Elucidating the effect of the Hofmeister effect on formation and rheological properties of soy protein/κ-carrageenan hydrogels

Hydrogels derived from soy protein isolates (SPI) offer numerous advantages such as sustainability, biodegradability, and non-toxicity. However, the weak mechanical properties of SPI-based hydrogels limit their practical applications. To address this issue, a soaking strategy employing the Hofmeister effect was proposed to prepare SPI-based hydrogels. In this work, we looked at the possibilities of enhancing the rheological and mechanical characteristics of SPI-based hydrogels utilizing the Hofmeister series. SPI hydrogels were fabricated by introducing κ-carrageenan (SPIK). The SPIK hydrogels were soaked in different concentrations of Hofmeister salts (SO42−, Cl−, and SCN−). The results showed that the mechanical properties of SPIK hybrid hydrogels soaked with kosmotropic anion (SO42−) were obviously enhanced. The neutral ion (Cl−) soaked SPIK hybrid hydrogels showed no apparent difference in mechanical properties compared to the control, while the mechanical properties of chaotropic anion soaked SPIK hybrid hydrogels were weakened and the SPIK hybrid hydrogels were softened. The rheological test results showed that the order of anion effect on the G′ of the SPIK hybrid hydrogels were SO42− > Cl− > SCN−. Meanwhile, the G′ of the SPIK hybrid hydrogel containing SO42− was remarkably higher than the other samples. Moreover, the effect of different ratios of water, salt, and SPI on the SPIK hybrid hydrogel properties, structure, and microstructure was evaluated using a hybrid design. The results of rheological regression analysis showed a strong interaction between protein and salt. Frequency scan tests, strain scan tests, and texture analyzer measurements revealed that the SPIK hybrid hydrogels exhibited superior rheological and mechanical properties when the salt to SPI concentration ratio was 2:1, for both SO42− and Cl− ions. Overall, our results reveal the influence of the Hofmeister effect on SPI-based hydrogels.