Lactulosucrose (4 F-β-galactosylsucrose), a new trisaccharide synthesized by cultures of Leuconostoc mesenteroides strain K (NRRL B-1299)

Abstract

Leuconostoc mesenteroides strain K has been found to synthesize a new nonreducing trisaccharide of melezitose-planteose type, lactulosucrose. This trisaccharide has been isolated in crystalline form and shown to have the structure, O-β- d-galactopyranosyl-(1 → 4)- O-β- d-fructofuranosyl-(2 → 1)-α- d-glucopyranoside (4 F-β-galactosylsucrose). An experiment with C 14-sucrose established that lactulosucrose is formed by α-glucosyl transfer from sucrose to the anomeric carbon of lactulose (β-fructofuranose form). Discovery of the new saccharide followed an unsuccessful attempt to confirm a recent report that L. mesenteroides K (or B-1299) converts a mixture of sucrose and lactose to lactsucrose (4 G-β-galactosylsucrose). Synthesis of the latter saccharide was verified in the case of the NRRL B-512 strain of L. mesenteroides, and would be due to levansucrase-catalyzed β-fructosyl transfer from sucrose to lactose in this culture.