STUDIES ON THE INTERMOLECULAR DISTRIBUTION OF INDUSTRIAL PECTINS BY MEANS OF PREPARATIVE ION-EXCHANGE CHROMATOGRAPHY

Three industrial high methoxyl pectins have been fractionated by ion-exchange chromatography on a preparative scale. Chemical analysis of the resulting fractions revealed that pectin molecules varying in charge, also differ in composition. Neutral sugars, phenolic and proteinaceous compounds were found to coelute with pectin molecules. The nonuronide material appeared to be associated with all pectin molecules, but mainly attached to those requiring a high ionic strength to be released from the ion exchanger. Moreover, despite large quantitative differences, the distribution of individual neutral sugars among the molecules was found to be very similar for pectins from lemon and apple, indicating a great similarity in structural features. Separation of pectin molecules by ion-exchange chromatography was found to depend on many different chemical parameters such as degree of methoxylation, but, probably also the intramolecular distribution of free carboxyl groups and the presence of phenolics. This renders the interpretation of ion-exchange elution profiles difficult and uncertain.