18 February 202014 min reading

The quality control is an important part of the flour milling industry. The objectives of the quality control laboratory at a flour mill are to monitor uniformity throughout the mill run; ensure uniformity between flour shipments; ensure that the flour meets the customer’s specifications, and verify that the flour has desirable characteristics for a product. Millers should consider quality control the core of their operations.

The utmost priority of every manufacturing company and specifically flour millers is to compete favorably and possibly control the largest market share. This ambitious goal can only be achieved by the production of consistently good quality products for the customers. The companies that are investing in quality departments to improve the quality of their final products and meeting customer’s expectations have an outstanding profile to gain a major position in the market.

Quality control and quality assurance in field of flour milling also plays great role in food security. The implementation of quality system such as; quality management system, food safety, HACCP and health and safety systems has developed the environment of production, reduce the waste of food and raw materials which used to happen in the past as a result of mishandling and lack of quality approach. Nowadays quality members took the responsibility for inspections of coming raw materials, flow up the proper storage practices and required pest control applications which are practices help to save the product. The food safety and ISO certification had belt trust and prepare the atmosphere to maintain food safety and security.

High-quality flour cannot be produced from low-quality wheat, or from high-quality wheat in a failed manufacture. Wheat quality characteristics change according to the user (farmer, miller, and end-user). The millers need to control on both raw materials and manufacture to produce a good flour baking quality and continuous uniformity.

The wheat flour quality is determined by its suitability for a specific final product. Flour quality characteristics are affected not merely by wheat suitability for the specific final product, which can be determined by some wheat quality characteristics classified as direct factors, but by the type of processing equipment and the suitability of this kind of wheat for milling process all classified as indirect factors.

The manager of a mill laboratory has to manage all of the wheat, milling streams, and produced flour characteristics. The quality department and lab facility should be as much as possible closed and nearby the mill, providing the service of sampling, inspections, analysis, and reporting, with reliable quality plan and system.

It is important to use appropriate standard methods and procedures in the flour quality testing laboratory. Common standard methods used in the food industry that are most applicable to a milling quality control laboratory are published by the American Association of Cereal Chemists International (AACCI) and the International Association for Cereal Science and Technology (ICC).

The production of uniform bakery products requires control over the raw materials used in their formation. Flour is a biological material and when obtained from different sources can vary considerably in its protein quality, protein quantity, ash, moisture, enzymatic activity, color, and physical properties. The baker needs to be aware of any variations in these characteristics from one flour shipment to the next. The purpose of flour testing is to measure specific characteristics of flour. Ideally, the results of these tests can be related to the flour’s performance in the bakery.

MOISTURE The moisture content of the flour is important for two reasons. Firstly, the higher the moisture content, the lower the number of dry solids in the flour. Flour specifications usually limit the flour moisture to 14% or less. It is in the miller’s interest to hold the moisture as close to 14% as possible. Secondly, flour with greater than 14% moisture is not stable at room temperature. Organisms naturally present in the flour will start to grow at high moistures, producing off-odors and flavors.

ASH Ash is the mineral material in flour. The ash content of any given flour is affected primarily by the ash content of the wheat from which it was milled and it’s milling extraction. The goal of milling is to separate the endosperm from the non-endosperm parts of the wheat kernel. This separating is difficult and never clean. Thus, there is always contamination of endosperm with non-endosperm and vice versa. As flour yield is increased, the amount of contamination with non-endosperm increases and the ash content increases. Thus, the ash content is a good and sensitive measure of the contamination of the endosperm.

PROTEIN The flour protein content is an important parameter for bread flour. Flours containing higher protein content are more expensive than flours of lower protein content. Likewise, flours with very low proteins for cakes are also more expensive. There is usually, but not always, a good correlation between protein content and bakery performance of flour. The quantity of protein is extremely important in the baking performance of flour.

FREE FATTY ACIDS The level of free fatty acids in flour milled from sound wheat is very low. However, if either the wheat or the flour is subjected to poor storage conditions (high moisture and/or high temperature), enzymes will degrade the native grain lipids and produce free fatty acids. Thus, the level of free fatty acids is a good measure of the storage conditions of either the grain or the flour. Flours with high levels of free fatty acids will be more subjected to rancidity than will sound flours. This is of little importance in bread but quite important in dry products (cookies, crackers, croutons, pretzels, etc.).

