Abstract
The rheological behaviour of the chocolate at different temperatures was studied using a concentric cylinder viscometer with precision small samples adapter, temperature sensor and standard spindle. BIO chocolate (100% organic cocoa) has been used for the whole types of experiments. At the first, the range of temperature has been chosen 36 °C, 38 °C, 40 °C, 42 °C, and 44 °C. The shear deformation rate was established from the 0.1 s-1 up to 68 s-1. Rheological behaviour was non-Newtonian (plastic) with inconsiderable yield stress in all temperatures. The chocolate unambiguously demonstrated plastic behaviour and flow curves were fitted by the power law model (Herschel-Bulkley model), Bingham model, and Casson model with taking into account the coefficient of determination R2. The obtained results of rheological behaviour of chocolate can be best described as Casson fluid. Exactly coefficients of models can be used for modelling of flow velocity, volume flow, friction factor, Reynolds number, two dimensional and three dimensional velocity profiles and much more for flow in the real technical elements e.g. pipes, trough, tubes. Finally, temperature dependence of apparent viscosity of chocolate was also continuously measured in the range from 35 °C up to 62 °C. The apparent viscosity decreased in the temperature range. This decrease was fitted using power law equation. The knowledge of the plastic flow behaviour of chocolate is very important, because it is not quite common flow behaviour of foodstuffs.
Highlights
In the paper (Lapčík et al, 2017) states that chocolate is unique as a food in that fact which is solid at normal room temperatures it melts in the mouth
Most of the researchers studied the rheological characteristics of chocolate reported as non-Newtonian plastic fluid with inconsiderable yield stress (Ačkar et al, 2015; Cikrikci et al, 2017)
AND DISCUSSION it is provided a careful analysis of the rheological behaviour of pure chocolate in the different temperatures
Summary
In the paper (Lapčík et al, 2017) states that chocolate is unique as a food in that fact which is solid at normal room temperatures it melts in the mouth. Rheological behaviour was non– Newtonian (plastic) with inconsiderable yield stress in all temperatures. The chocolate unambiguously demonstrated plastic behaviour and flow curves were fitted by the power law model (Herschel–Bulkley model), Bingham model, and Casson model with taking into account the coefficient of determination R2.
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