Reaction Rates in Organic Media Show Similar Dependence on Water Activity with Lipase Catalyst Immobilized on Different Supports

Lipase (E.C. 3.1.1.3) from Rhizomucor miehei was adsorbed on silica, zirconia and five alumina support materials. The immobilised preparations were used to catalyse esterincation reactions of decanoic acid and dodecanol in hexane. The immobilised lipase and the organic phase were separately preequilibrated to the desired water activities. The various support materials adsorbed widely different amounts of water at a given water activity. The reaction rates with all the support materials show similar dependence on water activity when the rates were normalised with the optimal rate for that support material. Hence water activity predicts the optimal conditions much better than water content.