Ultrasound pretreatment combined with emulsion coagulant: Synergistic effects on soybean protein gel properties and salt-coagulated tofu quality

Controlling the quality characteristics of tofu by adjusting the soybean protein gelling behavior has always been a challenging and intriguing task. While tofu prepared with emulsion coagulants exhibits high yield, it suffers from compromised gel strength and water-holding capacity. This study introduced ultrasound pretreatment coupled with emulsion coagulants to modulate soy protein gelation during tofu formation. The results demonstrated that the combined approach significantly enhanced textural parameters (hardness, gumminess, and chewiness) and water retention compared to emulsion coagulant alone. These improvements were primarily attributed to ultrasound-induced cavitation, which dissociated protein aggregates and exposed basic amino acid residues, free sulfhydryl groups, and hydrophobic domains. This structural modification reduced the particle size of soy milk and oil bodies, facilitated disulfide bond formation and hydrophobic interactions during coagulation, and ultimately improved gel strength. This structural modification reduced the particle size of soy milk and oil bodies, facilitated disulfide bond formation and hydrophobic interactions during coagulation, and ultimately improved gel strength. On this basis, the slow ion release from emulsion coagulants complemented these effects, promoting a uniform and dense gel network that effectively restricted water mobility in tofu. Furthermore, principal component analysis (PCA) revealed that ultrasound-coagulant coordination predominantly altered tofu hardness and water state through PC1 (46.45 % variance contribution). This dual-modulation strategy provides new insights for diversified, customized tofu production. The findings not only propose an innovative quality enhancement methodology but also offer empirical support for scaling up ultrasound applications in tofu industrialization.