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 na tive state. When heated over the critical temperature for conformational ch ange (helix --> coil), the xanthan is denatured and renatured when it is co oled down in a localy double helical structure. A galactomannan was also ch aracterized and its persistence length was obtained (Lp approximate to 90A degrees). Then mixtures of the galactomannan and xanthan were investigated to propose a mechanism for the specific gelation. From the results of micro calorimetry and circular dichroism, it is concluded that a complex is forme d between one disordered xanthan chain and one galactomannan chain and that an ordered conformation is stabilized at temperatures lower than 25 degree s C when the galactomannan has a M/G ratio of approximate to 3. This temper ature corresponds to the sol-gel transition. This is the first time that a structure of the crosslink points is demonstrated.