During tangential filtration of solid-liquid suspensions, cake formation occurs at membrane surface, a major consequence of which is a decline of flux to, at best, a limit value. In order to show the influence of the composition and properties of the fluid on cake formation, experiments have been performed with a colloidal suspension of clay in the absence or in the presence of protein. We have studied the effects of solution characteristics (ionic strength and pH) on physico-chemical properties of the suspension, such as mean diameter and zeta potential and on separation performances such as ultrafiltration Limiting flux. By taking into account electrostatic interactions, it has been possible to explain (i) the evolution in the adsorption isotherms of the protein on the clay with the physico-chemical conditions (ii) the consequences of this adsorption on the limiting flux.