The Gelatinisation of Pectin in Solutions of the Alkalies and the Alkaline Earths

Pectin substances have been known since the year 1825, when Bracannot1 extracted from the roots and stems of a number of plants a substance to which he gave the name of pectic acid; about the same time Payen extracted a similar substance from the root of Ailanthus glandulosa. This discovery was followed up by other investigators, and Fremy's researches [1848] placed beyond doubt the existence in plant tissues of a class of substances distinct from the celluloses, though strongly resembling them. Fremy shewed that the parent substance, to which he gave the name of pectose, exists together with cellulose in the cell walls of green fruits, as well as in other parts of plants, and passes into solution during the process of ripening; it may also be brought into solution by boiling with acids. To this soluble variety he gave the name of pectin. Pectin undergoes further changes in boiling, and Fremy recognised two distinct varieties, parapectin, which is precipitated by neutral lead acetate, and metapectin, which is produced by boiling pectin or parapectin with acids, and is precipitated by barium chloride. Fremy also discovered the coagulating action of the enzyme pectase. These results have been confirmed and extended by later observers, especially by Mangin [1892Mangin [ , 1893]], and a series of pectin substances has been recognised, differing in solubility, coagulable under different conditions, and marked by increasing acidity.