VISCOMETRIC STUDIES ON XANTHAN AND GALACTOMANNAN SYSTEMS

The synergistic effect obtained by mixing xanthan and galactomannans f rom Brazilian seeds (Mimosa scabrella Bentham and Schizolobium parahyb um (Vell) Blake), with mannose:galactose ratios of 1.1:1 and 3:1 respe ctively, were examined. Viscosity measurements were performed under di fferent 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/l iter, in water) despite the latter high galactose content, an increase in viscosity of 32% was observed over that calculated assuming no int eraction. The results showed the formation of a gel-like structure wit h hysteresis between increasing and decreasing shear rate. The interac tion occurred mainly when the system was previously subjected to 80 de grees C in water, independent of the conformation of xanthan. The stro nger interactions were obtained in aqueous systems. Since the main cha in of the M. scabrella galactomannan is almost completely substituted, the synergistic effect must have an interaction mechanism different f rom 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.