| In chocolate manufacture, surfactants are added at the end of the process of conching to modify the rheological properties (e.g., viscosity, yield stress) of the molten chocolate. Molten chocolate is a dispersion of colloidal particles (sugar and cocoa), in an oil phase containing small amounts of surfactants (e.g., lecithin and/or polyglycerol polyricinoleate, PGPR). As with any colloidal system, the bulk properties of molten chocolate are controlled by its microstructure and, in particular, the behavior of the various molecules at the interfaces. The effect of surfactants is to induce repulsive forces among the particles, reducing the extent of agglomeration of the dispersion and therefore the viscosity. In the present work, it was hypothesized that water strongly adsorbs on the surface of the dispersed particles, thus hindering the adsorption of the surfactants.; In order to understand the effects of surfactants and moisture on the colloidal and rheological properties of molten chocolate, sugar and cocoa dispersions were used as model systems. Solids bed density, particle size distribution, yield stress and apparent viscosity were evaluated for the chocolate model systems. In addition, the surface binding of surfactants to the solid particles was quantified.; Lecithin adsorbed in multilayers on the surface of sugar particles. The solids bed density was increased by addition of lecithin in the dispersions, suggesting the stabilization of the particles by repulsive forces. Due to these repulsive forces, lecithin was effective in reducing the size of the agglomerates formed by capillary condensation forces at high water activities. The multilayers of lecithin on the surface of the particles formed a lubricating film that lowered the yield stress of the dispersions. |
