The Isolation of Pectic Substances From Wood

Pectin is considered by many investigators to be the tetramethyl ester of an acid composed of 4 molecules of d-galacturonic acid, 1 molecule of d-galactose, and 1 molecule of Larabinose (1).However, experimental work described by Morell, Baur, and Link (2) indicates that the pectin molecule is more complex and contains between 8 and 10 molecules of d-galacturonic acid.The data obtained by repeatedly crystallizing calcium pectate and analyzing the various crops support the view of Link and his collaborators.Pectic substances readily lose a part of their combined sugar during purification.As a result, the data obtained on analysis of a pectate will depend on the previous treatment of the material.Several explanations have been given for the origin of pectic substances, hemicelluloses, and lignin in plants.Candlin and Schryver (3) suggested that the hemicelluloses are formed from pectic substances.Other workers believe that lignin is formed from pectin.Buston (4) has discussed the relation among these classes of compounds.He concludes that they are not formed from each other.The present investigation supports the conclusions of Buston.It is possible that pectic substances, hemicelluloses, lignin, and perhaps some phenolic bodies are formed from carbohydrates by a process of intermolecular oxidation and reduction whereby energy is liberated for use by the growing plant.