Occurrence of pectic hairy regions in various plant cell wall materials and their degradability by rhamnogalacturonase

Abstract

Pectic polysaccharide fractions of high molecular weight, resistant to further degradation by pectolytic, hemicellulolytic, and cellulolytic enzymes, were isolated from potato fibre and from pear, carrot, leek, and onion tissue by the liquefaction process. The fractions, referred to as modified hairy regions (MHR), were characterized by the determination of their sugar composition, linkage type composition, degree of esterification (methyl ester and O-acetyl groups), and molecular weight distribution. Galacturonic acid, galactose, and rhamnose were found to be the major sugar residues in most of the MHR preparations, while arabinose was the main sugar in pear MHR. The rhamnose-galacturonic acid ranged between 0.44 for pear MHR to 0.63 for MHR from leek. High degrees of acetylation (da) were calculated assuming that acetyl groups were only attached to galacturonic acid residues. All MHR fractions had a similar molecular weight distribution which was rather heterogeneous. It was observed that all MHR preparations were degraded by RGase in a similar fashion. In all digests, a characteristic population of reaction products having a molecular weight of ca. 1000-2000, representing rhamnogalacturonan oligomers, was present. It was concluded that pectic hairy regions with comparable structural features are common to a variety of fruit and vegetable tissues.