Characterization of a methyl-esterified tetragalacturonide fragment isolated from a commercial pectin with a medium degree of methyl-esterification

A galacturonan fragment was obtained from a 38% DM commercial apple pectin by endopolygalacturonase digestion followed by separation using ion exchange chromatography. By NMR, MALDI-TOF MS and chemical analysis the structure of this oligomer was found to be a tetramer of galacturonic acid with a single methyl ester on the GalA next to the reducing end residue. Assignment of all the 13C and 1H chemical shifts for this oligomer will be helpful in determining the structure of more complex pectin fragments.