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Pure Na+ forms of furcellaran (β/κ-hybrid carrageenan), κ-carrageenan, κ/ι-hybrid carrageenan, ι-carrageenan and a hybrid carrageenan mix (made up of κ-, ι-, λ- and ν-carrageenans) were tested as beer wort fining agents. To find out which of the used carrageenans are the best beer wort clarifiers and whether they are prone to overdosage, polysaccharides with varying concentrations and molecular weights were tested. The polysaccharides were characterized by 1H NMR spectroscopy and size-exclusion chromatography. The fining efficiency of the tested polysaccharides was measured nephelometrically. Ultrasonicated and alkali treated carrageenan preparations were tested as beer wort fining agents and compared to the native samples. Undegraded furcellaran, κ-carrageenan and κ/ι-hybrids were efficient in lowering the turbidity of various beer worts, but the addition of ι-carrageenan and the carrageenan mix caused the turbidity to rise above the unfined sample value. Compared to the degraded samples, native galactans were more effective in lowering the beer wort turbidity. Higher concentrations of ultrasonicated carrageenans are needed to clarify the beer wort to similar turbidity values. Alkali treated carrageenans were more efficient beer wort fining agents compared to the native samples.

Highly pure monocationic forms of κ-, ι-, λ-carrageenans and furcellaran were prepared with the aid of successive dialysis and ion exchange steps. Two approaches were used to obtain the samples: direct exchange of the galactan-bound cations with the aid of ion-exchange resin and generation of H+-forms of the polysaccharides followed by neutralization process. The galactan samples were characterized by 1H-NMR, 13C-NMR, pulsed-field-gradient stimulated echo 1H-NMR, FTIR, FT-Raman spectroscopy, ICP-OES, size exclusion chromatography, viscometry, static and dynamic rheometry methods. The ability of cations to enhance gelation follows the order of Li+ 1 × 105 Pa) in the presence of equal amounts of Rb+ and Sr2+ ions. The rheological properties are notably pH-dependent. Among the monocationic samples, Ba2+-forms of κ-carrageenan and furcellaran yield the strongest gels in alkaline media, whereas Rb+- and Cs+-forms show the highest gelling capacities under acidic conditions. The widely employed method involving excessive dialysis against water as the final purification step causes cation depletion, acidification of the carrageenan sample and significant degradation during the freeze-drying step.

Furcellaran (β/κ-carrageenan hybrid) samples were extracted from the drifting (n = 36) and attached (n = 46) forms of red algae Furcellaria lumbricalis, collected from the Estonian waters in the Baltic Sea. The extracted polysaccharides were characterised with 1H NMR and size-exclusion chromatography. Additionally, the gelling points, storage moduli and melting points of furcellaran samples were determined with a dynamic rheometer. Results showed that the extracted furcellaran samples contained a sulphate ester group per every 3.3 to 4.5 monosaccharide residues. On average, the furcellarans had a sulphate group for every 3.9 monomers, indicating nearly equimolar amounts of β- and κ-carrageenans in the tested polysaccharide samples. The estimated peak average molecular weights of the samples were higher for the furcellarans extracted from attached specimens. Furcellaran gels exhibited a three-time decrease in storage moduli (from ~30000 Pa to ~9300 Pa) when KCl concentrations were reduced from 40 mM to 10 mM. Also, on average, the furcellaran gels (1.5% w/w) in 40 mM KCl solutions exhibited a degree hysteresis of 31 °C.

Mixed gels containing κ-carrageenan, ι-carrageenan, konjac glucomannan and xanthan were investigated. In binary mixtures, the only interactions identified from differential scanning calorimetry were between konjac glucomannan and κ-carrageenan or xanthan. The effect of konjac addition on κ-carrageenan-ι-carrageenan mixed gels was similar to that on κ-carrageenan gels, namely, an initial increase of the elastic modulus was observed up to a certain stoichiometric ratio, followed by a plateau of the elastic modulus and a strong increase of the fracture strain when konjac was added in excess. Addition of xanthan led to maxima and minima of the elastic modulus and fracture strain and stress. Interestingly, characteristic features of the elastic modulus appeared at the same concentration of xanthan added to kappa-carrageenan/konjac glucomannan mixtures with or without iota-carrageenan, indicating that xanthan is present in the kappa-carrageenan/konjac phase and absent from the iota-carrageenan phase. Characteristic features of the fracture properties, however, were shifted to higher concentrations of xanthan when iota-carrageenan was added. We tentatively conclude that xanthan chains that are concentrated in the kappa-carrageenan/konjac phase under quiescent conditions achieve homogeneous distribution under large mechanical deformation.

