Why it is Important to Measure Food Texture?

Texture testing is a well-known and popular technique used to evaluate the physical and mechanical properties of the raw ingredients, food structure and designs; as well as for pre- and post-production quality assurance.

By: Toby Rogers, Director of Lloyd Instruments Materials Testing Equipment and Chatillon Force Testing Instruments

Texture testing has practical uses among a diverse range of food types such as baked goods, confectionaries, cereals, dairy, snacks, fruit, vegetables, meat, poultry, fish, gelatins, pasta and even within pet food.

As texture is a property linked to the consumer’s sense of touch, it is possible to easily measure texture using mechanical methods such as force.

Standard tests like compression, flexure and tension are used within food texture testing to measure factors such as crispiness, hardness, softness, crunchiness, springiness, tackiness and a range of other food properties.

Users can compare the results from this mechanical texture analysis with highly trained, human sensory panels, and this has shown that these measurements have a strong correlation with the sensory attributes that are associated with textural quality.

The textural properties of natural products like vegetables, fruit, fish or meat can be traced back to the way the product is grown or reared. For processed food however, the textural properties can be used to optimize the process, while food texture analysis can be used to pinpoint opportunity for quality improvement through the whole production process and supply chain.

While the product is at the research and development stage, new or alternative ingredients can be compared against existing ingredients. During production, food texture analysis can be used to measure and control process variations like humidity, temperature and cooking time.

Texture Analysis Instrumentation

Figure 1: Chatillon MT150 manual food texture tester

AMETEK STC can provide a range of testing instrumentation which ranges from both manual and motorized food firmness testers through to a completely software-controlled texture analyzer. Instrumental testing means that standards can be introduced and implemented, as well as being able to provide fully documented, evidencable test procedures.

Shown below, the Chatillon MT150 Series is a manual mechanical tester that is ideal for ascertaining the firmness of fruit and vegetables. It makes use of a portable digital or mechanical force gauge to conduct tensile or compressive measurements. The tester is driven via either a hand wheel or lever, and a ruler or digital indicator can provide a means of measuring the puncture depth.

Firmness testing or associated puncture, cutting-shear, compressive-extrusion, tensile and compressive testing can be conducted using the manually controlled, motorized Chatillon LTCM-100 Series tester. This device features a hand switch, or an optional foot switch to control the tester’s direction and speed.

A digital force gauge can be used to discover the peak forces encountered. This allowed the firmness characteristics of the sample to be tested, with force accuracy achieved up to 0.1 % of full scale. The tester is suitable for use in the production environment, QA/QC laboratory or research settings.

Shown below, the TA1 texture analyzer is an advanced, high performance food texture analyzer design for fully automated texture analysis. It offers mechanical texture analysis via a calibrated texture tester that is run by software. The device uses fundamental algorithms to ensure that all testing conducted is wholly objective.

This 200 lbf (102 kgf, 1,000 N) capacity food analyzer is easy to use and can undertake routine and complex texture analysis using the NEXYGENPlus materials testing and control software. The unit is extremely precise, with measurements accurate to ±0.5 % of the reading and speeds accurate to <0.2 %.

The system includes the base instrument, food testing base, drip tray and a half-inch probe as standard, making it suitable for most routine applications out-of-the-box. The closed-loop drive system allows for precise control of the instrument during any test.

The system’s precision means that sample height measurement is accurate, allowing for samples to be tested as a percentage of their original size and offering the ability to adjust test speed relative to the dimensions of the sample.

The analyzer itself offers a substantial working area, meaning that it can accommodate large samples. It can be fitted with a diverse range of specific fixtures and probes, as well as multipurpose grips for more generalized applications like packaging testing. The analyzer can be controlled easily via the highly configurable NEXYGENPlus software, which also includes a comprehensive library of food industry-standard tests.

Figure 2: The TA1 food texture analyzer

Typical Tests

A texture analyzer can be used to measure a whole range of parameters including:

• Adhesiveness
• Cohesiveness
• Chewiness
• Crispiness
• Consistency
• Elasticity
• Crunchiness
• Firmness
• Extensibility
• Fracturability
• Gumminess
• Gel strength
• Hardness
• Rupture strength
• Springiness
• Stringiness
• Stiffness
• Toughness
• Texture profile analysis (TPA)
• Work to penetrate
• Work to cut
• Work to shear

The core factor in the versatility of the texture analysis technique comes from the availability of more than 70 probes, jigs and fixtures which allow one instrument to conduct a whole range of measurements within an array of food applications.

The Volodkevitch Bite Set fixture is a useful example of how the instrument can translate a common human action into a measurable quantity. The Bite Set has been developed to imitate incisor teeth as they shear through meat, fruit, vegetables, crunchy or crispy food products. The set is made up of the upper and lower “teeth” (shown below) which are brought together until they are almost touching.

