SUPRAMOLECULAR STRUCTURE OF MICROBIAL POLYSACCHARIDES IN SOLUTION - FROM CHAIN CONFORMATION TO RHEOLOGICAL PROPERTIES

Literature data and unpublished results have been used to correlate the primary and secondary structures of gellan, welan, rhamsan, succinoglycan and galactoglucan in solution with their rheological properties. In dilute solution the chain conformation ranges from that of the random coil of galactoglucan to that of the stiffer double helix of gellan, and possibly a similar conformation exists for welan and rhamsan. In semidilute solution the rheological behaviour of the above microbial polysaccharides is mainly determined by their conformation in solution. Ordered regions along the polysaccharide chains seem to be the prerequisite to establish intermolecular interactions which lead to non-transient polymer networks. The lack of ordered secondary structure leads to entangled networks in which the topological constraints govern the rheological behaviour. Experimental evidence is reported to support the hypothesis that the chain conformation and rigidity can be qualitatively predicted on the basis of rheological measurements.