Lesson 14. Objective Texture measurement
Foods are classified into different groups:
- Liquids, gels, fibrous foods, agglomerates of turgid cells, unctuous foods, friable structures, glassy foods, agglomerates of gas filled vesicles and combination of these (Matz, 1962).
- Liquid, fruits and vegetables, meats and others (Amerine et al., 1965)
- Gel like foods, fibriform foods, edible oils and fats and powdered foods (Sone, 1972).
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Objective |
Subjective |
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Direct |
Indirect |
Direct |
Indirect |
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fundamental |
optical |
mechanical |
fingers |
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empirical |
chemical |
geometrical |
hand |
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Imitative |
Acoustical |
chemical |
other |
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Electromagnetic |
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other |
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Fundamental tests:
These tests measure well-defined rheological properties.
Most commonly used fundamental tests are:
The relationship between these parameters are following:
Fundamental tests generally assume that
Small strains (1-3%), 2. The material is continuous, isotropic, and homogenous, 3. The test piece is of uniform and regular shape.
Force measuring instruments:
1. Puncture, 2. Compression-extrusion, 3. Shear, 4. Crushing, 5. Tensile, 6. Torque and 7. Bending and snapping.
Puncture test: This test measures the force required to push a punch or probe into a food. The puncture test assumes that the sample is semi-infinite in size. That is, the sample is much larger than the punch that the edge effects and bottom effects are insignificant.
Bloom gelometer,
Texture analyser
Compression-extrusion testing: this test consists of applying force to a food until it flow through an outlet that may be in the form of one or more slots or holes that are in the test cell.
Eg. Compression-extrusion testing of fresh green peas
Back extrusion cell
Shear testing: for food technologist shear testing means cutting the food across the food. Eg. Warner-Bratzler shear test. Kramer shear press, texture analyser shear testing unit.
Fig. Shear testing of foods
Compression and crushing:
Compression and crushing are widely used tests done for food materials as mastication involves compression. There are two main types of compression tests.
Uniaxial compression: the sample is compressed in one direction and is unstrained in other two dimensions
Bulk compression: the sample is compressed in all directions
Since most foods are viscoelastic in nature rather than elastic and are usually subjected to large compression tests, the concept of young’s modulus is seldom applied, however Young’s modulus of elasticity is applied as well as poison’s ratio.
Tensile tests: Tensile tests are not widely used in foods, which is understandable because the process of mastication involves compression , not tension, of the foods between molars. Eg. Tensile test for meat, chewing gum, or as a stickiness measurement, brabender extensograph, Instron, texture analyser.
Fig. Noodle tensile testing (source: stable microsystem ltd.)
Torsion: in a torsion test force is provided that tends to rotate or twist one part of the object around an axis with respect to the other part.
Farnograph and mixographs are torsion measuring equipments for dough
Bending and snapping: bending and snapping tests are usually applied to foods that are in the shape of bar or sheet.
3 point bending tests, for cookies, crackers, food bars