40 Proc. Estonian Acad. Sci. Chem., 2006, 55, 1, 40–53 Extraction and quantification of hybrid carrageenans from the biomass of the red algae Furcellaria lumbricalis and Coccotylus truncatus Rando Tuvikene a* , Kalle Truus a , Merike Vaher b , Tiiu Kailas b , Georg Martin c , and Priit Kersen c a Department of Natural Sciences, Tallinn University, Narva mnt. 25, 10120 Tallinn, Estonia b Institute of Chemistry, Tallinn University of Technology, Akadeemia tee 15, 12618 Tallinn, Estonia c Estonian Marine Institute, University of Tartu, Mäealuse 10a, 12618 Tallinn, Estonia Received 26 August 2005, in revised form 2 November 2005 Abstract. The main isolation procedures (extraction, alkali modification, and precipitation) of hybrid carrageenan blend from seaweeds of the Kassari algal stratum (the Baltic Sea, Estonia) were quantitatively investigated. In the case of all extracting agents (water, KOH and NaOH solutions) used, a sharp rise occurred in the extracting rate during the first 2 h. Pure water was the most efficient extracting medium for carrageenans from the biomass of Furcellaria lumbricalis– Coccotylus truncatus with regard to yield but certainly not gelling properties (gel strength) of polysaccharides extracted. Long-time alkali extraction causes great losses due to degradation of carrageenans; however, alkali treatment is an obligatory step for the isolation of high-quality gelling galactans from the Kassari algal stratum, resulting in a more than 3-fold increase in gel strength. In the case of a typical algal blend from this stratum (69% F. lumbricalis and 10% C. truncatus), the most effective medium for the isolation of carrageenan mixture is 0.05 M KOH solution and the preferred duration of extraction is 3–4 h. Key words: carrageenan, furcellaran, Furcellaria lumbricalis, Coccotylus truncatus, sulphated polysaccharide, gelling galactan, alkali treatment. INTRODUCTION Carrageenans [1, 2] are a family of linear sulphated polysaccharides, obtained by extraction from certain species of red seaweeds (Rhodophyta). They have a backbone built up of alternating 3-linked -D-galactopyranose and 4-linked -D-galactopyranose residues. A substantial part or even all the -galacto- * Corresponding author, rtu@akvaarium.com