Effects of Formulation and Processing Variables on the Rheology of Chitosan-Vanillin-Stabilized Olive Oil-Water...

The rheological behavior of chitosan-vanillin crosslinked olive oil-in-water emulsions (Φ = 0.52) was investigated to identify formulation and processing conditions suitable for designing oleogel precursors. The effects of homogenization conditions, reaction temperature, chitosan concentration, vanillin-to-chitosan molar ratio, and non-ionic surfactants were systematically evaluated. Surfactant-free emulsions exhibited a structured, gel-like response and non-thixotropic shear-thinning flow, which was well described by the Herschel-Bulkley model within the investigated shear-rate range. Optimal homogenization (4 min, ≥9500 rpm) refined the microstructure without compromising stability. Increasing the reaction temperature to 55 °C, the chitosan concentration to ~0.9% (w/w), and the vanillin-to-chitosan molar ratio to 0.7 maximized yield stress, consistency, and thermal robustness, consistent with enhanced network formation. In contrast, Tween^® surfactants produced divergent responses, increasing small-amplitude oscillatory stiffness while markedly reducing resistance under steady shear, likely due to surfactant-driven interfacial displacement. Among the tested surfactants, Tween^® 20 provided the highest thermal stability. Overall, these results define processing and formulation windows to obtain surfactant-free, structured emulsions with improved structuring performance, supporting their use as effective templates for olive oil oleogel development.