Solution Properties of κ-Carrageenan and Its Interaction with Other Polysaccharides in Aqueous Media

America from Boston to Halifax and the Eucheuma species, which is obtained mainly from cultivation in shallow waters around the Philippines (Whistler & BeMiller, 1997).Carrageenans constitute from 30 to 80% of the cell wall of these algae, and their functionality depends on the species, season, and growing conditions.They are composed of linear chains of D-galactopyranosyl units linked via alternated (1→3)-β-D-and (1→4)-α-D-glucoside (Chandrasekaran, 1998), in which sugar units have one or two sulfate groups.Some units contain a 3,6-anhydro ring.This provides a sulfate content of 15 to 40% (Fennema, 2002).Depending on the amount and position of the SO 3 -groups carrageenans are classified as µ, ν, λ, ξ, κ, ι, and θ types (Stanley, 1987) (Figure 1).The chemical and functional properties of each type of carrageenan are different due to the presence of sulfate groups.For example, ι and κ-carrageenan do form gels in the presence of counterions, whereas λ-carrageenan does not.The commercially available carrageenans are utilized to prepare a wide variety of gels; clear or cloudy, rigid or elastic, hard or soft, thermo-stable and with or without syneresis (Whistler & BeMiller, 1997).Carrageenan gels do not require refrigeration since they do not melt at room temperature.Fig. 1.Ideal repeating unit of carrageenans: (a) µ (b) ν (c) λ (d) ξ , (e) κ (f) ι and (g) θ carrageenan (adapted from Stanley, 1987).www.intechopen.comSolution Properties of ĸ-Carrageenan and Its Interaction with Other Polysaccharides in Aqueous Media 243Due to their hydrophilic nature, carrageenans are used as thickening agents (mainly λcarrageenan), gelling agents (κ and ι-carrageenan), stabilizers or combinations of these functions in a number of food products, standardized with the necessary amounts of sucrose, glucose, salts or gelling aids, such as KCl.