Structure of fructopolysaccharide (asparagosin) from roots of asparagus (Asparagus officinalis L.)



Fructopolysaccharide (asparagosin, fructan) was prepared from an extract of asparagus roots by chromatography on carbon-Celite, paper and Toyopearl HW-40S (gel permeation). The asparagus fructopolysaccharide was a mixture of saccharides ranging from DP (degree of polymerization) 12 to 22 approximately. It yielded fructose and glucose by hydrolyzing with acid or yeast β-fructofuranosidase. The ratio of fructose to glucose in the enzyme hydrolysate was 13:1 by HPLC analysis. Structural determinations were made by 13C-NMR spectroscopy. Strong signals corresponding to carbon-1 (C-l), C-2, C-3, C-4, C-6 and C-5 of fructose residues in the fructopolysaccharide were observed at δ61.08–61.77, 103.64–104.26, 77.42–78.08, 74.43–75.09, 62.71–63.00 and 81.74 respectively. These chemical shifts were similar to those of inulin. Moreover, weaker signals were also detected at δ92.85, 71.80, 73.13, 69.79 and 72.23 due to C-l, C-2, C-3, C-4 and C-5 of the glucose residue. The chemical shifts are almost identical to those of glucose carbons in raffinose, neokestose, 6G(l-β-D-fructofuranosyl)2sucrose and lF,6G-di-β-D-fructofuranosyl sucrose. These findings were confirmed by analysis of methanolysate from permethylated fructopolysaccharide by using gas-liquid chromatography. The fructopolysaccharide from asparagus roots was composed of saccharides possessing approximately 11–21 fructose residues linked by β-2,l bonds and a non-terminal glucose residue bound with fructose residues at positions C-l and C-6.