POLYIONIC HYDROGELS OBTAINED BY COMPLEXATION BETWEEN XANTHAN AND CHITOSAN - THEIR PROPERTIES AS SUPPORTS FOR ENZYME IMMOBILIZATION

A method for the preparation of hydrogels from the complexation of chitosan and xanthan is reported. Stable hydrogels capable of retaining between 65 and 95% weight water were prepared. The water retention and properties of the hydrogels were studied as a function of the degree of acetylation of chitosan and the ratio chitosan/xanthan used in the preparation of the gel. Spectroscopic FTIR was used to confirm complexation between the amine (chitosan) and carboxylic (xanthan) groups. Electron micrographs (SEM and TEM) show the formation of a fibrillar structure with characteristic pore sizes between 100 and 1000 nm and fibril diameters between 50 and 100 nm. The diffusion coefficient of 4-0-methyl-d-glucurono-D-xylan Remazol Brilliant Blue R (RBB-xylan) in the complex chitosan-xanthan was 2.02 x 10(-12) m2s-1 at 30-degrees-C. The chitosan-xanthan complex was used to immobilize two enzymes (endo-1,4-beta-xylanase and protease) either as single enzymes or as a binary system. Immobilization varied between 85 and 98%. The immobilized xylanase activity was significantly greater with respect to the free enzyme while the binary enzyme system promoted protease activity.