fluorescence spectroscopy (Brown et al., 1993; Marangoni, 1993; Miyake et al.,
1993a; Walde et al., 1993; Otero et al., 1995). Furthermore, the presence of FFA
was reported to reduce the degree of structural change (Walde et al., 1993). The
same study demonstrated the need of the protein co-lipase to yield an active w/
o-ME-encapsulated porcine pancreatic lipase (Walde et al., 1993).
In contrast to AOT, enzyme stability in CTAB and lecithin w/o-ME systems is
significantly improved compared to AOT (Rees and Robinson, 1995; Avramiotis
et al., 1996).
3.2.6 Influence of lipase on microemulsion structural properties
It would be expected that the presence of lipase, a molecule with geometric dimen-
sions on the same order of magnitude as the diameter of the w/o-MEs, would perturb
the structure and behavior of w/o-MEs. In addition, the occurrence of lipases near
interfacesin vivowould support this hypothesis. In agreement, small angle X-ray
scattering results demonstrate that the lipases reduce w/o-ME size, presumably
by acting as a surface-active agent (Papadimitriou et al., 1995). Further evidence
of w/o-ME structural changes were detected using time-resolved fluorescence
energy transfer experiments (Avramiotis et al., 1996).
3.2 Lipases encapsulated in water-in-oil microemulsions 57
Figure 4. Effect of solvent onR. delemarstability in glycerol and fatty acid-containing microemulsions
of the AOT system. (Reproduced with permission from Hayes, 1991).