29B-13 |
Crystallization of cocoa butter under liquid shear |
R. CAMPOS and A. G. Marangoni. Dept. of Food Science, Univ. of Guelph, Food Science Bldg., Guelph, ON N1H 2W1, Canada In the manufacture of confectionery products, the physical behavior of the final product is partly determined by its crystal habit. An understanding of cocoa butter crystallization under different processing conditions will allow a better control of the processing of chocolate and confections. The objective of this study was to study the effect of shear and cooling rate prior to crystallization at 24°C of cocoa butter. Molten samples were cooled at different cooling rates (0.1, 1 and 5°C/min), under two shear regimes (0 and 220s-1), and stored at 24°C. Crystallization kinetics were quantified using the Avrami model. The polymorphic forms present in the samples were determined by differential scanning calorimetry (DSC). The microstructure was imaged at different time points with polarized light microscopy. The nucleation rate (defined as dNp/dt) and the box counting fractal dimension (Df) were determined from the micrographs. Samples cooled under shear had higher crystallization rates than statically crystallized samples. At a high cooling rate, the nucleation mechanism tends to be more sporadic, indicated by a higher Avrami constatn (n) and a higher number of particles. The nucleation rate was found to be proportional to the cooling rate and is higher when the molten fat is subjected to shear. Higher fractal dimensions are observed in the presence of shear and under high cooling rates. All samples crystallized in an initial b polymorphic form with no significant transformations taking place during a 28 day storage period. Crystallization kinetics, early nucleation stages and development of primary microstructures can be altered by heat and mass transfer of the liquid phase.
Session 29B, Food Chemistry: Lipids, antioxidants and emulsifiers
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