Effect of freezing-thawing treatment on the quality and structure of soymilk gels induced by different coagulants

This study aims to evaluate the quality and structure changes of frozen soymilk gels induced by three salt coagulants (CaCl₂, CaSO₄, and MgCl₂) during freeze-thawing (F-T) cycles (0, 1, 2, 3, 4, and 5). The study found that soymilk gels prepared with CaCl₂, CaSO₄, and MgCl₂ exhibited the stable backbone of the protein gel network. The SEM analysis revealed that the surface of the soymilk gel produced with CaCl₂ exhibited a smooth and regular texture with small and uniform pores. The hardness, chewiness, and cooking loss of frozen soymilk gels showed an increasing and then decreasing trend as the number of freeze-thaw cycles increased, while the opposite trend was observed for WHC. Soymilk gels induced by Mg²⁺ peaked at F-T-3, while those induced by Ca²⁺ peaked at F-T-4. This resulted in a harder gel texture due to the production of ice crystals, which transformed water-protein interactions into protein-protein interactions in the gel backbone. When F-T-5 was secularized, the hardness and chewability remained high. Meanwhile, SEM analysis revealed that the gel structure was rough with irregular pores and an uneven surface. Overall, freeze-thawed soymilk gels result from multiple molecular interactions between proteins. However, excessive freezing and thawing can lead to the emergence of macromolecular aggregates in the gels, which can disrupt the gel network of frozen soymilk gels.