Objective measurement of food textural properties
Texture analysis uses instruments to measure the physical properties of food products to complement the information from trained sensory panels. These are objective tests that measure the physical properties of foods and can thus provide information about their tactile properties such as hardness, springiness and fracturability. Tactile properties influence the consumer’s sensory perception of foods and can be devised to determine the acceptability of a food when textural properties are of prime importance. These measurements can be made quickly and accurately and can quantify subtle aspects of texture. Application of texture analysis includes quality control to ensure that a product is consistent from one batch to the next, which is particularly important when an ingredient or process is changed and its impact on texture needs to be evaluated. Instrument based tests can also be valuable tools, both in product development, where a large number of samples need to be tested quickly, and in research, where product innovation is essential to create new products.
This white paper details the essentials of texture analysis as well as the typical applications to a range of foods systems.
Texture of foods includes a complex group of physical properties that result from the structural make up of the food. Texture is an important element of most food products that affects consumers’ acceptance and repeat sales. Texture is a sensory attribute that can be perceived, described and quantified by human beings (Szczesniak, 1987) and can be determined either by sensory or instrumental methods. Instrumental methods of assessing texture can offer advantages over sensory analysis as they are economic, rapid and objective, offer a potential ease of standardisation, and can be carried out under strictly defined and controlled conditions. The food industry is making increasing use of instrument based measurements to assess final product quality before their release. However, it must be emphasised that any instrumental method used to determine physical texture must correlate closely with sensory evaluation for it to be appropriate. Sensory evaluations are equally important as objective measurements, particularly when developing new products where specific sensory parameters form a key element of the product quality.
Textural properties are measured with instruments commonly known as texture analysers that can compress or stretch food materials. This is done by applying controlled forces to the product and recording the response in the form of force, deformation and time. A number of instruments are available that offer a range of force measuring capability. Basic requirements include equipment capable of driving a probe for a given distance into a sample at a fixed speed. The instrument must continuously log the force required to maintain this speed, respond to a trigger force (signal to start of test), detect initial height of the sample and compress it to a fixed portion of this height (% strain). A number of accessories are found for most instruments that provide consistent sample presentation, thus improving the accuracy obtained from the test method.
The choice of probe (platen, cone, cylinder, blade, ball, or wire) is important and depends on the nature of the food to be tested and the specific consumer action that is to be simulated. For example, a blade probe can imitate the first bite by the front teeth and a platen can give indication of firmness of bread as perceived by the consumer from a squeeze test. Other test parameters to consider include the speed at which the probe moves before it touches the sample, and the actual speed during the measurement. For accurate comparison of a set of samples all test conditions should be kept constant.
A number of different approaches and instruments are employed to study the texture of food products and they attempt to replicate some attributes of sensory methods. These can be summarised as follows:
- Fundamental tests
- Fundamental tests are based on measurement of physical properties such as stress and strain. Tests are performed under well-defined conditions using precise sample geometries. Fundamental tests usually require expensive equipment and can be slow to carry out. A major disadvantage is that that test results do not correlate well with sensory evaluation.
- Empirical methods
- This class of tests measures parameters that are not well defined, but are widely used in the food industry as they correlate well with textural quality. Foods are subjected to mechanical deformation applied in sequence or as a combination of stresses. Typical examples include the penetrometer, puncture, compression and Warner-Bratzler Shear Test. Each of these tests is only applicable to a limited number of food systems.
- Imitative methods
- These methods, as the name suggests, are designed to imitate the conditions to which a food is likely to be subjected in practice. Examples include the squeezometer, which has special attachments imitating finger tips and thumb tips on the Instron Universal Testing Machine, the Farinograph which imitates dough handling, Bostwick Consistometer and Adams Consistometer that measure the flow of foods such as ketchup and purees on a plate. These methods are carried out under poorly defined conditions, but like the empirical methods correlate well with sensory methods.