Welcome to Stable Micro Systems User News: February 2011 | www.stablemicrosystems.com
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In this Edition: | Testing kelp elasticity | Testing non-homogeneous products | New online video | Available resources | Regular information | Contact us...
Top: Kelp sample in preparation
Centre: Kelp sample mounted
on the TA.XTplus texture analyser
Bottom: Katja Schweikert with Peter Bailey of Food Tech Solutions
A NOVEL TESTING APPLICATION
FROM NEW ZEALAND
The importance of kelp elasticity to South Island Māori (and others):
an unexpected relationship
Katja Schweikert is a doctorate student in the Department of Botany at the University of Otago – the oldest in New Zealand – which has an international reputation for research excellence and leads the latest Government university research performance assessment.
Katja’s research was geared towards investigating the environmental influences on the kelp as it grows; and she was particularly interested in finding a method of quantifying and comparing the strength of the various kelp samples.
A decrease in natural resources has brought to light a corresponding increase in awareness of the value of traditional practices and knowledge in the management of natural resources. The Māori people of New Zealand’s South Island have used rimurapa or bullkelp (Durvillaea antarctica) for hundreds of years to preserve their staple food (pōhā tītī), the seasonally harvested tītī bird, muttonbird or Sooty Shearwater (Puffinus griseus). They do this by inserting the birds into a kelp bag containing brine.
It is clear from observations by local residents that many areas along the South Island’s shores, where once healthy and dense stocks of bullkelp grew, have been completely decimated by a range of adverse environmental factors. In addition, some kelp stocks have lost the very qualities which are so vital for the traditional uses such as pōhā-making. These most regrettable developments have been proven to correspond in part to an increase in the discharge of untreated sewage and in part to changes in land use.
Although the University’s Food Science department has its own HD texture analyser, Stable Micro Systems’ New Zealand distributor, Food Tech Solutions, offered Katya the opportunity to bring her samples to Auckland for detailed examination. The test procedure selected utilised a tension project originally set up for packaging film, which proved to work extremely well with this rather different natural material!
In a preliminary experiment, traditionally cured kelp from a site with low human impact (Brighton) was compared to samples from locations badly affected by sewage (Tahuna) and both sewage and industrial effluent (Bluff). In addition, samples of freshly harvested kelp from a site with low human impact (Kaka Point) were tested.
Elasticity was used as an indicator of tissue health, as local users described a change in the tissue from highly elastic to powdery and easily torn. The initial results indicated a clear reduction in elasticity in samples from Bluff when compared to those from Brighton or Tahuna. It was also discovered that the elasticity of traditionally cured kelp was between 4 and 6 times higher than that of freshly harvested material. How this difference in blade elasticity correlates to environmental contamination and dislodgement, and hence to the loss of resource and habitat has yet to be fully investigated.
So here we have seen something a little different from our usual subject matter, and an indication of the adaptability of a Stable Micro Systems texture analyser – and of our distributors.
Katja.schweikert@otago.ac.nz
Empirical methods of assessing texture are often challenged by lack of homogeneity or uniformity in samples – a challenge which is almost impossible to approach with fundamental methods. Heterogeneous systems have structural elements that can vary considerably for the same overall chemical composition depending upon how they were created.
Sometimes the sample to be analysed may be of variable configuration or structure from piece to piece, such as breakfast cereal flakes. In the case of fruit testing, for example, whilst the preferred method of testing might be compression, the inherent variability of natural products and the range of sizes of fruit from piece to piece may preclude the option of testing the pieces one at a time. On the other hand a manufactured sample such as a cereal bar, or indeed a natural product such as meat, may have uniformity in its sample shape and size but consist of an entirely variable texture throughout.
Click here to download this poster as a PDF
These challenges call for a range of tests which deal with the compromise of sample heterogeneity. In some instances, the preferred method of testing (such as compression, penetration or shearing) can be adapted to improve the chance of obtaining a repeatable result. What all of these methods have in common is the fact that by testing a larger number of pieces, or a wider surface area with more testing surfaces, an averaging effect is created which is the result of a representative set of pieces or surfaces.
