Neutral Sugar Side Chains Research Articles

Enzymic degradation of isolated pectic substances and cell wall from pulp of grape berries

Pectic substances sequentially extracted with water (WSP), oxalate (OXP), acid (HP) and alkali (OHP) from an alcohol-insoluble residue (AIR) from pulp of grape berries, and further purified, were degraded with two pectic enzymes, namely endopolygalacturonase (endopg) and endopectinylase (endopel). Degradation products were fractionated by gel permeation chromatography (Bio-gel P2, Sephadex G100, Sepharose CL 6B) or by ion-exchange chromatography (DEAE-Sephacel). The results suggest that pectic substances from grape berries are constituted of ‘smooth’ homogalacturonan areas, interspersed with very densely branched ‘hairy’ regions where neutral sugar side-chains are located. WSP on one hand and HP, OXP, OHP on the other hand were differentiated by their side-chain length. Treatment of AIR previously extracted with water and oxalate by endopel are reported and degradation products are compared with HP ‘hairy’ fragments.

Comparison of the structural features of apple and citrus pectic substances

Pectic substances were extracted from Alcohol Insoluble Solids from lemon peel (albedo) and fractionated by ion exchange chromatography and gelfiltration. The pectin molecules contained rhamnose, arabinose, galactose, glucose and galacturonic acid residues; xylose residues were almost absent. Degradation with purified pectolytic enzymes and subsequent gelfiltration of the resulting pectin fragments showed that the neutral sugar side chains were present in ‘hairy regions’ (blocks of neutral sugar side chains). The distribution of the methoxyl groups was studied by HPLC analysis of enzyme-degraded pectins. Some influence of native pectinesterase on the distribution of the methoxyl groups was found. The results are compared with those of similarly extracted and purified apple pectic substances.

Structural features of the neutral sugar side chains of apple pectic substances

The ‘hairy regions’ of apple pectic substances (fragments of the rhamnogalacturonan chains carrying the neutral sugar side chains) have been subjected to enzymic, acidic and alkaline degradation. The results show that the hairy regions consist of rhamnogalacturonan fragments carrying arabinogalactans and galacturonan fragments carrying single unit xylose side chains. A separate population of molecules is present consisting of galacturonan main chains and side chains of 1,3/1,6-linked galactans. The structural relations of pectic substances from different plant species are discussed.