THE INFLUENCE OF PROCESS STEPS ON MICROSTRUCTURAL, RHEOLOGICAL AND THERMAL PROPERTIES OF DARK CHOCOLATE

The aim of this research was to investigate the influence of different process steps on microstructural, rheological and calorimetric properties of dark chocolate. Samples were obtained at each phase of the manufacturing process: mixing, pre-refining, refining, conching and tempering. Microstructural properties, fundamental rheological parameters (yield stress, apparent viscosity, G’ and G”) and thermal ones (Tonset, Tend and ΔH) were evaluated by using an environmental scanning electron microscope (ESEM), a controlled strain – stress rheometer and a differential scanning calorimetry (DSC) respectively. ESEM analysis revealed an increase of the aggregation and contact point between particles from mixing to refining step, that underwent a drastic raising of all considered rheological (yield stress, apparent viscosity, G’, G’’) and thermal parameters (Tonset, Tend, ΔH). Samples obtained from the conching and tempering steps were characterized by less dense aggregate structure and lower particle–particle interactions, due to the adding of further cocoa butter and lecithin. The addition of fat and lecithin in fact covering the sugar and cocoa particles, reduced interactions and caused a decrease in all rheological and thermal parameters.