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Carrageenan
Sources and Extraction
Carrageenans form the structural substance of red seaweed (Rodophyceae class). Species of Chondrus, Gigartina and Eucheuma serve as key resources which are to be found on the coasts of the North Atlantic and the Pacific Ocean. The most important producing countries are USA, Canada, France, Denmark, Norway and Ireland. To extract Carrageenans, the seaweed is gathered, dried and under compression leached with slightly alkaline water at 100 – 140° C. The raw extract is purified by filtration or centrifugation and charcoal treatment, and the carrageenans are isolated from the solution by precipitation with Isopropyl or roll drying. Another processing method is to extract the accompanying substances in a strongly alkaline environment from the Carrageenan/Cellulose basis (= semi-refined Carrageenan 407a, PNG). The annual production is estimated at approx. 40'000 tons.
Properties
Appearance
Carrageenan is a colourless to slightly yellowish, odourless powder.
Composition
Carrageenan is the term for a family of salts of sulfated galactans with a sulfate content of 18 – 40 %. The macromolecule consists of the components D-galactose, D-3.6-anhydrogalactose and sulfate ester groups. The most important Carrageenan fractions are the κ-, λ- and ι-Carrageenans , which differ in quantity and position of the sulfate ester groups and in their content of 3.6-anhydrogalactose components. κ-Carrageen form a chain of alternate galactose and anhydrogalactose units, which are linked together by β-(1-4)- and α-(1-3) bond. The galactoses in position 4 are provided with a sulfate ester group. ι-Carrageenan at the anhydrogalactose carries an additional sulfate ester group in position 2. λ-Carrageenan forms a alternate chain of β-(1-4)- und α-(1-3) linked galactose units, whereby the galactose linked in position 4 mainly exists as 2.6 disulfate, the galactose linked in position 3 mainly as 2-sulfate. The average molecular weights of Carrageenans range between 230 000 and 790 000.
Solubility
The solubility of Carrageenans depends on structure, temperature and cation. Potassium and calcium salts of the κ- und ι-Carrageenans are completely soluble in water at 50-60° C. The Na-salts of all Carrageenans are cold-water-soluble, like all alkali salts and earth alkali salts of the λ-Carrageenan. The solutions are high viscous. In the presence of alkali salts and earth alkali salts, gelation occurs with κ- and ι-Carrageenans. The viscous solutions are pseudo-plastic. Increasing temperature reduces the viscosity. This decrease of viscosity is reversible provided that the increase of temperature happens close to the pH optimum (pH 7-9); otherwise termal degradation can occur. At normal temperatures, the viscosity remains stable over a wide pH range.
Application properties
The properties relevant for the application depend on the type of the Carrageenan. The basis of many applications in the food industry is the ability of the κ- and ι-Carrageenans to form gels in the presence of K and Ca-ions caused by the relatively high content of hydrophobic anhydrogalactose and the small to average content of sulfate ester groups. κ-Carrageenans produce starchy, brittle, thermo-reversible gels which show a strong tendency to syneresis. The gel structure can be improved by adding water-soluble, neutral hydrocolloids, whereby syneresis can be prevented. ι-Carrageenan gels are without syneresis but quite weak. λ-Carrageenans do not only form gels. Like Agar, κ-Carrageenan shows a pronounced synergistic effect with carob bean gum, whereby gel strength and elasticity of gels can be improved considerably. κ-Carrageenan together with α-S2-and κ-casein gives a gel meshwork. With the aid of very small quantities of Carrageenan (0.02 %), cacao and other additives for milk form a weak gel and thus can be kept in suspension without excessive increase of the viscosity.
According to their properties, Carrageenans are used as gelling agents for jellies and puddings, as thickening agents for soups and sauces, as stabilizers for ice cream, whipped cream and froth, as emulsifiers for dairy products and cacao drinks, as well as for clarification of beer, fining of wine and as glazing agent in the textile industry.
Toxicologic Evaluation
Carrageenan is only insignificantly absorbed. Short- and long-term tests have not given any negative results. Foods containing Carrageenan have been used for a long time for human nutrition without any noticeable negative effects on health.
In human alimentation (AD), an allowed daily intake of max. 75 mg/kg body weight is considered as harmless. As tests with animals have shown, partially depolymerised low-molecular Carrageenans can cause gastric ulcer. Therefore, such partially depolymerised Carrageenans should not be used for foodstuffs. It should also be guaranteed that during the production of acid foods particularly. no degradation of the Carrageenan occurs.