ANALYSIS OF PARTIALLY METHYL-ESTERIFIED GALACTURONIC ACID OLIGOMERS BY HIGH-PERFORMANCE ANION-EXCHANGE CHROMATOGRAPHY AND MATRIX-ASSISTED-LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY/

Two methods were developed to detect partially methyl-esterified galac turonic acid oligomers, generated by endopolygalacturonase treatment o f a 30% methyl-esterified pectin. The enzyme digest was shown, by matr ix-assisted laser desorption/ionization time-of-flight mass spectromet ry, to contain sodiated galacturonic acid oligomers with a degree of p olymerization of 2-12, containing 0-6 methyl esters, Galacturonic acid (monomer) could not be detected because of matrix ions interference i n the low mass region. Using high-performance anion-exchange chromatog raphy, with a sodium acetate gradient at pH 5.0 and postcolumn sodium hydroxide addition to allow pulsed amplified detection, a complex elut ion profile was obtained with the endopolygalacturonase-treated 30% me thyl-esterified pectin. All the components eluted before nonesterified tetragalacturonic acid. The partially methyl-esterified oligogalactur onic acids eluted in a discernible series of oligomers with an identic al number of nonesterified carboxylic acid groups; the large, more est erified oligomers eluted before small, less esterified oligomers. The methyl esters may hinder the interaction of the neighboring carboxylic acid groups with the anion-exchange resin, thereby giving the compone nts an apparent lower overall negative charge, (C) 1998 Academic Press .