IMMOBILIZATION OF ASPERGILLUS-NIGER NRC-107 XYLANASE AND BETA-XYLOSIDASE, AND PROPERTIES OF THE IMMOBILIZED ENZYMES

Aspergillus niger NRC 107 xylanase and beta-xylosidase were immobiliized on various carriers by different methods of immobilization, including physical adsorption, covalant binding, ionic binding, and entrapment. The immobilized enzymes were prepared by physical adsorption on tannin-chitosan, ionic binding onto Dowex-50W, covalent binding on chitosan beads through glutaraldehyde, and entrapment in polyacrylamide had the highest activities. In most cases, the optimum pH of the immobilized enzymes were shifted to lower than those of free enzymes. The optimum reaction temperature of immobilized xylanase was shifted from 50-degrees-C to 52.5-65-degrees-C, whereas that of immobilized beta-xylosidase was shifted from 45-degrees-C to 50-60-degrees-C. The K(m) values of immobilized enzymes were higher than those of native enzymes. The operational stability of the immobilized enzymes was evaluated in continuous operation in packed-bead column-type reactors. The enzymes covalently bounded to chitosan showed the highest operational stability. However, the enzymes immobilized by physical adsorption or by ionic binding showed a low operational stability. The enzymes entrapped in polyacrylamide exhibited lower activity, but better operational stability.