WEAK GEL PROPERTIES OF KHAN FLOUR FROM BELSCHMIEDIA SP - A TRADITIONAL FOOD THICKENER FROM TROPICAL WEST-AFRICA

Khan flour front Belschmiedia sp. has a long history of use in tropica l West Africa as a food thickener. The polysaccharide fraction, which is the principal constituent of the flour, shows typical polyelectroly te behaviour in solution, giving an intrinsic viscosity of[eta] = 6.4 dl/g in 0.1 mol/dm(3) NaCl. The solutions comply with the general form of shear thinning observed for disordered polysaccharide coils, with close Cox-Merz superposition of eta(omega) and eta(gamma). The concen tration dependence of 'zero shear' specific viscosity, however, shows departure from dilute solution behaviour at c[eta] approximate to 2.5, in comparison with the typical value of similar to 4.0 for most disor dered polysaccharides, and the slope of log eta(sp) versus log c at hi gher concentrations is unusually steep (similar to 2.5, in comparison with the usual value of similar to 3.3). Similar behaviour has been re ported previously for plant galactomannans, and attributed to chain-ch ain associations augmenting physical entanglement. Khan flour hydrates readily in water, and at concentrations within the approximate range 3-6% w/v gives 'weak gel' properties similar to those of ordered xanth an (G' > G ''; little frequency clepeizdence in either modulus; eta(o mega) > eta(gamma)). The gel-like character decreases with decreasing concentration, and is attributed to weak interactions between swollen particles within a surrounding matrix of dissolved polysaccharide.