LIPASE-CATALYZED INTERFACIAL REACTIONS IN REVERSE MICELLAR SYSTEMS - ROLE OF WATER AND MICROENVIRONMENT IN DETERMINING ENZYME-ACTIVITY OR DORMANCY

Studies of the effect of water content on the equilibrium position of a lipase-catalysed hydrolysis/esterification reaction in an AOT revers e micellar system show that the extent of reaction is apparently indep endent of omega(o), the mole ratio of water to surfactant, over the st udied range (2-40). Near-IR spectroscopy is shown to be a useful techn ique for the in situ monitoring of hydrolysis and synthesis reactions in reverse micelle-water-in-oil (w/o) microemulsion systems, and the m ethods applied are applicable to other low water systems. The hydrolys is and esterification activity of lipases tends to zero at low omega(o ), where the thermodynamic water activity much less than 1. It is show n that a state of reversible enzyme dormancy can be induced by dehydra ting the enzyme-containing w/o microemulsion. Molecular sieve beads we re considered unsuitable for this purpose because in addition to water , AOT and lipase were also adsorbed from the microemulsion. Molecular sieve powder was more effective, rapidly dehydrating w/o microemulsion s whilst leaving AOT and most of the lipase in solution. Drying throug h vapour-phase equilibration of the microemulsion with a saturated sal t solution in a closed system allowed the water activity to be precise ly controlled. Although relatively slow, vapour phase drying is 'clean ' in that it is specific only to water. AOT reverse micellar media con taining dormant Chromobacterium viscosum lipase can be stored for at l east a month with the lipase activity immediately regenerated on rehyd ration, with good recovery of catalytic activity. This phenomenon may have application in the food industry for the instant biogeneration of aroma and flavour compounds.