Linear and non-linear rheological assessments of long-term stable water-in-water emulsions made with starch- basil seed gum mixtures.

This study focused on understanding the stabilization mechanism of water-in-water (W/W) emulsions formulated using three biological macromolecules: basil seed gum (BSG, an anionic polysaccharide), waxy corn starch (WCS), and high-pressure-treated waxy corn starch (HWCS). For this purpose, the steady shear, small-amplitude oscillatory shear (SAOS), and large-amplitude oscillatory shear (LAOS) rheological properties of the W/W emulsions were investigated in detail. The results indicated that increasing the concentration of WCS/HWCS (up to 2 wt%) led to a significant increase in the elastic modulus (G'), with the 0.2 % BSG + 2 % HWCS emulsion, showing the highest G' (0.790 Pa) and complex viscosity (η = 0.140 Pa·s) at 1 Hz. The extent of nonlinearity, whether elastic or viscous, decreased with increasing WCS and HWCS concentrations, whereas shear thickening and strain hardening increased. The steady shear rheological behavior fitted well to the Cross model (R > 0.99), revealing significant shear-thinning characteristics, particularly at higher starch concentrations. Additionally, the Cross model showed that the zero-shear viscosity (η₀) increased from 1.899 Pa.s in BSG + 0.5 % HWCS to 26.072 Pa.s in BSG + 2 % HWCS, confirming a robust internal structure and greater flow resistance. The findings confirmed that BSG, in combination with WCS or HWCS at specific concentrations, effectively stabilized W/W emulsions for up to 14 days without phase separation. This stability can be attributed to the high zero-shear viscosity, strong shear-thinning, and robust structural integrity of these natural macromolecules.