range was broadened to between 4 and 6, whereas for free chitosanase, the pH was only 5.6. The optimum temperature was also increased from 60 degrees C to 80 degrees C after the immobilization. The activity of immobilized chitosanase remained at 95% of its initial activity level after 225 h of incubation at 50 degrees C, whereas for free chitosanase, it decreased to 20% after 1 h of incubation. The immobilization markedly increased the thermostability of chitosanase. These changes in the reaction characteristics are favorable for the practical use of chitosanase in industrial processes. The effect of glycidol concentration in the activation of agar gel was also examined. The surface density of the aldehyde residue increased with increasing glycidol concentration. A maximal activity of 11.9 U/g-support was obtained when the glycidol concentration was 0.7 M. At concentrations higher than this, thermostability was almost the same. It was therefore proven that the optimal glycidol concentration in this system is 0.7 M. The effects of glycidol concentration on the activity and the thermostability of chitosanase are discussed in relation to the number of covalent bonds between the chitosanase and its support. Chitosan oligosaccharides were continuously produced using a column reactor packed with the immobilized chitosanase. The percentage of hydrolyzed chitosan after 28 reaction days was 44%. This was a slight decrease from the 48% observed on the first day. The total concentration of pentamer and hexamer ranged from 1.3 mg/ml to 1.5 mg/ml during the 28 reaction days. This was approximately 30% of the chitosan concentration in the supplied substrate solution.