Synthesis of galactooligosaccharides and transgalactosylation modeling in reverse micelles

Galactooligosaccharides (GOS) were synthesized by β-galactosidase (Escherichia coli) under controllable water concentration in reverse micelles. The products were precipitated by adding acetonitrile, and then separated by a semi-preparative HPLC column. Allolactose as one of the major products was purified and verified by the 13C NMR analysis. The highest production of GOS was 29.7% (w/w) allolactose and 14% of other oligosaccharides under experimental conditions of pH 6.5, 37 °C and molar ratio of water to surfactant Wo=19.32. Increasing Wo decreased the production of GOS. Increasing temperature did not enhance the synthesis of GOS, but more allolactose (45%) could be produced at 45 °C, pH 6.5 and Wo=19.32. This study proposes a transgalactosylation model that involves free water in reverse micelles and shows a good correlation with experimental data.