Structural identification of novel oligosaccharides produced by Lactobacillus bulgaricus and Lactobacillus plantarum.

beta-Galactosidases (beta-Gal) of lactic acid bacteria produce oligosaccharides from lactose when suitable acceptor carbohydrates are present. This study aimed to elucidate the structure of oligosaccharides formed by galactosylation of N-acetylglucosamine (GlcNAc) and fucose. Crude cellular extract of Lactobacillus bulgaricus and LacLM of Lactobacillus plantarum were used as sources of beta-Gal activity. Disaccharides obtained by galactosylation of GlcNAc were identified as Gal-beta-(1 -> 4)-GlcNAc or Gal-beta-(1 -> 6)-GlcNAc by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and comparison with external standards. Trisaccharides were identified as Gal-beta-(1 -> 6)-Gal-beta-(1 ->[4 or 6])-GlcNAc by LC-MS, analysis of the MS/MS spectra of selected in-source fragment ions, and their relative retention times. LC-MS analysis revealed the presence of five galactosylated fucosides, but their linkage type could not be identified, partly due to the lack of reference compounds. beta-Gal of lactic acid bacteria may serve as suitable tools for the chemoenzymatic synthesis of therapeutic oligosaccharides.