XANTHAN-GALACTOMANNAN INTERACTIONS AS RELATED TO XANTHAN CONFORMATIONS

The influence of xanthan conformation on the physicochemical behaviour of their mixtures with galactomannan from Schizolobium parahybae mann ose:galactose ratio (M/G = 3), was studied by viscoelastic measurement s, differential scanning calorimetry (DSC) and chiroptical (circular d ichroism) methods. The results suggested a more effective interaction of the galactomannan with disordered xanthan segments, which are more abundant in low salt concentrations but are still present in lower pro portion at temperatures lower than the temperature of xanthan conforma tional transition (T-m). The dependence of ellipticity with temperatur e in a circular dichroism (CD) spectra suggested an ordering of the xa nthan chains induced by galactomannan at the temperature of gel format ion (T-g approximate to 25 degrees C), under conditions where xanthan alone exhibits a disordered conformation. The lower T-g value found (a pproximate to 25 degrees C) compared with that (60 degrees C) usually described in the literature is certainly related to the M/G ratio and the galactosyl unit distribution along the mannan main chain. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.