How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Tuesday, 25 April 2017

The Importance of Texture Analysis in Cosmetic Stability Testing

Cosmetics companies! Can you say with confidence that a product your customer buys in bulk today will have the same excellent qualities they expect from your brand when they open it in six months’ time?

If not, you need to start stability testing, pronto.

Stability testing is simply the assessment of the lasting power of a cosmetic, during which samples of it are put under different environmental conditions for a set time period, and its properties analysed. These conditions vary in light, temperature, pressure and humidity levels and are designed to imitate what the product may be subjected to during its lifetime.

A sample to be stability tested will typically be a new product, an existing product with an altered formula, a new raw material supplier, a new manufacturing procedure, a shift in production to a new manufacturing site or new or altered packaging. A suite of stability tests should precisely target the most important points of testing; physical, chemical and performance characteristics are evaluated at set intervals to see how they have changed.

The qualities of paramount importance are:

• organoleptic (appearance, colour, odour and texture)
• physiochemical (pH, mass, preservatives)
• microbiological (microbial count and preservation efficacy)

• compatibility between the product and its container

If these changes are small according to the standards set by the manufacturer, the new or altered product has passed stability testing and it can be confidently shipped to consumers. Very few products have to pass international or national standard tests (with the exception of functional products such as sun creams, anti-dandruff products or anti-perspirants).

Accelerated Testing

Once a new cosmetic has begun development it must reach the market as quickly as possible, as each extra day spent on development is another day a turnover cannot be made. Due to this time shortage, it is wise for manufacturers to have a standard set of tests ready for each sample. 

Additionally, real-time stability testing before a product launch is rarely an option – for instance, a sun cream can remain stable for two to three years. Very few manufacturers have the luxury of testing a product over a three-year period before they release it. Instead, accelerated stability studies take place in which different accelerated storage conditions are used, involving elevated temperature, humidity, light or pressure.

These accelerated tests help to predict the product’s stability behaviour and are often used alongside  post-release “real-time” tests. After a sample is launched it is stored under ambient conditions and monitored to help refine the accelerated testing method. These post-release tests can also be used to further improve the product.

All tests, real-time and accelerated, include an evaluation of the physical properties of products after storage, transport and use, and the compatibility between the products and the container. These can be performed using Texture Analysers and Rheometers. Additionally, the stability of a product after opening its container can be a useful measure.

Predicting Cosmetic Shelf Life

Shelf life prediction using accelerated methods is not an area that has been widely generalised for scientific publication and so there is a lack of public information on the subject. Part of the problem lies in the wide complexity and variety of both the cosmetic products and their packaging as well as the large number of changes that need to be tested (be they physical, aesthetic, functional, chemical or microbial). Additionally, the cosmetics industry is a guarded place, with both products and test methods under high protection by patents and trademarks.

However, there are some general guidelines that can be followed. For accelerated testing, the temperature and time components are chosen according to the product type and the company’s prior experience. Conditions do not have to be limited to a single time and temperature test – a range of temperatures spanning 30° to 45°C is often used, over a time period of a few months. These conditions depend on the product type and place of storage. 

The fundamental assumption in stability testing is that an increase in storage temperature will speed up ageing reactions. A useful rule of thumb is that a sample stored at 45˚C for two months is equivalent to one that is stored at room temperature for one year.

The combination of results from accelerated testing and the company’s prior knowledge help to give a good prediction of the product’s shelf life.

Some Points to Consider

Small scale testing: if only small quantities of a product are available in its early stages of development, small samples from laboratory batches can be tested for an early prediction of stability behaviour. Once development has moved along and the product is being manufactured using full scale equipment, the information on stability behaviour will be more accurate.

Colour and fragrance:
various additives are used to achieve the colour and fragrance variations of a product that will be brought to market, and these are likely to affect stability behaviour. Different combinations can react adversely with each other, with the product itself or with the container. If there will be a low number of variations released, it is advisable to test them all. If there are tens of different shades, however, then the evaluation of a representative selection will suffice, as long as testing continues past the product release.

the containers used in stability testing should be as similar to the final product container as possible (using the same materials, shape and size). As with colour and shade, if there will be a range of package sizes or types, then they should all be tested if possible. A control container made of glass or another inert material can be used, and if testing is to be very thorough then different orientations can also be tested, with the container upside down or on its side.

Extreme Conditions

Manufacturers decide whether to perform such specialised testing based on the weaknesses of any particular cosmetic product and its anticipated shipping, storage, display and use. For example, an emulsion will not typically survive being frozen and re-thawed, a suspension may become cloudy, packaging may distort and its label come loose, or corrosion may occur on the inside of an aluminium container that has been coated in a lacquer.

Finally, mechanical shock testing is performed to check for vulnerabilities during shipping, and vibration testing used to check for the likelihood of separation of components in a granular product, whereas light stability testing is used to mimic the light intensity that a product will be exposed to if stored in a clear container.

Where does a Texture Analyser fit into all of this?
Many of the tests mentioned involve physical properties. The team developing a product will have spent a long time assessing its ideal assets. These might be the consistency of a cream, the extrusion force of a toothpaste from its tube, the cohesion behaviour of a powder, the cake strength of a compact, the shear strength of a lipstick, the drying time of a nail polish, the adhesive strength of depilatory wax… the list goes on.

All of these products can be reliably tested using one of the Stable Micro Systems Texture Analyser range to give reliable, repeatable results. If time is an important parameter, there are methods to help increase sample throughput such as the ALIS – an automated indexing system that enables multiple tests to be performed automatically. 

Additionally, the Exponent software is designed to make the testing process fast and simple, with flawless comparison of samples within a batch or between batches themselves, and automated macros to analyse all the experimental data at the press of a button. 

All the tests are archived with date and time information to help compare real-time tests after the release of the product with the accelerated stability tests that were performed pre-release, with the ability to constantly update the accelerated testing procedure and help it to be as representative of real storage as possible.

Help is always on hand at Stable Micro Systems with texture experts and a software team a phone call away to make your stability testing procedures go as smoothly as possible.

We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.


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

TA.XTplus texture analyser with bloom jar 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.

No-one understands texture analysis like we do!

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