The effect of shear on the crystallization of cocoa butter |
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Authors: | S Sonwai M R Mackley |
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Affiliation: | (1) Department of Chemical Engineering, University of Cambridge, New Museums Site, CB2 3RA Cambridge, England;(2) Dept. of Food Technology, Faculty of Engineering and Industrial Technology, Silpakorn University, 73000 Nakorn Prathom, Thailand |
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Abstract: | This paper examines the effect of shear on the crystallization of cocoa butter using a combination of three different experimental
techniques and a single crystallization temperature of 20°C. Rheological measurements were carried out to study the effect
of a shear step on the crystallization kinetics of the fat. Without a shear step, little rheological change was observed at
20°C; however, with the application of a shear step the onset of significant rheological change occurred and was strongly
influenced by the magnitude of the shear step. Detailed crystallographic measurements could be made with in situ X-ray experiments during flow-induced crystallization. The imposition of continuous shear changed both crystal polymorphic
structure and crystallization kinetics in a systematic way. Finally, optical measurements were used to follow changes in crystal
morphology as a consequence of continuous shear. These results revealed the form and kinetics of crystal growth. In general
the results complemented each other, and an overall picture of the way shear influenced cocoa butter growth could be formed.
The observations could be the basis for a future mathematical model of growth kinetics and provide insight into the way shear
influences crystallization kinetics, morphology, and polymorphic structure. |
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Keywords: | Cocoa butter crystallization crystallization kinetics morphology polymorphism rheology shear X-ray diffraction |
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