On the structure of κ/ι-hybrid carrageenans

The coil-to-helix transition and temperature dependence of the viscosity of commercial kappa/iota -hybrid carrageenans produced by the red algae Sarcothalia crispata, Mazaella laminarioides, and Chondrus crispus were studied using rheometry and optical rotation. The structure of these kappa/iota -hybrid carrageenans was determined by H-1 and C-13 NMR spectroscopy combined with monosaccharide composition analysis. The coil-to-helix transitions, measured by polarimetry and rheometry, of the kappa/iota -hybrid carrageenans are significantly different from those of pure kappa- and iota -carrageenan, and from hand-made mixtures thereof. This provides evidence that the kappa/iota -hybrid carrageenans are mixed chains, containing both kappa- and iota -repeating units. (C) 2001 Elsevier Science Ltd. Ali rights reserved.