Diffusion of Moisture through Chocolate-flavoured Confectionery Coatings

Abstract

The mechanism of moisture migration through chocolate-flavoured coatings was investigated. Approaches used by researchers in chemical engineering to study diffusion through heterogeneous systems were applied to study moisture diffusion in chocolate-flavoured coatings. The unsteady-state diffusivity of moisture through the coatings could be estimated from the diffusivity of water through the continuous fat phase and the partition coefficient of moisture between sucrose and cocoa powder and the fat phase. The experimental results obtained in this study were consistent with the proposed mechanistic hypotheses. For coatings containing just oil and cocoa powder, the diffusion of moisture in the dispersed phase, i.e. cocoa powder, occurred through the cocoa powder particle. In coatings containing sugar in the dispersed phase, moisture diffused along the surface of the sugar particles. When lecithin was added, the water molecules diffused through the cocoa powder particles as well as along their surfaces. The water vapour permeability of the coatings increased with addition of cocoa powder and lecithin while it decreased with the addition of sugar. With the diffusion of moisture, structural changes were observed within the coating that altered the diffusivity of moisture through the coating. These structural changes occurred due to the dissolution of sucrose particles in the migrating moisture and due to the swelling of cocoa powder in the presence of moisture.