Effect of NaCl on gel mechanical behavior of bovine serum albumin–soy protein blends

Abstract

Soy protein gels are widely used in the food industry but have weak structures, even at high concentrations, limiting their functionality. This study explored how blending bovine serum albumin (BSA) with soy protein isolate (SPI) at different ratios and NaCl concentrations affects rheology, mechanical properties, water-holding capacity (WHC), and microstructure. Protein profile and particle size analyses revealed that moderate NaCl concentrations (50 mM) enhanced protein aggregation by reducing electrostatic repulsion and exposing reactive sites essential for gel network formation. Textural analysis confirmed that BSA-dominant gels exhibited higher hardness, springiness, and chewiness, whereas SPI-dominant gels formed weaker networks. At a 7:3 BSA: SPI ratio with 50 mM NaCl, gel hardness increased 1.4-fold higher than the no-NaCl control, reaching a peak of 5142 g. However, increasing NaCl to 100 mM caused over-aggregation and structural heterogeneity, reducing WHC by 8 % (from 95.2 % to 87.3 %) in pure BSA gels. The sample structure with 7:3 BSA: SPI ratio and 100 mM NaCl maintained its strength and consistency, with the storage modulus (G') increasing 1.3-fold compared to BSA-only gels. This treatment achieved an optimal balance of protein interactions, network stability, and textural properties. Intermolecular force disruption experiments demonstrated that disulfide bonds and hydrophobic interactions dominated BSA-rich gels. In contrast, hydrogen bonding and electrostatic interactions played a more significant role in SPI-rich gels. These findings indicate that optimizing BSA: SPI ratios and NaCl concentrations can be applied to achieve the desirable gel texture, strength, and moisture retention, which can be used in developing tailored protein-based food systems.