Donald J. Brasch

Cell-wall polysaccharides of kiwifruit (Actinidia deliciosa): Chemical features in different tissue zones of the fruit at harvest

Abstract Cell-wall material (CWM) was isolated from cryo-milled (− 196°) powders prepared from 4 different tissue zones of kiwifruit ( Actinidia deliciosa ). Polysaccharides were solubilised by stepwise extraction with cyclohexane- trans -1,2-diaminetetra-acetate (CDTA), 0.05 m Na 2 CO 3 , 6 m guanidinium thiocyanate (GTC), and 4 m KOH. A heterogeneous mixture of pectic galactans accounted for 40–50% of the CWMs, while hemicelluloses, the bulk of which were xyloglucans, accounted for 15–25%. Each tissue zone contained similar types of polysaccharide. Variability in their amount and sugar composition are thought to reflect different stages in the physiological development of the fruit at harvest, in the 4 zones. Polymers from the outer pericarp tissue were fractionated by anion-exchange chromatography and subjected to methylation analysis. The CDTA- and Na 2 CO 3 -soluble polymers were rhamnogalacturonans substituted to varying degrees with galactan and arabinogalactan side-chains containing 4-, 2,4-, 3,4- and 4,6-linked galactose and 5- and 3,5-linked arabinose. Side chains were terminated by galactose and arabinose and lesser amounts of rhamnose, fucose, xylose, and galacturonic acid. The pectic polysaccharides of the GTC- and KOH-soluble fractions had more highly branched rhamnogalacturonan backbones than the CDTA- and Na 2 CO 3 -soluble polymers and contained hemicellulosic elements. The major hemicellulose was a xyloglucan, but lesser amounts of a 4- O -methylglucuronoxylan and a branched mannan were partially characterised. Several polymers were associated with proteins low in hydroxyproline. Evidence is presented that a polysaccharide of the rhamnogalacturonan II type is associated with the pectic polymers of kiwifruit.

Cell-wall polysaccharides of kiwifruit (Actinidia deliciosa) : effect of ripening on the structural features of cell-wall materials

Abstract Cell-wall polysaccharides were solubilised from cell-wall materials (CWMs) isolated from kiwifruit at 2 ripening stages, after treatment for 1 and 7 days with ethylene. The fractions soluble in cyclohexane- trans -1,2-diaminetetra-acetate (CDTA), Na 2 CO 3 , guanidinium thiocyanate (GTC), and KOH were purified by ion-exchange and gel-permeation chromatography, and subjected to methylation analysis. The pectic polymers in the 7-day fractions had increased proportions of 4-linked galactosyl, 2- and 2,4-linked rhamnosyl, and terminal arabinosyl, xylosyl, and galactosyl residues, and decreased proportions of 4-linked galacturonosyl residues. In the major Na 2 CO 3 -soluble pectic fraction, there was an increase in the proportion of branched polymers of high molecular weight during ripening. Therefore, a large proportion of the polyuronides may have been solubilised without significant structural modification, indicating that the action of endo-polygalacturonase was not involved. There was a decrease in M w of the xyloglucan fraction during ripening, but no detectable changes in the primary structure or in the 4- O -methylglucuronoxylan and galactoglucomannan fractions.

Cell wall changes in kiwifruit following post harvest ethylene treatment

Abstract The composition of the cell walls from four tissue zones of kiwifruit at three times after harvest have been investigated. Cell wall breakdown triggered by ethylene did not occur simultaneously in different tissue zones of kiwifruit, being more pronounced in the outer pericarp and inner pericarp but much less in the locule wall and core tissues. Cell wall material (CWM) from the outer pericarp lost 80 and 64% of the CDTA (cyclohexanediamine tetraacetic acid) and sodium carbonate-soluble fractions respectively. However, the amounts of these fractions remaining in the CWM of ripe fruit contained higher proportions of galactose, arabinose and rhamnose, than fruit at harvest. These sugars occur at branchpoints or in sidechains in kiwifruit pectic polymers; a fact that pointed to a non-random degradation of the wall polysaccharides and the preferential release of the less branched parts of the rhamnogalacturonan backbone of the pectic substances. There was a 50% decrease in outer pericarp cell wall galactose, 80% of which occurred in the KOH-soluble and CWM residue fractions. Comparison of whole kiwifruit at harvest and seven days after ethylene treatment showed a net decrease in galactose (33%) and arabinose (22%). Absence of sufficient free galactose or galactose-containing oligosaccharides to account for the galactose released from the wall polysaccharides during ripening, implied post harvest metabolism of cell wall derived galactose. In contrast, the uronic acid in the cell wall was partially converted to soluble forms during ripening without any apparent loss due to metabolism.

