Mapping sugar beet pectin acetylation pattern

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Homogalacturonan-derived partly methylated and/or acetylated oligogalacturonates were recovered after enzymatic hydrolysis ( endo-polygalacturonase + pectin methyl esterase + side-chain degrading enzymes) of sugar beet pectin followed by anion-exchange and size exclusion chromatography. Around 90% of the GalA and 75% of the acetyl groups present in the initial sugar beet pectin were recovered as homogalacturonan-derived oligogalacturonates, the remaining GalA and acetyl belonging to rhamnogalacturonic regions. Around 50% of the acetyl groups present in sugar beet homogalacturonans were recovered as partly methylated and/or acetylated oligogalacturonates of degree of polymerisation ⩽5 whose structures were determined by electrospray ionization ion trap mass spectrometry (ESI-IT-MS n ). 2- O-acetyl- and 3- O-acetyl-GalA were detected in roughly similar amounts but 2,3-di- O-acetylation was absent. Methyl-esterified GalA residues occurred mainly upstream 2- O-acetyl GalA. Oligogalacturonates containing GalA residues that are at once methyl- and acetyl-esterified were recovered in very limited amounts. A tentative mapping of the distribution of acetyl and methyl esters within sugar beet homogalacturonans is proposed. Unsubstituted GalA residues are likely to be present in limited amounts (∼10% of total GalA residues), due to the fact that methyl and acetyl groups are assumed to be most often not carried by the same residues.