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 galacturonic acid oligomers, generated by endopolygalacturonase treatment of a 30% methyl-esterified pectin. The enzyme digest was shown, by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, to contain sodiated galacturonic acid oligomers with a degree of polymerization of 2-12, containing 0-6 methyl esters. Galacturonic acid (monomer) could not be detected because of matrix ions interference in the low mass region. Using high-performance anion-exchange chromatography, with a sodium acetate gradient at pH 5.0 and postcolumn sodium hydroxide addition to allow pulsed amplified detection, a complex elution profile was obtained with the endopolygalacturonase-treated 30% methyl-esterified pectin. All the components eluted before nonesterified tetragalacturonic acid. The partially methyl-esterified oligogalacturonic acids eluted in a discernible series of oligomers with an identical number of nonesterified carboxylic acid groups; the large, more esterified 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 components an apparent lower overall negative charge.
Daas
P J
PJ
Department of Food Technology and Nutritional Sciences, Wageningen Agricultural University, The Netherlands.
Arisz
P W
PW
Schols
H A
HA
De Ruiter
G A
GA
Voragen
A G
AG
D002852:Chromatography, Ion Exchange; D004952:Esters; D006863:Hydrogen-Ion Concentration; D010368:Pectins / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D011096:Polygalacturonase / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D004952:Esters; D010368:Pectins; D011096:Polygalacturonase; C003181:polygalacturonic acid