The primary issue of these types of samples is that they are usually of varying sizes or are of non-homogeneous nature, and therefore make comparisons difficult. They have a high variability from piece to piece within the same batch and require a large sample set to be tested. Puncture or compression tests to rupture are possible, but usually produce results with poor repeatability. To ensure that repeatable results are obtained when testing by compression, it is essential that the dimensions of the test pieces are consistent. To do this, fruit cylinders or cubes would therefore need to be prepared, which might be impractical in terms of time available or ease of testing.
In this instance, it is advisable to take a certain number or certain weight of samples and perform a bulk compression or shearing test. This type of test creates an ‘averaging effect’ and gives the result of a representative number or weight of fruit pieces.
The result is an average of the forces required to compress, shear, puncture or extrude the sample of variable geometry. The maximum force and area under the curve are usually recorded for all of these types of test and taken as an indication of bulk firmness. The area under the curve is usually termed the ‘work of shear/compression/penetration’ – a larger value indicating a firmer sample.
TESTING via COMPRESSION
Bulk Compression
When compression is the preferred testing method, the repeatability relies heavily on the uniformity of the sample in terms of size, shape, configuration and homogeneity. A small change in sample size has an immediate effect on surface area for testing, which will obviously affect the magnitude of the force to be measured, and thereby affect the repeatability.
Bulk compression is where the sample is compressed in three dimensions. It is commonly used for fruit and vegetables, breakfast cereals, etc. where a chosen number of pieces or weight of sample is tested at the same time. Normally, as these products are oddly shaped and therefore have inherent variability, a bulk compression test is the most reliable way of assessing their texture. An averaging effect takes place within one test where the variation in piece to piece size, shape and configuration is accommodated. A standard compression test using a cylinder probe can be used for a certain number of sample pieces such as pellets where sample size is more uniform, but in compression tests on single pieces has proven to be disappointingly unrepeatable.
Errors due to changes in the shape of the sample during compression testing may be reduced by confining the sample in a close-fitting cell and compressing it with a plunger that just fits into the cell with little or no clearance between it and the inner surface of the cell wall; these are bulk compression tests.
Due to its relatively small testing diameter and volume, the Granule Compaction Rig is the recommended solution for granular materials, such as tabletting material, whilst the most common bulk compression device for food products is an Ottawa Cell which is comprised of a square section test cell and loose fitting plunger.
Test samples are typically extruded through an extrusion plate located in the base of the cell. Extrusion plates feature holes, wire, blades or bars, to suit the sample. A watertight base and liquid catchment tray expands the range of products which may be tested using this attachment, such as ‘bowl life’ assessment of breakfast cereals.TESTING via SHEARING
Kramer Shear Cell
Bulk testing can also be performed with a Kramer Shear Cell, which uses a stationary rectangular box with slots in the base to hold the sample and a moving probe composed of 5 or 10 blades to drive through the test specimen. Pieces are placed into the cell to the same filling volume or by weight, and the blades positioned at a constant position above the sample surface. The blades then move down into the sample, compressing, shearing and extruding the bulk to a point close to, or slightly through, the base of the cell. Because individual peas, beans, berries, and similar multi-particle products can be tested, the apparatus permits the determination of the distribution pattern, as well as of an average resistance for a batch of the test material. Both maximum force readings and areas under the peak (work function) can be determined.
For products with variable texture across their length – for example, meat or cereal bars – results from single blade tests may be highly variable. This is because for one test of a typical cereal bar, the blade might come into contact with a peanut and a chocolate chip, and the next blade test of the same bar might slice through a raisin and an apricot piece; in this case the blade is almost testing different samples. The Kramer Shear Cell method is made on a defined sample quantity. The multiple blades provide a measurement on several positions simultaneously, compensating for local texture deviations. So this method provides an averaging effect and has shown to be more reproducible for such highly variable samples.
