Selective synthesis of galactooligosaccharides containing β(1→3) linkages with - β galactosidase from Bifidobacterium bifidum (Saphera)

The transglycosylation activity of a novel commercial β-galactosidase from Bifidobacterium bifidum (Saphera) was evaluated. The optimal conditions of operation of this enzyme, measured with o-nitrophenyl-β-D-galactopyranoside, were pH 6.0 and 40 °C. Although at low lactose concentrations the character 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 β-galactosidases, for which the highest  GOS  yield  is  achieved  at  40-50%  lactose  conversion.  Using  HPAEC-PAD, semipreparative HPLC-HILIC, MS, 1D and 2D NMR, we determined the structure of most of the GOS synthesized by this enzyme. The main identified products were Gal-β(1®3)-Gal-β(1®4)-Glc  (3´-O-b-galactosyl-lactose), Gal-β(1→6)-Glc (allolactose), Gal-β(1®3)-Glc (3-galactosyl-glucose), Gal-β(1→3)-Gal (3-galactobiose) and the tetrasaccharide Gal-β(1®3)-Gal-β(1®3)-Gal-β(1®4)-Glc. In general, the B. bifidum β-galactosidase showed a tendency to form β(1®3) linkages followed by β(1®6), and more scarcely β(1®4) .