Rheology, texture and texturing of food products

Food is a living material, constantly changing shape, size and structure. They are sensitive to humidity, temperature, oxygen and so on. The food product is therefore studied mainly from a nutritional point of view, on the one hand, and from a biochemical point of view, on the other, since most of the transformations that take place in food during technological or preservation operations are of a biochemical nature. All too often, we forget that food is also a material on which it can be interesting to measure mechanical properties. For example, solids of biological origin have an elasticity that changes with age and various physiological causes. Liquids of biological origin generally behave in a non-Newtonian way. However, during the preparation, processing or formulation of these raw materials, numerous techniques are employed and numerous interactions take place between the constituents, which profoundly and irreversibly modify the texture of these materials.

To measure these mechanical properties, rheological methods are commonly used. Rheology (the term was coined by Eugene Bingham in 1928, from the Greek word ρειν, meaning flow) is thus the science that studies and describes the flow, deformation and rupture of bodies under stress. In this context, bodies can be liquids, solids or powdery materials. By measuring the rheological properties of food products, it is possible to predict their mechanical behavior during the various stages of food processing. Rheological properties are also at the origin of the behaviors perceived during sensory evaluation of texture.

In the food industry, texture is considered essentially as a sensory property, and encompasses a wide range of terms, such as tenderness for meat, creaminess or firmness for cheese, stickiness for pasta, and crunchiness, crumbliness, hardness and crispness for cookies.

Nevertheless, non-sensory methods for measuring textural parameters have been developed. They are based on rheology and can be :

• fundamental methods (measuring the viscosity, hardness, strength or brittleness of a food material);

• Empirical methods (these techniques are based on three fundamental principles of deformation: bending, shearing and compression);

• imitative methods (which imitate the action of teeth, for example). Measurements obtained by instrumental analysis can, in some cases, be linked to sensory values: this is known as psycho-chorheology.

By applying certain fundamental principles of mechanics and rheology, we can gain a better understanding of the mechanical behavior of these substances, in their natural state or when modified by a texturing process....