Effect of manufacturing process on the microstructural and rheological properties of milk chocolate

The effect of different process steps on microstructural, rheological and visual properties of milk chocolate was studied. Each process step affects the microstructural characteristics of milk chocolate, involving modifications on its macroscopic properties, such as rheological attributes. Milk chocolate samples were obtained at each phase of the manufacture process: mixing, pre-refining, refining, conching and tempering. Microstructural properties (network structure and particle size) and rheological parameters (yield stress, apparent viscosity, thixotropy, G′ and G″) were evaluated by using respectively an environmental scanning electron microscope (ESEM), and a controlled strain-stress rheometer. Colorimetric analyses (L∗, h° and C∗) were also performed. ESEM analysis revealed important changes in the network structure during process, with a reduction in particle size and an increase in the voids between aggregates, from the mixing to the refining step. Moreover, an increase of all rheological analyzed parameters from mixed sample to the refined one was found. Samples obtained from the conching and tempering steps were characterized by the lowest statistically significantly values of all rheological parameters. This could be related to the changes in the structure aggregation evidenced by ESEM analysis. From colour results, the samples with the finest particles appeared lighter and more saturated than those with coarse particles.