Imperfect squeezing flow viscometry of mustards with suspended particulates

Abstract

Samples of commercial mustard and a mustard spread all with suspended particulates were placed in a wide Teflon R container and were compressed with a wide Teflon R plate to induce imperfect ‘squeezing flow’. The recorded force vs. height relationships were plotted on logarithmic coordinates. The resulting curves had a clear linear part marking the region where squeezing flow was dominant. The slope of this linear region was on the order of −0.8 to −1.0. When the upper plate was stopped at a preset height the force decayed to a level well above that which is produced by buoyancy, indicating a yield stress of a considerable magnitude. The tests reproducibility was on the order of about 10%, more than sufficient to detect textural differences between the products and to monitor the effect of the compression rate and the upper plate diameter (or gap). The textural differences between the products were expressed in terms of apparent compressive stress at 0.5, 1 and 2 mm height and the residual apparent compressive stress after 60 and 120 s relaxation. The magnitude of all the mechanical parameters had a modest dependence on the upper plate diameter but which had no effect on their sensitivity as measures of product consistency. Increasing the compression rate from 0.1 to 0.2 mm s −1 had relatively small effect on the magnitude of the apparent stress which was probably due, atleast in part, to the considerable yield stress of these products. It was concluded that the imperfect squeezing flow viscometry is a convenient and sensitive method to evaluate the texture of mustard and mustard products whether or not they contain seed parts.