Physical characterisation of the rhamnogalacturonan and homogalacturonan fractions of sugar beet ( Beta vulgaris) pectin

Abstract

Acid extracted sugar beet ( Beta vulgaris) pectin was subjected to enzymatic hydrolysis using fungal pectin methyl esterase (f-PME) and two endopolygalacturonanases (PGs I and II). From the hydrolysate, the RG-I fraction was separated and purified by chromatographic techniques. This RG-I fraction was shown to be of high weight average molar mass (188,000 g/mol), but low intrinsic viscosity (36 ml/g), which is consistent with a random coil conformation ( L p = 1.4 nm). The HG fraction was prepared by mild acid hydrolysis of acid extracted pectin. The HG fraction was found to have a relatively low weight average molar mass (20,000 g/mol), but a rather high intrinsic viscosity (77 ml/g), which is consistent with the HG fraction being rigid in solution ( L p = 9.8 nm). Lower molar mass pectins are richer in HG regions and pectins of higher molar mass are richer in RG-I regions. We conclude that the degradation of the HG region has an important impact on intrinsic viscosity, but less on molar mass and the inverse is true for the degradation of RG-I region. This has important consequences in terms of the functionality of sugar beet pectin molecules.