Abstract: This study investigated the effects of freeze-thaw cycles on the texture, structure and freeze-thaw stability of soybean protein isolate (SPI) gels, and examined the improving effects of methylcellulose (MC), sodium hexametaphosphate (SHMP) and their combination on the gel properties of SPI. Different SPI gels were prepared and subjected to zero to five freeze-thaw cycles. Water-holding capacity (WHC), moisture distribution, texture profile analysis (TPA), rheological measurements, surface hydrophobicity, intermolecular forces, turbidity, particle size and zeta potential analysis, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) were employed to systematically evaluate gel texture, structure, and freeze-thaw stability. The results showed that freeze-thaw cycles significantly reduced the water-holding capacity of SPI gels, increased their hardness and viscosity, disrupted the microstructure, and induced changes in intermolecular forces and secondary structure. Gels containing MC exhibited higher WHC and hardness but poorer freeze-thaw stability; gels containing SHMP demonstrated better freeze-thaw stability, although the improvement in gel network structure was not significant. The combined addition of MC and SHMP significantly enhanced WHC, firmness, resilience, and freeze-thaw stability. The combined cross-linking effect of MC and SHMP facilitated the formation of a denser gel network, suppressed ice crystal growth, and preserved network integrity. This study provides a theoretical basis for the utilization of soy protein gels in the food industry.

Key words: soy protein isolate gels; freeze-thaw stability; texture; combined effect