Gelation properties of extruded lemon cell walls and their water-soluble pectins

The amount of water-soluble pectins was largely increased after extrusion-cooking of lemon fibres. These pectins showed the ability to form a gel in the presence of sucrose and at acidic pH. The gels obtained with the water-extracted pectins after extrusion-cooking and with pectins acid-extracted on a laboratory scale were softer than those prepared with commercial citrus pectins. The water-extracted pectins after extrusion-cooking and the pectins acid-extracted on a laboratory scale contained long neutral side-chains and required a higher sucrose concentration to gel than the commercial citrus pectins. The extruded lemon fibres showed the ability to form gels in the presence of sucrose and at acidic pH. The gels obtained with the extruded fibres containing some water-solube pectins of high molecular weight were stronger than those obtained with the extruded fibres containing higher amounts of more depolymerised water-soluble pectins. The extruded fibres containing 12.5–14.9% of water-soluble pectins of high molecular weight (intrinsic viscosity: 413–504 mL/g) were those showing the better gelation properties.     

Pectins from the albedo of immature lemon fruitlets have high water binding capacity

The white part of citrus peel, the albedo, has a special role in water relations of both fruit and leaves from early on in fruit development. In times of drought, this tissue acts as a water reservoir for juice sacs, seeds and leaves. When water was injected into the albedo, free water was undetectable using magnetic resonance imaging. Microscopy showed tightly packed cells with little intercellular space, and thick cell walls. Cell wall material comprised 21% of the fresh albedo weight, and contained 26.1% galacturonic acid, the main constituent of pectin. From this, we postulated that pectin of the cell wall was responsible for the high water-binding capacity of the immature lemon albedo. Cell wall material was extracted using mild procedures that keep polymers intact, and four pectic fractions were recovered. Of these fractions, the SDS and chelator-soluble fractions showed viscosities ten and twenty times higher than laboratory-grade citrus pectin or the other albedo-derived pectins. The yield of these two pectins represented 28% of the cell walls and 62% of the galacturonic acid content of immature lemon albedo. We concluded that, from viscosity and abundance, these types of pectin account for the high water-binding capacity of this tissue. Compositional analyses showed that the two highly viscous pectic fractions differ in galacturonic acid content, degree of branching and length of side chains from the less viscous albedo-derived pectins. The most striking feature of these highly viscous pectins, however, was their high molecular weight distribution compared to the other pectic fractions.     

Characterization of hop pectins shows the presence of an arabinogalactan-protein

Hop pectins were extracted from spent hops using acid extraction conditions and were characterized chemically. The acid extraction of spent hops resulted in a yield of 2%, containing 59% of polysaccharides. The hop pectins under investigation had a relatively high molecular weight and an intrinsic viscosity comparable to that of commercially available apple and citrus pectins. The low degree of methyl esterification of these pectins implicates that they are mainly suitable for use in calcium gels. The degree of acetylation and the neutral sugar content were relatively high.

A high molecular weight fraction which contained arabinogalactan-proteins was shown to be present in the hop pectin extract after preparative size-exclusion chromatography. Additionally, a fraction with a lower molecular weight was present containing mainly homogalacturonans. The arabinogalactans in the high molecular weight population consisted of (1→3)- and (1→3,6)-linked galactans highly branched with arabinose and galactose side-chains. The protein part of the arabinogalactan-protein (13%) was found to be rich in cystein, threonin, serinin, alanin, and hydroxyprolin. The molecular weight distribution of the hop pectin after degradation with the enzymes endopolygalacturonase plus pectin methyl esterase suggested that the arabinogalactan-protein present in the hop pectin extract was linked to the pectin and that the arabinogalactan-protein itself had a fairly low molecular weight.     

End-products of enzymic saccharification of beet pulp, with a special attention to feruloylated oligosaccharides

Sugar-beet pulp was hydrolysed by a ‘pectinase’ preparation (‘SP 584’ from Novo Nordisk A/S). High degradation of pectins was observed with release of ~75–85% of the pectic sugars and 70% of the ferulic acid. Of the sugars and ferulic acid initially present in the pulp, ~60–70 and ~40% were released as monomers, respectively. The solubilised material was composed of these monomers and also of some resistant materials, rhamnogalacturonans and feruloylated oligosaccharides. Rhamnogalacturonans, representing only ~5% of the galacturonic and neutral sugars from the pulp, were separated on a Bio-Gel P-4 column eluted by sodium acetate buffer. Two-thirds of these rhamnogalacturonans still carried residual side-chains, the remaining was only constituted of rhamnose and galacturonic acid in a ratio of 1:2. Feruloylated compounds were purified on Sephadex LH-20 and Bio-Gel P-2 columns eluted by water. The main compound was a feruloylated galactobiose, which represented 14% of the initial ferulic acid amount in the pulp. Feruloylated arabinobiose and galactose were also identified, representing only ~3% each of the ferulic acid initially present in pulp.     

Pectins in the fruits of Japanese quince (Chaenomeles japonica)

The pectin content, composition and physico-chemical properties were studied in the fruits of two genotypes of Japanese quince. On average, the fruits contained 11 g pectins/100 g dry fruit and 1.4 g pectins/100 g fresh fruit. A sequential extraction was used to isolate the pectins from the fruits. The cells from the flesh were examined using a confocal laser scan microscope, fresh and after each extraction step of the sequence. The dilute acid conditions were the most efficient for pectin extraction. Pectins extracted by water or potassium oxalate had higher (>600 ml/g) intrinsic viscosities than the pectins extracted by dilute acid (<400 ml/g). Anionic exchange chromatography was performed on the acid-extracted pectins. They were constituted of four populations, the first one being mainly composed of arabinans, the second one of homogalacturonans, the third one of rhamnogalacturonans. The composition of the last one varied with the genotype studied.     

Oxidative cross-linking of chemically and enzymatically modified sugar-beet pectin

Hot acid-soluble pectins from sugar-beet pulp which do not gel in the presence of persulfate were submitted to hydrolysis with acid under different conditions of concentration, temperature and time, or with different combinations of enzymes. All the modified pectins have been chemically characterised and tested for their gelling capacity with persulfate ions. They varied primarily in the structure of the side-chains and only those obtained from cold acid hydrolysis and from degradation by arabino-furanosidase were able to gel. Accessibility of the feruloyl groups carried by the arabinose side-chains appeared essential for the gelling of beet pectins with persulfate.     

Lemon juice improves the extractability and quality characteristics of pectin from yellow passion fruit by-product as compared with commercial citric acid extractant

An environment-friendly procedure, allowing the extraction of safe pectin products with good functional properties from yellow passion fruit by-product, was developed using two natural acid extractants, namely, pure lemon juice and citric acid solvent. The results show that both of them solubilise, from cell wall material, pectins characterised by high galacturonic acid content (64–78% w/w), degree of esterification (52–73), viscosity-average molecular weight (70–95 kDa) and capable of forming gels in the presence of high soluble solids (sucrose) content and acid. However, compared to pure citric acid solvents, lemon natural juice and its concentrate isolate, under similar extraction conditions, pectins of superior quality characteristics, i.e., higher galacturonic acid content, degree of esterification, viscosity-average molecular weight and gelling power.     

Composition and properties of pectin polysaccharides of St. John’s wort Hypericum Perforatum L.

Three fractions of acidic water-soluble polysaccharides (concentration of glucuronic acid 10?C65%) were obtained from the above-ground part of St. Johns wort Hypericum perforatum L. by serial extraction with water and 0.7% aqueous solution of ammonium oxalate. Enzymatic hydrolysis of these polysaccharides using endo-polygalacturonase indicates that their carbohydrate chains contain the units of galacturone formed by 1,4-??-linked residues of non-substituted D-galacturonic acid. The extracted polysaccharides have been purified by means of gel filtration. It has been shown that water-soluble polysaccharides obtained by extraction with water manly contain the residues of galactose, mannose, glucose, and arabinose (the concentration of glucuronic acid being 10?C27%) while the polysaccharide fraction extracted using 0.7% aqueous solution of ammonium oxalate is presented by pectin polysaccharides. Only the residues of galacturonic acid (55?C72%) have been identified among glucuronic acids in its composition using chromatography/mass spectrometry of trimethylsilyl derivatives. In addition, this fraction contains the residues of the neutral monosaccharides which are typical for pectins: arabinoses, galactoses, rhamnoses, and glucose; there are also minor concentrations of residues of xylose and mannose. IR spectra of pectin polysaccharides of St. John??s wort have absorption bands in the ranges 1740, 1640?C1620, 1236?C1200, and 1200?C1000 cm^?1 which are typical for pectins. It has been demonstrated that aqueous solutions of pectin polysaccharides of St. John??s wort (2 mg/mL) have pronounced antioxidant activity (44% of the activity of trolox taken for 100%).     

Characterization of citrus pectin samples extracted under different conditions: influence of acid type and pH of extraction

Background and Aims

Pectin is a complex macromolecule, the fine structure of which is influenced by many factors. It is used as a gelling, thickening and emulsifying agent in a wide range of applications, from food to pharmaceutical products. Current industrial pectin extraction processes are based on fruit peel, a waste product from the juicing industry, in which thousands of tons of citrus are processed worldwide every year. This study examines how pectin components vary in relation to the plant source (orange, lemon, lime, grapefruit) and considers the influence of extraction conditions on the chemical and macromolecular characteristics of pectin samples.

Methods

Citrus peel (orange, lemon, lime and grapefruit) from a commercial supplier was used as raw material. Pectin samples were obtained on a bulk plant scale (kilograms; harsh nitric acid, mild nitric acid and harsh oxalic acid extraction) and on a laboratory scale (grams; mild oxalic acid extraction). Pectin composition (acidic and neutral sugars) and physicochemical properties (molar mass and intrinsic viscosity) were determined.

Key Results

Oxalic acid extraction allowed the recovery of pectin samples of high molecular weight. Mild oxalic acid-extracted pectins were rich in long homogalacturonan stretches and contained rhamnogalacturonan I stretches with conserved side chains. Nitric acid-extracted pectins exhibited lower molecular weights and contained rhamnogalacturonan I stretches encompassing few and/or short side chains. Grapefruit pectin was found to have short side chains compared with orange, lime and lemon. Orange and grapefruit pectin samples were both particularly rich in rhamnogalacturonan I backbones.

Conclusions

Structural, and hence macromolecular, variations within the different citrus pectin samples were mainly related to their rhamnogalacturonan I contents and integrity, and, to a lesser extent, to the length of their homogalacturonan domains.     

Water unextractable polysaccharides from three milling fractions of rye grain

Water unextractable material from bran, an intermediate milling fraction and sieved flour of rye grain were sequentially extracted at room temperature with saturated barium hydroxide, water, 4 M potassium hydroxide and water followed by extraction with 2 potassium hydroxide in a boiling water bath, giving repeatable recoveries of extracts and polysaccharide residue compositions in collected fractions. Total recoveries of polysaccharide residues in extracts and residue from the different water unextractable materials were 78–88%. Extracts in which 90–93% of the carbohydrates were arabinose and xylose residues were obtained by extraction with saturated barium hydroxide. Subsequent extraction with water yielded a fraction in which 64–68% of the carbohydrates were glucose residues. The extraction with hot alkali resulted in extracts in which 85–89% of the carbohydrates were arabinose and xylose residues. The ara/xyl ratio in the collected fractions ranged from 0.1–1.3, with the lowest ratios in fractions that precipitated after neutralisation of the 4 potassium hydroxide extract and the highest ratios in the unextractable residues. Structural characterisation with ¹H-NMR spectroscopy revealed varying substitution patterns for arabinoxylans in the different extracts and that glucose residues in the extracts essentially originated from mixed-linked β-glucan. The proportion of disubstituted xylose residues was lower in barium hydroxide extracts compared to the other main extracts. A highly branched heteroxylan was extracted with hot alkali. The polysaccharides found in the corresponding extracts for all the starting materials had generally similar structural features, but the yield differed considerably.     

Macromolecular modifications of manioc starch components by extrusion-cooking with and without lipids

Macromolecular structure of manioc starch, extruded without and with lipids (oleic acid, dimodan, soya lecithin and copra) was studied, using chemical, enzymic, viscometric and chromatographic methods. Twin screw extrusion-cooking led to a macromolecular degradation of both amylose and amylopectin. The formation of lower molecular weight material was observed by a decrease of intrinsic viscosities of both components and also by their behaviour on Sepharose CL-2B, whereas no modification of β-amylolysis and iodine-binding capacity could be detected. The macromolecular degradation was increased by higher temperature and screw speed of the extruder, and was decreased by adding lipids during extrusion. Lipids such as fatty acids, mono- and triglycerides have been shown to act as lubricants (each type in its distinctive way). Lipid extraction, by different solvents, appears to have a low efficiency. Although the addition of triglycerides during extrusion reduces the macromolecular degradation, leading to a high solubility, the amylose-lipid complexes reduce the water-soluble fraction. This fraction was shown to be mainly composed of aggregated amylopectin-like material and to be highly stable after successive freeze-thaw cycles.     

