FLOW PROPERTIES OF MILK IN A CAPILLARY AT LOW SHEAR STRESS

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Abstract
The flow properties of human milk, cow's milk, homogenized milk, skimmed milk and oleic acid emulsion of various concentrations of fat were studied by means of the Maron-Belner low shear capillary viscometer, combined with a photomicroscope under a shear stress range of 0.2—20 dynes/cm2 Non-Newtonian flow behaviors of human milk, cow's milk, and homogenized milk might be attributed to different mechanisms in the aggregation of milk fat droplets. Other effects, such as the orientational effect should contribute to the flow behavior of oleic acid emulsion. These results were also proved by the fluorescent microscope, centrifugal photosedimentometer and the photomicroscopic observation in a capillary under various shear stresses. Sizes of milk fat globules in cow's milk showed a remarkable change from those of the other samples because of their aggregates. These results coincided with those of fluidity measurements. These experimental results were represented by Ree-Eyring's flow formula for a flow system containing one Newtonian flow unit and one non-Newtonian flow unit contribution.
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