About the native and renatured conformation of xanthan exopolysaccharide

Low-angle laser light scattering (LALLS), size exclusion chromatography coupled with multi-angle light scattering (s.e.c./MALLS), low shear intrinsic viscosity and circular dichroism measurements were performed for elucidating the size and conformation changes associated with the temperature-induced denaturation and renaturation of native xanthan in different salt conditions (0.01M and 0.1M). Upon heating, at temperatures above the order-disorder transition temperature (T-m) the denaturation of the native ordered conformation occurs with a reduction of M-w by a factor of roughly two therefore indicating a double strand conformation for the native form. The molecular weight has been found invariant after renaturation on cooling that favours the hypothesis that the restoration of the ordered form of xanthan takes place through the same molecule. The most probable conformation for the renatured form of xanthan is that of an antiparallel double stranded structure consisting of one such chain folded as a hairpin loop. (C) 1997 Elsevier Science Ltd.