The Stickiness of Food

Stickiness is a difficult attribute to measure. Adhesion is characterised by the force of attraction between a material and a surface. This phenomenon occurs in several processes (such as baking, chocolate or powder production, bacterial adhesion to industrial plants), causing product losses and contamination. In this sense, parameters as surface energy and food composition play an essential role in adhesion study, being an essential field of understanding to optimise processes. A recent review approaches the adhesion fundamentals and their relation to food composition and surface properties. Moreover, it describes the tests usually applied to measure the adhesion of food on surfaces. Besides, this work shows that, regarding the literature, it is difficult to differentiate the adhesive from the cohesive forces. Food adhesion in different dryers and alternative to reduce the problem are discussed, considering that the deposition of dried material on supports and dryer walls causes low yields and operational and handling problems.

Adhesion of Food on Surfaces: The ory, Measurements, and Main Trends to Reduce It Prior to Industrial Drying

The same author, also wrote:

Artefacts and Errors in the Measurement of the Stickiness of Liquid Foods with Tack Tests

We encounter stickiness in many areas of our daily life and as humans we are able to discriminate different levels of stickiness. Yet attempts to measure stickiness with instruments has been challenging. One of the commonest approaches has been the “tack test” in which a probe is brought into contact with the sticky food and then pulled away while measuring the resisting force - various indices, such as the maximum force or the area below the force curve have been used to describe stickiness. This work rationalises results from tack tests for liquid foods and helps us explain the influence of probe geometry. Photographic evidence of the way that the liquid adheres/detaches from the probe suggests that the terms “cohesive” and “adhesive” failure depend on the speed of the test. Application of a fixed deformation with time shows rapid loss of adhesive force suggesting that liquid samples flow from the probe. We propose that stickiness of liquid foods is entirely due to the liquid’s viscosity and surface tension, and that measurements of tack for liquid foods – while highly reproducible – are entirely artefacts of the test method employed and are in effect snap shots in time of a non-equilibrium processes.

Another good publication is:

Stickiness in Foods: A Review of Mechanisms and Test Methods

Problems associated with the stickiness of food in processing and storage practices along with its causative factors are outlined. Fundamental mechanisms that explain why and how food products become sticky are discussed. Methods currently in use for characterising and overcoming stickiness problems in food processing and storage operations are described. The use of glass transition temperature-based model, which provides a rational basis for understanding and characterising the stickiness of many food products, is highlighted.

And back in 2007 Carl Hoseney and Jo Smewing wrote a paper in the Journal of Texture Studies:

Instrumental Measurement of Stickiness of Doughs and Other Foods

Universal Sample Clamp holding a range of samples on the TA.XTplusC Texture Analyser

The most commonly used test for measuring the range of adhesive properties in foods is the Probe Test. In this test, a probe applies a force over the sample for a chosen period of time to achieve a good bond between the two surfaces before being withdrawn to the point at which the sample completely separates (failure). A vessel and disc as used in a Back Extrusion test are also suitable; however, the disc would be used to test the surface of the material, rather than venture into the sample. One thing is clear, however – for successful adhesion testing, the sample needs to be held down in order to measure the force to separate the sample from the probe. If the whole sample is lifted up on the end of the probe when it attempts to withdraw, the force that is measured will be the weight of the sample. A range of solutions has been developed by Stable Micro Systems to provided a wide range of options depending upon the sample to be tested.

There are number of tips and tricks that we can share with you for optimising your adhesive measurements. To find out more, you can request our article 'Tips and Tricks for successful Adhesion Testing'

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.

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For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus 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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