Determination of the degree of substitution, degree of amidation and degree of blockiness of commercial pectins by using capillary electrophoresis

Abstract

It is more and more realised that pectins are complex mixtures of many different molecules and research is directed towards the fractionation and characterisation of these pectic sub-populations. Since fractionation of pectins generally results in only low amounts of purified material, rapid characterisation methods using low amounts of samples are required. In this study, capillary electrophoresis was chosen to characterise pectins because only tiny amounts of sample are needed for the analysis. A new capillary electrophoresis (CE) protocol was developed to determine the degree of amidation, the degree of methyl-esterification (DM) and consequently the degree of substitution (DS) of pectins by analysing the pectins before and after removal of the methyl-esters. The CE results were compared with results obtained for the same pectins by using titration and Fourier transform infra-red (FTIR) spectroscopy methods. The CE method was found to be rather reliable resulting in small standard deviations for the DS and DAm. The CE method had the advantage of being rapid due to the limited sample preparation and automation of the analysis. In addition, CE was used successfully to determine the degree of blockiness of the free GalA residues over the pectic backbone.