36D-5 |
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K. V. VYAKARANAM and J. L. Kokini. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, Center for Advanced Food Technology, 65 Dudley Rd., New Brunswick, NJ 08901-8520 The crispy texture of cellular foods results from the incorporation of an air/gas phase during the mixing and extrusion of doughs/melts. The final size distribution of the air/gas bubbles after mixing has a direct effect on the porous structure of the final product. Optimizing the process parameters in order to get a desired textural quality of the product is of great value to the food industry. The objective of this research was to study the effect of mixing parameters on the breakup and final size distribution of bubbles during continuous mixing of transparent dough-like model fluids. Bubble breakup and size distributions were monitored in the continuous twin-screw corotating mixer fitted with a transparent Plexiglas barrel. The model fluids used were a 2% shear-thinning carboxymethyl cellulose suspension and a high viscosity corn syrup. The experiment consisted of varying the mixer parameters such as rpm, flow rate and the blade configuration. High-speed videography was used to measure the bubble size distributions at the specific positions in the continuous mixer. The camera used was a Redlake MotionScope PCI at a frame rate of 250 fps and a resolution of 480x420 pixels. The individual frames were analyzed to get the bubble size distributions. High-speed videography helped to understand how air is incorporated and retained in a continuous mixer at different processing conditions. The maximum bubble size decreased with increasing rpm and the size distribution became more homogeneous. The breakup was highest for a paddle arrangement consisting of three flat in a row 0~{!c~} and three more flat at 90~{!c~}, which could be because of the high strain caused by this arrangement. The results of this study provide design guidelines for mixers and extruders in terms of achieving the needed air cell distribution, which leads to highly desirable product quality.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |