The carrageenan from Iridaea undulosa B.; Analysis, fractionation and alkaline treatment

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Abstract
The carrageenan extracted from the seaweed Iridaea undulosa is devoid of a k‐fraction and is composed of major amounts of ‘intermediate fractions’ (fractions which precipitate at potassium chloride concentrations higher than 0.125M) and lesser amounts of a ‘soluble fraction’ (soluble in 2.0M potassium chloride). It did not form gels in water or milk. The preparative fractionation of the carrageenan gave eight fractions which precipitated in narrow ranges of potassium chloride concentrations and on ultracentrifugation showed only one sharp peak. Analysis of these fractions, their infrared spectra, and the results of the periodate oxidation analysis permitted the identification of some structural units and suggested others. The alkaline treatment of the carrageenan gave a product comprising a k‐fraction and a soluble fraction. The k‐fraction, obtained with a high yield (53.6% of the modified polysaccharide), is capable of gelling.