Characterization of the Effect of Solutes on the Water‐Binding and Gel Strength Properties of Carrageenan

The water activity of carrageenan gels with incorporated solutes was determined by cryoscopic osmometry. Kappa (k), kappalambda (kλ) and iota (κ) carrageenan were utilized at concentrations of from 0.1 2% solids producing a sol, viscous sol, and gel. The solutes used were sucrose, NaCl, Na₂SO₄, KCl, NH₄Cl and urea at concentrations ranging from 0.05–1.0 kinetic units per kg H₂O. All the solutes were found to give a_w values as measured cryoscopically withhin 0.0005 units of literature values. The water activity of pure carrageenans at 0.1–2% solids was greater than 0.999. Addition of some solutes increased the water binding of the carrageenan‐solute‐water system as was found by a lower a_w than expected. This interaction effect increased with increasing concentration of solute and carrageenan and was greater for solutes with lower activity coefficients. The interaction effect increased in the following order: Na₂SO₄, NaCl, KCl, and NH₄ Cl. The force required to rupture the gel was measured using the Instron Universal Testing Machine. Solutes were found to influence the gel strength of k and kλ carrageenans, but not ι carrageenan. The solutes increased kλ carrageenan's gel strength in increasing order: urea, sucrose, Na₂SO₄, NaCl, NH₄Cl, and KCl and k carrageenan's gel strength in increasing order: sucrose, Na₂SO₄ and NaCl. There appears to be no simple relationship between gel strength and water‐binding when solutes are added to carrageenan.