Читать книгу Polysaccharides - Группа авторов - Страница 89

Carrageenan is, also a sulfated polysaccharide, consisting of bounds which α-1,3 and β-1,4 linked d-galactopyranose, also with other carbohydrate residues (xylose, glucose, etc.) and substituents (methyl ethers, pyruvates, etc.) [30]. There are 10 different structure (Figure 4.2) based on sulfate group numbers and positions, but the mostly known are these six groups, namely iota-(ι), kappa-(k), lambda-(l), mu-(m), nu-(n), and theta-(q) carrageenan [31]. These sulfate group positions and contents effect the functional and behavioral properties of carrageenan [24, 26, 30–34]. Commercially important carrageenan types are iota-(ι), kappa-(k) and lambda-(l) carrageenan.

Extraction of carrageenan is based on alkaline extraction, filtration or centrifugation of both are used for recovering. There are two extraction pathways after alkaline treatment for obtaining semi-refined or refined carrageenan forms. For the refined carrageenan, the carrageenan is precipitated with alcohol and in the second method (semi-refined carrageenan), it is dissolved in an alkali solution, like potassium chloride to form a strong gel which is then dried [35, 36].

Protein reactivity of carrageenan is an important property to be discussed for which application will be used of. Carrageenan is negatively charged, which means they are able to combine with positively charged particles, for example positively charged proteins, as in the three-dimensional gel network with the protein in milk (casein). Their main applications are in the food industry, especially in dairy products. As an emulsifier, carrageenan addition is necessary in dairy products to prevent separation of whey in cheese and ice creams and coffee whiteners. Carrageenan’s interactions with galactomannans are an important reason that it finds use in the production of fruit sorbet, poultry and meat products. Also, in pet foods semi-refined carrageenan are using for their gel forming structure. Carrageenan is found application areas in the structure of air freshener gels and toothpastes; also, biotechnological applications of carrageenan has been demonstrated as a medium for immobilizing enzymes or whole cells [32–39].

Figure 4.2 Chemical structure of carrageenan.