Galacturonic properties

Another microbial polysaccharide-based emulsifier is Hposan, produced by the yeast Candida lipolytica when grown on hydrocarbons (223). Liposan is apparentiy induced by certain water-immiscible hydrocarbons. It is composed of approximately 83% polysaccharide and 17% protein (224). The polysaccharide portion consists of D-glucose, D-galactose, 2-amino-2-deoxy-D-galactose, and D-galacturonic acid. The presence of fatty acyl groups has not been demonstrated the protein portion may confer some hydrophobic properties on the complex. 

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. 

Pectins is a general term for a group of natural polymers based on polymerized galacturonic acid partly esterified with methanol. In addition these polymers must be considered as copolymers due to existence of neutral sugar branched zones. [1]. Some uronic acid units may also be esterified on 0-2 or 0-3 position with acetic acid. The pectins occur in the cell wall of higher plants and control at least partly the mechanical properties, the ion exchange properties and the swelling of the cell walls. 

In the course of studies on the physicochemical properties of natural polymers in aqueous solution, attention has been drawn to pectic acid, i.e. poly (a-D)galacturonic acid as a potential model of a rigid polysaccharide. 

Polymers of uronic acids are encountered in nature in structures known as pectins, which are essentially chains of D-galacturonic acid residues linked al -> 4, though some of the carboxyl groups are present as methyl esters. These materials are present in the cell walls of fruit, and the property that aqueous solutions under acid conditions form gels is the basis of jam making. 

The role of the structural properties of pectins was described recently (1) where it was shown that interactions of calcium with pectic substances were directly related to the existence of unbranched and non-esterified galacturonic blocks. Calcium was able to ionically bind two or more chains... 

When particulate enzyme preparations from Lemna minor were incubated with UDP-[U-14C]galacturonic acid (UDP-GalA), radioactive label was incorporated into pectic acid and into material soluble in organic solvents. This radioactive material had the solubility properties, and the chromatographic behavior on paper and DEAE-cellulose, of a lipid derivative of GalA however, confirmation awaits further characterization. Its formation is enhanced by UMP, and by addition of a polar, lipid fraction prepared from Lemna minor.98 Transfer of radioactivity from this material to pectic acid has been obtained.177... 

Hourdet, D., and Muller, G. (1991). Solution properties of pectin polysaccharides II. Conformation and molecular size of high galacturonic acid content isolated pectin chains. Carbohydr. Polym. 16 113-135. 

Examination of the chemical properties of the active polysaccharide F-8 and F-9 shows that F-8 contained 89.3% carbohydrate as glucose and 7.2% uronic acid as galacturonic acid, while F-9 contained 95.5% carbohydrate and 7.5% uronic acid. These polysaccharide do not contain... 

Pectins are important in cell wall assembly and detailed information of their structure will help to elucidate the relationship between the structures and physical properties. One possible approach is the chemical degradation of pectins. The specific degradation of the methyl esterified galacturonic acid residues of pectin to the corresponding... 

Crystalline a-D-galacturonic acid monohydrate has been studied by C CPMAS NMR and X-ray crystallography. The molecular dynamics have been investigated by evaluating C spin-lattice relaxation in the rotating frame (Tip) and CSA properties of each carbon. It has been found that only limited molecular motions can be detected in the low frequency (<10 Hz) range by Tip( C) measurements and changes of CSA properties as a function of temperature. 

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