Selective Synthesis of Galactooligosaccharides Containing beta(1 -> 3) Linkages with beta-Galactosidase from Bifidobacterium bifidum (Saphera)

摘要

The transglycosylation activity of a novel commercial beta-galactosidase from Bifidobacterium bifidum ( Saphera) was evaluated. The optimal conditions for the operation of this enzyme, measured with o-nitrophenyl-beta-D-galactopyranoside, were 40 degrees C and pH around 6.0. Although at low lactose concentrations the property of this enzyme was basically hydrolytic, an increase of lactose concentration to 400 g/L resulted in a significant formation (107.2 g/L, 27% yield) of prebiotic galactooligosaccharides (GOS). The maximum amount of GOS was obtained at a lactose conversion of approximately 90%, which contrasts with other beta-galactosidases, for which the highest GOS yield is achieved at 40-50% lactose conversion. Using high-performance anion-exchange chromatography with pulsed amperometric detection, semipreparative high-performance liquid chromatography-hydrophilic interaction liquid chromatography, mass spectrometry, and 1D and 2D NMR, we determined the structure of most of the GOS synthesized by this enzyme. The main identified products were Gal-beta(1 -> 3)-Gal-beta(1 -> 4)-Glc (3'-O-beta-galactosyl-lactose), Gal-beta(1 -> 6)-Glc (allolactose), Gal-beta(1 -> 3)-Glc (3-galactosyl-glucose), Gal-beta(1 -> 3)-Gal (3-galactobiose), and the tetrasaccharide Gal-beta(1 -> 3)-Gal-beta(1 -> 3)-Gal-beta(1 -> 4)-Glc. In general, B. bifidum beta-galactosidase showed a tendency to form beta(1 -> 3) linkages followed by beta(1 -> 6) and more scarcely beta(1 -> 4).