The Sol-Gel Transition in Polysaccharide Gels

Abstract

The occurrence of thermal transitions in solutions of proteins, nucleic acids and other materials of biological origin, such as collagen, has been demonstrated on many occasions, and much useful information on the behaviour of such systems has been gained from a careful study of the temperature dependence of the properties of such systems. In addition to the proteins, etc. one other class of biologically important polymers undergoes thermal transitions which, up till now, have been relatively little studied. We are referring to the polysaccharides. An interesting series of polysaccharides is provided by the carrageenans, which occur in many seaweeds. These form thermally reversible gels, (1,2) which may be produced by as little as 1% polysaccharide, and this small amount of polysaccharide is capable of “immobilising” the 99% of water present in the gel. Clearly, such materials are of importance to industry, not least the food industry. The work reported here is a preliminary study of two polysaccharides of the carrageenan series, agarose and K-carrageenan, whose general structures are shown in Fig.1. It is clear that these polysaccharides form a series of increasing sulphate substitution on a galactose-3,6 anhydrogalactose framework.