Oxidative gelation of sugar-beet pectins: use of laccases and hydration properties of the cross-linked pectins

Beet pectins are known to have feruloyl groups on their neutral side-chains. It is possible to cross-link the beet pectin through the oxidative coupling of these feruloyl groups leading to a new gelation process. We have investigated a new way of cross-linking by the use of a single enzyme, namely a laccase. Pectins have been extracted from beet pulp by various methods, including acid treatment and extrusion-cooking. Results showed that beet pectins can gel on the addition of laccases. More or less gellable pectins can be obtained but the gelation may be favoured using another enzyme, an arabinofuranosidase which make the feruloyl groups accessible to the coupling reaction. Chemical gels can therefore be obtained and the cross-linked pectins may be obtained as powders after drying. The degree of cross-linking, which can be modulated by the amount of pectin, of enzyme added and the reaction time, was found to be very critical for the hydration properties of the powders. Swelling capacities were typically in the range 25-50 ml/g of product, leading possibly to new applications for the beet pectins. (C) 1999 Elsevier Science Ltd. All rights reserved.