The smell, the taste and perhaps most importantly the texture of food can determine how much we enjoy what we are eating. Food rheology is something we encounter on a daily basis, but probably haven’t given much thought.
What is Rheology?
Rheology is a branch of physics that studies the flow of matter in a liquid state, or soft solids where they respond with a plastic flow. Food rheology focuses on the consistency of foodstuff, it’s degree of fluidity and other mechanical properties, under tightly specified conditions, in order to help us understand how long it can be stored or remain stable, and the texture of the resulting product. Changing the rheological variables can help fine tune how foodstuffs are perceived, and can go as far as to help with how something feels in the mouth and the release of flavors.
Need for Food Rheology
Foods are structurally complex, a mixture of solids and fluids with differing properties within a single mass. The texture is often the determining factor in whether the product is acceptable to the consumer; this might be how well it spreads or how creamy a product is for example. Food is classified according to its rheological state – solid, gel, liquid or emulsion – with associated rheological behaviors, and its rheological properties can be measured. These properties can affect the design of food processing plants, shelf life, and the sensory properties that appeal to consumers. Rheology is seen as a functional property that is important during the entire production chain, right up to the moment of consumption and digestion.
An increased interest in human health and diet means fruit and vegetables are in high demand due to their nutritional properties. These functional foods are rich in polyphenols and carotenoids, which can protect against certain diseases, and have additional psychological benefits. Despite the analysis of food being costly and time consuming, research into product development and industrial processing of fruit- and vegetable-derived products has grown.
Cultivated fruit and vegetables are processed into fluid-like plant-tissue-based food suspensions, so soups, sauces and purees, with a particle fraction and continuous serum phase, which is the result of blending, mixing, sieving and high-pressure treatments. Particle concentration, size, and morphology are key structural elements in determining rheological properties of plant-tissue-based suspensions, each of which can be affected by different operations during processing.
Environmental Consequence of Food Rheology
Combined with this is the consumer demand for more convenient and varied food production, faster production rates, improved quality and longer shelf life, and healthier and better tasting foods – think great tasting low fat versions of favourite foods. This has led to technological developments in food preservation, pasteurization, sterilisation and cooking and drying, which have replaced traditional methods.
This increased interest and consumer demand isn’t without environmental consequences – and for once they’re not all bad. Compared with traditional means, some processes are more energy efficient, offer water savings and reduced emissions. Traditional heating methods rely on the generation of heat outside the product via combustion of fuels or electric resistive heating. The transference of heat to the product is via conduction and convection, but these methods are open to heat loss from the surface of the equipment and require high temperatures to ensure thorough heating.
Some of these issues can be negated with control and monitoring systems and clever design of equipment within the food processing plants, but there is a need for better technology in the industry. This could include electro-magnetic technologies to partially replace well-established preservation processes or ohmic and dielectric heating, which are promising alternatives to conventional heat processing methods. Such volumetric forms of heating see thermal energy generated directly within the food and so can help to reduce excessive cooking times, as well as being more energy and heat efficient.
Novel thermal and non-thermal technologies allow for production of high-quality products with improvements in terms of heating efficiency and therefore energy savings. The processes are often cleaner and environmentally friendly, and so have less of an environmental impact than traditional processes.
These novel processing technologies are attracting the attention of food processors as it will enable them to provide improved quality products with a reduced environmental footprint and lower processing costs.
References and Further Reading