Weakly Acidic Pectic Polysaccharides of Japanese Radish and Cabbage

Abstract

Pectic substances were extracted from the vegetables with oxalate buffer of pH 4.25 and, after saponification, fractionated into two components, weakly acidic pectic polysaccharide (WAP) and pectic acid, by DEAE-cellulose and Sephadex G-100 chromatographies. The galacturonic acid content (17.3~25.8%) of WAPs was much lower than that of pectic acids, though the neutral sugar compositions of both pectic substances were almost the same. The arabinose-galactose side chains were found to be very long or highly branched in WAPs compared with those in pectic acids.

All the WAPs were appreciably hydrolyzed by exo- and endopolygalacturonases. The limited-degradation products (the residual polysaccharides; i.e., the rhamnogalacturonan segments) obtained by endopolygalacturonase from both WAPs and pectic acids showed a similar behavior on Sephadex G-100 and Sepharose CL-4B gel filtrations; each of the rhamnogalacturonan segments was eluted in the void volume of the Sephadex G-100 column. From these results, we concluded that WAPs are probably an inherent pectic component of the cell walls of the vegetables.