Molar mass dependence of structure of xanthan thermally denatured and renatured in dilute solution

Double helical polysaccharide, xanthan samples with varying molar mass were thermally denatured and renatured in dilute solutions. Both the weight average molar mass, which was determined by size exclusion chromatography (SEC), and viscosity average molar mass decreased after denaturation and renaturation for samples with an initial molar mass of 10(6) g mol(-1), but those for the samples with an initial molar mass of 10(5) or 10(7) g mol(-1) decreased only slightly. Although the double helices of xanthan only partially dissociated into single chains, the molar mass distribution estimated by SEC did not broaden drastically by the denaturation and renaturation. These results can be explained by the formation of hairpin structures by the single chains, which are restricted to xanthan with a molar mass of 10(5) g mol(-1) by the strain of the hairpin loop, and for xanthan molar masses of 10(7) g mol(-1) by the incomplete dissociation of its long polymer chains.