Solid volume fraction as a determinant of rheological properties and storage stability in sesame paste

Sesame paste is a semi-solid food with complex rheological properties, prone to oil-solid separation during storage, which diminishes consumer sensory experience and shortens shelf life. This study systematically investigated the basic compositions, particle size distribution, rheological behaviors, and storage stability of sesame paste with varying solid volume fractions (15%-42%). Sesame paste was an oil-solid dispersion system characterized by polydisperse solid particles. It exhibited typical non-Newtonian fluid behavior, with shearthinning observed as shear rate increased. Moreover, higher solid volume fractions intensified thixotropic behavior and resulted in exponential growth in shear viscosity. Five distinct methods were employed to determine the steady-state and dynamic yield stresses of sesame paste. Although the yield stress values varied across methods, a consistent trend was observed: yield stress increased with the solid volume fraction. Storage stability evaluation revealed that higher solid volume fractions significantly reduced oil separation rates, likely due to increased yield stress hindering particle sedimentation during storage, thus enhancing stability. X-ray computed tomography (CT) offered in-depth insights into the microstructure, revealing changes in particle distribution and density. Notably, we studied the relationship among the CT gray value, solid volume fractions, and oil leakage rate of sesame paste, establishing a non-destructive method for assessing the stability of sesame paste based on the CT gray analysis. These findings provide actionable insights for optimizing sesame paste formulations, enhancing storage stability, and broadening its industrial applications.