Pectin linkage analysis

CWM was then extracted sequentially with water at 80 and with ammonium oxalate at 80, delignified with acidified sodium chlorite at 70 , and then further extracted with M and 4M sodium hydroxide. The crude polysaccharide extracts were likewise analyzed for constituent sugars and uronic acid (Table II). In order to obtain defined polysaccharide fractions the following separations were attempted. Polysaccharide fraction A was separated by ion-exchange chromatography on diethylaminoethyl(DEAE)-Sephadex A-50 and the neutral fraction afforded a virtually pure arablnan ( in Scheme 2) after selective precipitation with cetyltrimethylammonium hydroxide (7 ). Linkage analysis by methylation confirmed that this arablnan was of the highly branched type associated with pectins for which the representative, but not unique, structure (J ) may be advanced. 

Linkage analysis of pectins by methylation, designed to avoid the twin problans of base-catalyzed degradation during methylation and sugar decomposition under conditions required for... 

This review will describe the analytical methods available to determine the structural components of pectin. These features determine the important physical, chemical, and biological properties of pectin. Included will be discussion of galacturonic acid determinations, degree of esterification with methyl groups, the neutral-sugar composition, and analysis of some less-common entities, such as 0-acetyl and 0-feruloyl linkages. 

The analysis of acidic cell wall polymers (notably pectins) can also be complicated by their tendency to precipitate in acidic media. Jermyn and Isherwood (1956) found that aqueous solutions of pectic polymers from pear cell walls precipitated on the addition of nitric acid. If, however, the sample was warmed prior to the slow addition of acid, precipitation could be avoided. Ford (1982) has shown that quantitative analysis of water-soluble pectic polysaccharides can be improved by depolymerization with a poly-( 1,4-a-D-galacturonide)-glycanohydrolase (EC 3.2.1.15). This treatment can also be used prior to acid hydrolysis to prevent polymer aggregation. Although the recovery of neutral monosaccharides is increased, the stability of the glycosiduronic linkage still prevents its complete hydrolysis. 

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