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Lipase-catalyzed hydrolysis of triglycerides yields glycerol and free fatty-acids, provided that the enzyme is non-regioselective. For an Sn-1,3 regioselective enzyme, such as lipase from Thermomyces lanuginosus, the final product is no longer glycerol but Sn-2 monoglyceride instead. However, surface active molecules generated by lipolysis may have a detrimental effect on the interfacial biocatalysis since it is known that low molecular weight surfactants can displace proteins from interfaces. By using drop profile analysis tensiometry, we evaluated the interfacial properties of the lipase-generated molecules and their competitive effect on the adsorption behavior of the lipase and on the proceeding lipolysis. Our results show that even at concentration ratios of 8.64×10 -4 M (Sn-2 monoglyceride) to 2.5×10 -7 M (lipase), the final interfacial pressure values are very similar as for the system containing the lipase alone (i.e. ∼26 mN/m). This is a strong indication that monoglycerides, as the most interfacially active products generated during regioselective lipolysis, are expelled from the oil-water interface by the lipase. We attribute this effect to intermolecular lipase-lipase interactions, resulting in a low desorption probability of the lipase. For low oleic acid concentrations, the interfacial tension is solely determined by the lipase, while for higher concentrations, lipase and oleic acid both contribute to the tension values. We propose a hypothesis based on the preferential interaction of oleic acid molecules with hydrophobic sites on the lipase. The pH dependence of the adsorption rate and the interfacial activity of the lipase were also investigated., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Ellipsometric studies of very thin organic films suffer from the low refractive index contrast between layer and bulk substrate. We demonstrate that null ellipsometry can not only provide detailed information about the adsorption kinetics and surface excess values, but in addition on layer thicknesses with submonolayer resolution of a lipase from Thermomyces lanuginosus at the air-water interface. While measuring very close to the Brewster angle, refractive indices and layer-thicknesses can both be determined with a precision that is sufficiently high to make conclusions on the density and orientation of the molecules at the interface. The orientation was found to be concentration- and pH value-dependent. At the isoelectric point, the lipase was almost vertically oriented with respect to the surface, while for pure distilled water and low lipase concentration a rather horizontal alignment was found. Further experiments, varying the size of the interfacial area in a Langmuir trough, confirm the different layer structures., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In order to assess the capillary segmented flow reactor as a potentially appropriate reactor device for the enzymatic hydrolysis of vegetable oils, a study was made to reveal the impact of incident mass transfer processes on the hydrolysis rate. As demonstrated by means of experiments performed in a modified Lewis-cell type contactor, which allows the independent adjustment of flow rates for both phases, the enzymatic hydrolysis rate of rapeseed oil is strongly governed by mass transport processes taking place in both phases. In the oil phase, any increase in convective mass transfer results in an enhancement of hydrolysis rate due to facilitated removal of fatty acids from interface layer which is known to inhibit the activity of the enzyme adsorbed at the interface. At asynchronous condition when solely the water phase is agitated, however, convective mass transport in the interface layer has an inverse effect on the hydrolysis rate due to the generation of considerable shear stress in the vicinity of the interface unfavorable for the performance of the enzymes. By operating at synchronous agitation conditions, the shear stress can considerably be reduced. Generally, the positive effect of mass transport in the oil phase compensates the negative one in the aqueous phase thus resulting in an overall increase in hydrolysis rate of 57% with increasing stirrer rates. The results can be applied to the operation of segmented-flow capillary reactors by choosing the oil phase as disperse phase and the water phase as continuous phase, respectively.