Steady shear flow behavior of commercial dark chocolates at different temperatures

The objective of this study was to determine the rheological properties of commercial dark chocolates with high cocoa content (86%, 95%, and 100%) at different temperatures (25°C, 35°C, and 45°C). The pH values ranged from 6.14 to 6.47, the soluble solids content ranged from 0.64 to 1.34 (°Brix), and the moisture content ranged from 1.29% to 1.66% (wb). No significant differences were observed between the samples with 86% and 95% cocoa content in terms of all color coordinate values (p>0.05). However, samples with 100% cocoa content exhibited significantly higher coordinate values for L*, a*, and b* (p<0.05). The molten chocolate was found to exhibit non-Newtonian fluid behavior, following the Herschel-Bulkley model, with flow behavior index (n) values ranging from 0.83 to 0.89, indicating pseudoplastic behavior. The yield limit (σy) decreased as the cocoa content increased at the same temperature, and decreased as the temperature increased within the same sample. An Arrhenius-type relationship was used to correlate the consistency coefficient (K) to temperature. The activation energy (Ea) values exhibited a positive correlation with cocoa content, ranging from 32.54 to 39.64 kJ/mol.