29E-21 |
Sugar crystallization kinetics monitored by digital video-microscopy |
M. P. Arellano, J. M. Aguilera, and P. BOUCHON. Chemical and Bioprocess Engineering, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago, 6904411, Chile Crystallization kinetics of various types of sugars has been studied for several years by use of refractometry, gravimetric and polarimetric methods. However, during the last decades, new methods for food quality characterization have been developed. Among those techniques, video-microscopy and image analysis methods have been increasingly used to understand and quantify dynamic changes occurring at the microstructural level. Our objective was to develop a method to monitor and characterize sugar crystallization kinetics in model systems (supersaturated lactose and/or in aqueous solutions) continuously by digital imaging. The solution temperature was fixed using a thermally controlled microscope stage mounted under the lens of a polarized light microscope and images were acquired with a digital camera. Subsequently, the recorded images were processed and analyzed using Image Pro Plus 4.5 software. Simultaneously, crystallization was followed under the same experimental conditions using refractometry. We found that the microscopy technique was instrumental in assessing geometrical changes during crystallization in real time when crystallizing at 20, 30 and 40°C; in addition, several crystal parameters such as perimeter, area and circularity were quantified. Results showed that crystallization rates obtained using quantitative microscopy were in agreement with those found by refractometry. These results suggest that the digital imaging technique can be utilized to assess crystal growth, in real time, at the relevant scale of structural changes in sugar containing solutions. This technique could be used to study crystallization in semisolids systems, such as dulce de leche, a typical South American dairy product similar to sweetened condensed milk, which is difficult to characterize by traditional techniques and whose lactose crystallization kinetics is only partially understood.
Session 29E, Food Engineering: Transport processes and kinetics
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