Galacturonic acid in pectins

Total Galacturonic Acid in Pectin Component Not less than 65.0%, calculated on the ash-free, dried basis. 

A more rapid and somewhat simpler procedure for uronic acid determination was described in 1973 (8). This method is advantageous for determining galacturonic acid in pectin, as interference by neutral sugars is reduced. This method is based on the color formation which accompanies the addition of m-hydroxybi-phenyl to heated solutions of uronic acids in sulfuric acid/boric... 

It has also been shown that, in pollen tubes, both the cell wall and the contents of the Golgi vesicles can be removed by pectinase, or stained with specific, pectin reagents. When these tubes were treated with tritium-labeled mi/o-inositol (which serves as a precursor of D-galacturonic acid in pectin ) and tritiated methyl-methionine (which is a methyl-group donor ), the labeled materials were found first in the Golgi vacuoles. ... 

Komalavilas, P. and Mort, A.J. (1989) The acetylation at 0-3 of galacturonic acid in the rhamnose-rich portion of pectins. CarbohydrJies. 187 261-272. 

Figure 4. Content of galacturonic acid in the soiuble fraction after hydrolysis of AIS with polygalacturonases [a], with polygalacturonases and pectin methylesterase [b], with pectinases and cellulases [c].

Pectins. The basic building unit of pectins is known to be a-1,4 linked D-galacturonic acid which forms the polygalacturonic acid chain. The carboxyl groups of the D-galacturonic acid in the chain are methylated to various degrees. 

Note The following Requirements and Tests apply to the Pectins as supplied, whether standardized or not, except for specifications covering amide substitution and the weight percent of total galacturonic acid in the Pectin component, in which cases the test procedures include provisions for removing the sugars and soluble salts before analysis of the Pectin component. 

Degree of Amide Substitution and Total Galacturonic Acid in the Pectin Component... 

Revision Correction made to Degree of Amide Substitution and Total Galacturonic Acid in the Pectin Component Heavy Metals (as Pb) specification and determination deleted. 

Chemical Methods. Determinations of galacturonic acid of pectin usually includes both the free and esterified forms, since strongly acidic media are employed in the colorimetric methods. Procedures which continue to be used widely are modifications of those described early by Dische. One is based upon reaction with cysteine (3) and the other with carbazole (4). One modification of the carbazole method, which gave a doubling in sensitivity, along with an increased stability in color and greater reproducibility, was reported in 1962 (5). Inclusion of borate into the assay medium was responsible for the enhancement of the method. 

Rees (22) proposed four levels of structure for polysaccharides like pectin. Primary structure refers to the nature and mode of linkage of the component galacturonlc acids. In pectin, poly-D-galacturonate forms a regular, buckled, two-fold conformation... 

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