Colloid-chemical studies on pectic substances

Deuel, H.E.

Ber Schweiz Bot Ges 53: 219-316


Accession: 024351198

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The pectic and pectinic acids (of different degrees of esterification with methanol) were isolated from commercial apple pomace. These purified products proved to be of high mol. wt. Elec-trometric detns. of pectic substances in aqueous soln. showed that the acid behavior was similar to that of weak acids of low mol. wt. The amt. of carboxyl groups can easily be detd. by tit ration. Yet the simple formulas derived from the mass action law cannot be applied to the dissociation of pectic substances. One does not obtain an invarying dissociation constant. The "dissociation constant" depends on the pectin cone, and the degree of esterification and neutralization. The kinetics of the alkaline deesterification of pectinic acids show deviations from the equation for a 2d-order process. The differences-compared with acids and esters of low mol. wts.- are caused by the linkage of many reactive groups in one mac-romolecule. The viscosities of solns. of pectic substances in water and of nitro-pectins in acetone were detd. under various conditions. Extensive discussion of results and literature.