Enzymatic synthesis and identification of oligosaccharides obtained by transgalactosylation of lactose in the presence of fructose using β-galactosidase from Kluyveromyces lactis

► Allo-lactulose(β-d-galactopyranosyl-(1 → 1)-fructose) is the major product. ► Lactulose(β-d-galactopyranosyl-(1 → 4)-fructose) is the minor product. ► Allo-lactulose is about three times the amount of lactulose. ► The major isomer for allo-lactulose is β-d-galactopyranosyl-(1 → 1)-fructopyranose.