Molecular Origin of the Rheological Characteristics of .IOTA.-Carrageenan Isolated from Togekirinsai(Eucheuma serra).

Abstract

The rheological properties of -carrageenan isolated from Togekirinsai (Eucheuma serra) were measured with a rheogoniometer. The flow curves of a Ca-salt of -carrageenan solution showed plastic behavior and the yield value was estimated to be 0.4, 1.7 and 7.7 Pa at 0.1, 0.2 and 0.3% (w/v) concentration, respectively. The dynamic modulus of Ca-salt of -carrageenan increased with increase in concentration and gelation occurred at a concentration of 0.3% (w/v) at room temperature. The Ca-salt showed larger values than did of Na-and K-salts of -carrageenan in dynamic viscoelasticity. The Na-and K-salts of -carrageenan had very large values in the presence of CaCl 2 (6.8 mM) in dynamic modulus which maintained a constant value as the temperature increased to 40˚C. A transition temperature, at which dynamic modulus decreased rapidly, was observed at 40˚C. The Ca-salt of -carrageenan decreased with the addition of urea (4.0 M). The gel formation of the -carrageenan isolated from Togekirinsai might be essentially attributed to intra-and intermolecular associations, contributed by sulfate groups of adjacent D-galactose and 3,6-anhydro-D-galactose residues through Ca 2؉ bridges with ionic bonding and attractive electrostatic forces within and between molecules.

The Principle of Polysaccharide Gels

“…However, the least elastic modulus was observed in the presence of urea (4.0 M). Thus, we proposed an intra- [9]. The 3,6-anhydro-L-galactopyranosyl residue is a cage-like sugar that contributes by stabilizing the proposed intramolecular hydrogen bonding, even at high temperature > 60˚C.…”

“…As metioned above, we proposed gelation mechanism for κ-carrageenan [5]- [7], ι-carrageenan [8] [9], agarose (agar) [10], gellan gum [11] [12], amylose [13] [14], curdlan [15], alginate [16] [17], and deacetylated rhamsan gum [18] at the molecular level. Though xanthan gum which is one of bacterial polysaccharides produced commercially by Xanthomonas campestris does no gel alone, but shows curious rheological characteristics [34]- [39] and forms gel in a mixture solution with galactomannan [40]- [46] and glucomannan [47] [48].…”

Structure-Function Relationship of Rhamnan Sulfate Isolated from Commercially Cultured Edible Green Seaweed, <i>Monostroma nitidum</i>

“…For the 4.0% solution, the flow curve also showed plastic behavior, the yield value of which was 0.8 Pa, and increased linearly up to 9.5 s, then increased gradually. The yield value indicates that a secondary association (intra-and/or intermolecular) is involved in rhamnan sulfate molecules at high concentrations (3 and 4%) in aqueous solution [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…Each polysaccharide has special properties that result from its individual molecular structure. We discussed the structure-function relationship from the view point of rheological characteristics of the polysaccharides and proposed the gelation mechanism of κ-carrageenan [1][2][3], ι-carrageenan [4,5], agarose (agar) [6] gellan gum [7], amylose [8], curdlan [9], alginic acid [10,11], rice starch [12][13][14], potato starch [15], wheat starch [16,17], deacetylated rhamsan gum [18] and native gellan gum [19] at the molecular level in aqueous solutions. The hydroxyl, hemiacetal and/or methyl groups of sugar residues participated in intra-and/or intermolecular associations with hydrogen bonding and van der Waals forces of attraction in neutral polysaccharides solutions, such as agarose, amylose, curdlan, gellan gum, deacetylated rhamsan gum and starches.…”

Anticoagulant Activity of Rhamnan Sulfate Isolated from Commercially Cultured <i>Monostroma nitidum</i>

“…On the other hand, one of the authors, Tako, discussed the structure-function relationship from the viewpoint of the rheological characteristics of algal polysaccharides and the proposed gelation mechanism of κ-carrageenan [17][18][19], ι-carrageenan [20,21], agarose [22], and alginate [23,24]. Consequently, there are some basic thermodynamic and theoretical rules in gel-formation processes of polysaccharides including water molecules in principle [25][26][27].…”