IMMOBILIZATION AND CHARACTERIZATION OF A THERMOSTABLE β-GLUCOSIDASE FROM ASPERGILLUS TERREUS NRRL 265

Abstract

Partially purified β-glucosidase from Aspergillus terreus NRRL 265 was immobilized by entrapment in calcium-alginate beads. The activity of the free and immobilized enzymes as a function of pH, temperature, and periodic use were compared. Whey permeate, a by-product of cheese industry, was served as an inexpensive medium, which made the process economical and reduced the cost of enzyme production and also reduced the environmental pollution. The results indicated that, the immobilized β-glucosidase was retained about 73 % of the original activity exhibited by the free enzyme. The optimum temperature for the enzyme activity was improved by 5ºC after immobilization. Immobilized β-glucosidase was exhibited great thermal stability, whereas, at 70ºC, the free enzyme lost its activity after 30 min of incubation, while the immobilized enzyme showed more stability in comparison to the free form as it retained about 13.4 % of its initial activity under the same conditions. Moreover, the pH stability was improved following immobilization, whereas, the immobilized enzyme was stable in pH ranging from 4.0 to 7.0 with no change in activity, while its stability slightly decreases for more alkaline or acidic conditions (retaining 82.4 % and 67.4 % of the initial activity at pH 8.0 and 3.5, after 1 h of incubation). The results also indicated the possibility of reusing Ca alginate-immobilized β-glucosidase in industrial applications for 10 cycles with 53.7 % retained activity.