carrageenan

Description

Carrageenans are large, highly flexible molecules which curl forming helical structures. This gives them the ability to form a variety of different gels at room temperature. They are widely used in the food and other industries as thickening and stabilizing agents. A particular advantage is that they are pseudoplastic—they thin under shear stress and recover their viscosity once the stress is removed. This means that they are easy to pump but stiffen again afterwards. All carrageenans are high molecular weight polysaccharides made up of repeating galactose units and 3, 6 anhydrogalactose (3, *-AG), both sulfated and nonsulfated. The units are joined by alternating alpha **3 and beta **4 glycosidic linkages. There are three main commercial classes of carrageenan: Kappa: strong, rigid gels. Gels with potassium ions, reacts with dairy proteins. Mainly from Eucheuma cottonii. Iota: soft gels. Gels with calcium ions. Produced mainly from Eucheuma spinosum Lambda: Does not gel, used to thicken dairy products. The most common source is Gigartina from South America. The primary differences which influence the properties of kappa, iota and lambda carrageenan are the number and position of the ester sulfate groups on the repeating galactose units. Higher levels of ester sulfate lower the solubility temperature of the carrageenan and produce lower strength gels, or contribute to gel inhibition (lambda carrageenan). Many red algal species produce different types of carrageenans during their developmental history. For instance, the genus Gigartina produces mainly Kappa carrageenans during its gametophytic stage, and Lambda carrageenans during its sporophytic stage. See Alternation of generations. All are soluble in hot water, but in cold water only the Lambda form (and the sodium salts of the other two) are soluble. When used in food products, carrageenan has the EU additive E-number E**7 or E**7a when present as "Processed eucheuma seaweed.