rates, since in the micellar systems, biocatalysts are highly dispersed and the interfacial
area of contact is enormous. This reduces the detrimental effect of shear stress forces on
the enzyme structure.
The disadvantages are far fewer and include:
− Denaturing effects of surfactant; and
− Product recovery and enzyme re-use are still difficult.
ApplicationsThe early applications of microemulsions included their use in floor polishes, cutting oils
and pesticide formulations. The actual applications are mainly in the industrial and
household sectors. Three important applications of microemulsions were described by
Holmberg (1998) and include enhanced oil recovery (EOR) and cleaning and reaction
medium for organic reactions. The EOR application of microemulsions derives from its
ability to reduce oil-water interfacial tension to very low values and is still at the research
level. Finally, the biocatalytic applications are an emerging field and involve mainly w/o
microemulsions.
The examples of enzymes studied in reversed micelles and catalysed reactions are
numerous (for a review see Martinek, (1989); Martinek et al., 1987); Oldfield, 1994).
Among these processes some have potential industrial applications in areas such as foods,
pharmaceuticals, chemicals and bioremediation (see Table 7.1).
Biotranformation in reversed micelles has not been exclusively performed by isolated
enzymes. The inclusion of cells in reversed micellar aggregates functions as an
immobilisation process, with the advantages of substrate/product solubility and protection
against solvent effects. Furthermore, it avoids the time-consuming process of isolation/
purification of enzymes and permits the use of the cell factory and respective resources
such as co-factors. In spite of the fact that the process has these advantages, a few points
still have to be investigated. One is the effect of surfactants on cell viability, since they
can promote cell lysis. Another point to address is the structure of cell-encapsulated
reversed micelles.
Some of the examples found in the literature on cell microencapsulation include:
Acinetobacter calcoaceticus and a strain of E. coli (Haering et al., 1985), Mycobacterium
sp. strain M156 (Prichanont et al., 1994) and Saccharomyces cerevisiae (Fadnavis et al.,
1989; 1990; Gajjar et al., 1997). The possibility of maintaining bacterial cells in a viable
state led Hochkoeppler and Luisi (1989) to study the microencapsulation of smaller
organelles such as mitochondria opening new perspectives for the use of cellular
machinery in reversed micellar biotransformations.
Reversed micellar technology has also been widespread in the antibodies field. A
catalytic monoclonal antibody preparation (abzyme) was reported to retain its activity in
Table 7.1 Areas of industrial application of
biocatalysis performed in reversed micellar systems
Industry Process References
Multiphase bioreactor design 194