Abstract
The rheology and conformational helix transition of κ-carrageenan in aqueous solutions of glycerol and sorbitol at low water activity are studied. Carrageenan forms a hydrated gel in water but a weakly flocculated network of partially hydrated particles in glycerol. The melting transitions of carrageenan in glycerol/water solutions show a single peak in the complex moduli at low glycerol concentrations, and two peaks when the glycerol concentration is higher than 40% (w/w). These are thought to be due to the breakage of hydrogen bonds (low temperature peak) and calcium ion dissociation (high temperature peak). The helix–coil transition is shifted to higher temperatures in solutions with higher glycerol or sorbitol content. The temperature of the conformational transition corresponds with that of gelation for all samples. However, there is more hysteresis between the cooling and heating curves (for both OR and rheology) at high water content. This suggests that gelation occurs through helix aggregation in water but the lower solubility of carrageenan results in a more random network of helices in low water activity solvents.
Published Version
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