Food comprises varied biological components with diverse rheological characters. An essential aspect of the food industry is to understand food and its behavior. Determination of food behavior answers some key questions, such as whether a particular food product will deform easily, flow through a pipe, or work well as a topping. Researchers believe that rheological characterization is essential for the development, optimization, and processing of foods.
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Food rheology also determines the food texture. Rheological flow properties deal with the perception of food when we touch or put it into our mouth. The primary foundation of food rheology is fluid mechanics. Rheologists believe that the correlation between stress and stain could be used to study the rheological properties of food systems in different models.
Food Behavior and Rheology
Food is a very complex structured material. It consists of proteins, carbohydrates, fats, fibers, and water. The flow and structural behavior of food depend on its components, and the stability of structured fluids depends on several factors. For example, the flow property of a food material depends on the viscosity of the liquid phase in dispersions. The behavior of a food product can be determined via its dispersion properties, i.e., emulsions or suspensions. For instance, in some commonly used foods such as mayonnaise, tomato paste, dressings, and baby food, food dispersion plays a vital role.
Certain parameters such as particle size distribution, particle concentration, and inter-particle interactions determine the rheological behavior of dispersions. Researchers have explained that suspensions consist of solid particles in a fluid medium. In contrast, emulsions consist of liquid droplets in a liquid medium (deformable particles). The rheological properties of food are also significantly influenced by the temperature and duration of the measurement.
Gel formation is an essential factor in food behavior. Most of the foods associated with proteins, starch, and polysaccharides form gels under the influence of temperature or pressure. Modifying a gel’s microstructure can result in the formation of a range of products differing in their physical attributes, e.g., hard rubbery plastics and soft hydrogels.
Importance of Rheology in Food Product Design
Food rheology describes the behavior of liquid food. In liquid food, its microstructure has an essential impact on the quantitative and qualitative attributes of the food product. The microstructure is the function of various physicochemical associations and inter/intra-molecular bonds between the complex food ingredients. Typically, microstructure has an impact on the flow characteristics of the material. For instance, the viscosity and elasticity, which are analogous to the liquid-like and solid-like components of the food, contribute to the heat and mass transfer associated with heating, pumping, and mixing of ingredients. This ensures that the liquid in the food components is appropriately processed.
For mass transfer, the rheological properties are vital to determine important operations such as drying, fermentation, and separation. These two rheological parameters can be measured via viscometers and rheometers.
Another important aspect of microstructure is the texture of the food material. Food texture imparts the perception of the food inside the mouth. Factors that can adversely impact the texture are over-or under-processing, for example, the application of excessive or insufficient shear or heat while processing the product. Measuring the rheological parameters ensures quality control of the finished food product.
Some researchers have explained that the behavior of liquid food depends on the stress applied to it. For example, fat-based spreads, molten chocolate, mashed potato, and certain salad dressings exhibit a liquid-like behavior at high stresses and a solid-like behavior at low stresses. An accurate understanding of food rheology and microstructure reduces textural shortcomings in the processed foods, which in turn enhances consumer satisfaction.
Application of Rheology in the Food Industry
Several scientists have defined food rheology as studying the deformation and flow of food material under well-defined conditions. They further stated that this study is essential in many areas of the food industry. Some of the important uses are as follows:
- Helps in creating a new product
- Aids in the determination of physical characteristics of fluid and semi-solid foods
- Assessing the quality of the raw materials to be used for the development of a specific product, while the quality of the food product is also evaluated at different stages of its developing process
- Determining the shelf-life of food products.
- Evaluating the sensory properties of food products
- Helping understand food microstructure (indirect study)
- Rheological data helps to develop industrial plant designs that include the selection of pumps and pipes. In process engineering, it provides calculations associated with extruders, mixers, coaters, and homogenizers.
The advancements in instrumentation have helped food rheologists to make a detailed evaluation of the microstructure and fluidity of food. The use of controlled stress/strain rheometer and advanced optimal Fourier transformation rheometry has helped increase the precision and reliability of rheological data. Another important instrument used to measure fluid food based on time is thixotropy.
A better understanding of food microstructure is essential for the development of food products, both in academia and the food industry.
References and Future Reading
Rheology Solutions. (2021) The Importance of Rheology in Food Product Design. [Online]. Available at: http://www.rheologysolutions.com/the-importance-of-rheology-in-food-product-design/
Food Physics Basic. (2017) An Introduction to Food Rheology – the Flow of Material. [Online] Available at: https://foodcrumbles.com/food-rheology-introduction-food-physics-analysis/
Ahmed, J. et al. (2017) Food Rheology: Scientific Development and Importance to Food Industry. Advances in Food Rheology and Its Applications, pp. 1-4, https://doi.org/10.1016/B978-0-08-100431-9.00001-2
Mckenna, B.M. and Lyng, J.G. (2003) Introduction to food rheology and its measurement. Texture in Food. 1, pp. 130-160 http://dx.doi.org/10.1533/9781855737082.1.130
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