Figure 3: Volodkevitch Bite Set fixture

The sample is positioned on the lower “tooth” with the result then measured as the peak force needed to bite through the sample. The results of this measurement correlate with the sample’s toughness, tenderness and firmness. Grips and fixtures can be provided in a range of sizes, styles, gripping surfaces and capacities to cater for numerous applications.

The specimen size will depend on the sample’s homogeneity. Food that has large voids will likely need a bigger sample size that a food without voids, in order to obtain similar repeatability. The choice of fixtures will depend on the sample – for example, should the sample have a flat surface then compression platens larger than the sample will generally be used. Small diameter probes are more suitable for uneven surfaces like those on fruits and vegetables.

Food Testing Fixtures

Texture analysis fixtures and grips are regularly developed to enhance the range of applications that can be accommodated. For example, test jigs for the TA1 texture analyzer include one specially designed for the analysis of hamburger patties, thus providing an objective measurement of burger consistency. Another is able to measure the stickiness of pasta.

There is a consistently large demand for burgers alongside competitive pricing, so their composition and quality can vary greatly. This can range from 100 % prime ground beef to low quality meat that consists of a large amount of bulking agents, salt, fat and additives.

In order to test it, the burger is placed on a support plate that contains a 27 mm diameter hole mounted on the TA1’s base table. A cylindrical probe is used to open out an inverted cone shape with a flat end of 25 mm diameter is then used to exert force to the burger. The same jig can be used to test reformed, cooked meat.

Figure 4: Burger consistency test jig

Figure 5: Lasagne stickiness test jig

Pasta’s starch content dictates the stickiness of the cooked sheets, and this in turn is related to the cooking time and temperature. All these parameters can be optimized by measuring the pasta’s stickiness.

The sheet of cooked pasta is mounted between the TA1’s base table and a rectangular plate that contains a rectangular hole. A matching rectangular probe is then used to apply a uniform compression force to the pasta, through the hole.

The instrument measures the force required to withdraw the probe. If required, the probe can be held in contact with the sheet of pasta for a specific, predefined length of time before being withdrawn.

While jigs like these are designed for specific applications, new test fixtures for more general applications are also available.

An alternative five-blade version of the Kramer Type Shear Cell is another option to the conventional 10-blade configuration. It is designed for measuring the bulk shear and extrusion forces of meats, cereals and fruits, particularly where the samples have irregular shapes and sizes and the forces expected may be too high for the traditional 10-blade version to handle.

The Kramer Type Shear Cell is made up of five parallel steel blades that are driven down through guide slots into a rectangular container, with corresponding slots in the base of the instrument.

Figure 6: 10 blade Kramer Type Shear Cell

The sample is then sheared, compressed and extruded through openings in the instrument’s bottom, and because the blades are further apart than the 10-blade version, the force of bulk shearing or compression is reduced in samples that contain many particles or foods that have a non-uniform consistency.

This accessory can function within ambient temperatures of up to 100 °C. It is also fitted with a spill container, which can also be used with the 10-blade version.

Software Control

Mechanical jigs and fixtures certainly allow for an increased range of testing options but controlling the texture analyzer with software allows the operator to directly monitor and control all aspect of the system and the tests being conducted.

The NEXYGENPlus texture analysis software for the TA1 texture analyzer includes a wide-ranging library of industry-standard test methods which cover food, cosmetics, and packaging tests to AACC, EN, ISO, ASTM, DIN and other recognized standards.

The software also allows users to create their own tests, collect data, report, export data, capture video and still images, test data security and audit trails as well as test customization and automation.

A standard user-configurable test is able to create specialist, multi-stage tests. This is especially useful for texture profile analysis (TPA) which can replicate the effect of two bites on a sample.

During the test, the software captures force, distance, and time. This allows parameters like chewiness, cohesiveness, firmness, adhesion force, adhesiveness, fracturability, gumminess, hardness modulus, resilience, springiness, and stringiness to be obtained and calculated.

As well as powerful measurement capabilities, the software offers additional features which can really improve the presentation and comprehension of test results.

For example, the entire test can be recorded as a video and then synchronized with the stress/strain data, then replayed for detailed analysis after the test. Still images can also be taken at certain points during the test. These images are recorded directly on the graph, allowing them to be analyzed easily.

External plug-and-play devices like humidity and temperature probes can also be connected to the system, meaning that these parameters can be monitored during a test and reported on alongside distance, time and force.

External devices can also be used to test start and stop conditions. The audit trail and the security module allows supervisors to manage user access and data traceability, while integrated audit trails cover operator usage and test results, thus ensuring that changes to test procedures are recorded in a simple, and most importantly, easily retrievable format.

This information has been sourced, reviewed and adapted from materials provided by Lloyd Instruments Ltd.

For more information on this source, please visit Lloyd Instruments Ltd.