Determination of pectic substances in plant material

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Abstract
Pectic substances have been extracted from plant material (a pasture legume, Stylosanthes humilis) by homogenisation with a solution of ammonium oxalate and oxalic acid and subsequently hydrolysed with polygalacturonase. The galacturonic acid produced was determined by a modified carbazole reaction. The enzymic hydrolysis step may be omitted by relying on the acid in the carbazole reaction partially to hydrolyse the pectic substances, but in doing so the sensitivity of the method is reduced sevenfold. Attempts to carry out the hydrolysis with sulphuric acid before the carbazole reaction gave incomplete hydrolysis and probably decarboxylation. Attempts to extract the pectic substances with alkali gave low values, probably because of incomplete extraction.