Front Matter

3.5.2 Lecithin gels

Luisi and co-workers combined lipase, triglyceride substrate, cyclooctane, and water

at determined proportions to produce a gel (Scartazzini and Luisi, 1990). Hydrolysis

occurred in the solid phase until a critical concentration of fatty acid was reached,

which led to a solid-to-liquid phase transition.

The research group from Turku, Finland, formed lecithin–gelatin gels using a

similar approach to that developed for the AOT–gelatin gels. They combined a bi-

continuous lecithin/ethanol/water/1-hexadecane system with aqueous gelatin solu-

tion to form a stable gel. The gel esterified 2-octanol with good enantioselectiv-

ity; however, the performance of this gel was inferior to that of AOT–gelatin gel

(Backlund et al., 1995). In addition, the ethanol existing in the gel phase served

as an acyl donor, producing fatty acid ethyl ester byproduct (Hedstro ̈m et al.,

1997). Xenakis and co-workers employed a similar aproach; except that several

gelation reagents were screened (Stamatis and Xenakis, 1999). Indeed, it was found

that agar outperformed gelatin (Stamatis and Xenakis, 1999). Their gels exhibited

excellent activity retention, but as the concentration of lipase in the gel was in-

creased, the observed reacstion rate did not increase proportionally (Stamatis and

Xenakis, 1999).

3.6 Lipid modification catalyzed by other

microemulsion-encapsulated enzymes

A brief survey of other enzyme-catalyzed lipid transformations in w/o-MEs will now

be given.

3.6.1 Phospholipases

Phospholipase A 2 has been employed to hydrolyze phosphatidylcholine (yielding

lyso-phosphatidylcholine and fatty acid as product) and to perform the reverse re-

action, esterification, in mixed AOT–lecithin w/o-MEs (Na et al., 1990; Holmberg

and Eriksson; Morgado et al., 1995). The important parameters in the operation of

these reactions include the presence of calcium, a necessary co-factor, and the pro-

cedure employed to form w/o-ME solution (Na et al., 1990; Holmberg and Eriksson,

1992; Morgado et al., 1995). Cabral and co-workers conducted the hydrolytic reac-

tion in a ultrafiltration membrane bioreactor (Morgado et al., 1996). Phospholipase

A 2 was unable to catalyze acidolysis of phosphatidylcholine (Holmberg and Eriks-

son, 1992). In addition to phospholipase A 2 , the hydrolysis of phosphatidylcholine

was conducted using Phospholipase D in Triton X-100/phosphatidylcholine w/o-

MEs in reasonably good yield (Subramani et al., 1996). The products from this re-

action are choline and phosphatidic acid.

62 3 Lipid Modification in Water-in-Oil Microemulsions