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  • 1 Unilever Research Laboratory Colworth House MK44 1LQ Sharnbrook Bedford UK
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Differential scanning calorimetry (DSC) has been used to probe ordered structures and glassing behaviour for a range of agars containing < 25% w/w water. Most commercial agars are supplied in an ordered (double-helical) state, show an endothermic helix-to-coil transition above 100‡C at low-moisture, and require 90–100‡C for solubilisation in excess water. Agars dried from the coil (single-chain) state show no corresponding endothermic transitions and only require a minimum of 45‡C for aqueous dissolution. Evidence from helix-to-coil transition enthalpies, equilibrium water content as a function of relative humidity, and solid-state13C NMR spectroscopy suggests that water molecules are associated enthalpically with double-helical agar. Single-chain agar is apparently not obtained in a glassy state by direct drying from solution, but in common with double-helical forms, exhibits rubber/glass transition behaviour following heating (in a DSC pan) to 180‡C.

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