Dependence of the activity of a rhizopus lipase on microemulsion composition

• 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 self-diffusion 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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