Structures and immunological activities of two pectic polysaccharides from the fruits of Ziziphus jujuba Mill. cv. jinsixiaozao Hort.

Abstract

Two pectic polysaccharides were isolated from Ziziphus jujuba Mill. cv. jinsixiaozao Hort. and their structures were characterized by acid hydrolysis, methylation, partial acid hydrolysis and NMR spectroscopy. The purified fraction Ju-B-3 had a molecular mass of over 2000 kDa and showed $[\alpha {]}_{\mathrm{D}}^{20}+151$ (c = 1.00, H₂O). Chemical and spectroscopic analyses indicated that Ju-B-3 was a polygalacturonan with 7.49% methoxylation. The purified fraction Ju-B-2 had a molecular weight of over 2000 kDa and showed $[\alpha {]}_{\mathrm{D}}^{20}+125$ (c = 1.00, H₂O). Ju-B-2 was proposed as a polygalacturonan interspersed with rhamnogalacturonan in the main chain. 10.47% d-galacturonic acid existed as methoxylation and O-acetyl groups were amounted to 2.5%. The branched side chains were mainly composed of 1,5-linked arabinofuranosyl residues and 1,6-linked galactopyranose residues attached to O-4 of rhamnose residues. Ju-B-2 induced a rat spleen cells proliferation in a dose-dependent manner while Ju-B-3 could not show any proliferation activity compared with control.

Introduction

Pectins are the most abundant polysaccharides in the cells wall of many higher plants which are a group of complex acidic polymers with 1,4-linked d-galacturonic acid residues (Habibi et al., 2004, Strasser and Amadò, 2001, Wang et al., 2005). Pectic polysaccharides include three different repeating units: homogalacturonan (HG), rhamonogalacturonan-I (RG-I) and substituted galacturonans (RG-II). The dominant feature of pectins is a linear chain of α-1,4-linked d-galacturonic acid in which varying proportions of the acid groups are present as methoxyl esters. These homogalacturonan sequences may be interspersed at intervals with a-l-rhamnopyranosyl residues carrying the major part of neutral sugar side chains, mainly arabinans, galactans or arabinogalactans.

Ziziphus jujuba as a native plant of China belongs to the genus Ziziphus (Rhamnaceae) and is widely distributed in China and South Korea. Its fruits are used as edible food and traditional Chinese medicine. The fruits are claimed to purify the blood and aid digestion (Tripathi et al., 2001). Among the bioactive constituents, polysaccharides may play an important role. Yamada et al. reported polysaccharides from the fruits had anti-complementary activities (Yamada et al., 1985). As to pectic polysaccharide, Shimizu N and Tomoda M reported a pectin from the fruits of Ziziphus jujuba Miller var. inermis REHD which was composed of d-galacturonic acid, l-rhamnose,d-galactose and l-arabinose in the molar ratio of 35:1:1:4 and had a molecular mass of 263,000. The major part (58%) of d-galacturonic acid exists as methyl ester, and O-acetyl groups were amounted to 2.3% (Shimizu and Tomoda, 1983).

In this paper, we reported structural characterization and immunological activities of two pectic polysaccharides from fruits of Zizizphus jujuba Mill. cv. jinsixiaozao Hort.