Imperfect lubricated squeezing flow viscometry for foods

Commercial mayonnaise and mustard samples placed in a wide, shallow Teflon container were compressed by a wide Teflon plate to induce an 'imperfect' lubricated squeezing flow. A dominant squeezing flow regime could be clearly identified as a linear region in the log F(t) vs log H(t) relationship, F(t) and H(t) being the momentary force and specimen height respectively. The slope of the relationship enabled the estimation of the flow index, n, and the consistency coefficient K. The n values of the mayonnaise were on the order of 0.6-0.85 and those of the mustard about 0.7. The corresponding K values were on the order of 6-13 and 4-5 kPas(n) respectively. Considering the crudeness of the array the measurements were highly reproducible and sensitive enough to detect differences (mayonnaise) or establish similarities (mustard) in products of different brands. The calculated flow index was practically independent of the plate's radius and of the consistency coefficient, which had a weak dependency on the latter. The calculated elongational viscosity vs biaxial strain rate relationship could also be used to compare the different products and brands. At 0.01 s(-1) the elongational viscosity of the maynonnaise was on the order of 150 kPas, and of the mustard 60 kPas.