The structure and composition of the polysaccharide fractions from the main species of the red algal genus Gloiopeltis – G. furcata, G. tenax and G. complanata, isolated by the successive cold and hot water extraction processes were comparatively investigated. The galactan samples were characterized by 1H-NMR, 13C-NMR, FTIR and FT-Raman spectroscopy, ICP-OES, size exclusion and gas chromatography methods. The basic components of the Gloiopeltis polysaccharides are 3,6-anhydro-α- l -galactose (3.0–34.4%) and β- d -galactose-6-sulfate, indicating the basic funoran backbone. Variable amounts of 6-O-methyl-β- d -galactose, 2-O-methyl-3,6-anhydro-α- l -galactose, α- l -galactose-6-sulfate, unsubstituted β- d -galactose and xylose (0.2–2.0%) are found to be present in all of the Gloiopeltis species. The sulfur content of the funorans isolated by hot water extraction process is 4.7–7.0%, notable quantity of uronic acids (up to 4.9%) and acetylated residues are present in the cold water extracted funoran preparations. The chemically heterogeneous Gloiopeltis polysaccharides are characterized by very high polydispersities. There is a slight dependency of the chemical composition of G. complanata funorans on the life-history stage of the alga. With the aid of 2D NMR techniques it was possible to assign the 1H and 13C NMR resonances of the β- d -galactose-6-sulfate – 2-O-methyl-3,6-anhydro-α- l -galactose diad (G6S-LA2M) for the first time.

The rheology and thermal properties of funorans from the main species of the red algal genus Gloiopeltis – G. furcata , G. tenax and G. complanata , isolated by the successive cold and hot water extraction processes were comparatively investigated with special attention given to the effect of co-solutes, thermal history and galactan concentration. The galactan samples were characterized by dynamic rheometry, differential scanning calorimetry, optical density studies and X-ray analysis. Funoran gel formation is a slow process depending highly on the presence of cationic substances. The ability of metal ions to enhance funoran gelation follows the order of Li + + 4 + + + + for monovalent and the sequence of Cu 2+ 2+ , Mn 2+ 2+ 2+ 2+ 2+ for divalent cations. The Ba 2+ ions exhibit a specific effect on the gel forming process of funoran. The ability of funoran to form very strong gels was observed for the first time, especially in the presence of Ba 2+ ions. Anionic substances exhibit a weak inhibitive effect on the gelation of funoran, with the strongest effect observed for SCN − and the weakest for Cl − . The galactans from G. furcata and G. tenax show similar rheological properties, latter giving solutions with somewhat higher viscosities; the presence of idealized agarose diads in the composition of G. complanata funorans notably enhances their gelling ability. The helical pitch of funoran (1.8 nm), determined by X-ray diffraction analysis, is slightly smaller than that of agarose.

The rheology of mixed κ-carrageenan/ι-carrageenan gels was investigated in the presence of 75 or 150 mM K + . The addition of ι-carrageenan to κ-carrageenan led to an initial weak increase of the Young's modulus. A maximum occurred at concentrations ratios close to 1:1, followed by a weak decrease at higher ι-carrageenan concentrations. When κ- and ι-carrageenan were mixed at a constant total polysaccharide concentration, a plateau of the Young's modulus and a clear local minimum in the fracture strain in both compression and extension were identified at ratios between 2:1 and 4:3 (ι:κ). At all other ratios, the expected strong increase of the Young's modulus and decrease of the fracture strain were observed with an increasing κ-carrageenan fraction. A weak maximum of the fracture stress in compression and extension was observed at ratios between 1:1 and 1:2 (ι:κ). The structural and rheological findings support segregative phase-separation of mixed carrageenan gels in the presence of K + . Phase separation could be promoted through curing of the gel network of ι-carrageenan at temperatures above the coil-to-helix transition of κ-carrageenan.