Insight into the structure of pectin by high performance chromatographic methods

Abstract

Various high performance chromatographic methods (analytical and preparative size exclusion chomatography, as well as ion exchange chromatography) have been developed in order to provide a deeper insight into the structure of pectin. The study mainly concentrated on commercial high-methoxy samples and products from the MRS research centre. By coupling size exclusion chromatography (SEC) and low angle laser light scattering (LALLS), realistic values of the molecular weight and molecular weight distribution can be obtained, as the contribution from aggregates may be easily determined. Differences between apple and lime pectin are shown. Preparative size exclusion chromatography allowed us to obtain information about the dependence of pectin composition on molecular weight by analysing the neutral sugars, the degree of esterification and the acetyl content in each individual molecular weight fraction. It was found that the high content of abrabinose and galactose in the low molecular weight fractions was associated with the ballast of free polysaccharides that accompany the actual pectic chain in all natural pectins. High resolution ion exchange chromatography was used to compare the intermolecular distribution of degrees of esterification (DE). Distributions of DE were found to be very narrow, with very few exceptions and by analysing SEC fractions, they were found to be constant with the molecular weight in all cases.