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Use of a dual speed mixing protocol as a rapid wheat screening tool for estimation of Alveograph values
Determination of wheat quality always represents a challenge. There is a need for standardized methods that are repeatable, reproducible and as predictive as possible of the end use quality. Over time, many methods have been proposed and accepted, most of them are routine standards within the industry today and the data they provide are used during transaction to qualify the quality of the product.
Beside this, there is a global trend toward time reduction. We all want everything done faster, and the cereal business is no exclusion to this trend. The tricky situation is how to predict what will be the result using a fast and simple method instead of a slow, traditional reference method.
Our engineers provide a satisfactory answer to users wanting to know the Alveograph values of wheat grain using a rheological test that takes less than 10 minutes. The aim of our study is to develop prediction models based on a new protocol (called “WiXO”) developed on the CHOPIN Mixolab. More than 350 wheat samples were analyzed with the Alveograph reference method (ISO 27971-2015) and, at the same time, on the WiXO protocol. The results show that, using the WiXO-based models, 50 to 80% (depending on the parameters, W, P, L, I.e.) of the samples can be predicted within the control limits of the reference method. This shows “WiXO” protocol is a very interesting and valuable fast grading/segregating tool.
The Alveograph is a world standard method (ICC 121, AACC 54-30.02, and many more…). In its more recent version, the international standard ISO 27971-2015 introduces important information on the test accuracy when starting the analysis from wheat grain (and not from already-made flour). This standard includes important information on ‘how to prepare and mill the grain’ and ‘what impact these operations have on the final repeatability and reproducibility of the test’. The ISO 27971-2015 Standard establishes a common language and fair rules for all wheat grain transactions.
As the Standard intends to create a wheat flour as representative as possible of the wheat kernel, the method had to include basic good milling practices. The first practice being to work on properly tempered wheat. ISO 27971-2015 stresses the importance of moistening grain to 16% H2O and to let all wheat samples rest for 24 hours. Many studies show that laboratory milling of dry grains do not give satisfactory results.
The second important item is to work on a representative laboratory mill. Every industrial mill in the world uses corrugated and smooth rolls. To be representative, the laboratory milling must also include these 2 kind of rolls. If not, starch damage and ash content will be greatly impacted, as well as the rheological properties.
When this method is used by wheat milling plants (to optimize wheat blends for example), the length of the procedure can be a drawback when a rapid answer are needed. This is the case when receiving a load of wheat and a rapid answer is required as to whether it can be accepted or not. In some countries, operators needs to make rapid decision in order to purchase a certain lot of wheat. Most of the time, transaction decisions are based on protein content. But today, there is a clear understanding that “quantity” does not necessarily relates with “quantity”. This is particularly the case in countries where wheat can be attacked by suni pest bugs, degrading the protein properties without substantially affecting its quantity.
There is a need for a fast determination of Alveograph values, and in particular the “W” value. Some attempts were made using NIR but where not judged accurate enough. Operators need a rheology-based test, that is simple to operate and fast enough to be performed at any point of the wheat chain, that is predictive of the well-known and accepted “W” value.
To reach such an objective we started by analyzing the ISO standard. The first drawback is the tempering time, necessary to prepare the wheat to milling. One simple solution is to work directly on ground wheat. While the Alveograph, as described in the standard method, may not be the best tool to work on whole meal, the Mixolab has proven to be perfectly suited to analyze this type of samples. In order to speed up the test, we made two decisions: 1) to use dry grain and 2) to have a total analysis time lower than 10 minutes. Our idea was based on the work of Kahraman et al. who used the device’s capability to change the speed during the test period.
MATERIALS AND METHODS
Sample set was composed of 362 wheat, coming from different parts of the world and covering a wide range of “W” values [38-545]. Each wheat was divided in 2 subsamples. The first subsample was processed according to the ISO 27971-2015 procedure, including the different steps:
- Measurement of dry wheat moisture (EM10 oven)
- Calculation and introduction of the correct amount of water to reach a final moisture of 16%
- Mixing of wheat + water (MR2L mixer)
- Resting during 24 hours
- Measurement of the tempered wheat moisture (EM10 Oven)
- Milling of the wheat (CD1 mill)
- Mixing of break and reduction flours (MR2L)
- Alveograph test
The second subsample was analyzed according to the new procedure:
- Grinding of the dry wheat using a hammer mill with a mesh of 0.8 mm (CHOPIN Grinder)
- Measurement of whole meal moisture by NIR (Infraneo)
- Measurement of the Mixolab profile using the following settings:
- Constant hydration (60% 14% m.b.)
- Dough weight: 75g
- Water T°C: 30°c
- Mixer T°C: 30°c
- Mixing Speed 1: 80 rpm
- Mixing Time 1: 4 min
- Mixing Speed 2: 240 rpm
- Mixing Time 2: 4 min
Results were analyzed by statistical software Minitab 17 (Minitab Inc. USA)
RESULTS AND DISCUSSION
The Figure 1 shows a typical curve obtained by testing whole meal on the dual speed protocol specifically developed for this purpose (WiXO). It exhibits dough development during the first 4 minutes where we can measure maximum consistency (C1) and consistency at the end of the test (Cs). When the speed suddenly raises to 240 rpm, we observe a sharp increase of consistency (Cmax). Our postulate was that stronger wheat will show major increase between CS and Cmax. We also measure final consistency (Cend). In theory, weaker wheat will have lower consistency at the end of mixing (poor mixing stability). All these parameters are used to build the prediction model.
The Figure 2 shows the results obtained when comparing W prediction from the WIXO models with the actual W value measured with the ISO 27971-2015 standard. For the 307 samples used during the development, the range is [36-545] the correlation coefficient (r²) is 0.74 and the average difference with reference is 36 points. For the 52 samples used for validation, the range is [64-501] the correlation coefficient (r²) is 0.77 and the average difference with reference is 39 points. A deeper look at our data showed that the model was particularly well performing in the area [100-400] where 65% of the sample were predicted within the uncertainty of the reference method. For values lower than 100 the model tends to overestimate the W and for values higher than 400, it tends to underestimate it.
It is important to remember that we are comparing a reference method that needs many operations and a long time (24 h resting time) with an extremely fast method, only 15 minutes all included) performed on dry ground wheat. One must reasonably admit that placing 2/3 of the 362 samples analyzed within the reference uncertainty is a very encouraging result.
The W value can be identical for Alveographic profiles of very different qualities of flour. Therefore, it is important to not just consider the W value, but to also include at least one other parameter.
The reason is that the W value is based on the calculation of an area under the curve. The fact is that the same result (area) can be obtained with a very stiff /no extensible dough and with a low stiffness/high extensibility one. This means that having a good “W” prediction might not be sufficient.
Consequently, recent work has focused on the parameters of tenacity (P), extensibility (L) and the elasticity index (I.e). In 139 samples, covering a wide range of flours, 50%, 70% and 80% of the samples were found to be within the reference control limits for the parameters of tenacity, extensibility and the elasticity index respectively (Figures, 3, 4 and 5)
These prediction models have been included into a new protocol, called “WiXO”, that is now available for Mixolab users.
Dubat, A., Rosell C.M., Gallagher E., Mixolab a new approach to rheology, St. Paul, MN: The American Association of Cereal Chemists
Dubois, M., Dubat A., Launay L. The AlveoConsistograph Handbook St. Paul, MN: The American Association of Cereal Chemists
Kahraman, Kevser & Köksel, H. (2013). A new tool to estimate the suni-bug damage in wheat: Mixolab. Proceedings of EUROFOODCHE XVII.