The Kramer Shear Cell allows the testing of a larger sample size and therefore can have the advantage of obtaining an averaging effect. While this is advantageous for the repeatable testing of highly non-uniform products, the drawback is that this type of test commonly requires a high force load cell, e.g. 500kg, and therefore lends itself to a TA.HDplus application.
A standard Kramer Shear Cell or Ottawa Cell test would ordinarily produce test results of high force. Reducing the volume of small sample pieces to be tested using a Miniature Kramer Shear/ Ottawa Cell consequently reduces the magnitude of the forces produced during the test, making the rig more suitable for use with the single column or low force Texture Analysers.
TESTING via PENETRATION
Using Penetration Testing
A penetration test could well be considered the most simple of all tests. As the size of the probe surface area is constant this often means that the sample size does not need to be carefully controlled, unlike compression testing. However, when faced with a non-homogeneous product, penetration is highly compromised as a smaller surface area for measurement is also more sensitive to variations in sample structure and low reproducibility and misleading data may be obtained. Results may show a wide variance between maximum and minimum forces, depending on whether the probe meets with, for example, an air pocket, hard particle or internal structure variation.
Multiple Puncture Probe
The use of a Multiple Puncture Probe that penetrates the sample in several regions serves to create an averaging effect and is therefore usually more repeatable. Using several testing pins, attached to the TA.XTplus texture analyser, manufacturers can test non-uniform products containing particulates of different size, shape, structure and levels of hardness, to provide repeatable results.
Such products have non-homogeneous textures due to the presence of, for example, dried fruits, vegetables or nuts, or consist of different layers to provide more interest to the consumer. By penetrating the product in several areas at the same time, the Multiple Puncture Probe produces an averaging effect and is therefore more representative. This probe also allows reduced forces by the removal of a proportion of the pins.
This probe quantifies the firmness and hardness of products such as petfood, jams and preserves containing fruit pieces or ice cream containing particulates. For example, these can be meringue pieces, chocolate chips or fruit chunks. These products can be difficult to measure as the number, size, shape and distribution of particulates is usually random within each container.
Multiple Chip Rig
This rig measures the force obtained by the penetration of a multiple sample of chips. Up to 10 chips can be tested at one time and the rig ensures that each chip is completely penetrated by two 2mm diameter probes per test.
Multiple Pea Rig
This rig measures the force to simultaneously penetrate up to 18 samples. The insert has 18 indentations surrounding a cone which allows the sample to locate easily into the test positions.
Puncture strength and penetration force are measured with 18 2mm cylinder probes and the penetration distance is set so that the probes penetrate completely through the sample. Other applications using this rig include beans and confectionery samples.
You can now see our latest online video commercial showcasing Volume.
Following on from our two recent Texture Analysis videos, the new compilation shows the versatility of the Volscan Profiler, Stable Micro Systems’ digital volume measurement instrument, with particular reference to its capabilities in the assessment of bakery products and fruit.
Access the film from the Video channel>Texture Channel menu item at www.stablemicrosystems.com
UK TRAINING COURSE DATES FOR 2011
Why come on a Texture Analysis course?
If you would like to improve your understanding of texture analysis and obtain maximum benefit from the use of your Stable Micro Systems Texture Analyser and software, we are here to help.
Our one day courses are held at our head office in Godalming, Surrey. Each course consists of Software and Applications training sections.
The Software Training module provides expert guidance in controlling the Texture Analyser; running a test, saving data, carrying out post-test analysis and producing graphs with different scales and axes to compare data; viewing calculated results in a custom made spreadsheet and producing charts and reports that include this calculated data; and Macros, Projects and their relevance to your application.
In our Applications Training module, the latest versions of the TA.XTplus and TA.HDplus will be set up for groups of four people to prepare samples and select suitable methods for applications; see and handle a wide range of probes and fixtures; calibrate the instrument, change a load cell and carry out simple maintenance; and obtain advice and guidance on your own difficult applications.
