Squeezing flow of semi liquid foods between parallel Teflon coated plates |
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Authors: | Maria G Corradini Veronique Stern Thongchai Suwonsichon Micha Peleg |
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Institution: | (1) Department of Food Science Chenoweth Laboratory University of Massachusetts Amherst, MA 01003, USA Fax: 001-413 545 1262 e-mail: micha.peleg@foodsci.umass.edu, US |
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Abstract: | Samples of commercial tomato paste, low fat mayonnaise and mustard about 6–8 mm thick were squeezed to 0.8 mm at various
speeds between 5 mm min−1 and 25 mm min−1 between Teflon-coated parallel plates 127 mm in diameter using an Instron UTM Model 5542. All the log force vs log height
relationships had a clearly identified linear region. This indicated that a dominant squeezing flow regime was achieved at
about 3 mm height, and that the machine has the proper stiffness to perform the tests. The stress level at a pre-selected
height in this region is a measure of consistency, sensitive enough to distinguish between products of different brands. The
residual stress after relaxation for about 2 min was on order of 10–50% of the initial stress, an indication that all three
foods have a considerable structural integrity. In all three products there was a considerable discrepancy between the observed
rate effects and predictions based on a pseudoplastic (power law) model. It could be described by the empirical relation (Fv1 − FR)/(Fv2 − FR)=(V1/V2)m where Fv1 and Fv2 are the forces at the given displacement reached at speeds v1 and v2 respectively, FR is the residual force after relaxation (found to be practically rate independent), and m is a constant of the order of 0.15–0.33,
independent of the compression velocities ratio but characteristic of the food and brand. The calculated elongational viscosity
was not a unique function of biaxial strain rate. To a certain extent, this was probably due to imperfect lubrication. But
it was also a manifestation of these products considerable structural integrity which cannot be accounted for by models developed
for ideal liquids.
Received: 1 November 1999 Accepted: 2 May 2000 |
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Keywords: | Squeezing flow Viscometry Elongational viscosity Texture Mayonnaise Mustard Tomato concentrates |
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