Composition and block structure of alginates from New Zealand brown seaweeds

Abstract Alginates have been extracted from seven brown algae found in the Southern Hemisphere and characterized by 1 H and 13 C NMR analyses. The results are compared with similar analyses obtained in this work for three commercially available alginates isolated from Macrocystis pyrifera , a species of the Northern Hemisphere. Overall the ten alginates display a wide range of compositions, ranging from the very high mannuronic acid containing alginate extracted from Durvillaea antarctica ( F M = 0.80) to the moderately high guluronic acid containing alginate from Marginariella boryana ( F G = 0.56). All data are examined in terms of two addition copolymerization models, namely the Bernoullian and the first-order Markov models. Monomer distributions in the high M and intermediate composition alginates have M-diad frequencies calculated from the NMR analyses that agree closely with Bernoullian distributions, the best agreements being obtained for those alginates in which F M is greater than 0.72. However, as the monomer composition tends towards a higher G content, both of the above statistical models fail to satisfactorily describe the distributions of either the M or the G residues. A feature of this work is the excellent agreement obtained for the 1 H and the 13 C NMR analyses

Structures of the pectic polysaccharides from the cell walls of kiwifruit

Abstract The structure and distribution of the neutral side chains of three pectic polysaccharide fractions of kiwifruit, possessing widely differing degrees of branching, were studied by chemical methods, gel-permeation chromatography, and 13 C-n.m.r. spectroscopy, following degradation with a purified endo-polygalacturonase. Three categories of side chain were identified: ( a )(1 → 4)-linked β- d -galactosyl residues, which occurred in regions where the galacturonan backbone contained little rhamnose and small proportions of other neutral sugars; ( b ) side chains containing proportionately less galactose and more arabinose, xylose, and fucose, which occurred in regions where the galacturonan backbone contained increased proportions of rhamnose; and ( c ) large (1 → 4)-β- d -galactans, which were attached to the rhamnogalacturonan backbone. The possible contribution of these side chains to cell-wall breakdown during kiwifruit ripening is discussed.

The galactan sulfate from the edible, red alga Porphyra columbina

Abstract A galactan sulfate has been isolated from the seaweed Porphyra columbina , and its structure established by a combination of methylation, methanolysis, treatment with alkali followed by methylation, and 13 C-n.m.r. spectroscopy. The polysaccharide belongs to the porphyran class, and consists of 3-linked β- d -galactosyl residues and 4-linked α- l -galactosyl residues. 3,6-Anhydro- l -galactose and l -galactose 6-sulfate residues total approximately half of the sugar units, the other half being made up of d -galactose and 6- O -methyl- d -galactose residues. Some evidence is presented that suggests that the galactan sulfate does not have a completely alternating structure.

Biosynthetic implications of NMR analyses of alginate homo- and heteropolymers from New Zealand brown seaweeds

