Insight

When creating a new product, or improving or changing the properties of an existing one, rheology, the science of body deformation and flow, plays an essential role. Rheology helps define product properties and provides information about what technological processes or marketing strategies should be used in product development and marketing.
Factors that make rheology important in the food industry: Food classification according to rheological characteristics: An emulsion is a dispersion system in which one liquid is suspended in another in the form of fine droplets. The components of an emulsion are called the continuous/solid phase (liquid in excess) and the dispersed/discontinuous phase (solidified in the continuous phase). Types of emulsion are water in oil and oil in water. Eg: Milk is an oil-in-water type emulsion where liquid fat globules are dissolved in water. Margarine, butter is a water-in-oil type emulsion.
Rheological characteristics are of great importance for the consumer, who has specific expectations for the texture and feel of the product, for example, a milkshake should be thick and creamy, and if the product does not meet these desired parameters, it will not be acceptable to the consumer, therefore, the food must be rheologically balanced.
Deformation, as we know, is the movement of the constituent parts of the body, which leads to a change in the shape of the existing body.
There are two types of deformation:
Reversible or elastic, when the body returns to its original shape after a force is applied to it.
Irreversible or viscous, when the body no longer has the ability to return to its original form.
There are 4 main factors that affect the flow and deformation of a substance: As we mentioned, the food must meet the desired requirements of the consumer. One of the important aspects that is paid attention to is the so-called "Mouthfeel", which in turn includes the commandment of texture. A good example is a steak, the method of preparation of which determines not only its taste, but also its sensitivity. Chewing a steak naturally changes its sensitivity in the mouth, which is directly related to the elasticity of the steak. After long-term heat treatment of steak, it becomes more difficult to handle. Remember, the higher the modulus of elasticity, the more resistant the material is.
It is also important to understand what happens at the internal level during deformation. Food consists of molecules, and in any impact on food, we change the positions of the molecules and accordingly change the distance between them, shortening or extending the bonds between the molecules. It is the change in the distance between these bonds that is the elongation.
We can transfer the relationship between bond energy and distance in food. For example, marshmallows contain the protein collagen, and steak contains muscle protein. In both of them, the proteins interact with each other to form a three-dimensional network, and therefore, in both of them, the protein molecules are connected by bonds that have similar energies. However, there is a big difference between the elasticity of these two foods, due to the fact that they have different numbers of bonds per unit volume. The bonds of steak are much denser, and therefore its modulus of elasticity is much higher, which means that more energy is required to deform it.
When talking about a liquid product, we must consider viscosity, a measure of the material's resistance to flow. The higher the viscosity, the higher the viscosity. It changes depending on temperature and pressure. Consider oil as an example. Its viscosity decreases with increasing temperature.
Fluid flow also depends on particle volume, that is, the volume that particles occupy in the fluid (volume fraction). The higher the volume fraction, the thicker the liquid and the less flow, so controlling the volume fraction is most critical when controlling the texture of sauces.
There are 4 main ways to thicken the sauce: In general, different materials in rheology represent mechanical models that are composed of simple, idealized bodies. The main rheological properties include: viscosity, elasticity and plasticity.
An ideal solid, or ideally dry substance, undergoes deformation instantly when a force is applied, and returns to its original state instantly after its removal. The mechanical model is a spring.
An ideal fluid undergoes deformation under conditions of constant velocity, during force modes, and when the force is removed, it does not return to its original state. The mechanical model is a hydraulic piston.
Most foods exhibit both of the above-mentioned natures, which is why they are called viscous-elastic substances. If a viscous-elastic substance undergoes deformation quickly, it resembles a solid substance in characteristics, and if slowly, it resembles a liquid.
According to the behavior of the flow, 2 types of liquid are separated:
Newtonian fluid - easily viscous substance, eg water, oil, glycerin. Viscosity depends on temperature and pressure.
Non-Newtonian fluid - viscosity depends on temperature, pressure, deformation rate of movement, structural properties of the environment.
Non-Newtonian fluids are: