Enzymic Degradation of Pectic Acid Part IV

Action of Carrot Exo-polygalacturonase on the Pectic Acids Prepared by Saponification of Pectin with Alkali and with Pectin Esterase

Abstract

Glycosidic bonds of pectin are cleaved in alkaline solutions by way of a transelimination. The rate of the reaction increases with temperature. In the cold, however, the reaction proceeds slowly and the de-esterification of pectin predominates over the transelimination. At 0°C, the latter can hardly occur, while the former proceeds to completion. In this case an unaccountable drop in viscosity is observed. The pectic acid having an unsaturated galacturonic acid unit at the non-reducing end of the molecule, which is a product of pectin transelimination, was resistant to CPG (carrot exo-polygalacturonase) action.
The pectic acid prepared by the saponification with PE (pectin esterase) contained no unsaturated galacturonic acid unit. This was susceptible to CPG action but the degradation was far from complete. From these results it is considered that the incompleteness of hydrolysis of pectic acid molecules by CPG is caused by the presence of this terminal unsaturated galacturonic acid unit together with neutral sugar units. In contrast to the reported partial de-esterification of pectin achieved by PE, almost complete de-esterification was obtained with PE prepared from peels of Citrus Unshiu.