Polymer Gels and Networks 4 (1996) 65-83 0 1996 Published by Else&r Science Limited Printed in Northern Ireland. All rights reserved 0966.7822/96/$1500 0%6-7822(95)00018-6 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON Effect of galactomannans on the viscoelastic behaviour of pectin/calcium networks J. A. Lopes da Silva,” M. P. Gonqalves,b J. L. Doublier’ & M. A. V. Axelos’ a Escola Superior de Biotecnologia, Universidade Catolica Portuguesa, Rua Dr. Antonio Bernardino de Almeida, 4200 Porto, Portugal h Departamento de Engenharia Quimica, Faculdade de Engenharia, Universidade do Porto, Rua dos Bragas, 4099 Porto Codex, Portugal ’ INRA, Laboratoire de Physico-Chimie des Macromokules, BP 1627,44316 Nantes Cedex 03, France (Received 24 May 1995; revised 2 October 1995; accepted 3 October 1995) zyxwvutsrqponm ABSTRACT An investigation w as carried out on the effect of the addition of galactomannans to pectin/calcium networks with different structural and rheological characteristics. For those pectin/calcium gels characterized by an elastic equilibrium modulus, the addition of the galactomannan increased both the storage and loss mod&i, especially at short time scales. This increase was greater than that which could be expected by simple additivity of the viscoelastic properties of each isolated system. The pectin/calcium network remained the continuous gel matrix con- trolling the viscoelastic behaviour of these systems at low frequency. For pectin/calcium systems close to the sol-gel transition or at low pH, the mixed systems evolved towards the behaviour of viscoelastic liquids in the presence of increasing concentration of the non-gelling poly mer. These overall results suggest that there is no specific interaction and that the changes in the rheological properties of the pectin gels are due to galactomannan microphase separation limited by the entrapment of these macromolecules in the pectin-calcium network. zyxwvutsrqponmlkjihgfedcbaZ 1 INTRODUCTION Pectins are a family of anionic polysaccharides, extracted from the primary cell walls of plants, composed of ‘smooth’ regions of (13 4)-linked cY-D-galacturonic acid residues alternating with some ‘hairy’ regions where the rhamnogalacturonan backbone carries side-chains, essentially galactose and arabinose residues. The homogalacturonic regions are composed of about 100 consecutive acid residues of which the carboxylic group can 65