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Mixing is important in ensuring the process uniformity of food products. There are few process sensors capable of measuring the uniformity of mixing during processing. Scientists are developing magnetic resonance imaging (MRI)-based sensors for characterizing the degree of mixing that occurs during processing. They used a noninvasive technique to quantify mixing as a function of axial position in a commercial twin-screw extruder. Two model systems were chosen, representing the case of two components mixing under laminar shear conditions. Researchers used glycerin and starch gel as test materials because of their high viscosity and structural stability. To improve the signal-to-noise ratio, each was mixed with paramagnetic doping material. The extent of mixing of the doped and undoped material was evaluated statistically at axial cross-sections of concentration images obtained by MRI. Concentration profiles were obtained by MRI to provide information regarding mixing in consecutive axial slices. The extent of mixing was characterized best in terms of the coefficient of variation (CV), which allows comparison from one image to another. For glycerin model systems, the CV changed by 60% during the mixing process. In the starch gel, there was a 12% change in mean signal intensity during the mixing process. The MRI technique differentiates between axial mixing and transverse mixing that takes place in the extruder channel. Contact: K. L. McCarthy, Biological and Agricultural Engineering, University of California, Davis, One Shields Ave., Davis, CA 95616. Phone: 530-752-0102. Email:
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Title Annotation:Executives: FYI...
Publication:Emerging Food R&D Report
Date:Dec 1, 2004
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