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.     

Dietary fibre components and pectin chemical features of peels during ripening in banana and plantain varieties

The effects of the ripeness stage of banana (Musa AAA) and plantain (Musa AAB) peels on neutral detergent fibre, acid detergent fibre, cellulose, hemicelluloses, lignin, pectin contents, and pectin chemical features were studied. Plantain peels contained a higher amount of lignin but had a lower hemicellulose content than banana peels. A sequential extraction of pectins showed that acid extraction was the most efficient to isolate banana peel pectins, whereas an ammonium oxalate extraction was more appropriate for plantain peels. In all the stages of maturation, the pectin content in banana peels was higher compared to plantain peels. Moreover, the galacturonic acid and methoxy group contents in banana peels were higher than in plantain peels. The average molecular weights of the extracted pectins were in the range of 132.6-573.8 kDa and were not dependant on peel variety, while the stage of maturation did not affect the dietary fibre yields and the composition in pectic polysaccharides in a consistent manner. This study has showed that banana peels are a potential source of dietary fibres and pectins.     

Preparation of cation exchanger from lemon and sorption of divalent heavy metals

A cation exchanging material was developed from lemon by modifying the pectic-cellulosic substances in the lemon peel by lemon juice having citric acid. For this purpose, chopped lemon removed from seeds and yellow skin was heated in two stages, firstly at 50 degrees C for 24h and subsequently at 120 degrees C for 2h. The material obtained was ground, repeatedly washed with water and dried. Lemon peel and lemon resin obtained were characterized through physicochemical analyses and FTIR spectroscopy. Heavy metal binding performance of this material was determined by removal tests conducted by using 10mM solutions of divalent metals. Experimental results show that the resin prepared from lemon is effective especially for Pb and Cu removals. For a lemon resin dosage of 10 g l(-1), sorption affinity of divalent metal ions is found to be in an order of Pb>Cu>Ni>Fe>Cd>Zn>Co>Mn. Typically, sorption capacities are about 0.87 and 0.43 mmol g(-1) for Pb and Mn, respectively.     

Structural investigation of an arabinan from cabbage (Brassica oleracea var. capitata)

An arabinan has been isolated from the hot water-soluble pectic substances of cabbage cell wall material. Methylation analysis involving GC-MS of methylated alditol acetates formed from the methylated arabinan has shown that the parent polysaccharide is highly branched and of the same structural type as other arabinans associated with seed pectins.     

The structure of the lipopolysaccharide from a galU mutant of Pseudomonas aeruginosa serogroup-O11

The lipopolysaccharide (LPS) of a galU mutant of Pseudomonas aeruginosa PA103, a serogroup O11 strain, was sequentially extracted with phenol–chloroform–petroleum ether (PCP) followed by hot phenol–water extraction of the bacterial pellet remaining after PCP extraction. LPS was found in both the PCP extract as well as in the water phase of the hot phenol–water extract. Analysis of the carbohydrate portion released by mild acid hydrolysis of both LPS preparations, both before and after removal of all phosphate groups by treatment with aqueous HF, was performed by glycosyl composition and linkage analyses as well as by NMR and mass spectrometric analyses. The results showed that the carbohydrate portion of these two LPS extracts contained the same structure: namely, -GalN(Ala)-(1→3)--(7-Cm)HepII-(1→3)--HepI-(1→5)--Kdo-(2→. The oligosaccharide preparation from PCP-extracted LPS consisted of a variety of structures containing up to six phosphate groups present as mono-, pyro-, and possibly triphosphate, primarily located on the HepI residue with some molecules having a monophosphate on HepII. The oligosaccharide preparation from the hot phenol–water-extracted LPS contained a similar variety of structures, but with an additional structure in which HepI contained a PPEA group at O-2. In addition, PAGE immunoblot analysis of the crude cellular extract with anti-A-antibodies revealed the presence of A-band material in both PA103 and the galU mutant. The A-band material was purified and characterized by glycosyl composition and linkage analyses, as well as by NMR spectroscopy, which confirmed that the A-band rhamnan polysaccharide was present but not as typical LPS since lipid-A or LPS core oligosaccharide components were not detected.     

