Influence of the welan gum biopolymer concentration on the rheological properties, droplet size distribution and physical stability of thyme oil/W emulsions.

The objective of this work is to obtain a stable and natural antimicrobial delivery system. Thus, the effect of the addition of a natural polysaccharide such as welan gum on the linear viscoelastic properties, flow behaviour, droplet size distribution and physical stability of thyme oil/W emulsions formulated with a wheat-derived surfactant was studied. All emulsions obtained show submicron diameters regardless of the concentration of welan. Emulsion without gum shows Newtonian behaviour under steady shear. Meanwhile, emulsions containing welan gum show a weak gel-like behaviour with higher G' and G″ values on increasing the content of gum in the emulsion. Their flow curves illustrate a shear thinning behaviour with much greater viscosity than that exhibited by emulsions without gum. This behaviour fits well to the Cross model. The main destabilization process of thyme oil/W emulsion without gum is creaming versus flocculation and coalescence in emulsions containing welan. Rheology, diffraction laser and multiple light scattering techniques have proved that welan gum is an important rheological modifier for thyme oil/W ecological emulsions, it being possible to control the rheological properties of these emulsions by adjusting the concentration of gum. However, welan gum does not improve the physical stability of these emulsions.