Stabilisation of W/O/W double emulsion by polysaccharides as weak gels

Aqueous solutions of scleroglucan, carageenan and mixture of xanthan and locust bean gum polysaccharides have been tested as the external aqueous phase in water in oil in water (W/O/W) double emulsion formulations. This has been done in order to stabilize the double emulsions in time by preventing the creaming and eventually the phenomenon of coalescence. For this purpose, rheological properties of polysaccharides aqueous solutions at low concentrations were studied. These so-called weak gels exhibit a yield stress (tau(c)). The existence of this threshold was validated by two methods. The measure of shear strain (gamma) induced by an increasing steady shear stress (tau) shows a sharp increase at tau approximate to tau(c). The oscillatory viscoelastic analysis by imposing an increasing sinusoidal shear stress shows that the viscous modulus (G) passes through a defined maximum at the critical value of stress. The obtained values of yield stresses are, as required, relatively low and the viscosities of the pseudo gels are sufficiently low which will allow preventing the breakdown of the double droplets during preparation. Moreover, the times necessary for the rebuilding of the tested weak gel after shearing have been estimated to few minutes indicating that they go back rapidly to their initial pseudo three-dimensional network. The W/O/W double emulsions prepared are relatively stable towards creaming especially those prepared with scleroglucan and mixture of xanthan and locust bean gum. (C) 2007 Elsevier B.V. All rights reserved.