Renáta Dufková

This study investigates the dynamic response of various chocolate types to direct impact at high strain rates, which has significant implications for practical applications such as production, packaging, and transportation. Five different chocolate types – extra dark, dark, milk, white, and ruby – were evaluated. Experiments were conducted using the Direct Impact Hopkinson Bar (DIHB) technique, which enables the study of the mechanical behaviour of materials at strain rates exceeding 10 ³ s-1. The influence of specimen length on the mechanical response of the chocolates was also examined. Impact responses were characterized in both the time and frequency domains. Results indicate that dark chocolate exhibited the highest resistance to impact loading. Furthermore, an enhancement in mechanical properties with increasing impact velocity was observed across all chocolate types.

Chocolate masses are one of the basic raw materials for the production of confectionery. Knowledge of their rheological and flow behaviour at different temperatures is absolutely necessary for the selection of a suitable technological process in their production and subsequent processing. In this article, the rheological properties (the effect of the shear strain rate on the shear stress or viscosity) of five different chocolate masses were determined—extra dark chocolate (EDC), dark chocolate (DC), milk chocolate (MC), white chocolate (WC), and ruby chocolate (RC). These chocolate masses showed thixotropic and plastic behaviour in the selected range of shear rates from 1 to 500 s⁻¹ and at the specified temperatures of 36, 38, 40, 42, and 44 °C. The degree of thixotropic behaviour was evaluated by the size of the hysteresis area, and flow curves were constructed using the Bingham, Herschel–Bulkley and Casson models with respect to the plastic behaviour of the chocolate masses. According to the values of the coefficients of determination R² and the sum of the squared estimate of errors (SSE), the models were chosen appropriately. The most suitable models are the Herschel–Bulkley and Casson models, which also model the shear thinning property of the liquids (pseudoplastic with a yield stress value). Using the coefficients of the rheological models and modified equations for the flow velocity of technical and biological fluids in standard piping, the 2D and 3D velocity profiles of the chocolate masses were further successfully modelled. The obtained values of coefficients and models can be used in conventional technical practice in the design of technological equipment structures and in current trends in the food industry, such as 3D food printing.