DAMAGED STARCH The starch in wheat occurs as partially crystalline granules. When placed in excess water, the granules will absorb about 30% of their weight. The crystallinity of the granules restricts it from absorbing additional water. During milling, some of the granules are damaged. The damage results from the shear of the granule during roller milling. The shear shatters/ruptures some of the crystals. The damage may include the entire granule or just a part of it. This loss of crystals allows the granule to take up more water and swell more. Damaged starch will absorb as much as 300X its weight in water. Hard wheat flour contains a much higher level of damaged starch than does soft wheat. This is because the soft wheat crushes easily during milling and does not subject the starch to as much shear.

Damaged starch is a positive factor in bread flour because it increases the water absorption. High water absorption increases the yield of dough and bread from flour, which has obvious positive effects on bakery profits. Damaged starch is a strong negative in flours for cookies and other dry finished products.

The damaged starch is highly susceptible to α- amylase attack. Much of the damaged starch is degraded to maltose and small dextrins by the combination of α- and β- amylase. This is the major reason that bread flours are malted (α- amylase added) at the mill. If the damaged starch is not removed during fermentation it interacts with the gluten and reduces bread volume. Most hard wheat flours will have from 6-9% damaged starch by the AACC procedure.

COLOR Flour color is important because it affects the crumb color of the finished product. The color of the flour used for variety bread, that has a dark color because of non-wheat components in the formula, is not important. Unbleached flours have a creamy color because of the presence of carotenoid pigments in the endosperm. The level of these pigments and therefore the color of the flour will vary from flour to another. The level of pigments is under genetic control. The pigments can be readily bleached with benzoyl peroxide (mixed with the dry flour at the mill) or by enzyme active soy flour in the bread formula.

Flour color can be judged by visual comparison with standard patent flour. In the Pekar (slick test), the sample flour is slicked alongside the standard sample and their colors compared visually. This procedure is also useful to determine if the sample is contaminated with bran. Any color differences between the samples can then be readily evaluated.

ENZYME ACTIVITY Although flour contains a large number of enzymes, only a few are measured and/or controlled. The most important enzymes in bread flour are the amylases. Beta-amylase is found in sufficient quantities in all flours. It has no action on native starch granules but does attack gelatinized and damaged starch. It acts from the non-reducing end of the gelatinized starch chain to produce maltose. It cannot go past a branch point so its action is stopped with a large part of the molecule still intact. This is called the beta limit dextrin. It will convert about 30% of the amylase and 45% of the amylopectin to maltose.

The other amylase of importance in wheat flour is α-amylase. Flour milled from sound wheat contains little or no α-amylase. Bread produced from flours with low levels of α-amylase will be low in volume and have a rough-textured crumb. Thus, it is common to add malted barley or malted wheat flour to increase the α-amylase activity. Some millers will add fungal amylase preparations to increase the α-amylase activity. This requires a modified method of analysis. Although sound grain contains low levels of α-amylase, the level of activity increases rapidly if the grain is sprouted. This greatly increases the level of α-amylase and other enzymes.

α-Amylase Activity α-Amylase breaks the α-1 – 4 bonds in starch in a more or less random attack. It is not truly random as it does not break those bonds near a α-1 – 6 branch point. Because of its attack pattern, each break dramatically reduces the size of the resulting dextrin. As a result, the viscosity of the starch-water paste decreases rapidly. This is why α-amylase is sometimes referred to as the liquefying enzyme. Because of the rapid decrease in viscosity with each bond broken, the measurement of viscosity is a sensitive measure of enzyme activity.

The following three methods to measure α-amylase activity are all viscosity measuring procedures.

1) Falling Number The falling number apparatus consists of a boiling water bath, matched test tubes (to conduct heat at the same rate), a stirrer, a stirring apparatus, and a timing mechanism. Flour plus a known amount of excess water is placed in a test tube and shaken to disperse the flour. The tube is placed in the apparatus that stirs the sample as if it is heated. At the end of stirring, the stirrer is dropped from the top position. The number of seconds required for the stirrer to fall through the flour-water paste is the falling number.

Sound flour will have a falling number of 400 seconds or greater. Increased enzyme activity will decrease the falling number. Flour milled from badly sprouted wheat may have falling numbers of 50 to 100 sec. Bread flours are generally adjusted to 250-300 seconds. The procedure is rapid and reasonably reproducible. It can be used for either whole-wheat meal or flour.

2) Amylograph In this procedure, flour and a buffer solution are stirred in a rotating bowl that is heated by an air bath. The sample is heated from room temperature to 95˚C (203˚F) at a rate of 1.5˚C/minute. If one is only interested in the α-amylase activity, the test can be ended when the slurry reaches 95˚C (203˚F). If the flour contains no α-amylase activity the viscosity (consistency) of the sample will continue to increase as the temperature rises to 95˚C. Optimally treated bread flours are in the range of 400-600 BU. If there is increased enzyme activity, the curve will peak at a lower viscosity (consistency) and at a lower temperature. The peak height is taken as the measure of enzyme activity. The amylograph procedure is relatively slow The procedure is reproducible and still widely used to control the level of malt addition.

