Pectin Chemistry and Nomenclature

It is now clear that the basic skeletons of all pectic substances consist essentially of poly-a-D-galacturonic acids the constituent units of which contain the pyranose ring and are linked glycosidically in a configuration through positions 1 and 4.s 6 

Molecular weight values reported for various pectic substances are obviously averages and cover a wide range7 from 20,000 to over 200,000. 

Pectin.—This general term has been retained to designate pectinic acids which will form the customary pectin-sugar-acid gels. 

Pectic Add.—This term is used for colloidal polygalacturonic acids free of ester groups. The term colloidal is used here to define the size or condition in which a polygalacturonic acid becomes a pectic acid. 

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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The subject of pectic enzymes has been previously reviewed by the senior author3 and others4 and therefore this article will be confined to advances made during the past decade. Although the chemistry of pectic materials has been dealt with in a previous volume of this series by Hirst and Jones,6 we feel that a short review of the general status of pectin chemistry and especially of nomenclature is needed here to facilitate later discussions. 

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