Enzymatic solvolysis of a model triglyceride, palm oil, was performed in microemulsions containing isooctane, sodiumbis(2‐ethylhexyl)sulfosuccinate (AOT), palm oil and a combination of water and glycerol as the polar component. Using a 1,3‐specific lipase both hydrolysis, leading to the formation of fatty acid and one mole of monoglyceride, and glycerolysis, giving three moles of monoglyceride, occur. The reaction was very slow in a completely nonaqueous system. Addition of a small amount of water led to an increased rate of glycerolysis, in addition to hydrolysis. It was found that by using3H labelled material reaction products originating from the two reactions were formed in equimolar amounts. The products probably emanate from a common intermediate. The molar ratio, R, of water and glycerol to surfactant turned out to be critical, optimum R‐value being 3.4. Four different lipases, one from porcine pancreas and three of fungal origin, were tested. No marked differences in ratio of monoglyceride to fatty acid formed were obtained, indicating that the ratio between glycerolysis and hydrolysis is constant regardless of the lipase used.

Lipase from Rhizopus sp. has been immobilized covalently on tresyl activated silica. Three different coupling media were evaluated: aqueous buffer, n-hexane, and a microemulsion based on n-hexane, aqueous buffer, and the nonionic surfactant triethylene glycol monododecyl ether. In addition, coupling via a very long, hydrophilic spacer arm, polyethylene glycol 1500 (PEG 1500), was compared with attachment to the silica via a short silane bridge only. The enzyme preparations were tested in hydrolysis and transesterification reactions. In the hydrolysis no marked differences in activity were found between the coupling media used. In the transesterification, on the other hand, the choice of immobilization medium had a very large effect on lipase activity, the preparation from microemulsion being the most active one. The use of the hydrophilic spacer had a large effect on activity in the hydrolysis reaction. Whereas direct coupling gave an activity of immobilized lipase of 26-34% of that of free enzyme, depending on the reaction medium, lipase bound via the spacer exhibited 56-67% activity. The latter values are considerably higher than previously reported in the literature for covalently immobilized lipase. The hydrophilic spacer had no effect on enzyme activity in the transesterification, however, a fact which is attributed to the hydrophobic medium of this reaction. The spacer is incompatible with the reaction medium and will, therefore, adsorb on the particles rather than stretch out into the bulk phase. The stability of the bound lipase was extremely good, no loss in activity being observed after a period of three weeks in aqueous solution of 37 degrees C.

Enzymatic hydrolysis of a model triglyceride, palm oil, was carried out with lipase from Rhizopus sp. in microemulsions with varying water content. The microemulsions were based on a nonionic surfactant, pentaethylene glycol monododecyl ether (C12 EO5), buffered water solution and an oil component consisting of isooctane and palm oil at a weight ratio of 20:1. The structure of the microemulsions was characterized using Fourier transform pulsed-gradient spin-echo 1H NMR. The rate of reaction decreased as the water content of the reaction medium was increased. The seifidiffusion coefficient of water, Dw, was found to be constant within the interval 1-20% water. The difference in reactivity is believed to be due to a difference in structure of the palisade layer between water and hydrocarbon microdomains. The nonionic surfactant was demonstrated to be unsuitable for enzymatic reactions since only partial hydrolysis was obtained in all experiments. The surfactant, however, did not cause enzyme deactivation, even at very high concentrations.

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