Monitoring the crystallization process and polymorphism in cocoa-based products via solid-state ¹³C NMR

The crystallization time and polymorphic transitions of cocoa butter (CB), dark (DC) and milk (MC) chocolate samples, which underwent thermal pretreatment at 80 °C, 50 °C and 40 °C, were monitored via solid-state ¹³C NMR spectroscopy. Measurements were performed alternating between low flip angle direct polarization (HPDEC pulse sequence) and cross-polarization (CPMAS pulse sequence) that were used to monitor the crystallization process (using solid fat content) and polymorphism, respectively. Hexagonal or orthorhombic forms were observed at the beginning of the process and converted into triclinic structures, for thermal pretreatment at 80 °C and 50 °C, except for MC after melting the sample at 80 °C. However, thermal pretreatment at 40 °C showed faster crystallization and direct formation of triclinic structures. When compared to X-ray diffraction, this approach is more selective to monitor CB crystallization present in chocolates, without interference of other solid components. The proposed method provides a framework for studying fat crystallization in other fat-rich foods.