| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程學系 === 107 === Cocoa butter is one of the components of chocolate. It is the key factor of affecting the polymorph of chocolate. In this research, we used temperature history method (T-history method) to calculated the thermal properties of cocoa butter and chocolate and compared the polymorph of two samples which made by T-history method. Otherwise, we used the thermal properties which calculated by T-history method to predict the crystal layer thickness of samples of melt crystallization and also analyzed polymorph of two samples. For melt crystallization, we investigate the crystal layer growth versus time curve of samples and compared with the theoretical calculation. We use low temperature differential scanning calorimetry (LT-DSC) to determine the melting point and the equilibrium state and combine with X-ray diffraction to characterize the polymorph of cocoa butter and chocolate. By using T-history method, thermal properties of cocoa butter are: melting point (Tm) = 287.3 ± 0.3 K, heat capacity of liquid state (Cpl) = 3.46 ± 0.34 kJ kg-1 K-1, heat capacity of solid state (Cps) = 7.35 ± 1.47 kJ kg-1 K-1, liquid-solid enthalpy change (ΔHls) = 30.1 ± 1.7 kJ kg-1 K-1, and thermal conductivity (ks) = 0.173 ± 0.07 W m-1 K-1 and the thermal properties of chocolate are: Tm = 290.9 ± 0.3 K, Cpl = 2.92 ± 0.94 kJ kg-1 K-1, Cps=6.39±0.52 kJ kg-1 K-1, ΔHls = 12.3 ± 2.6 kJ kg-1 K-1 and ks = 0.215 ± 0.006 W m-1 K-1.
The LT-DSC and X-ray diffraction showed that the cocoa butter and chocolate made by T-history are both form IV and form V, respectively. Melt crystallization showed the crystal layer of samples would increase as time went on. The layer thickness of cocoa butter from melt crystallization was between 0.05 cm and 0.13 cm, and would produce the Form V crystal, which was the most ideal form for chocolate manufacturing. The layer thickness of chocolate made by the same process was between 0.46 cm to 1.27 cm which was ten times larger than cocoa butter. However, it generated the Form II, Form III and Form V crystals. In this research, we investigated the possibility of the application of commercial manufacturing of chocolate without the annealing process.
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