The basic premise of flour milling is to separate, at the highest efficiencies possible, the bran from the endosperm to produce a good quality flour. One of the newer technologies that promises to increase wheat milling efficiency and net product value is pre-processing, or debranning.
The traditional five-break mill, with associated screening, aspiration and separation systems is designed to efficiently break clean, dry wheat, after a tempering stage, into particle sizes that can be segregated into separate flour grades, bran and middlings.
The Tkac Debranning Process offers several benefits to the flour milling process.
Benefit No. 1: Higher extraction rates.
In older mills, typically low yields of 75% to 76% good quality flours are generally a result of the fact that a portion of the bran layers remain fused to endosperm particles, and those particles cannot be further sheared and segregated to produce good quality flour.
The principle of debranning is to remove the majority of the bran before the wheat enters the first break. The result is that the wheat-to-roll requires less subsequent processing to produce good quality flour. As well, the effective bran separation from the endosperm (except for that portion that remains in the crease of the wheat), can lead to a higher net flour yield, typically in the 79% to 80% range of clean dry wheat input to the debranning system.
The clean removal of the bran layers in the Tkac process also leads to a whiter flour after the milling process, as most of the bran that would contaminate the flour and raise the color number is no longer present.
The Tkac Debranning Process also provides for higher net yields of semolina from durum wheat, and has been proven to increase semolina quality.
Benefit No. 2: Higher throughput in conventional mills.
The debranning process, which removes about two-thirds of the bran, increases the ability of older conventional wheat milling systems to produce up to 40% more flour from the same amount of down-stream processing equipment. As most of the bran has already been removed prior to the first break, less screening surface is required to separate the remaining bran from the endosperm particles.
In that case, older mill designs would be reconfigured to provide more efficient processing and higher throughput while still utilizing the existing hardware.
Benefit No. 3: Processing wheat with elevated levels of alpha amylase.
The Tkac Debranning Process also can provide other benefits where lower grades of wheat are available, such as feed grades or sprouted wheat.
With sprouted wheat, the debranning process can effectively remove the sprout, which contains the enzyme alpha amylase. This enzyme is not desirable in flour as it reduces the falling number.
The removal of the sprout through debranning can result in flour falling numbers that can be increased very significantly, often in the neighborhood of 100 points. This increase permits production of higher quality flour than would otherwise be available from sprouted wheat. The lower cost of sprouted wheat means higher profits for the mill.
Benefit No. 4: Milling of wheat containing mycotoxins.
With wheat that has suffered fusarium head blight, the level of residual mycotoxins (vomitoxin) can be reduced by debranning. The toxins are mainly on the surface of the wheat, and are thus carried off with the debranning byproducts.
Debranning and milling of mycotoxin-contaminated wheat shows that wheat with relatively high levels of myco- toxins (<6 mg/kg) can still be used for flour production, especially when resultant flour is blended out with uncontaminated flour to reduce overall levels of mycotoxins in the finished flour. The permissible amount of mycotoxins in finished flour may vary from country to country, but are generally in the 1 to 1.5 mg/kg range.
Observations indicate that when mycotoxins appear at rates higher than 6 mg/kg, there will be increasing density reduction and shriveling of the wheat kernels. This is the result of the more mature mold consuming the endosperm portion of the kernel, rather than appearing only on the outside of the kernel. These lower density kernels can usually be separated in an air classification system, leaving the remaining higher density kernels that do not appear to have as high a level of toxins.
It has been found that the mycotoxins will appear in very high amounts in the debranning products, making them unsuitable for use as human food or animal feed products.
A combination of air scouring, to remove loose mold, followed by the debranning process would produce the best overall results.
Benefit No. 5: Potential new value-added products.
The Tkac Debranning Process can also produce three distinct new products that can add value to the flour milling process. Dietary fiber from the outer bran layers, nutrient-rich intermediate bran and high protein aleurone flour have values in the functional food, cereal and nutraceutical industries. The values of these products can be significantly higher than mill feed. Markets for these products are being continuously developed, and specialty companies are prepared to sign agreements to place materials into a growing marketplace.
The three products reflect the properties of the different layers in the wheat bran. The outer layers generally contain the dietary fiber, but low percentages of protein and ash (minerals). The intermediate layers contain the pigments and many of the other nutrients, with a moderate protein level. The inner layers (nucelar and aleurone) have elevated levels of protein, nutrients and ash.
The specific properties of each bran fraction allow for food scientists to increase levels of fiber, vitamins or minerals by selectively blending the bran fractions into food formulations.
The high dietary fiber content of the outer fraction can be further ground to a fine powder that, when hydrated, produces microscopic "mush balls" that have a mouth feel similar to fat molecules. These fine powders have application as fat replacers and dietary fiber enhancers in a variety of products ranging from meal replacement beverages to cereals and bakery products.
In addition, the phytate level in the dietary fiber fraction is lower than in the other fractions. This leads to use of the dietary fiber fraction in food applications where phytate may be detrimental because of its ability to inhibit the uptake of minerals in the digestive tract.
The inner fraction, high in nucelar and aleurone cell material is also believed to contain elevated levels of folic acid, an important compound that can help reduce birth defects when consumed in sufficient quantities by pregnant women. This fraction also has an elevated level of protein, but generally not the vital wheat gluten type. The vital wheat gluten is contained mainly in the interstitial spaces between the starch granules in the endosperm.
The general characteristics of bran fractions derived from Canadian hard red spring wheat using the Tkac Debranning Process is described in the table shown on page 61.
Benefit No. 7: Value-added products in wheat-ethanol plants.
In wheat ethanol plants, the Tkac Debranning Process can add value by producing high-value human food components at the front of the process, that would otherwise become low-value animal feed at the end of the process. As a result of milling the wheat before the ethanol process, a gluten washing process may be commercially viable, with all residual starches in slurry form sent to the ethanol plant as feed stock.
The production of human food products at the front end of the system converts the usually low-value resultant animal feed byproducts to a much higher value, thus significantly increasing the net revenue from the plant.
In summary, the Tkac Debranning Process offers many opportunities for adding value in wheat milling applications.
Tkac Debranning Process equipment, known as PTMT Technology, is manufactured by the Prokop Milling Machine Company, Pardubice, Czech Republic, and is available worldwide through its sales network.
W. J. (Wally) Butts is a grain processing consultant working mainly with ethanol plants at Wheat Projects International Limited, St. Williams, Ontario, Canada.