Microstructural and Rheological Properties of White Chocolate During Processing

The relationship between the microstructural and rheological properties of white chocolate was studied during the main steps (mixing, pre-refining, refining, conching and tempering) of the manufacturing process. Laser light diffraction and light microscope techniques were used to study the particle size distribution (PSD) and the modifications of the network structure of the samples. Rheological parameters in terms of yield stress, apparent viscosity and thixotropy were evaluated by using a stress-strain controlled rheometer. The Casson and Windhab rheological models, which are widely used for dark and milk chocolate matrices, were used in order to explain better the rheological values obtained from the flow curves. Particle analysis revealed significant changes in the network structure during process. In particular, from the mixed sample to the refined one, a reduction in particle size was found; Sauter (D[3.2]) and Feret diameters decreased, the former from 18.6 to 6.67 mu m and the latter from 320 to 33 mu m. Consequently, an increase in the matrix aggregation was observed. The white chocolate samples obtained from the conching and tempering steps were characterized by the statistically lowest values of yield stress and apparent viscosity and by the weak structure. Moreover, the samples were well discriminated by both rheological models applied.