Sodium pectate

Pectin belongs to a family of plant polysaccharides in which the polymer backbone consists of (1— 4)-linked a-D-galacturonic acid repeating-units. Often, (1— 2)-linked a-L-rhamnose residues interrupt the regular polygalacturonate sequence. The high viscosity and gelling properties of pectins are exploited by the food and pharmaceutical industries. X-Ray studies on sodium pectate, calcium pectate, pectic acid, and pectinic acid (methyl ester of pectic acid) have disclosed their structural details. 

Fig. 15.—X-ray diffraction pattern from a polycrystalline and well-oriented fiber of sodium pectate (13), diagnostic of 3-fold helix symmetry.

Fig. 16.—Antiparallel packing arrangement of 3-fold sodium pectate (13) helices, (a) Stereo view of two unit cells roughly normal to the fcc-plane. The helix at the center (open bonds) is antiparallel to the two in the front (tilled bonds). Intrachain hydrogen bonds stabilize each helix. Sodium ions (crossed circles) and water molecules (open circles) connect adjacent helices, (b) A view of the unitcell contents down the t -axis highlights the ions and water molecules located between the helices.

The rheological behaviour in the range of LM pectin was analyzed and the sol-gel diagram established [59] for different stoichiometric ratios. In their paper, these authors determined the gel times for sodium pectate during calcium-induced gelation and the variation of the gel time with polymer concentration, stoichrometric ratio and temperature. 

Lips A., Clark A.H., Cutler N. Durand D. (1991) Measurement of cooperativity of binding of calcium to neutral sodium pectate. Food Hydrocolloids 5,87-99. 

Pectin lyase and pectate lyase activities were assayed by measuring the increasing of the absorbancy at 235 nm by the method of Albersheim and Killias (12, 13) when pectin or sodium pectate was used as the substrate, repectively. 

The purified enzyme could hydrolyze pectin and sodium pectate. However, the absorbancy at 253 nm and pH of the reaction mixture were not changed. The purified enzyme showed the activity to be polymethyl-galacturonase (PMG)and polygalacturonase (PG). 

Fig. 1. Separation of two exopolygalacturonase groups (Fraction A, Fraction B) on CM-Sephadex C-50. Column size, 20x250 mm. Stepwise elution with 0.05 M acetate buffer, pH 3.8 (starting at arrow marked a), 0.10 M acetate buffer, pH 4.8 (at arrow marked b), 0.15 M acetate, pH 5.6 (at arrow marked c) and the latter buffer plus 1.0 M NaCl (at arrow marked d). Fraction size 6 ml per half hr. Exopolygalacturonase activity determined with sodium pectate, pH 5.0 (o—O) 2nd expressed as A,, .

Candida boidinii (CCY 29-37-13) was obtained as an isolate from contaminated colunm of immobilized polygalacturonase, where 0.5% sodium pectate in 0.1 M acetate buffer, pH 4.6 was used as a substrate. Four other strains for comparison were obtained from Culture Collection of Yeasts, Institute of Chemistry (strains CCY 29-37-1, CCY 29-37-2, CCY 29-37-8, CCY 29-37-12). 

Candida boidinii was cultured at pH 3.51, 5.49 and 7.01, respectively. Czapek s Dox medium with citrus pectin (GENU Pectin, Denmark), sodium pectate or citrus pectin with 20% of D-galactopyranuronic acid (Fluka, Switzerland) as a carbon source were used. The growth curves were performed by measuring the optical density (OD) at 660 nm. 

The use of polyethylene glycol ethers in a process in which a high viscosity emulsion is formed on contact with residual crude oil has also been tested as a means of plugging thief zones using surfactants (248-250). Precipitation of sodium pectate when fresh water solutions contact brine has been proposed as a method of plugging high permeability zones (251). 

For three endo-D-galacturonanases, isolated from the culture filtrate of Coniothyrium diplodiella,114-116 that differed in the extent of degradation of sodium pectate, a 50% decrease of viscosity of the substrate solution corresponded to the splitting of 3, 4, and 10% of the glycosidic bonds, respectively. A similar difference was found between two endo-D-galacturonanases isolated from tomatoes117 one... 

At the optimal sodium pectate concentration, the efflux time of the substrate solution in the viscometer should be in the range of 115 to 120 sec. 

Set up a third reaction system using heat-inactivated enzyme diluted in 20 mM sodium acetate buffer alone (no sodium pectate substrate solution). Use the efflux time of this reaction as V%. 

