The Estimation of Pectin as Calcium Pectate and the Application of this Method to the Determination of the Soluble Pectin in Apples

Abstract

IN order to follow the changes which take place in the pectic constituents of stored apples, a number of preliminary investigations have been found to be necessary. In the first place a method was required by which pectin could be estimated accurately in dilute solution. This having been established, it has become possible to proceed to an investigation of the means by which the various pectic constituents of the fruit can be separately extracted. The present communication, in so far as the extractions are concerned, is confined to an examination of methods for extracting the soluble pectin of fruits. The difficulties which are encountered in the course of this extraction are almost entirely mechanical-difficulties inseparable from the process of washing out this soluble colloidal material from the insoluble colloids of the cell wall with which it is intimately associated. The clearing up of these mechanical difficulties is a necessary preliminary to any further investigation of methods of extraction, for unless suitable methods of washing out are adopted much soluble pectin may remain behind to form a mixture with the pectin dissolved out by subsequent treatment.It has been the general practice hitherto to estimate the pectin content of solutions by precipitating the pectin with alcohol. This method at its best is inconvenient and lacking in accuracy. The pectin obtained is necessarily of variable composition, since pectin probably exists in a number of forms intermediate between neutral pectin and pectic acid. Moreover, as dilution increases precipitation becomes increasingly difficult, until at very low concentrations no precipitate is obtained, even after prolonged standing with a large excess of alcohol. By the method now adopted the difficulty of precipitation is avoided, for calcium pectate can be made to flocculate from solutions of very low concentration, and a product of definite chemical composition is obtained. A comparison of the results of precipitating pectin with alcohol and as calcium pectate is given in the sequel.

Pectic Content of Plant Materials

“…All the plants studied are rapidly growing and BUSTON'S (5) The natural process of pectin alteration in plants follows a course of protopectin hydrolysis followed by hydrolysis of soluble pectic compounds and pectates (7,8). From data concerning the change of pectic material during storage in mountain ash, and high bush cranberry, it is concluded that during ripening the type of pectin that is obtained by the third extraction undergoes the most rapid change of the three types of pectic compounds.…”

Carbohydrate Fractions of Lemon Peel

“…These substances are probably celluloses and hemicelluloses. The (7) and from apple pectins (5), and they are higher than would be expected from the CO2 content-that is, on the basis that calcium pectate should contain 7.45 per cent. calcium.…”

“…Pectin in the water extract was determined as calcium pectate by the method of CARRE and HAYNES (5). with slight modifications.…”

Some Chemical Changes Incident to Ripening and Storage in the Grimes Apple

“…The combined extracts were neutralized and brought to volume. Aliquots were taken for soluble pectin determination by precipitation as calcium pectate according to the method of CARRE and HAYNES (5).…”