title: Enzymatic production and complete nuclear magnetic resonance assignment of the sugar lactulose.
abstract: The enzymatic transgalactosylation from lactose to fructose leading to the prebiotic disaccharide lactulose was investigated using the beta-galactosidase from Aspergillus oryzae and the hyperthermostable beta-glycosidase from Pyrococcus furiosus (CelB). The conditions for highest lactulose yields relative to the initial lactose concentration were established on a 1 mL scale. Dependent on the initial molar ratio of lactose to fructose, more or fewer oligosaccharides other than lactulose were generated. Bioconversions on a 30 mL scale in a stirred glass reactor were performed, and lactulose yields of 46 mmol/L (44% relative to lactose) for CelB and 30 mmol/L (30% relative to lactose) for A. oryzae beta-galactosidase were achieved. Only <5% of other oligosaccharides were detectable. The corresponding productivities were 24 and 16 mmol/L/h, respectively. The molecular structure of lactulose was investigated in detail and confirmed after purification of the reaction solution by LC-MS and 1D and 2D NMR. Lactulose (4-O-beta-D-galactopyranosyl-D-fructose) was unambiguously proved to be the major transglycosylation disaccharide.
authors.affiliation: Department of Biotechnology, Institute of Food Technology, University of Hohenheim, Emil-Wolff-Strasse 14, 70599 Stuttgart, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Mayer
authors.forename: Jürgen
authors.initials: J
authors.lastname: Conrad
authors.forename: Iris
authors.initials: I
authors.lastname: Klaiber
authors.forename: Sabine
authors.initials: S
authors.lastname: Lutz-Wahl
authors.forename: Uwe
authors.initials: U
authors.lastname: Beifuss
authors.forename: Lutz
authors.initials: L
authors.lastname: Fischer
mesh_terms: D001236:Aspergillus oryzae / Q000201:enzymology; D044602:Cellulases / Q000378:metabolism; D005632:Fructose / Q000378:metabolism; D007536:Isomerism; D007785:Lactose / Q000378:metabolism; D007792:Lactulose / Q000096:biosynthesis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D020027:Pyrococcus furiosus / Q000201:enzymology; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D005632:Fructose; D007792:Lactulose; D044602:Cellulases; D001616:beta-Galactosidase; D007785:Lactose