Optimisation of β-glucosidase entrapment in alginate and polyacrylamide gels

Immobilisation of β-glucosidase, isolated from Aspergillus niger, by entrapment in both calcium alginate and polyacrylamide gels was studied. A retention of 66% of initial activity was observed in the alginate beads prepared with 3% (w/v) alginate, 0.2 CaCl2 and 1 h of treatment. The maximum β-glucosidase activity in polyacrylamide gels ( 55%) was achieved in gels prepared with 20% acrylamide and 1.2% of crosslinking agent (bisacrylamide). β-Glucosidase immobilised in alginate gel did not follow pure Michaelis kinetics, exhibiting substrate inhibition. The Km of this enzyme was larger than that of the free β-glucosidase, suggesting that the alginate network limited the permeation rate of substrate and product. However, β-glucosidase entrapped in polyacrylamide gel showed a similar Km value to that of native enzyme. The pH value for maximum activity of free and immobilised enzymes was 4.0. The pH-activity curves were coincident, except at very low pH values where the enzyme trapped in alginate was more stable.