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The effects of molar mass on the coil to helix transition of sodium-type gellan gums in aqueous solution with 25 mmol NaCI were studied. Six samples of well purified sodium-type gellan gums, ranging in weight average molar mass M w from 120×10 3 to 17×10 3 at 40 °C, were used for light scattering and circular dichroism measurements, viscometry, and differential scanning calorimetry. These measurements were carried out in the temperature range from 5 to 90 °C. It was found that on lowering temperature, the coil to double-helix transition for G1-G5 samples (M w = 120 × 10 3 - 32 ×10 3 ) took place at the same temperatures, and the coil to double-helix transition is accelerated with increase of M w . The G6 sample (M w = 17 X 10 3 ) did not form a double-helix at 25 °C. It is concluded that the lowest molar mass below which no helix is formed at 25 °C in aqueous solutions with 25 mmol NaCI lies between M w = 32×10 3 and M w =17×10 3 . |
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