Mechanical properties of food materials
Understanding the mechanical properties of food is important in food processing and product development as it allows manufacturers to optimize the texture and sensory properties of their products to meet consumer preferences.
Mechanical properties of food are the physical characteristics that govern texture, quality and sensory attributes. The structure, physical state and rheology of a food all determine how it behaves mechanically. These characteristics are required for process design, for estimating other characteristics, for describing foods and for determining quality — which is why they sit at the front end of any serious plant or product engineering exercise.
Five families of properties are normally considered. Acoustic properties describe the way sound waves interact with food, and are used to assess food quality such as the tenderness of meat or the ripeness of fruit by analysing the sound emitted when the product is struck or squeezed (crispness). Mass-volume-area-related properties describe the relationship between mass, volume and surface area, and are used to determine density (Density = Mass/Volume), porosity and texture. Morphometric properties describe the size, shape and dimension of food products, and are used to determine product uniformity and the distribution of its components. Surface properties describe the physical and chemical characteristics of the product surface, and are used to determine adhesion, friction and other properties affecting appearance, shelf life and quality. Rheological properties describe flow and deformation behaviour, and are used to determine viscosity, elasticity and other properties that affect texture and mouthfeel.
Within these, elastic properties describe how a material deforms under a load and returns to its original shape when the load is removed — examples include elastic modulus or Young's modulus and Poisson's ratio. Plastic properties describe deformation beyond the elastic limit, leading to permanent deformation or failure — examples include yield stress, ductility and toughness. Stress and strain are the fundamental concepts underlying both.
The practical uses fall into three areas. In food quality: quality control, product development, consumer acceptance and shelf life. In equipment design: material selection, equipment design, equipment optimisation and equipment maintenance. In processing: size reduction, mixing, extrusion and packaging.