Molecular Origin of the Characteristics of ι-Carrageenan Isolated from Togekirinsai (Eucheuma serra)

Abstract

The rheological properties of ι-carrageenan isolated from Togekirinsai (Eucheuma serra) were measured with a rheogoniometer. The flow curves of a Ca-salt of ι-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 ι-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 ι-carrageenan in dynamic viscoelasticity. The Na- and K-salts of ι-carrageenan had very large values in the presence of CaCl2 (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 ι-carrageenan decreased with the addition of urea (4.0 M). The gel formation of the ι-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 Ca2+ bridges with ionic bonding and attractive electrostatic forces within and between molecules.