Physical properties of xanthan,galactomannan and their mixtures in aqueous solutions

Some new information on the conformation of xanthan in aqueous solutions is given. A single helical chain conformation characterizes xanthan in the native state. When heated over the critical temperature for conformational change ( helixŕ coil), the xanthan is denatured and renatured when it is cooled down in a localy double helical structure. A galactomannan was also characterized and its persistence length was obtained (Lp ≈︁ 90A°). Then mixtures of the galactomannan and xanthan were investigated to propose a mechanism for the specific gelation. From the results of microcalorimetry and circular dichroism, it is concluded that a complex is formed between one disordered xanthan chain and one galactomannan chain and that an ordered conformation is stabilized at temperatures lower than 25°C when the galactomannan has a M/G ratio of ≈︁ 3. This temperature corresponds to the sol-gel transition. This is the first time that a structure of the crosslink points is demonstrated.