Engineering Properties of Biological Materials and Food Quality 3(2+1)

Lesson 14. Objective Texture measurement

Objective		Subjective
Direct	Indirect	Direct	Indirect
fundamental	optical	mechanical	fingers
empirical	chemical	geometrical	hand
Imitative	Acoustical	chemical	other
	Electromagnetic
	other

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

1. 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.

1. Uniaxial compression: the sample is compressed in one direction and is unstrained in other two dimensions

2. 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

Distance measuring instruments:

• Linear measuring instruments

• Area measurement with dimension length²

• Volume measurement with dimension length³

Linear measuring instruments: simple distance measuring instruments.

Penetration distance (cone penetrometer for butter firmness), Rebound distance (cooked peas), Deformation (defoemation test of foods in Instron), Eg. Botstwick consistometer, penetrometer

volume measuring instruments

eg. loaf volume meter, succulometer (volume of juice)

Multiple measuring instruments:

Texture profile analysis:

Simulation of mastication of food in mouth

Hardness: The hardness value is the peak force of the first compression of the product. The hardness need not occur at the point of deepest compression, although it typically does for most products. (Newton, Dyne,gforce, kgf,  M¹L¹T^-2)

Fracturability/brittleness: it is defined as the force of the significant break in the curve on the first bite of the force and deformation curve. (force: unit, N, gf, gforce dimensional analysis: M¹L¹T^-2)

Cohesiveness: Cohesiveness is how well the product withstands a second deformation relative to how it behaved under the first  deformation. It is measured as the area of work during the second compression divided by the area of work during the first compression. (A2/A1).

Adhesiveness: The negative force area (A3) of the first bite, represents the work necessary to pull the compressing plunger away from the sample.

Springiness: Springiness is how well a product physically springs back after it has been deformed during the first compression. The spring back is measured at the downstroke of the second compression. Springiness  is measured by the distance of the detected height of the product on the second compression (Length 2 on the below graph), as divided by the original compression distance (Length 1).  

Gumminess: Product of hardness and cohesiveness (units force: Newton, Dyne, M¹L¹T^-2); generally applied to semisolid foods.

Chewiness: Product of gumminess and springiness, generally applied to solid food. It is the energy required to make the solid food ready to swallow.

Resilience: Resilience is how well a product "fights to regain its original position. The calculation is the area during the withdrawal of the first compression, divided by the area of the first compression. (Area 5/Area4).

Fig. Typical force –deformation curve in texture profile analysis

References:

Bourne, M. C. 1982. Food Texture and Viscosity: concepts and measurement, Academic Press, USA

Sahin S. & Sumnu, S. G. 2006. Physical Properties of Foods. Springer, USA