Microstructural and rheological characteristics of dark, milk and white chocolate: A comparative study

Three different chocolate types: dark, milk and white were characterized and compared for the microstructural and rheological (fundamental and empirical) characteristics. A light microscope coupled to an image analysis system was employed in order to evaluate the particle size, the network structure and the distance between particles of each matrix. Rheological parameters (yield stress, viscosity, thixotropy) were evaluated by using a stress-strain rheometer, while mechanical properties (consistency and cohesiveness) were analysed using a texture analyzer. The Power law, Casson and Windhab rheological models were used in order to better explain the rheological behaviour of chocolate samples. Results showed that white chocolate, with the highest amount of fat in formulation, had the smallest sized particles, the less aggregate structure and the lowest yield stress, viscosity and thixotropic values. Dark chocolate samples instead presented the highest aggregate structure, with less void spaces between particles that involved the highest rheological parameter values. Milk chocolate matrix exhibited intermediate microstructural and rheological characteristics compared to dark and white chocolate ones.