Physicochemical properties of pectins in solution and gel states

This paper concerns the main properties of water soluble pectins in sol and gel states. First of all, the methods of purification and characteization are discussed. The method of steric exclusion chromatography equipped with different detectors is demonstrated as the most useful to determine the macromolecular characteristics of these polymers; the role of aggregation is pointed out. The worm like chain behaviour of the pectins is developped allowing to predict the dimensions of the chain as soon as the persistence length is known. The experimental data are compared with the theoretical prediction obtained from conformational analysis. The polyelectrolyte properties of pectins are breefly exposed; specially the role of the carboxylic groups distribution along the chain is demonstrated to control the electrostatic properties. The viscometric behaviour depends on the ionic concentration and on the nature of the counterions in relation with electrostatic repulsions. Then, the ionic selectivity is discussed and related to the mechanism of crosslinking with divalent counterions. The sol-gel transition is then examined for LM and HM pectins and the mechanisms described in these two cases. The physical properties of the gels are related to the microstructure of the polymers and few data are examined.