Effects of Formulation and Processing Variables on the Rheology of Chitosan–Vanillin Stabilized Olive Oil–Water Emulsions for Oleogel Applications

The rheological behavior of chitosan–vanillin crosslinked olive oil–in–water emulsions (Φ=0.52) was systematically studied as a function of key processing (homogenization time and speed, reaction temperature) and compositional variables (chitosan concentration, vanillin-to-chitosan molar ratio, and Tween® surfactant) to optimize their performance as oleogel precursors. All emulsions displayed viscous-dominant behavior, with a characteristic inflection in the storage modulus slope at ~0.1 Hz, except for Tween®-containing systems, which superimposable flow curves confirmed non-thixotropic Herschel–Bulkley pseudoplastic behavior (n ≈ 0.73) was observed. Optimal homogenization conditions (4 min, ≥ 9,500 rpm) promoted microstructural refinement without compromising emulsion stability. Increasing reaction temperature to 55 °C, approaching the chitosan percolation threshold (~0.8–0.9% w/w), and a vanillin-to-chitosan molar ratio of 0.7 maximized yield stress (up to 14.21 Pa), consistency, and thermal robustness, attributed to enhanced Schiff-base crosslinking and network densification. Tween® 20 and Tween® 60 induced oscillatory stiffening but caused pronounced softening under rotational shear due to interfacial displacement effects, with Tween® 20 providing superior thermal stability. Overall, a surfactant-free formulation (0.9% w/w chitosan, molar ratio 0.7, 55 °C) yielded highly structured, gel-like emulsions, demonstrating enhanced suitability as templates for olive oil oleogel development compared to conventional stabilization strategies.