Pectic acid methyl ester

Pectins are generally classed according to their ester content as high methoxyl pectins (>50% of the carboxyl groups esterified) or low methoxyl pectins (<50% of carboxyl groups esterified) (pectic acid, methyl ester [9049-34-1]). Low methoxyl pectins, like algins, require calcium for gelation. 

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. 

C-6 Pectic carboxyl, methyl ester, free acid... 

The specificity of pectinesterase is not so marked with respect to the alcohol moiety of the ester, as it hydrolyzes ethyl esters of D-galacturonans at a rate 6-16% that of de-esterification of the methyl esters.36 Citrus natsudaidai pectinesterase de-esterifies the ethyl esters of pectic acid at a rate l/5th to l/7th of that for the methyl esters the propyl and allyl esters are attacked at l/20th to l/80th of the rate.38 The tomato, citrus, alfalfa, and papaya pectinesterases do not hydrolyze the glycol and glycerol esters of pectin.39... 

Another method is based on the same principle,112 in which the [14C]labelled methyl ester of D-galacturonan is prepared by esterification of pectic acid with [,4C]diazomethane. In the course of the enzymic de-esterification, aliquots are removed, and the unreacted substrate is precipitated with acidified ethanol or 1-propanol. After centrifugation, the labelled methanol in the supernatant liquor is determined in a liquid scintillation counter. An advantage of this method lies in the possibility of using, as substrates, short-chain oligo-D-galactosiduronates partially esterified with [14C]methanol. These substrates, beginning with the trisaccharide, are not soluble in 1 4 80% phenol-diethyl ether, which is used for the extraction of enzymically released, labelled methanol. 

In pectic acids, all carboxyl groups are free, or at least not present as the methyl ester. Under suitable conditions, pectins will form jellies with sugar and acid, whereas the low-ester pectins will form gels with traces of polyvalent ions. The general structure of pectin is ... 

Pectins are present in plant juices. These are now considered to be polymers containing a basic chain, designated pectic acid, of 4-linked D-galactopyranuronic acids, the-carboxyl groups of which exist in part as methyl esters and in part as salts. Variable amounts of an araban and a galactan are associated with this polysaccharide.12 A method of approximate assay for pectic substances13 depends upon saponification... 

The pectic substances are polysaccharides composed principally of a-1,4 linked galacturonic acid or its methyl ester. The term pectin refers to material with a significant amount of esterification in contrast to unesterified polymers called pectic or polygalacturonic acids (Figure 1). The esterification degree of a particular pectin depends upon its source and extraction method. Some pectic substances are partially acetylated at the C2 and C3 positions of galacturonide residues. 

Studies of the methylation products have also supplied evidence for the identification of these acids. After complete methylation and hydrolysis of the aldobionic or polyuronic acid, it is often possible to isolate the methylated uronide as the lactone, or methyl ester. The acid may also be oxidized to the methylated dibasic acid and identified as such. Furthermore, after methylation and hydrolysis of pectic and... 

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