29C-31 |
Crystallization kinetics of coco butter measured by rheological parameters |
J. F. TORO-VAZQUEZ1, M. Charó-Alonso, D. Pérez-Vargas, and E. Dibildox-Alvarado. (1) Facultad de Ciencias Químicas-CIEP, Univ. Autónoma de San Luis Potosí, Av. Dr. Manuel Nava 6, Zona Universitaria, San Luis Potosí, 78210, Mexico The phase transitions of cocoa butter (CB) play a crucial role in the quality and stability of products like chocolates and confectionery coatings. Therefore, operating conditions (i.e., temperature, stirring rate) during the manufacturing process are selected to control the crystallization, and subsequently the melting profile of the lipid phase of such products. Although CB is composed mainly of triacylglycerides (TAGS) of homogeneous fatty acid composition, its crystallization is a complex process due to the time-temperature effect in the polymorph behavior of TAGS. The objective of the present investigation was to evaluate CB crystallization at defined crystallization temperatures (T°) between 18.0 and 26.5°C under static and stirring (1, 60, 120, and 400 rpm) conditions. Phase transitions were monitored by differential scanning calorimetry (DSC) and rheological measurements (i.e., phase shift angle, torque) along with polarized light microscopy. Phase shift angle (d) measurements were done with a parallel plate geometry, while torque measurements were done with a ribbon-type stirring device equipped with an 8 mL sample container. Under static conditions the d profile followed quite close TAGS crystallization in CB during both the non isothermal and the isothermal period. The d profile varied as a function of T° and the d peaks observed were associated to the corresponding polymorphic behavior of CB crystallization at the particular T°. In the same way, DSC crystallization thermograms followed quite close the d profile. In contrast, torque was less sensible than d measurements to follow polymorphism. However, under stirring conditions at a particular T° the polymorph and crystal size developed by CB, established by DSC melting thermograms and polarized light microscopy respectively, was the result of the interaction between the shear rate applied and stirring time used during crystallization. Results showed that besides the time-temperature variable, the interaction between shear rate and stirring time must be considered as an important processing variable to obtain the polymorph state of interest in products based in CB crystallization.
Session 29C, Food Engineering: Rheology and texture
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