Osmotically driven gelation in double emulsions

We describe a gelation process based on the osmotically driven water flux between the two aqueous compartments of double emulsions. We first prepare fluid water-in-oil-in-water (W/O/W) double emulsions whose external aqueous phase contains hydrocolloids and/or proteins at moderate concentration. The initial osmotic pressure in the innermost droplets is considerably larger than that in the external phase. An inward water transfer (swelling) is thus likely to occur in order to restore osmotic equilibrium. In the initial state, the globules are large and so the transfer is slow because of the limited exchange surface area. The emulsions are then submitted to a short and intense shear that provokes globule breakup, in order to increase the rate of water diffusion. As a consequence, the initially fluid materials undergo a sudden rheological transition. During that process, the hydrocolloids and/or proteins are concentrated in the continuous phase until a point that a gel is formed. The final rheological properties can be tuned from weak to strong gels depending on the initial composition. The inner droplet fraction strongly increases during the swelling process and droplet-globule coalescence occurs above a critical volume fraction that determines the maximum swelling capacity and thus final state of the system. The proposed approach demonstrates a simple, yet versatile and adaptable solution for making texturized emulsions with reduced fat content and limited amount of hydrocolloids/proteins. (C) 2013 Elsevier Ltd. All rights reserved.