The influence of glucose on the storage and operational stability of almond β-glucosidase during the glucosylation of cyclohexanol

The effect of glucose concentration on the stability of almond beta-glucosidase was investigated. The apparent productivity of the enzyme in a buffer solution with 10 g:glucose;kg buffer solution was about 4 mmol product/U enzyme, whereas it was over 22 mmol product/U enzyme in a 500 g glucose/kg buffer solution. This stabilising effect of glucose is an advantage for an industrially competitive enzyme catalysed glucosylation reaction. The operational stability of the enzyme during a glucosylation reaction was determined using cyclohexanol as the aglycon. The optimum glucoside yield was 65%, based on glucose. However, the optimum glucoside yield based on cyclohexanol was only 0.2%. The glucoside concentration in a reaction with a glucose concentration of 500 gi;kg Has ol-sr four times higher than in a reaction with 100 g;kg glucose. This effect could nor be attributed to substrate deficit, since both glucose and cyclohexanol were still present in sufficiently large amounts. Thr enzymatic glucosylation of cyclohexanol showed complex reaction kinetics, partially caused by substrate and co-solvent inhibition. However the calculated concentrations of both substrate and co-solvent in the aqueous phase did not correlate with the observed reaction rates, indicating that other factors play a role as well.