Lemon-peel pectin. II. Isolation of homogeneous pectins and examination of some associated polysaccharides

Abstract

Two electrophoretically homogeneous pectins have been isolated from dried lemon-peel under conditions of minimum degradation by extraction with cold water and with disodium ethylenediaminetetraacetate. Some properties of polysaccharides which occur in association with the pectins are reported.Canadian Journal of Chemistry, 48, 1283Chemistry, 48, (1970 Previous studies on dried lemon-peel (1) have shown that extraction under the mildest possible conditions, namely with water at room temperature, furnishes pectin A which, after chromatography on diethylaminoethyl-Sephadex, may be obtained in chemically homogeneous form as pectin C. This pectin was shown to contain 75 % of galacturonic acid residues, of which approximately 80% were esterified. Neutral sugars, including galactose, arabinose, rhamnose, xylose, and fucose, were present as constituents, and characterization of oligosaccharides formed on depolymerization provided direct evidence for the structural role of rhamnose and xylose residues in the acidic polysaccharide. The waterextracted pectin, however, accounts for only about a third of the total pectin in the peel, and we now report the extraction of a second homogeneous pectin, under non-degradative conditions, together with an examination of certain structural features of polysaccharides which occur in association with pectin C.Dried lemon-peel was extracted with water at room temperature, as described previously (I), to give pectin A together with a polysaccharide fraction from which polysaccharide F was isolated. Pectin A gave a single peak on electrophoresis in pyridine -acetic acid buffer (Fig. I), but two minor peaks were detected in addition to the main peak in borate buffer (Fig. 2). Fractionation of pectin A by chromatography on diethylaminoethyl-Sephadex furnished electrophoretically homogeneous pectin C (Fig. 3), and small amounts of polysaccharide fractions D and E. Partial acid hydrolysis of pectin C afforded inter alia acidic oligosaccharides with the chromatographic mobilities of 2-0-(a-D-galactopyranosyl-ranosyluronic acid)-L-fucose, and 6-0-(P-D-glucopyranosyluronic acid) -D -galactose, thus providing further evidence that these oligosaccharides were genuine fragments from the pectin and did not arise solely from associated polysaccharides.Samples of water-extracted lemon-peel were further extracted at 90" with (i) water acidified to p H 2.1, (ii) disodium ethylenediaminetetraacetatelsodium lauryl sulfate at p H 5,' and (iii) sodium hexametaphosphate at p H 4.2 to give pectins G, H, and J (see Table 1). Pectins G and H were essentially identical in composition, but in each case electrophoresis showed that the major component was contaminated with a component of the same mobility as pectin C. Control experiments showing that treatment of pectin A under extraction conditions (i) and (ii) caused no change in electrophoretic mobility indicated that the two components in pectins G and H are not artifacts arising from the extraction procedures. Pectin J, however, had a much higher electrophor...

Polysaccharides of Soybeans. VI. Neutral Polysaccharides from Cotyledon Meal

“…Insofar as the present results again failed to provide any -indication for branching through arabinose residues mass spectrum (12). The cleavage products from in the polysaccharide, the evidence requires that methylated lemon-peel arabinan (13) were also the main component of the polysaccharide prepexamined by this procedure. The quantitative aration is a true arabinogalactan.…”

“…Methylated Alditol Acetates froin Met/zylated Polysaccharides Samples of the following methylated polysaccharides were examined: methylated soybean arabinan, methylated soybean arabinogalactan, methylated lemon-peel arabinan (13), and methylated mustard seed arabinan. The latter methylated polysaccharide was prepared as described by Hirst et al (6).…”

Other Plant Polysaccharides

“…Partial acid hydrolysis and methylation analysis experiments (796,797) indicate a structure (14) in (198), although the presence of (1->3)-and (1->6)-linked D-Galp residues is an indication that an arabinogalactan structure of type II is involved. This applies equally to a polysaccharide fraction containing arabinosyl and galactosyl residues (but no GalA) from cold water extracts of lemon peel (4,163). Other types of sugar unit, includ ing (1->3)-linked D-Galp residues and chain units of L-Arap, were found on methylation analysis and Smith degradation of an aqueous extract of Centrosema plumieri seeds.…”

The solubilisation and hydrolysis of spinach cell wall polysaccharides in gastric and pancreatic fluids

“…At pH 1-2 and 37"C, some hydrolysis of particular glycosidic bonds could occur: for example, apiofuranose residues are especially labile to acid, and certain galacturonic acid residues may be exceptionally susceptible to autocatalytic hydrolysis (Smidsrerd et a1 1966). Conversely, at pH 8-9 and 37"C, some hydrolysis of ester bonds is likely (Brown and Fry 1993); in addition, some fl-elimination of methyl galacturonate residues is possible, which would cleave pectic polysaccharide chains by a non-hydrolytic mechanism and may be enhanced by the metal ions also present in the gut (Aspinall and Cottrell 1970).…”