Gelling characteristics of curdlan aqueous dispersions in the presence of salts

Gelling characteristics of curdlan aqueous dispersions were investigated in the presence or absence of various inorganic salts by dynamic viscoelasticity measurements and puncture tests. Increases in dynamic storage modulus G′ for curdlan aqueous dispersion arising from (a) moisture uptake (i.e. swelling) upon heating, (b) formation of thermo-irreversible gels upon heating occurring at higher temperatures than swelling, and (c) formation of thermo-reversible gels upon cooling were all depressed by the addition of salts, which was validated by puncture tests elucidating that failure stress and strain of curdlan gels were decreased with increasing addition level. These results suggested that hydration or disordering of curdlan molecules, involving breakages of inter- or intra-molecular hydrogen bonds, was repressed by salts added, leading to decrease in the molecular mobility and subsequently to inhibition of hydrophobic interactions between (or partially within) the molecules upon heating that induce the formation of irreversible gels. The results also suggested that new or re-natured hydrogen bonds between (or partially within) the molecules upon cooling that induce the formation of reversible gels was depressed by salts added through decrease in the number of the molecules participating in the junction zones. Some hypotheses were drawn to deduce changes in the gelation behavior of curdlan occurring in the presence of salts.