Enzymatic production and complete nuclear magnetic resonance assignment of the sugar lactulose

Publication Type

Journal contribution (peer reviewed)

Authors

Mayer, J.; Conrad, J.; Klaiber, I.; Lutz-Wahl, S.; Beifuss, U.; Fischer, L.

Year of publication

2004

Published in

J. Agric. Food. Chem.

Band/Volume

52/23

DOI

10.1021/jf048912y

Page (from - to)

6983-6690

The enzymic transgalactosylation from lactose to fructose leading to the prebiotic disaccharide lactulose was investigated using the -galactosidase from Aspergillus oryzae and the hyperthermostable -glycosidase from Pyrococcus furiosus (CelB). The conditions for highest lactulose yields relative to the initial lactose concn. 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 -galactosidase were achieved. Only <5% of other oligosaccharides were detectable. The corresponding productivities were 24 and 16 mmol/L/h, resp. The mol. structure of lactulose was investigated in detail and confirmed after purifn. of the reaction soln. by LC-MS and 1D and 2D NMR. Lactulose (4-O- -D-galactopyranosyl-D-fructose) was unambiguously proved to be the major transglycosylation disaccharide.