Food rheology is studying the rheological traits of food, for example, its flow and consistency under certain states. It is essential in establishing the mechanical properties such as the degree of fluidity and the consistency in order to figure out how stable it will be and how long it can be stored. The food texture is one of the most important elements that convince the client to accept food products and the appearance of food is based on the Rheology analysis of its components, like pastes, emulsions and spreads. Foods can behave differently, depending on their rheological attributes, varying from low viscosity fluid, for example juices or milk, to hard solids like hard cheese and dry pasta. Food systems are complex and various, but their rheological properties can be divided in simple types: the ideal liquid, the ideal plastic and the ideal solid. The systems can combine two or even more of these types. |
The ideal liquid is also named Newtonian liquids, after Sir Isaac Newton, the first scientist that described it. This type of liquid should be homogenous or structureless, isotropic, meaning that its properties must be the same regardless the directions and incompressible, namely o force that is applied can change its volume.
The ideal plastic characterizes many foods that show plasticity, which is a rheological behaviour. The ideal plastic is also known as Bingham Plastic, after the scientist who first suggested this form of rheological behaviour.
The ideal solid is also known as Hookean solid, after the scientist who first represented it, Robert Hooke. He discovered that there is a connection between the deformity of a solid material and the dimension of the applied force. People are surrounded everyday by solid materials that have different rheological properties. They can be hard, soft, breakable or gristly.
Quality food is important to consumers, therefore, measuring have to be efficient and precise. Viscosity is essential in industrial areas that involve liquids. For example, honey is a high-viscosity liquid, while water is a low- viscosity one. In industrial food processing, different types of sugar are used every day. For example, glucose syrup sweetens beverages and food. The syrups are used as adhesives in sauces or chocolate, because they are sticky. The viscosity depends on the adhesive properties of the amidin. Amidin has different traits, depending on the environment and temperature. It has a solidifying effect when the temperature is high or a liquefying effect when it boils. Viscosity is essential in establishing the flow properties of mayonnaises or sauces and in changing the consistency and appearance of a food product. The importance of measuring viscosity is undeniable, and there are professional devices that define it. Viscometers measure the strength of a liquid and they can vary in the measuring principle. Different types of devices are used, depending on the quantity or application of a sample. They can be falling body viscometers, capillary viscometers, process viscometers and rotational viscometers. A rotational viscometer is used for the majority of the viscosity measurements in quality control, being efficient and precise.
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