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Testing the firmness of the whole fruit allows the manufacturer to predict its ability to withstand further processing

Sias carries out back extrusion tests 
on processed strawberries

Fruit texture analysis

A needle probe is used to measure the firmness of fruit skins and give an indication of their ripeness

Sias Foods is a major producer of fruit preparations for yoghurts, desserts, such as trifles, mousses, pies and ice cream for the British market. The parent company, £450 million French group Sias MPA, has manufacturing facilities all over Europe, including the UK, France, Germany, Italy, Austria, Poland and Czech Republic. Sias also operates factories in Asia Pacific, the US, South Africa, Mexico and Latin America.

The UK factory, based in Corby, Northamptonshire, processes dozens of fruit varieties. Quality control is an integral part of the production process and one of the priorities for the company's customers in the dairy and dessert industries. Of particular importance was the consistency of the fruit after processing. Two years ago, Sias' management team identified the need to further improve quality control procedures and contacted Stable Micro Systems, a leading provider of texture analysis instruments to the food industry.

The need for objectivity

Sias had previously relied on organoleptic testing by its quality control team. Whilst of significant value to any food processor, human taste panels have limited value - primarily because of their subjectivity. But in order to ensure continuity and repeatability of tests, Sias wanted to install equipment that would carry out texture analysis measurements objectively. The results of these tests could then be used in conjunction with, and as a complement to, organoleptic analysers to provide a fuller and more accurate profile of the fruit's textural characteristics.

Sias evaluated several systems, and installed Stable Micro Systems' TA.XT2i in late 1998, selected for its accuracy and the potential to perform a wide variety of tests on just one machine.

Texture analysis - improving quality

Although the original aim of installing the texture analyser was end product testing, Sias is now also using it in new product development. Having identified the ideal consistency for an apple puree for example, it may be possible to develop a blackcurrant product with a similar viscosity and mouthfeel. Steven Smallwood, Sias NPD Manager, comments: "Each year, different fruits come into fashion and we could find ourselves handling fruits we haven't processed before.  Using texture analysis enables us to quickly assess how a new fruit will process, and adjust equipment or procedures accordingly, without wasting time or money."

Testing can be carried out at any stage of the production process - from the incoming raw materials (whole fresh fruits) to the finished product. Because fruits need to be handled with care, particularly before processing begins, carrying out texture analysis tests throughout manufacture enables users to monitor their condition - the timing and degree of breakdown of structure - and could help to identify which processing methods best maintain the integrity of the fruit.

The fruit, the whole fruit

The 'back extrusion' test is a simple but valuable tool for measuring not only the consistency of a fruit preparation, but also of whole fruit pieces after processing. For Sias, the objective was to measure the firmness of the fruit in order to predict its ability to withstand further processing, normally at the dairy or dessert manufacturer's factory. A defined protocol is adhered to, in order to minimise the risk of distorting test results. After production, samples are removed and washed. Sias only tests whole fruit pieces rather than damaged ones, which by definition, have been shown to be relatively weak. Every batch of finished product is tested using the back extrusion technique.

The sample is placed in a transparent plastic vessel with a 50mm internal diameter and then compressed using a disc of an appropriate size. The choice of disc will depend on the size of the fruit pieces in the preparation. As the disc descends, the sample is forced up and around its edge and data is captured throughout - normally at a rate of about 200 points per second.

Tangible benefits

Since automated texture analysis began at Sias the quality control department has been able to test thousands of batches of fruit preparation accurately. Results have been recorded and used to define acceptable fruit hardness parameters, further tightening quality standards and providing objective analyses to complement ongoing human taste testing.

Further fruit tests

The back extrusion test is one of a number of texture analysis techniques which can be employed in fruit processing factories. These include:

Fruit hardness

The ripeness and freshness of a fruit are often defined by their firmness, particularly their skin. Using a needle probe, a fruit's skin strength (or yield point) can be measured. Alternatively, spherical probes, carrying out indentation tests, provide valuable information on a fruit's surface hardness. A simple cutting test, or Volodkevich Bite Jaws, which simulate a biting action, can measure the force required to 'bite' through the product.  Indentation and cutting tests can also be conducted on processed fruits.

Fruit preparation consistency

Back extrusion tests can be used to measure the viscosity of finished furit preparations as well as the fruit pieces within them. Forward extrusion also gives useful information on the products consistency by forcing it down through a hole in the base of the sample container. Stable Micro Systems provides containers with outlets with various diameters to suit different applications. Properties such as firmness, visco-elastic creep, and stickiness can all be assessed using a simple cylinder probe test.

Easy integration, a competitive advantage

Because texture analysis is so flexible, it can be used throughout the food industry to test ingredients as well as finished products. Stable Micro Systems stresses that it should not be viewed as a substitute for human taste testing, but as a complement to it.

As Hido Malic, Sias quality and development manager, comments: 'Installing the texture analyser was a simple way of upgrading our quality control procedures. Organoleptic testing remains very important, but the TA.XT2i is now an integral part of the process. Our customers can be confident of consistently high quality, and that obviously brings great benefits to the business.' Texture analysis has brough tangiable benefits to Sias and other major European food processors by improving quality, reducing rejected product and saving time.



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