Freeze-thaw stability and rheological properties of soy protein isolate emulsion gels induced by NaCl

This article focused on the freeze-thaw stability and rheological properties of soy protein isolate (SPI) emulsion gels induced by NaCl. The freeze-thaw stability was characterized by particle size, zeta-potential, and differential scanning calorimetry (DSC) measurements. The salt concentration (200-400 mM) could promote protein aggregation and improve freeze-thaw stability. The study of both linear and nonlinear rheology properties proved that SPI emulsion gels exhibited the maximal gel strength at 300 mM NaCl that could resist structure disruption and oil droplet migration. The nonlinear responses were further analyzed using Lissajous plots. Initial SPI emulsion gels had higher peak stress values at 300 mM NaCl, indicating more resistance to deformation and increased elastic-dominant behavior as well as improved freeze-thaw stability. While the area of the elastic and viscous Lissajous plots narrowed as the salt concentration exceeded 300 mM, suggesting the viscosity and elasticity decreased. Scanning electron microscopy (SEM) images further confirmed that the SPI emulsion gels had smaller pores and denser structures at 300 mM NaCl, resulting in good freeze-thaw stability. Besides, the maximum gel strength emerged in 300 mM NaCl and 100 mM NaCl before and after freeze-thaw cycles, respectively, which was due to moderate dehydration and a small amount of oil leakage from the network. These findings provide valuable information for the relationships between freeze-thaw stability and rheology property of emulsion gels.