Extraction of Kappa-Carrageenan from Red Seaweed

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Carbohydrates are macromolecules whose basic units are called monosaccharides (or simple sugars). These simple sugars are polyhydroxy aldehydes (aldoses) or ketones (ketoses), depending on the chemical nature of their carbonyl group, containing at least three carbon atoms. The smallest monosaccharides with only three carbon atoms are collectively known as trioses; while those with four, five, six, and so on carbon atoms are called tetroses, pentoses, hexoses and so on, respectively. Carbohydrates may also be classified according to the number of combining monosaccharide units, forming an oligosaccharide or polysaccharide.

In the experiment, the sulfated polysaccharide, κ-carrageenan is extracted. Carrageenans, in general, have high molecular weights polysaccharides made up of repeating galactose units and 3,6 anhydrogalactose (3,6-AG), joined by alternating alpha 1-3 and beta 1-4 glycosidic linkages. There are various types of the polysaccharide which include alpha, beta, lamba, kappa, mu, and iota carrageenan (figure 1). However, iota, kappa and lambda are the three carrageenans of commercial interest. The primary factors influencing the properties of these three are the number and position of the ester sulfate groups on the repeating galactose units. Nevertheless, all carrageenans are extracted from red seaweed and assume a gelatinous structure.


Figure 1.Different types of carrageenan. They differ in structure, properties and uses.

Production of carrageenan, particularly κ-carrageenan can be done in either of two ways. The first method, which is considered as the original one, involves the extraction of carrageenan into an aqueous solution, filtration to remove the seaweed residue and finally, the recovery of the carrageenan from the solution. Hence, product of this extraction is called refined or filtered carrageenan. In the second method, carrageenan is not actually extracted but rather, everything soluble in alkali and water is washed out...
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