Texture Analysis to Measure the Effects of Enzyme Addition on the Staling of Artisanal Bread: Part 3 – Texture Analysis Techniques

Texture Analysis techniques

Chemical tests are a major part of the research that can be performed to assess the extent of staling. These include the measurement of water activity, alkaline water retention capacity and the amount of soluble starch. However, it is the changes in physical properties listed above that are felt directly by the consumer when eating a loaf, and it is essential that these properties are monitored when developing new formulations. Texture Analysis can be used to test the properties of bread from dough to loaf.

Dough

The main properties of the dough itself that are tailored using enzymes are softness, extensibility and stickiness.

In bakery, measurements of dough and gluten extensibility are important in pre-determining the rise qualities and structure of the finished product. Stable Micro Systems offer two solutions for measuring dough extensibility, both widely used in academic environments and bakeries. Firstly, the Dobrascycyk-Roberts Dough Inflation System enables the rheological properties of both dough and gluten to be measured during biaxial stretching.

Dobrascycyk-Roberts Dough Inflation System

In the Dobrascycyk-Roberts Dough Inflation System, conditions similar to the strain experienced during proofing and baking around a slowly expanding gas cell are reproduced. The device inflates a sheet of dough by volume displacement of air using a piston driven by a Texture Analyser. Pressure during inflation is measured using a pressure transducer, and the volume of the inflating dough sheet is calculated from piston displacement.

Dough rheological properties (stress, strain and viscosity) are then calculated directly from pressure, volume, and time using fundamental equations. The procedure requires minimum handling of the dough when preparing samples. Typical results include baking strength, tenacity, extensibility and elasticity. 

Kieffer Dough and Gluten Extensibility Rig

On a smaller sample scale, the Kieffer Dough and Gluten Extensibility Rig provides an effective method for the accurate determination of dough and gluten extensibility. Only small samples are required (approx 10g flour or 1-2g gluten), which is of particular interest to wheat breeders requiring information on rheological qualities at an early stage for the development of hybrids.

Parallel tests of dough and gluten can reveal particular characteristics arising from homogenisation, long relaxation times or from adding oxidants, salts, emulsifiers or enzymes. The maximum force (resistance to extension) and distance to break (extensibility) are measured using this rig.

Warburtons Dough Stickiness System

The Warburtons Dough Stickiness System measures dough stickiness as well as the firmness of the dough. It features a sample testing box into which dough samples of 500g or 1Kg can be placed quickly and with minimum exposure of the cut surface to the atmosphere. A retaining plate is placed on top of the dough, applying slight compression to the sample and a narrow blade is driven through a slot in the retaining plate to a defined distance.

The force measurement during this action obtains the compression peak and compression area of the dough, indicators of its consistency (firmness/softness). As the blade is withdrawn upwards, Exponent software calculates the adhesion peak and adhesion area. The higher the peak, and/or larger the area, the stickier the dough. This rig enables more realistic assessment of dough stickiness than traditional open techniques as it minimises the dough’s exposure to atmospheric variables by testing under controlled conditions.

12mm cylindrical probe

Crust

A fresh loaf of bread has a crust that is much crispier than the interior, a property that degrades over the staling period. This property can be measured using a penetration test using a cylindrical penetration probe. A crispier crust will show a series of high force peaks followed by a drop once the probe reaches the interior, as opposed to a loaf that has simply gone stale and hard, which will show a monotonous high resistance to the probe. The measurement of Peak Count and Linear Distance will give a good indication of crispness. This test can be further enhanced by the use of an Acoustic Envelope Detector. This allows quantitative measurement of the sound pressure level produced during a crust penetration, which can be related directly to the sounds heard when a customer cuts through the crust with a knife or takes a bite from the crust of a bread slice.

Acoustic Envelope Detector

Crumb

The Bread Resilience method included in Exponent software measures two key properties in staling of bread crumb: elasticity and firmness. It uses a radiused 36mm cylinder probe to test a stack of two bread slices. This method was developed to mimic a manual test performed by the line operators of a large industrial bakery. The manual test involved squashing two stacked slices of bread with a thumb by approximately 60% for 2 seconds.  After allowing the bread to recover for approximately 15 seconds a visual assessment was made on the % of recovery. This was the factory’s definition of ‘resilience’. This manual method has inherent variability and is very subjective. The Bread Resilience method replicates this manual test in a controlled way giving an objective resilience result.

Bread firmness test using a cylinder probe

The first part of the test is in accordance with the AACC standard firmness method – force to 25% strain. The percentage ratio of original height to post-test height gives resilience in %. This shows the tendency of a sample to recover.

