Static crystallization of cocoa butter

Experimental Study and Computer Modeling of the Dynamic and Static Crystallization of Cocoa Butter... 

Fig. 7. Dynamic-static crystallization of cocoa butter. Effect of the shear time, on A. finish time of solidification, B. density of nuclei sites. Dynamic stage is at 600 rpm, and large dots are the results for purely dynamic experiments.

Figure 20 Times of onset and finish of the dynamic-static crystallization of cocoa butter for the three cooling paths considered and presented in Figure 19, measured experimentally and calculated with the FEM-TTT model. (From Ref. 50.)... 

In the first part of this work, static, dynamic, and intermediate dynamic-static crystallization kinetics of cocoa butter measured under isothermal conditions are reported. The effect of shear rate and time is analyzed using a kinetics theory previously developed for polymers. In the second part, these isothermal experimental... 

Fig. 5. Morphology map of cocoa butter crystals forming during the isothermal experiments of the dynamic-static TTT diagram presented in Figure 4. PLM views illustrate the morphology observed in each domain. See Figures 1 and 2 for abbreviations.

Dimick, P.S. and Manning, D.M. (1987) Thermal and compositional properties of cocoa butter during static crystallization. J. Am. Oil Chem. Soc. 64,1663-1669. 

Static Crystallization Behavior of Cocoa Butter and Its Relationship to Network Microstructure... 

Figure 2 Overlay of three characteristic melting profiles obtained by DSC (a) of the different polymorphic forms of cocoa butter. Melting curves of cocoa butter statically crystallized at (b) 0°C, (c) 20°C for 6 days and (d) —20°C for 2 days are also shown. 

Figure 3 Peak melting temperature as a function of crystallization temperature obtained from DSC melting profiles of cocoa butter statically crystallized for 7 days. Symbols represent the average standard error of four replicates.

Figure 6 X-ray diffraction pattern of cocoa butter statically crystallized at 26°C for 1 day with a broad short spacing at 4.45 A. 

Figure 19 Fractal dimension as a function of time of cocoa butter statically crystallized at (a) — 20°C, (b) 5°C, (c) 20°C, and (d) 26°C. Symbols represent tbe average standard error of at least seven replicates. 

Three different isothermal crystallization experiments were performed in this work classical static (i.e., quiescent) crystallization in the DSC apparatus, dynamic crystallization with the apparatus described above, and dynamic-static crystallization. Dynamic isothermal crystallization consisted in completely solidifying cocoa butter under a shear in the Couette apparatus. Comparison of shear effect with results from literature was done using the average shear rate y. This experiment did not allow direct measurement of the solid content in the sample. However, characteristic times of crystallization were estimated. The corresponded visually to the cloud point and to an increase of the cocoa butter temperature 1 t) due to latent heat release. The finish time, was evaluated from the temperature evolution in cocoa butter. At tp the temperature Tit) suddenly increases sharply because of the apparition of a coherent crystalline structure in cocoa butter. This induces a loss of contact with the outer wall and a sharp decrease in the heat extraction. 

For the second example, cocoa butter was dynamically cooled from an initial liquid state at 42°C, under three cooling conditions. Just before the dynamic time was reached (the dynamic was first determined fw each of the three cooling rates), a sample was taken and put in the DSC FP900 apparatus, where it was submitted to an isothermal plateau at the last temperature it was taken. The complete thermal paths for the three cases considered are presented in Figure 9. For the three cases, a mixture of Forms IV and V crystallizes. The same crystal morphology as for the isothermal dynamic-static crystallization is observed, i.e., masses growing radially from nucleation centers. The number of nuclei decreases when the cooling rate is smaller. 

Fig. 9. Cooling curves of a cocoa butter sample for three cases of dynamic-static crystallization. Anisothermal part is under shear at 600 rpm. Isothermal part is static in the DSC apparatus. See Figure 4 for abbreviation.

The aim of this work is to establish a relationship between lipid composition, polymorphism, crystallization kinetics, and microstructure of statically crystallized cocoa butter. 

Figure 5 Time-temperature state diagram for the polymorphism of statically crystallized cocoa butter. The star symbol represents the polymorphic forms that have been determined by XRD.

Figure 10 Comparison of the polymorphic forms as determined from peak temperatures obtained (a) from DSC melting profiles and (b) from crystallization curves of statically crystallized cocoa butter. Symbols represent the average standard error of three replicates.

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