Enzymatic Synthesis of Hexyl Glycosides from Lactose At Low Water Activity and High Temperature Using Hyperthermostable β-glycosidases

Abstract

Optimization of hexyl-g-glycoside synthesis from lactose in hexanol at low water activity and high temperature was investigated using g-glycosidases from hyperthermophilic organisms: Sulfolobus solfataricus (LacS) and Pyrococcus furiosus (CelB). The method for water activity adjustment by equilibration with saturated salt solutions was adapted for use at high temperature. The influence of enzyme immobilization (on XAD-4, XAD-16, or Celite), addition of surfactants (AOT or SDS), substrate concentration, water activity, and temperature (60-90°C) on enzymatic activity and hexyl-g-glycoside yield were examined. Compared to other g-glycosidases in lactose conversion into alkyl glycoside, these enzymes showed high activity in a hexanol one-phase system and synthesized high yields of both hexyl-g-galactoside and hexyl-g-glucoside. Using 32 u g/l lactose (93 u mM), LacS synthesized yields of 41% galactoside (38.1 u mM) and 29% glucoside (27.0 u mM), and CelB synthesized yields of 63% galactoside (58.6 u mM) and 28% glucoside (26.1 u mM). With the addition of SDS to the reaction it was possible to increase the initial reaction rate of LacS and hexyl-g-galactoside yield (from 41 to 51%). The activity of the lyophilized enzyme was more influenced by the water content in the reaction than the enzyme on solid support. In addition, it was concluded that for the lyophilized enzyme preparation the enzymatic activity was much more influenced by the temperature when the water activity was increased. A variety of different glycosides were prepared using different alcohols as acceptors.