Assessment of the extent of consistency loss in semiliquid foods by compression and shear

The consistency of commercial mayonnaise, mustard and tomato paste samples was assessed by squeezing flow before and after compression or stirring, by hand and with a domestic blender which caused intensive shearing. The specimens before and after these treatments were squeezed between Teflon(R) coated parallel plates mounted on an Instron UTM model 5542 to a final height of 0.8 mm and had been let to relax before the crosshead was withdrawn. Their consistency was assessed in terms of their apparent stress at three heights, and after relaxation for I and 2 min at 0.8 mm height. Compression of the specimen prior to its testing (1-3 times) has very little effect on the specimen's consistency which supports the view that there was little friction between the Teflon(R) coated plates and the samples. Shearing caused measurable loss of consistency in the mustard and tomato paste which was not fully restored even after three hours. The sheared mayonnaise restored much of its consistency after about an hour as Judged by the apparent stress at a given height, and almost fully recovered it if Judged by the apparent residual stress after relaxation.