IMPERFECT SQUEEZING FLOW VISCOSIMETRY OF SELECTED TOMATO PRODUCTS

The rheological properties of different brands of commercial tomato pa ste, sauce, puree and ketchup were estimated by imperfect squeezing fl ow viscosimetry using a wide plate and a shallow container. The tests were performed with polished and grooved surfaces. In both, slip was p rominent to such an extent that the equations for lubricated squeezing flow had to be used for the calculation of rheological parameters. De spite its crudeness, the procedure was sensitive enough to consistentl y monitor rheological differences between commercial products of diffe rent brands in terms of the apparent stress at a given specimen height , the consistency, K, and flow index, n, of the pseudoplastic liquid c onstitutive equation, and the apparent biaxial elongational viscosity, mu(b) and its strain rate dependency. In tomato paste, the flow behav ior index was approximately the same in all the brands (n similar to 0 .5), and the values of K and mu(b) had a linear relationship. Residual forces after relaxation provided an additional textural measure relat ed to the yield stress. Differences between products of different bran ds could be consistently monitored regardless of whether the test was performed at a fired specimen height or a preset initial force.