29E-20 |
Crystallization degree in cocoa butter determined by a video microscopy technique |
I. Romero, J. M. Aguilera, and P. BOUCHON. Chemical and Bioprocess Engineering, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago, 6904411, Chile Most of chocolate sensorial properties as well as important quality attributes such as color, gloss, hardness and shelf-life are determined by cocoa butter crystallization kinetics. Thermal analysis methods such as dynamic thermal analysis and differential scanning calorimetry (DSC) have been used to determine isothermal crystallization kinetics in many materials, including cocoa butter. The common feature of these analyses is the use of the Avrami equation of isothermal phase transformation kinetics. Our objective was to develop a method to monitor and characterize isothermal cocoa butter crystallization continuously using video microscopy and image analysis as an alternative to traditional thermal analysis. Cocoa butter temperature was fixed using a thermally controlled microscope stage mounted under the lens of a polarized light microscope and images were acquired with a video camera. Consequently, the recorded images were processed and analyzed. Crystallization degree through time was expressed as the ratio between the average luminance of the acquired image and the average luminance obtained after total crystallization of the sample. Subsequently, calculated data were analyzed by applying the Avrami equation. Results obtained after isothermal crystallization experiments carried out at different temperatures ranging from 15°C to 27°C were in agreement with those obtained by traditional thermal methods. For instance, isothermal experiments at 27°C gave an Avrami exponent (n) of 2.01 and a crystallization constant of 1.1*10-5 min. These results suggest that the developed video imaging technique can be used to follow and quantify cocoa butter crystal growth in isothermal conditions. In addition, these preliminary experiments suggest that it could be possible to extend this technique to a real system such as chocolate, with the potential added benefit of direct and on-line observation.
Session 29E, Food Engineering: Transport processes and kinetics
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