Lipase-catalysed interfacial reactions in reverse micellar systems. Role of water and microenvironment in determining enzyme activity or dormancy

Abstract

Studies of the effect of water content on the equilibrium position of a lipase-catalysed hydrolysis/esterification reaction in an AOT reverse micellar system show that the extent of reaction is apparently independent of ω_o, the mole ratio of water to surfactant, over the studied range (2–40). Near-IR spectroscopy is shown to be a useful technique for the in situ monitoring of hydrolysis and synthesis reactions in reverse micelle–water-in-oil (w/o) microemulsion systems, and the methods applied are applicable to other low water systems. The hydrolysis and esterification activity of lipases tends to zero at low ω_o where the thermodynamic water activity 1. It is shown that a state of reversible enzyme dormancy can be induced by dehydrating the enzyme-containing w/o microemulsion. Molecular sieve beads were 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 microemulsions whilst leaving AOT and most of the lipase in solution. Drying through vapour-phase equilibration of the microemulsion with a saturated salt solution in a closed system allowed the water activity to be precisely controlled. Although relatively slow, vapour phase drying is ‘clean’ in that it is specific only to water. AOT reverse micellar media containing dormant Chromobacterium viscosum lipase can be stored for at least a month with the lipase activity immediately regenerated on rehydration, with good recovery of catalytic activity. This phenomenon may have application in the food industry for the instant biogeneration of aroma and flavour compounds.