Читать книгу Polysaccharides - Группа авторов - Страница 61

Carrageenans are hydrocolloids (water-soluble gums) present in the intracellular matrices of Rhodophyta (red seaweeds); its function in land plants is similar to that of cellulose. These comprise of linear high-molecular polysaccharides (100–1,000 kDa) consisting of D-galactose and a sulfatic substitution of 3,6-anhydro-D-galactose units with methyl ethers [31]. Carrageenans are divided in to six classes: [i] kappa (κ); [ii] lambda (λ); [iii] iota (ι); [iv] mu (μ); [v] nu (ѵ); [vi] theta (θ). κ-carrageenan, sourced from Kappaphycus alvarezii, consists of D-galactose sulfated at C4. It reacts in existence of K⁺ with milk proteins and form gels. ι-carrageenan, sourced from Eucheuma denticulatum, is composed of C4 sulfated D-galactose linked to a C2 sulfated anhydro-galactose. In the midst of Ca²⁺, it usually gels. Λ-carrageenan is composed of C2 sulfated D-galactose linked to C2, C6 sulfated D-galactose [32]. It does not have gelling capabilities; hence, itis used in dairy products as thickening agents. Generally, carrageenans are highly anionic polymers, with food-based applications due to their gelling, thickening, and stabilizing characteristics. They are also a potential feedstock for third generation biofuels [33, 34]. Carrageenans are hygroscopic however, in organic compounds are insoluble, an important feature for their gelling ability; the solubility varies according to pH and temperature. The gels are reversible, i.e. they melt at specific temperatures and reform after cooling [35, 36].