Isolation and structure characterization of a low methyl-esterified pectin from the tuber of Dioscorea opposita Thunb.

A low methyl-esterified pectin (33.2% methyl-esterification degree) was isolated from the tuber of Dioscorea opposita Thunb., which was an edible and medicinal material in China. This pectin (Mw of 1.3 x 104 g/mol) contained the -59.1% homogalacturonan (HG) and -38.1% highly branched rhamnogalacturonan I (RG-I) region with possible side chains embracing arabinogalactan II, arabinan or arabinogalactan I. The fragments including HG backbone consisting of -> 4)-alpha-GalpA-(1 -> and -> 4)-alpha-GalpA-6-O-methyl-(1 -> with molar ratio of -2:1, and repeating unit of arabinogalactan II side chain composed of alpha-Araf-(1 -> and -> 3,6)-beta-Galp-(1 ->, were speculated through methylation analysis and NMR spectra. However, the linkage pattern for RG-I backbone and side chains were indiscernible due to limited resolution of NMR spectra. Besides, the pectin adopted a flexible chain conformation in 0.1 M NaNO3 solution. These results provided a structural basis for study on polysaccharide from D. opposite, which was benefit for development of functional food of yam.

Automated summary

A low methyl-esterified pectin was isolated from the tuber of Dioscorea opposita Thunb., containing high proportions of homogalacturonan and highly branched rhamnogalacturonan I. Through methylation analysis and NMR spectra, the composition of the pectin's backbone and side chains were speculated. Additionally, the pectin exhibited a flexible chain conformation in a specific solution.