Enzymic and chemical degradation and the fine structure of pectins from sugar-beet pulp

Abstract

Pectins sequentially extracted from sugar-beet pulp with water (WSP), oxalate (OXP), hot acid (HP), and cold alkali (OHP) have been degraded variously by base-catalysed β-elimination, de-esterification, endopectin lyase, pectin methyl esterase, endopolygalacturonase, and endopectate lyase. The products were studied mainly by chromatography on Sephadex G-100. The pectins contain various amounts of degradation-resistant (hairy) fragments in which the molar ratios of neutral sugar residues to galacturonic acid residues were 4.8, 4.6, 3.8, and 3.7 for WSP, OXP, HP, and OHP, respectively. The molar ratios of rhamnose residues to galacturonic acid residues in these fragments were 0.15, 0.20, 0.38 and 0.35, respectively. The pectins also contained sequences of galacturonic acid residues with relatively little neutral sugar residues attached (smooth fragments). Methyl ester and acetyl groups were distributed fairly regularly along the smooth fragments. Evidence is presented for an association of oligogalacturonic acids with the hairy fragments under the conditions of gel chromatography. Feruloyl groups are located in the hairy fragments. Other phenolic compounds, associated with the purified pectins, appear not to be covalently linked.