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 chi tosan and xanthan is reported. Stable hydrogels capable of retaining b etween 65 and 95% weight water were prepared. The water retention and properties of the hydrogels were studied as a function of the degree o f acetylation of chitosan and the ratio chitosan/xanthan used in the p reparation of the gel. Spectroscopic FTIR was used to confirm complexa tion between the amine (chitosan) and carboxylic (xanthan) groups. Ele ctron micrographs (SEM and TEM) show the formation of a fibrillar stru cture with characteristic pore sizes between 100 and 1000 nm and fibri l diameters between 50 and 100 nm. The diffusion coefficient of 4-0-me thyl-d-glucurono-D-xylan Remazol Brilliant Blue R (RBB-xylan) in the c omplex 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 sy stem. Immobilization varied between 85 and 98%. The immobilized xylana se activity was significantly greater with respect to the free enzyme while the binary enzyme system promoted protease activity.