Extracellular microbial lipases can be used as catalysts for the interesterification of oils and fats. Use of specific lipases gives products which are unobtainable by chemical interesterification methods. Some of these products have properties of value to the oils and fats industry. The catalysts for enzymatic interesterification are prepared by coating inorganic support materials with the lipases. For batch interesterification reactions, the catalyst particles are activated by addition of a small amount of water and then stirred with a reactant mixture dissolved in petroleum ether. At the end of the reaction period, the catalyst particles are removed by filtration, and the interesterified triglycerides isolated by conventional fat fractionation techniques. The catalyst can be used in subsequent batch reactions. As an alternative to the batch reaction system, continuous enzymatic interesterification processes can be operated by pumping water containing feedstock through a packed bed of activated catalyst.

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The rates of synthesis of dodecyl decanoate in hexane have been measured as a function of water activity (a,), for various immobilised preparations of the lipases from Rhizomucor miehei and Candida rugosa. Only very large changes in the amount of enzyme adsorbed to the support affect the shape of the ratela, profile; at the highest loadings the profiles tend to become somewhat flatter. A similar levelling can be obtained by pre-adsorbing an inert protein. The effect is probably due to adjacent protein molecules effectively replacing water ; it does not simply reflect mass transfer or interfacial area limitation. The activityla, profile was essentially the same with most supports tested : polypropylene, anion-exchange resin, celite, anion-exchange modified silica. A hydrophobic porous glass support reduced the rate somewhat at intermediate a, values with both enzymes; a polyamide material had this effect only with the lipase from Rh. miehei. The shape of the activityla, profile was not affected by large differences in purity of the lipase preparation, but did differ between forms that probably differ in glycosylation. Overall, relatively few manipulations of the system can significantly affect the shape of the ratela, profiles, which seem to be mainly an intrinsic property of the enzyme molecules used.