Hofmeister Effect on Gel and Rheological Properties of Soy Protein Isolate

In this study, the effects of four Hofmeister salts (KCl, NaCl, CaCl₂ and MgCl₂) at different concentrations (0.02, 0.04 and 0.06 mol/L) on gel properties and rheological properties of soy protein isolate (SPI) were systematically explored. The results showed that the addition of salt ions could improve the gel strength of SPI, but higher concentrations (0.04 and 0.06 mol/L) of CaCl₂ and MgCl₂ reduced the gel stickiness of the samples. In the dynamic rheological test, each salt ion increased the storage modulus (G’) and loss modulus (G”) of the samples to varying degrees. Higher concentrations of CaCl₂ and MgCl₂ caused excessive aggregation of SPI, whereas lower concentrations of CaCl₂ and MgCl₂ exerted an opposite effect. In the temperature sweep test, CaCl₂ and MgCl₂ changed the trend of G’ and G”, while KCl and NaCl simply increased G’ and G” without changing their trend. In the steady rheological test, higher concentrations of CaCl₂ and MgCl₂ reduced the apparent viscosity and shear force of the samples, while an opposite effect was observed under the other salt conditions. The decreasing order of the effects of higher concentrations of salt ions on the apparent viscosity and shear force was K⁺ > Na⁺ > Mg²⁺ > Ca²⁺. In summary, at specific salt ion concentrations (0.04 and 0.06 mol/L), the changes in gel and rheological properties of SPI were consistent with the Hofmeister effect.