RHEOLOGICAL PROPERTIES OF SEED GALACTOMANNAN FROM CASSIA-NODOSA BUCH-HEM

The solution properties of the galactomannan polysaccharide isolated f rom the seed of Cassia nodosa have been determined for a wide range of concentrations. The gum used has a mannose-to-galactose ratio of abou t 3.5, <($$)over bar>M(W) = 7.01 x 10(5) and an intrinsic viscosity of 1210 ml/g. The transition from dilute to semi-dilute regime, determin ed from viscometry, occurs at a critical concentration C(c) similar t o 2.5 +/- 0.5/[eta] which is Similar to the values obtained for some g alactomannans and other polysaccharides although it is higher than the value obtained for more rigid polysaccharides. The slope of the log-l og plot of specific viscosity versus C at zero shear rate is 6.5 in th e more concentrated regime. These rheological studies clearly reveal t he characteristics of a coil in dilute solutions. However, the large d ependence of the viscosity on the coil overlap parameter is probably d ue to interactions because of low galactose content. The concentrated domain is characterized for polymer concentrations higher than 15 g/l where the rheological behaviour reached that of a pseudonetwork (weak gel-like behaviour).