A unit of activity is arbitrarily defined as that amount of enzyme that will reduce the viscosity of the sodium pectate solution by 50% in a 5-min period. The time required to reach A = 50% is typically inversely proportional to the concentration of enzyme (Mill and Tuttobello, 1961 Gusakov et al., 2002). 

Because of the polyelectroly tic nature, pectin solutions need to be made in excess of salt, usually in 0.05 0.1 M sodium chloride or phosphate, and use the same solvent for dilution (isoionic dilution) (Pals and Hermans, 1952). This is because, unlike neutrol polymers, the viscosity of dilute solution of polyelectrolytes displays unique dependence on concentration. As shown in Figure 9.5, the qsp of sodium pectate exhibits a maximum in pure water and low concentration of salt, a phenomenon caused by the so-called electroviscous effect. When the salt concentration is... 

FIGURE 9.5 Zero shear rate reduced viscosity (r sp0/c) vs. concentration of sodium pectate at various NaCl concentrations 1-7 0, 0.2, 0.4, 1.0, 2.5, 5.0 and 50 mM. From Pals and Hermans (1952), with permission of Elsevier Applied Science. 

Mitchell, J.R. and Blanshard, J.M.V. 1976. Rheological properties of citrus sodium pectate gels, J. Texture Stud., 7(3) 341-351. 

Walkinshaw, M.D. and Amott, S. 1981a. Conformations and interactions of pectins. I. X-ray diffraction analyses of sodium pectate in neutral and acidified forms,. /. Mol. Biol., 153 1055-1073. 

It is clear that the quality of the fiber diagrams so far achieved for sodium pectate leaves much to be desired, and that x-ray study of this important polysaccharide should be conducted on well-characterized samples. A single-crystal study on a model oligosaccharide would be most helpful. 

Figure 1. Dependence of the reduced osmotic pressure on the polymer concentration, Cp. of sodium pectate in 0.1 M ionic strength at 27 C (O ) pH 6.5 ( ) pH 3.5.

Figure 2. Dependence of the corrected volume change of mixing sodium pectate with Cu + <0 > and with Ca + ( ) in 0.05 M aqueous NaC104. at 25 C. R is the ion-to-polymer repeating unit molar ratio.

Figure 3. Dependence of Che corrected enthalpy of mixing (see text) sodium pectate with different counterions in 0.05 M aqueous NaC104 at 25 C. R Me+ and R Me + denote Che ion-to-polymer repeating unit molar ratio for monovalent and divalent ions, respectively.

Sodium pectate was obtained by purification and successive neutralization with NaOH of a sample of pectic acid purchased from Sigma Chemical Co. (Catalogue No. P-3889, sold as polygalacturonic acid). Purification and preparation of the solutions have been previously reported... 

Some work has been done on acetyl derivatives of the g um (27), The purified gum was dissolved in formamide and treated with acetic anhydride and pyridine at 10 C. for a few minutes. The ester was precipitated by pouring the reaction mixture into an alcohol-ether solution. The partially acetylated gum which contained 1 acetyl group per 2.5 hexose units is easily soluble in cold water, more soluble than the gum itself. This preparation resembles the naturally acetylated salep and konyaku mannans. The alkaline saponification of the partially acetylated locust bean gum was studied. This deacetylation can be described by a rate constant, fc, for second-order reactions. The acetylated gum is much more rapidly saponified than acetylated sodium pectate (Table III). It is assumed that the hydroxyl anions may easily attack the uncharged macromolecules of acetylated locust bean gum, while they are repulsed by the negatively charged molecules of acetylated sodium pectate. Therefore, the latter substance is much more slowly saponified. The results shown in Table III demonstrate that the alkaline saponification of acetylated locust bean gum is little affected by neutral salts the reaction velocity is slightly decreased. The deacetylation of sodium pectate, however, is accelerated by such an addition. This may be explained by the decrease of the electrokinetic potential of the pectate molecules by the added neutral salts. 

Sodium pectate can be cross-linked with epichlorhydrin in an alkaline medium. Different degrees of cross-linking can be obtained by varying the concentration of epichlorhydrin. These materials could be used for the separation of the two pectinesterase isoenzymes from oranges. Both components had a 7-8 fold increase in activity and could saponify 93% of the pectin. 

Use of a specific, immobilised hydrolase which cleaves a-l- 4 bonds of sodium pectate gave access to the correspondingly linked di-D-galactosiduronic acid. °... 

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