Araban associated with pectin

So far as we are aware, the galactan associated with pectin has hitherto been isolated in a reasonable degree of purity in one instance only,2 namely from the seeds of Lwpinua albus. This source contains a comparatively high proportion of the galactan component ([< ]d + 35° in water) and the isolation of the galactan is thus facilitated. The araban was partially removed by repeated reprecipitation from aqueous solution... 

Methyl-L-arabinose has been isolated from the products of hydrolysis of methylated damson gum37 and the araban found associated with pectin.84 88 This sugar has been synthesized by the conversion of methyl /3-L-arabopyranoside to the 3,4-benzylidene derivative (XXIX) which on methylation gave methyl 2-methyl-3,4-benzylidene-/J-L-arabopyrano-side (XXX) from which the desired 2-methyl ether was obtained by hydrolysis.40... 

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 present authors and their collaborators have also investigated arabans derived from apple and citrus pectins and here again it is to be noted that the arabans are associated in nature with galactan and pectic acid. The methylated derivatives of all these arabans have very similar properties and on hydrolysis give approximately the same proportions of 2,3,5-trimethyl-L-arabofuranose, 2,3-dimethyl-L-arabinose and... 

It will be clear that in this nomenclature arabans and galactans are not included as components of pectinic or pectic acids. They have been found in pectic preparations, but it is not known whether they represent chemically bound constituents such as side chains or are to be regarded as separate substances closely associated physically with the predominating pectinic or pectic acids. The nomenclature is thus based upon an ideal conception and should be regarded as provisional and subject to more accurate specification as knowledge increases. 

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