3) Rapid Visco Analyzer (RvA) The RvA was developed as a faster and more rugged version of the amylograph. Stimulating the amylograph, the temperature control can be programmed to heat at various rates. This viscosity is determined by the load on the stirring motor. As is the case with the amylograph, the height of the viscosity vs. temperature curve is related to the α-amylase activity of the sample. Because of the flexibility in controlling heating/cooling profile, the RVA has found many uses in cereal laboratories in addition to determining α-amylase activity. The RVA can also stimulate the falling number method when samples are heated at 95˚C (203˚F) for three minutes. The stirring number is reported as the viscosity at the test’s end.

PROTEOLYTIC ACTIVITY Proteolytic enzymes hydrolyze proteins. Proteolytic activity can be divided into two basic types. Some enzymes hydrolyze an amino acid from the end of a protein molecule while other proteolytic enzymes attack the protein chain internally. The attack is not random but instead occurs between specific amino acids. The two types of the enzyme are classified as exo- (which releases amino acids from the exterior) and endo- (which breaks the protein chain internally).

• Soluble Nitrogen The most popular method is to measure soluble nitrogen produced from a suitable substrate. The buffered enzyme is incubated with hemoglobin (substrate) for a suitable time. The protein is precipitated and the remaining soluble nitrogen determined. The results are reported as hemoglobin units (H.U.). This is a very popular method to measure proteolytic activity but it can be misleading. The test is biased to measure exo-enzyme activity. There can be considerable endo-activity with little or no soluble nitrogen produced. Additionally, flour proteins may be degraded differently than hemoglobin.

• Rheological Measurement The chemical determination of endo-proteolytic activity is complicated and difficult. Because the endo-proteolytic enzyme significantly reduces the size of the protein molecule by its activity, it changes the rheological properties (viscosity or consistency) of the system. Thus, the dough becomes more viscous and less elastic as the result of the endo-proteolytic activity. The enzyme activity can then be estimated by following the change in rheological properties as a function of time. One of the advantages of using a rheological test is that it is not affected by the exo-proteolytic activity. Reducing the size of the protein by one amino acid is insignificant from a rheological viewpoint. The other advantage is that the substrate used (native gluten) and the conditions of the test (dough) both apply directly to our area of concern. A number of rheological tests have been used to follow endo-proteolytic activity. The most appropriate appears to be the extensograph, alveograph, and lubricated compression.

GLUTEN INDEX Gluten index provides a qualitative measure of the gluten forming proteins. Gluten separated from the whole wheat meal or wheat flour by the Glutomatic equipment is centrifuged to force wet gluten through a specially constructed sieve under standardized conditions. The percentage of wet gluten remaining on the sieve after centrifugation is defined as the Gluten Index. If the gluten is very weak, all of the gluten may pass through the sieve, the gluten index is 0. When nothing passes through the sieve, the index is 100.

It is pertinent to point out that all the outlined objectives cannot be achieved without full cooperation from all the stakeholders and most importantly ownership of quality by stakeholders. However, implementation of some of the quality control objective is not always acceptable to the millers because while the quality control ensures that sampled products conform to set standards by subjecting them to tests and if an off-norm situation is detected in some of the samples. Depending on how critical nature of the off-norms, it may require mills being shut down before the exception could be corrected, bagging operations being halted or some bagged products being quarantined for proper checks before their eventual release after passing the quality checks. The ability of quality control in propagating the culture of quality as the responsibility of everyone as well as the ability to embark on quality education to make all stakeholders interested in the production of quality products.

The importance of quality control cannot be over-emphasized thereby making it expedient on all flour mills that want to be competitive, remain in business and profitable need to appreciate quality’s contribution and be ready for investment in its personnel and operation.

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  • Fit for the digital laboratory with a ‘Smart Workflow’ The precise measurement of ingredients and rheological parameters is a key prerequisite for quality management in day-to-day laboratory work for the milling, baked goods, and starch industries as well as the grain sector and other sectors in the food industry. With its digital “Smart Workflow” concept for the laboratory of the future, Brabender is focusing on more transparency and higher efficiency via the automated transmission of measured values, clear data management, web-based data transfer, time savings, and the associated cost savings. [button color="red" size="small" link="" icon="" target="true"]Read More »[/button]
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