Abstract
Fresh edible burdock roots were stored in soil of 1 m depth underground from November to May. Three fructooligosaccharide derivatives without a terminal glucose residue, designated saccharides 1, 2 and 3, were generated in the stored burdock roots. They were purified from the sugar extract using carbon-Celite column chromatography. Saccharides 1, 2 and 3 have R-sucrose values (retention time of sucrose = 1) of 1.55, 2.15 and 2.73 by HPAEC, reducing terminal, molar ratios (reducing sugar to D-fructose) of 0.50, 0.33 and 0.25 and degrees of polymerization of 2, 3 and 4 by TOF-MS, respectively. Analyses by GLC and NMR confirmed the three different following structures: first was inulobiose [β-D-fructofuranosyl-(2→1)-β-D-fructopyranose], and the two others were inulotriose [β-D-fructofuranosyl-(2→1)-β-D-fructofuranosyl-(2→1)-β-D-fructopyranose] and inulotetraose [β-D-fructofuranosyl-(2→1)-β-D-fructofuranosyl-(2→1)-β-D-fructofuranosyl-(2→1)-β-D-fructopyranose]. The NMR spectra showed that 70 to 80% of the terminal fructose residue of the three saccharides is pyranosyl form, while 20 to 30% is furanosyl form. The 13C- and 1H-signals were also assigned by 2D-NMR including COSY, HSQC, HSQC-TOCSY and HMBC. These saccharides could be synthesized by purified burdock fructan:fructan 1-fructosyltransferase from 1-kestose to free D-fructopyranose giving inulobiose and sucrose, while elongation of fructofuranosyl units occurred at this transferred fructofuranosyl residue to produce inulooligosaccharides having one, two and more additional units of fructofuranose.
