Enhanced catalytic efficiency of enzymes in organic media with the addition of the solid support: Effect of silica gel on reaction rates and enzyme agglomeration

Abstract

Enzymatic esterification of octanoic acid with methanol in cyclohexane was investigated using Candida rugosa lipase in the absence or presence of silica gel. The lipase was added in the form of a suspended dried powder, and the effects of water content and shaking rate on the reaction rates were examined. It was found that the maximal reaction rate could be markedly enhanced by the addition of silica gel to the medium with shifting the optimal water content to a higher value. In order to identify the reasons for the rate improvement in the presence of the support, the effects of water content and silica gel on the distribution of water, partitioning of the substrates, enzyme inactivation, and agglomeration of enzyme particles were examined. Under the conditions studied, enzyme agglomeration was the largest factor reducing activity at high water contents and the enhanced activity with the addition of silica gel was mainly attributed to effective reduction of agglomerate size in the solvent medium. It was also shown that repeated use of the enzyme is very effective in the presence of silica gel. The yields in successive batch runs increased with increasing the ratio of silica gel to the enzyme.