Effects of salt mixtures on in vitro digestion of sodium-substituted myofibrillar protein gel: Disintegration and gastric juice diffusion.

The effects of salt mixtures on the in vitro gastric digestion, disintegration, and gastric juice diffusion of sodium-substituted myofibrillar protein gels were investigated. The results showed that gel disintegration occurred via surface erosion, with no significant differences in apparent morphology among substitution treatments. However, KCl/CaCl2-substituted gels exhibited preferential early decomposition of soft regions, leaving rigid structures that impeded later digestion. Acid swelling tests and magnetic resonance imaging revealed that the sodium-substituted gels containing CaCl2 had lower inherent moisture content and inflexible structural units, resulting in lower swelling ratios and hydrogen proton signal intensities compared with KCl/MgCl2-substituted gels. At a 40% substitution level, CaCl2-substituted gels exhibited lower liquid loss during digestion, and post-digestion inter-particle extrusion enhanced their elastic recovery ability. Acid diffusion experiments indicated that methylene blue-labeled acid water penetrated deeper into KCl/MgCl2-substituted gels, which possessed a uniform porous network. The bleaching radius of fluorescein isothiocyanate-labeled pepsin was smaller in CaCl2-substituted gels, attributable to the reduced cluster gaps from dehydration during gel formation and numerous clustered protein aggregates, leading to increased steric hindrance and decreased pepsin diffusivity. These findings may provide a mechanistic baseline for understanding how sodium substitution strategies influence the gastric digestion of protein gels, thereby guiding the design of meat products with controlled digestibility and texture.