Modification of cell-wall polymers of onion waste: III. Effect of extrusion-cooking on cell-wall material of outer fleshy tissues

The polymers of onion cell walls are known to be modified by heating, but there is little information on the effects of extrusion-cooking. This work investigates the effects of extrusion-cooking on the physico-chemical characteristics and microstructure of cell walls of onion waste in relation to cell-wall chemistry. Cell-wall material from white fleshy outer scale leaves of waste onions was extruded at a range of moisture contents, barrel temperatures and screw speeds through a co-rotating twin-screw extruder. Extrusion-cooking had little effect on the carbohydrate composition of cell-wall material. However, it resulted in an increase in the solubility of pectic polymers and hemicelluloses, and this was accompanied by an increase in swelling of the cell-wall material. The degree of solubility of the pectic polysaccharides was largely dependent on the barrel temperature, and involved depolymerisation.     

Extraction, purification and turnover of rat brain glycogen

Abstract— Glycogen was prepared from rapidly frozen rat brain by the usual techniques and found to contain considerable amounts of non-glycogen carbohydrate. The crude glycogen was partially purified by extraction with hot or cold water and reprecipitation. Enzymic estimation showed that the carbohydrate extracted into hot water contained only 50 per cent of glucose after hydrolysis; of the hot water insoluble material, namely some 30 per cent of the total carbohydrate present in the crude glycogen, less than half of the carbohydrate was released by hydrolysis in 1 M-HC1. The glycogen soluble in hot water incorporated ¹⁴C from [¹⁴C]glucose at considerably higher rates than the residual material and also decreased more rapidly during post-mortem autolysis. Glycogen extracted into cold water was of higher purity than that extracted by hot water; although the material behaved as glycogen during precipitation and re-extraction it contained only 75 per cent of its carbohydrate as glucose. Contaminants included fucose, galactose and hexuronic acid. The rates of metabolism of the partially purified glycogen are compared with published rates; it is suggested that the observed rates are inaccurate due to the impurities present in brain glycogen prepared by classical techniques.     

Methods for obtaining neutral and acid oligosaccharides from flax pectins

Esterified acid soluble pectins from flax (Linun usitatissimum L.) were degraded either with HCl or pectin lyase. Centrifugation and 2-propanol precipitation led to the isolation of two low molecular weight polygalacturonates after acid hydrolysis of pectins. However, after pectin lyase digestion and purification by size-exclusion HPLC, ¹H NMR analyses indicated that acetylated hairy regions, large methylated and acetylated oligogalacturonides together with small unsubstituted oligogalacturonides were produced. Thus, in a few steps, a panel of substituted neutral and acidic oligosaccharides was produced from a raw plant material. Such oligosaccharides could be useful for further fractionations such as chemical saponification and enzymatic removal of neutral sugar chains from the hairy regions. The procedures used for pectin extraction, for degradation, and for the purification of fragments seem appropriate for large-scale production of biologically active oligosaccharides from flax.Revisions requested 24 September 2004; Revisions received 4 November 2004     

The size and distribution of polysaccharides during their synthesis within the membrane system of maize root cells

Summary The polymers contained within pellets rich in either dictyosomes or the endoplasmic reticulum have been investigated. These were detected by the incorporation of radioactivity from D-[U-¹⁴C]glucose into the sugars in the intact root. Three types of material were obtained 1) water-soluble 2) soluble in chloroform 3) insoluble. The relative proportions of each of these 3 fractions were different in the 2 membrane preparations. The dictyosome pellet contained a high proportion of water-soluble material, some of the water-soluble polysaccharides contained in both membrane preparations had a molecular weight greater than 40,000. These polymers resembled the pectins and xylans deposited in the cell wall. Some of the insoluble material could be rendered soluble by incubation with proteolytic enzymes and all of this from the dictyosome pellet had a molecular weight greater than 4,000 whereas most of that obtained from the endoplasmic reticulum had a molecular weight less than 4,000 and it did not contain fucose.Abbreviations RER rough endoplasmic reticulum - GA golgi apparatus