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Chemical and Physical Quality Control Parameters in Maize Kernels and Maize Flour

Sweetcorn

Maize (Zea mays L.) is one of the most important cereal crops in the world in terms of production quantity and uses. Maize kernels and maize flour milled from these kernels are used as raw materials for human food, animal feed, and numerous industrial products such as starch, oil, and biofuels. Therefore, ensuring the quality of maize kernels and maize flour is critically important in terms of nutritional value, processability, and shelf life. Quality control of maize involves the analysis of both chemical parameters (such as moisture, ash content, protein, fat content, and starch level) and physical parameters (such as kernel hardness, color, and particle size distribution, ie, granulometry). These quality parameters directly affect the suitability and safety of maize for different uses. For example, moisture content determines storage stability – high moisture accelerates mold growth and mycotoxin formation – while kernel hardness can affect milling efficiency and the texture of the final product. This article reviews the main quality control parameters in maize kernels and maize flour, highlighting typical value ranges and their importance.

Chemical and physical quality control characteristics of maize.

Standard analytical methods are used to measure the chemical and physical quality characteristics of maize. Moisture content is generally determined by drying at 105 °C (or under vacuum) until constant weight is reached; for this purpose, official standard methods such as ISO 6540 or AACC 44-15.02 are used. Ash content (total mineral content) is measured by burning the sample in a muffle oven until constant weight is reached ("burning at 550 °C"; ISO 749 standard). Protein content is determined by nitrogen determination (Kjeldahl or Dumas method) and the amount of nitrogen found is converted to protein by multiplying it by a standard factor (~6.25) (AACC 46-16.01 protocol). Fat (lipid) content is generally determined by solvent extraction (Soxhlet method; AOAC 920.85). Starch content can be determined by enzymatic analysis or indirect calculation; since it is the main component of the maize kernel, starch constitutes approximately 60–75% of the mass.

Appropriate instruments and tests are used to measure physical properties: Color measurement is performed with a colorimeter (L*, a*, b* color values ​​in the CIELAB system). Grain hardness can be measured indirectly by methods such as the flotation test in concentrated salt solution; instruments measuring crushing force or indicators such as hectoliter weight also provide information about hardness. Granulometry (particle size distribution) is analyzed by sieving with standard sieve sets or by laser diffraction methods; the percentage passing through specific sieve openings and the average particle diameter are calculated. All these measurements are performed on representative samples taken from corn kernels or flour, and control samples are analyzed in parallel to ensure the accuracy of the analyses.

Moisture content is a critical quality parameter for both corn kernels and cornmeal. Corn is generally harvested with a high moisture content (20% and above) and then dried for safe storage. For long-term storage, the moisture content of corn is reduced to around 13–14% to prevent mold growth. If corn is stored or milled with high moisture content, harmful molds can grow on it, and the mycotoxins they produce can make the food unsafe. Cornmeal generally has a lower moisture content than the kernel; dry cornmeal with a moisture content below 13% is considered a long-shelf-life product. In practice, the moisture content of commercial cornmeal is mostly kept around 10–12%. Therefore, moisture control is essential.

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Ash is an indicator of the total mineral content of corn. The ash content of a whole corn kernel is approximately 1% on average (typically in the range of 0.7–1.9%). In cornmeal, the ash content indicates the extent to which the mineral-rich bran and germ portions are incorporated into the flour. Whole cornmeal has an ash content similar to that of the kernel (~1.2–1.5%); however, refined cornmeal has a much lower ash content (typically around 0.3–0.5%), as the mineral-containing portions have been largely removed. Measuring ash content is a quality indicator that directly affects the yield and nutritional value of the flour. Achieve maximum efficiency in corn moisture measurement with the Bastak 12000 Ash Oven!

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Protein is one of the main components determining the nutritional value of corn. Corn kernels generally contain 8–11% crude protein by weight, and in common yellow corn varieties, the protein content is usually around 9–10%. Zein proteins, stored in the endosperm, make up the majority of the total protein in corn; the total protein amount can vary depending on the genotype. In refined cornmeal, the protein content may be slightly lower due to the removal of the germ and aleuron layer during milling. Corn kernels contain a significant amount of fat, especially in the germ portion. Typically, the crude fat content of a whole corn kernel is around 3–5%. Since most of the fat concentrates in the germ during milling, whole cornmeal retains this fat; in germinated flours, the fat content is significantly reduced. Fat content directly affects the energy value, flavor, and shelf life of the product. Determine the highest quality corn according to European standards with the Bastak Fat Meter.

Starch is the largest fraction of corn in terms of dry matter, typically ranging from 60–75%. Starch content is a key criterion in determining the energy value and industrial use of corn. Determine the highest quality in dry matter with the Bastak Polarimeter device.

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In conclusion, chemical and physical analyses used in the quality control of corn kernels and corn flour play a critical role in determining the product's suitability, nutritional value, and safety. These analyses are important for optimizing production processes, controlling storage conditions, and improving the quality of the final product. Monitoring the determined parameters in accordance with standards ensures the effective utilization of corn within the sustainable agriculture and food chain. Achieve perfect optimization in your process with Bastak Quality Control Devices, available in 54 different types, conforming to ICC 189 and 192 Standards.