Abstract Homopolymeric (M- and G-) and heteropolymeric (MG-) blocks have been prepared from alginates that have been isolated from seven Southern Hemisphere brown seaweeds and from three commercial algal alginates. The blocks have been analysed by 1 H and 13 C NMR spectroscopy, and the analyses show that well-defined M- and G-homopolymers are obtained only from the five polysaccharides that have been previously designated as either high-M or high-G alginates. However, the five intermediate algal alginates (which have F M values between 0.6 and 0.7) appear to contain mainly MG or heteropolymeric blocks. It is concluded that the results of NMR spectroscopic analysis of whole alginates can give a misleading picture of the block structure of some alginates. The NMR analyses of the homopolymers isolated from both the high-M and high-G alginates also show that the order of the d -mannuronosyl and l -guluronosyl residues in these blocks fits a first-order Markov distribution pattern. This suggests that 5-epimerization of some of the GDP- d -mannuronosyl residues at the monomer level, followed by addition copolymerization catalyzed by a GDP-guluronic acid transferase system, as originally suggested by Lin and Hassid [1,2], may contribute to the biosynthesis of the homopolymeric block structures in these high-M and high-G alginates isolated from brown algae. The NMR analysis of homopolymeric blocks from several algal alginates are shown to have first-order Markov distributions of d -mannuronosyl and l -guluronosyl residues. This is consistent with a biosynthetic pathway that involves a C-5 epimerisation at the monomer level.

A study of the glucofructofuranan from the New Zealand cabbage tree Cordyline australis

Abstract Extraction of the roots of the New Zealand cabbage tree Cordyline australis with water gave a glucofructofuranan in 60% yield (dry-weight basis). Viscosity measurements on aqueous solutions of the polysaccharide, and vapor pressure osmometry of the polysaccharide peracetate, showed the number average molecular weight of the glucofructofuranan to be ∼3000. Complete hydrolysis with dilute acid gave only d -fructose and d -glucose, in the ratio of 16:1. The polysaccharide was methylated by using dimethyl sulfoxide—sodium hydroxide—methyl iodide, and the methylated polymer was hydrolyzed to give 1,3,4,6-tetra- O -methylfructose (5.6 mol), 2,3,4,6-tetra- O -methylglucose (1 mol), 1,3,4-tri- O -methylfructose (8.4 mol), 2,3,4-tri- O -methylglucose (0.1 mol), and 3,4-di- O -methylfructose (2.7 mol). These results, supported by 13 C-n.m.r. analyses, showed that the polymer is a highly branched glucofructofuranan containing mainly (1→2)-linked β- d -fructofuranosyl residues, with branching at O-6 of 15% of the d -fructosyl residues.

The agar-type polysaccharide from the red alga Gracilaria secundata

Abstract Aqueous extraction of the red alga Gracilaria secundata gives a low-sulfated, agar-type polysaccharide which gels strongly. The structure of the polysaccharide has been investigated by methylation, partial hydrolysis of the permethylated agar, enzymic oxidation, and 13C-n.m.r. spectroscopy. The agar is mainly composed of the familiar (1→3)-linked β- d -galactosyl residues and (1→4)-linked 3,6-anhydro-α- l -galactosyl residues, but important variations occur. The distribution of 6-O-methyl- d -galactosyl residues is considered to be in “blocks”.

Isolation and characterisation of a partially methylated galacto–glucurono–xylo-glycan, a unique polysaccharide from the red seaweed Apophloea lyallii

Abstract Polysaccharides of the red seaweed Apophloea lyallii were extracted with hot water in a yield of 63.6% w/w of the dry seaweed. The polysaccharides were non-sulphated and were composed of various proportions of d -xylose, 2-O-methyl d -galactose, d -glucuronic acid, d - and l -galactose, 3-O-methyl galactose, and d -glucose. The aldobiuronic acid 3-O-(β- d -glucopyranosyluronic acid)- d -xylopyranose was isolated from the acid hydrolysate of the polysaccharides. The polysaccharides were fractionated by DEAE-sephadex ion exchange chromatography, and two of the fractions obtained were characterised by neutral sugar analyses, linkage analyses, and NMR spectroscopy. A major fraction obtained was shown to be largely composed of a unique (2-O-methyl galacto)–glucurono–xylo-glycan with a repeating unit represented by [α- d -(2-O-Me-Galp)-(1→4)-β- d -GlcAp-(1→3)-α- d -Xylp-(1→4)-]n. The structure of this new glycan was explored by beta-elimination analyses. A minor fraction obtained by ion exchange chromatography contained (1→4)-linked xylose, (1→4)-linked galactose, (1→4)-linked 3-O-methyl galactose, (1,3,4)-linked galactose, and terminal uronic acid in a ratio of approximately 1:0.3:0.5:0.4:0.4.