Chemical and rheological characterization of the carrageenans from Hypnea musciformis (Wulfen) Lamoroux

This work reports a chemical and rheological study of the carrageenans from Hypnea musciformis, a red seaweed commercially known for its production of κ-carrageenan. The polysaccharides were extracted with water both at room temperature and at 90 °C: the yield of the latter was about six times larger than the former. Fractionation with KCl yielded a large proportion (50–67%) of a precipitate with 0.125 M of this salt for both extracts, with characteristics of a nearly pure κ-carrageenan, as determined by methylation analysis and NMR spectroscopy. Smaller amounts of fractions precipitating at higher concentrations showed a basic κ-carrageenan structure, but included some ι-carrageenan diads. The KCl-soluble polysaccharides showed a larger complexity, containing d- and l-galactans or d/l-hybrids. Some differences in the rheological properties of these carrageenans have been found. Although all KCl-precipitating polysaccharides form true gels at 10 °C in presence of KCl, those extracted with hot water form stronger gels than those extracted at room temperature. Both purified κ-carrageenans show lower gelling and melting temperature than the whole polysaccharides from which they were originated.