Fresh bread shows an immediate return to its initial state after stress release, whereas stale bread shows plastic deformation resulting from cracking and crumbling upon stress application, preventing the bread from springing back into place. These cracks might be microscopic; bread resilience testing will show irreversible damage for whatever reason it has occurred.

To measure staling objectively, perform firmness and resilience tests during the storage period and measure away from the crust to avoid dry edge effects. It is recommended to use a radiused probe such as the P/36R to prevent cutting at the edges.

SMS/Miller-Hoseney Toughness Rig

Another option for measuring bread firmness is the SMS/Miller-Hoseney Toughness Rig. This was developed in conjunction with Professor Hoseney and Dr Miller of the Kansas State University and is used to determine the toughness and firmness of bread and other sliceable products. The rig comprises two adjustable angled base plates which fix on the texture analyser and a support frame, holding a stainless steel cutting wire, which connects directly to the loadcell. The force to cut through the sample is measured. This provides a test very closely imitative of the procedure carried out by a customer when slicing their loaf.

Bread V Squeeze Rig

Loaf

The test commonly used by a consumer to test loaf softness is the ‘squeeze test’, squashing it between the thumb and fingers, creating a ‘V’ shape with the hand. Staleness is equated to increased firmness of a loaf of bread on the store shelf. The Bread V Squeeze Rig enables testing of the softness and springiness of both packaged and unpackaged loaves, giving a good indication of freshness.

The rig imitates the customer’s squeeze process and allows repeatable, scientific analysis of the freshness and appeal of bread. It consists of ‘V’ shaped rounded ‘fingers’, which are lowered onto a packaged or unpackaged loaf, and the force required to compress the bread is measured. Post-test calculations are then used as an indication of freshness – the lower the force and higher the value of springiness, the fresher the loaf. This non-destructive test offers simplicity and speed as the loaf requires no sample preparation and can be analysed within the packaging.

Volscan Profiler

As mentioned above, the volume of a loaf is a key indicator of its propensity to stale quickly. This property can be measured rapidly and accurately using the Volscan Profiler by Stable Micro Systems. This is a benchtop laser-based scanner that measures the volume, density and dimensional profiles of solid products. It is a non-contact technique and offers considerable advantages over contact and displacement techniques that purely measure volume.

The rapid 3-dimensional digitisation of products enables the automatic calculation of several detailed dimensional parameters, the results of which may be mathematically manipulated for immediate use or future retrieval in a variety of data formats.

This technique enables manufacturers to have a precise and fast method for the measurement of the volume, density and dimensions of bread to help control and monitor their manufacture.

During a test, the bread loaf is speared at each end. Parameters for each batch under test are entered into the software by the operator and include sample ID, name, date, and bakery-specific parameters such as flour weight. The product is then automatically weighed and an eye-safe laser device is used to scan vertically to measure the contours of the product at selectable intervals whilst it rotates.

Each interval consists of 400 data points providing a detailed profile of the product. This assessment can be performed rapidly, the results being obtained in a period ranging from a few seconds to a few minutes depending upon the chosen interval (0.05mm to 50mm) and the preferred precision. Temperature of the testing chamber is measured automatically.
Due to the samples being scanned by the laser in a linear manner the mounted sample can be analysed in ‘slices’. This means that every measurement step increment possesses data and statistics of its own such as circumference, average radius and minimal enclosing circle. This provides more detailed dimensional analysis than any other similar measuring instrument.

Due to the rapid development of biochemistry and enzyme technology, as well as increasing interest in enzyme applications for the baking industry, more and improved enzyme products will continue to appear on the market. There will also be more reports and studies giving a better understanding of the mechanisms of baking enzymes, leading to further improved products. The improvements in products resulting from this new technology is only proven by the quantification of property alterations using techniques such as Texture Analysis.

A whole host of Texture Analysis techniques can be used to test other aspects of a bread loaf, from the flow properties of the flour to the packaging used for the final product. The range of Stable Micro Systems Texture Analysers combines ease of use with automatic data collection and rapid project-based data analysis. To discover our whole range of testing techniques, contact Stable Micro Systems today.

References

Chemistry World article, 2009
‘Not a stale subject’, Bakery Business,Taylor 1998
‘Characterisation of the staling process of wholemeal bread’, Polish Journal of Food and Nutrition Sciences, Fik 2000
‘Strategies to stop staling’, Baking and Snack, Stauffer 1996
‘Effects of enzyme preparations for baking, mixing time and resting time on bread quality and bread staling’, Food Chemistry, Sahlstrom 1996
‘Comparison of methods for the assessment of staling in bread’, Food Chemistry, Sidhu 1996
‘Synergistic effect of enzymes for breadbaking’, American Association of Cereal Chemists, Qi Si 1997

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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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