Viscometric studies on xanthan and galactomannan systems

The synergistic effect obtained by mixing xanthan and galactomannans from Brazilian seeds (Mimosa scabrella Bentham and Schizolobium parahybum (Vell) Blake), with mannose:galactose ratios of 1.1:1 and 3:1 respectively, were examined. Viscosity measurements were performed under different conditions. A strong interaction was ob served wi th xanthan: galactomannan (X:G) from S. parahybum, in water at 1 and 2g/liter. For the mixture of xanthan:galactomannan from M. scarbella (X:G 3:1 2 g/liter, in water) despite the latter high galactose content, an increase in viscosity of 32% was observed over that calculated assuming no interaction. The results showed the formation of a gel-like structure with hysteresis between increasing and decreasing shear rate. The interaction occurred mainly when the system was previously subjected to 80 degrees C in water, independent of the conformation of xanthan. The stronger interactions were obtained in aqueous systems. Since the main chain of the M. scabrella galactomannan is almost completely substituted, the synergistic effect must have an interaction mechanism different from that previously described by Dea and Morrison (1975), Dea et al. (1977), Morris et al. (1977), and Lundin and Hermansson (1995) in which xanthan interacts with galactomannan via the unsubstituted region of the latter. (C) 1997 Elsevier Science Ltd.