Kinetics of galacturonic acid release from sugar-beet pulp

Extracted sugar-beet pulp was studied as a source of galacturonic acid. For this purpose a commercial enzyme mixture (Pectinex® 100 l from Novo Nordisk) was used to degrade extracted sugar-beet pulp to galacturonic acid in high yields and at short retention times. Because sugar-beet is a very complex substrate with a varying, non-standardisable composition, the kinetics of this enzyme mixture were studied at first with citrus- and sugar-beet pectin as model substrates, in order to define a starting point for a comparison. The degradation of the citrus- and sugar-beet pectin was carried out in acetate buffer (pH 4) and the decomposition of extracted sugar-beet pulp in water (pH 4.4), with a view to an industrial application. It was found, that for all substrates no substrate inhibition, but a strong product inhibition is given. Therefore, the use of extracted sugar-beet (and other related compounds) can enzymatically yield only low concentrations of galacturonic acid.