Production and identification of galacto-oligosaccharides from lactose using β-D-galactosidases from Lactobacillus leichmannii 313

Crude β-D-galactosidase from Lactobacillus leichmannii 313 was used to synthesise galacto-oligosaccharides (GOS) from lactose. Using an initial lactose concentration of 170 g/L, the yield of GOS was 52 g/L (i.e. 62% lactose conversion) after 2 h of enzymatic reaction. The highest number of unique individual GOS were generated after 48 h of reaction. ESI-MS and HPAEC analysis of the GOS enriched fractions obtained from 48 h mixtures showed the presence of sugars with degrees of polymerization (DP) ranging from 2 to 6. Further analysis (by NMR spectroscopy) of GOS in fraction 3 (containing ~ 96% w/w GOS) showed non-reducing terminals that were mostly Galp; and reducing ends that were →4)-Glcp, and →6)-Glcp. The most abundant internal linkages in fraction 3 were deduced to be →3)-Galp-(1→, and →6)-Galp-(1→. The predominance of β-D-(1→3, or 6) linkages in GOS fractions suggests that β-D-galactosidase from LL313 is suitable for generating unique GOS from lactose.