Course topics include: The Principles of Texture Analysis; Exponent software; Tips for better testing; and Interactive practicals.
More detailed training courses on specialist testing topics may be arranged by request.
The course costs £75 + VAT per person. If you have a Maintenance Plan, one place on the course is included free of charge.
Please contact us to arrange a place:
Tel: 01483 427345 Fax: 01483 427600
Email: sales@stablemicrosystems.com
Accommodation can be arranged at extra cost.The coming year’s courses will run as follows:
• Wednesday, 23rd February 2011
• Wednesday, 23rd March 2011
• Wednesday, 20th April 2011
• Wednesday, 25th May 2011
• Wednesday, 22nd June 2011
• Wednesday, 20th July 2011
• Wednesday, 21st September 2011
• Wednesday, 26th October 2011
• Wednesday, 23rd November 2011
Would you like the latest Application Overview which highlights methods for Bakery Products?
Application Overviews give a detailed summary of all of the methods and fixtures that are currently in use in this field of testing. They include testing points to consider and a comprehensive list of academic references.
To request the Bakery Product Application Overview please contact: jo.smewing@stablemicrosystems.com
"It’s not only the appearance and taste of food that gets the consumer on your side. Texture is a key factor which influences food sampling, buying and repurchase and is vital for ensuring consumer appeal and product success".
Particularly useful in the case of instruments with multiple users who are looking for a quick step by step guide to obtaining good data, there is now a range of A3 posters available.
These feature the TA.XTplus/TA.HDplus Texture Analyser (both instrument setup and operational safety guides are now available), the Volscan Profiler, the Powder Flow Analyser and the Dobraszczyk/Roberts Dough Inflation System.
If you would like to request a complimentary copy of any of these, please contact jo.smewing@stablemicrosystems.com with your instrument serial number and postal address.
We can now make a number of articles from Laboratory News and Manufacturing Chemist available to our users.
The first of these are studies of texture analyser use in the fields of Adhesives and Packaging.
To receive a copy, please send your name, company name and address to: jo.smewing@stablemicrosystems.com
UPGRADING TA.XT2i TEXTURE ANALYSERS
Stable Micro Systems are still able to offer upgrade paths for TA.XT2i Texture Analyser instruments to the latest specification TA.XTplus Texture Analyser.
To investigate the benefits and receive a quotation please contact: sales@stablemicrosystems.com
EXHIBITIONS AND CONFERENCES 2011
Stable Micro Systems will be attending the following Exhibitions and Conferences:
• NutraFormulate
2-3 March 2011 / Coventry, UK / Website...
• In-Cosmetics
29-31 March 2011 / Milan, Italy / Website...
• BCCC 2011 Annual Technology Conference
6-7 April 2011 / Thame, UK / Website...
• AACC 3rd International Spring Meeting
11-13 April 2011 / Freising, Germany / Website...
• ICC 2nd Latino-American ICC Cereals Conference
10-13 April 2011 / Santiago, Chile / Website...
SOFTWARE VERSIONS AND RECENT UPDATES
The software packages below are available for download free of charge (to existing users) from our website within the Software Download section:
• Exponent – 5.0.9.0
• Volscan Profiler software – 0.0.5.0
• Application Help Files last updated – July 2010
• Abstract Help file last updated – July 2010
Vienna Court, Lammas Road, Godalming, Surrey GU7 1YL, UK
Telephone: +44 (0) 1483 427345 | Facsimile: +44 (0) 1483 427600
E-mail: sales@stablemicrosystems.com | Website: www.stablemicrosystems.com
Registered at Cardiff No. 1702660 | Registered Office as above.
©2011 Stable Micro Systems Ltd. All rights reserved. Products and specifications subject to change without notice.
Volscan Profiler, TA.XTplus, TA.HDplus, TA.XT2i, Exponent, Texture Expert and Texture Expert Exceed are trademarks of Stable Micro Systems.
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