Time
The accuracy of time measurements is dependent upon the accuracy of the clock on which the time measurements are based. Time data is generally derived from a crystal oscillator that produces high precision pulses that drive the sample system. This is used to feed time data from the Texture Analyser to the graph viewed by the user. The resolution of time data corresponds to the number of data points per second on the final graph. This is controlled by the data acquisition rate.
Speed
Texture analysis techniques are frequently designed to be imitative, with the test setup based on a real-life situation in many cases. For example, the Volodkevich Bite Jaws use a pair of blunt wedges with the aim of simulating the biting action of the front incisor teeth. This method is used to measure the bite hardness of cheese or the tenderness of meat. Other imitative tests include three-point bend testing of biscuits, imitating the snapping motion performed by consumers before they are eaten, the use of a Warner-Bratzler Blade on sausages to imitate the forces experienced during consumption, or the tensile measurement of a piece of pizza to imitate the process of pulling with the teeth. Consequently, the test settings in many cases aim to imitate the process as much as the experimental setup does. The results of many texture analysis measurements are influenced by the test speed used, including those measured during Texture Profile Analysis. The velocity of the jaw during a standard chewing cycle, for example, ranges approximately from 0 to 50 mm.s-1, and so the test speeds used in the majority of cases sit somewhere in this range.
Other food properties of interest to the researcher or manufacturer do not centre around the chewing process, and instead focus on other aspects of the cooking or eating experience. For example, bundles of dry spaghetti and chocolate bars are frequently snapped in the hands before use. The sensory aspects of this process are important to the consumer’s perception as well as those during consumption, and so tests are used to imitate these actions. The associated speeds are moderate, and still within the range of 0 to 50 mm.s-1.
Food properties that are completely separate from the user experience are also of interest to the food manufacturer. These may be related to transport and storage longevity, or as part of the process to reduce manufacturing costs (assessing the use of a cheaper ingredient alternative, for example). Tests in this area include adhesive tests, examining the reliability of an adhesive for securing coatings to a food sample, or measuring the stickiness of dough during the bread baking process in a factory.
Adhesive tests often combine two very different speeds – a slow speed used to apply a force to the adhesive in a controlled manner (for example, 0.05 mm.s-1), and a fast speed to pull away (for example, 40 mm.s-1). These methods are more likely to test the limits of a Texture Analyser’s speed capabilities than standard food testing.
When measuring the property of adhesiveness/stickiness the speed of withdrawal should be considered and controlled. A slow speed of withdrawal of a probe from the adhesive sample encourages or allows viscoelastic flow whereas a high speed of withdrawal encourages quick separation and more obvious measurement of adhesiveness.
Time and time sensitivity – Data acquisition rate
Data acquisition rate is the speed that data is recorded and is measured in points per second (pps). When performing crispness measurements on a bulk sample such as a breakfast cereal, thousands of small fractures may occur in a short test period. The frequency and magnitude of these fractures are used in part to determine sample crispness. If a system has a low data acquisition rate, for example, 20pps, many of these fracture events will not be registered on the graph, and so two samples of different crispness may not be as easily differentiated from one another than if a higher acquisition rate was used, for example, 2000pps.
The diagram below illustrates the importance of choosing the correct data acquisition rate for a test with a rapidly changing force response. The topmost graph demonstrates a force signal recorded at 2000pps. The following three graphs show the equivalent test recorded at 1600pps, 800pps and 200pps. The decreasing data acquisition rate corresponds to an increasing period of time between data point collection. For 200pps, the Texture Analyser records a data point every 0.005 seconds. Using this example, the force is only recorded at times 0, 0.005, 0.01 and 0.015 seconds, hence the crude graph form which lacks detail and true measurement of what occurs during a test. As the data acquisition rate is increased, points are collected more frequently, and more detail becomes available on the graph output with each increase allowing a full picture of sample properties to be determined.
Options for collection of data
Tests with long hold times or very slow test speeds may require a reduced data acquisition rate during hold periods, or even a period with no data collection, to optimise the use of computer memory. These include creep and relaxation tests. High acquisition rates are generally reserved for periods of tests that contain rapidly changing data that needs to be recorded, including fracture and adhesive tests. For those tests containing a rapid succession of events, it is imperative to collect data at the highest data acquisition rate available, ensuring the collection of all detail.
The storage capacity of the computer being used to interface with the Texture Analyser may provide a limit to the data acquisition rate. Some slower computers, or computers lacking memory, may crash if a test is carried out over a long time period at a high data acquisition rate.
There is also the option of varying data acquisition rate during a test sequence. It may be preferable that data acquisition rate be very low at all stages apart from true sample deformation (such as when the probe is moving through the air to contact the sample and when the probe is being unloaded). Data capture may alternatively be switched off during insignificant test periods.
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There is a Texture Analysis test for virtually any physical property. Contact Stable Micro Systems today to learn more about our full range of solutions.
For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.
The TA.XTplusC Texture Analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.
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