Measuring textural properties

Texture Analysers are used to measure many properties, such as hardness, brittleness, spreadability, adhesiveness, tensile strength, extensibility etc., on a vast range of products by compressing, bending, stretching, extruding, penetration or shearing a sample.

Our range of instruments can carry out fundamental, empirical and imitative tests, covering those relating to texture analysis, materials science and rheology of solid, semi-solid, viscous liquid, powder and granulate materials.

Foods are a selection of semi-solid, soft-solid, viscoelastic materials, and occasionally hard solids. Oral processing of these foods starts with either biting a portion from a larger piece or placing a piece in the mouth. Food texture is one of the key properties consumers evaluate when determining food quality and acceptability and embraces a large number of textural characteristics or properties.

Specific textural elements of a food are evaluated by descriptive sensory analysis; however, the time and costs of sensory analysis have motivated the empirical development of mechanical tests that correlate with sensory analysis of texture. Now parameters can be objectively obtained that present measures of, for example, crispness of a potato chip, spreadability of margarine or the firmness of an old fashioned, New York style bagel.

While food scientists were evaluating mechanical properties to understand subjective texture, material scientists were developing rheological and fracture-mechanics approaches to understand material properties in general. Materials have physical or textural/mechanical properties that are also perceived and are measurable. From an engineering perspective, an engineer would need to know and usually measure the mechanical properties of a material in order to make an informed decision when designing something to ensure that it is fit for purpose.

The main physical concept behind measuring mechanical properties is stress. Stress tells you how big a force applies to an area. The second important concept is strain which is a ratio of lengths. From these two concepts, the Young’s Modulus can be derived, which is a measure of stiffness/elasticity – important factors for engineers when deciding material suitability for a certain application. In addition, such parameters as adhesion, abrasion, friction, flexure, strength etc. can be measured.

Specialist attachments enable the instrument to emulate forces applied to products in everyday consumption or usage. The data captured by Exponent software during the test procedure is used to generate graphs which provide a visual interpretation of how materials respond to different types of forces. Interpreting these texture measurement/physical property graphs is essential for evaluating material characteristics such as hardness, cohesiveness, elasticity, and brittleness.

Understanding these graphs not only aids in quality control and product development but also helps in ensuring that materials meet specific performance criteria. This guide delves into the intricacies of interpreting texture measurement/physical property graphs, offering insights into the key features of these graphs and how they can be used to derive meaningful conclusions about material properties.

Whether you are a researcher, quality control specialist, or a product developer, mastering the interpretation of these graphs will equip you with the knowledge to make informed decisions about material selection and product formulation. Whether your sample is a food, cosmetic, adhesive, pharmaceutical or type of material is irrespective of what the graph shape and its values indicate to your in terms of its behaviour. Samples from different industries can possess the sample physical properties and whether the sample can be eaten or applied to the skin, for example, does not mean that the results cannot be interpreted and understood in the same way. Through a detailed examination of typical graph features and real-world examples, this guide aims to enhance your ability to analyse and utilise texture analysis/physical property data effectively.

For a typical test the Texture Analyser collects force, distance, and time data as the probe interacts with the sample. This data is typically displayed as a force vs. distance (or time) curve on a graph.

For scientific/academic purposes it is best to display a Force vs. Distance graph, especially when analysing data that requires the compound units of force-distance e.g. area.  However, for the untrained eye this type of graph can be confusing as the distance data wraps back around to zero once the destination is reached.  For this reason, many people prefer to look at data that is plotted as Force vs. Time so that they can see their data laid out as it happened with respect to time.

When tests are performed where a target force has been specified, then the required data axes are Distance vs. Time. A typical example of this test would be when measuring the disintegration of a tablet. The Texture Analyser holds a certain force on the tablet which is immersed in fluid and during the disintegration the distance is tracked down until the table has completely dissolved. Displaying data as Distance vs. Time allows you to see the rate of change of distance as the tablet dissolves and hence the rate of tablet disintegration – which may have multiple stages. The graph below also shows a positive distance which shows that the tablet swells before it starts to disintegrate. Disintegration occurs when the distance data crosses the x axes and continues to track negatively due to the downward movement of the Texture Analyser to continue tracking the required force.

When measuring fundamental properties such as Youngs modulus the data needs to be displayed as stress vs. strain. 

As all data is related to the originally collected Force, Distance and Time data it can be easily converted to be displayed as any axes combination. Some axes however, require additional data available such as the contact area of the probe/sample (for the display of stress) or the width of the sample (for the display of strength which is Force/unit width).

The first thing to understand is that the name of the textural parameter or physical property changes depending upon the industry and sample being tested. Let’s take hardness for example: Hardness is usually measured as the peak force during a compression cycle. Hardness is on the same scale as firmness and softness and is a common term when testing materials, confectionery or pharmaceutical products, whilst renamed as firmness when testing such products as fruit and vegetables and softness when related to bakery product properties.