INFLUENCE OF NUMBER AND THICKNESS OF BLADES ON THE PERFORMANCE OF THE KRAMER TYPE SHEAR-COMPRESSION CELL2

A study was undertaken to determine the influence of number of blades and their thickness on the performance of the Kramer type shear compression cell Cells with 4, 6, 8, 10 and 12 blades, with corresponding blade thicknesses ranging from 6.4 to 0.4 mm, were manufactured and compared against a standard Kramer shear cell Seven canned vegetables were used in the trials. Maximum force, bio-yield force, firmness and energy to maximum force were recorded and compared in testing these products in the different cell configurations. Very thin blades proved to be a source of mechanical problems when used with firm products and will not be used in any further studies. Readings obtained with the various cell configurations were product dependent and forces with the standard cell were higher. Blade spacing is a critical factor in the cell design.     

A METHOD FOR RECORDING THE AMPLITUDE OF FORCE FLUCTUATIONS DURING TEXTURE TESTS1

A means of measuring the amplitude of force fluctuations during texture tests is described. A maximum-minimum module added to the electronic force recording system gives a direct readout of amplitude. The method has potential applications in research and quality control The technique is demonstrated with the back extrusion test applied to tomato juice. The results show that the maximum amplitude of the force fluctuations during extrusion is related to the graininess of the juice.     

EFFECT OF CELL SIZE ON THE PERFORMANCE OF THE SHEAR-COMPRESSION TEXTURE TEST CELL

Shear compression cells were manufactured to have dimensions 0.75, 0.5 and 0.25% that of the standard cell and used to test a range of foods. Maximum force and energy increased nonlinearly with increasing cell size and sample weight. The results demonstrate that cells of various sizes are practical for testing foods.
Friction in the cell is dependent on alignment of the cell components in the test machine. To obtain comparable readings the cell body must be oriented in the machine the same way for every test.     

CONTROL OF DEFORMATION IN TEXTURE TESTS *

Abstract. The motion of the Instron crosshead during small deformations (e. g. 0.25 mm) in tensile tests performed at the available range of deformation rates was examined. Large errors are introduced in the deformation readings if it is assumed that the deformation rate was constant at the rate selected because, as with any instrument of this type, the crosshead requires time to accelerate to the selected speed. The characteristic behaviour of the food is subject to misinterpretation if the applied deformation profile is unknown. It was found that the errors are larger when the instrument is used incorrectly by performing tensile tests below the crosshead. The work demonstrated some of the limitations that must be recognized when applying the Instron, or any deformation mechanism, to certain texture tests. It is concluded that food behaviour, under small deformations, could be recorded precisely and interpreted correctly providing that both the force and deformation are recorded against time. Control of the crosshead stopping and reversal points was also examined, particularly in relation to the instrumental texture profile analysis. Crosshead acceleration affects the readings and interpretation of the data at the reversal point. If the deformation rate is changed, the stopping point must be adjusted.     

A DIGITAL POSITION INDICATOR FOR THE INSTRON CROSSHEAD1

An accessory for indicating the position of the crosshead of the Instron Universal Testing Machine relative to the machine frame is described. A linear displacement transducer allows the crosshead position to be selected within 0.35 mm or returned to a previous setting within at least 0.0083 mm. This facilitates accurate crosshead positioning and reproduction of the settings for different tests. The transducer also has the potential to indicate or record test sample deformations.     

A METHOD FOR TESTING THE EASE OF EXTRUSION OF ICING MARKETED IN PLASTIC TUBES1

An instrumental method for evaluating the ease of extrusion of a decorative cake icing marketed in plastic tubes is demonstrated. The force is measured to pull the tube between two rollers to extrude the contents through the tube nozzle or, by increasing the gap between the rollers, to back extrude the contents within the tube. The maximum force, used as a textural indexy correlated with sensory assessments. The instrumental readings were affected by sample temperature, deformation rate and nozzle size and shape so that these conditions must be standardized. The method has potential use in testing a variety of products marketed in tubes.