By: Rabia Tiryaki, Food Engineer, Bastak Instruments
Maize (Zea mays L.) is one of the most important cereal crops worldwide in terms of production volume and diversity of use. Maize kernels and the flour derived from them are used as raw materials for human consumption, animal feed, and a wide range of industrial products such as starch, oil, and biofuels. Therefore, ensuring the quality of maize grain and maize flour is of critical importance in terms of nutritional value, processability, and shelf life. Quality control of maize involves the analysis of 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 or granulometry). These quality indicators directly affect the suitability and safety of maize for various uses. For example, moisture content determines storage durability – high moisture accelerates mold growth and mycotoxin formation – while kernel hardness affects milling performance and the texture of the final product. This article reviews the main quality control parameters of maize grain and flour, emphasizing typical value ranges and the significance of each parameter.
Standard analytical methods are used to determine the chemical and physical quality characteristics of maize. Moisture content is generally measured by drying the sample at 105 °C (or under vacuum) until a constant weight is reached; ISO 6540 or AACC 44-15.02 are commonly used official methods. Ash content (total mineral content) is determined by incinerating the sample in a muffle furnace at 550 °C until a constant weight is achieved (ISO 749 standard). Protein content is measured by nitrogen determination (Kjeldahl or Dumas method) and converting the nitrogen value using a standard factor (~6.25) according to the AACC 46-16.01 protocol. Fat (lipid) content is usually measured using solvent extraction (Soxhlet method; AOAC 920.85). Starch content can be measured via enzymatic analysis or by difference; since starch is the major component of maize, it typically makes up about 60–75% of the dry weight.
For physical properties, appropriate equipment and tests are used. Color is measured using a colorimeter based on CIELAB system values (L*, a*, b*). Kernel hardness can be assessed using indirect methods such as floatation tests in salt solutions; additionally, devices that measure crushing force or indicators like hectoliter weight also provide insights. Granulometry (particle size distribution) is measured by sieving with standard mesh sets or using laser diffraction systems to determine the proportion of material passing through specific mesh sizes and the average particle diameter. All of these measurements are conducted on representative samples of maize grain or flour, and control samples are analyzed in parallel to ensure accuracy.
Moisture content is a critical quality parameter for both maize grain and flour. Maize is typically harvested at high moisture levels (20% and above) and then dried for safe storage. For long-term storage, maize is dried to approximately 13–14% to prevent mold development. When stored or milled at high moisture, harmful molds may grow and produce mycotoxins that compromise food safety. Maize flour typically contains less moisture than whole grain; dry maize flours with moisture below 13% are considered shelf-stable. In practice, commercial maize flour usually contains about 10–12% moisture. Therefore, controlling moisture is essential. With the Bastak 16000 Moisture Meter, moisture measurement is performed in 8–10 seconds using the dielectric principle on 40 different raw materials.
Ash content is an indicator of the total mineral content of maize. Whole maize kernels contain approximately 1% ash on average (typically ranging from 0.7% to 1.9%). Ash content in flour reflects how much of the mineral-rich bran and germ is present. Whole grain maize flour has a similar ash level to the kernel (~1.2–1.5%), while refined maize flour has significantly lower ash content (typically 0.3–0.5%) since much of the mineral content is removed during milling. Measuring ash content directly affects flour yield and nutritional quality. Maximize efficiency in ash determination in maize with the Bastak 12000 Ash Oven!
Protein is one of the key components determining the nutritional value of maize. Maize kernels generally contain 8–11% crude protein by weight, with common yellow maize varieties typically having protein levels around 9–10%. Zein proteins stored in the endosperm make up most of the total protein in maize, and the overall content varies depending on the genotype. Refined maize flour may have slightly lower protein content due to removal of the germ and aleurone layers during milling. Enhance your lab experience with the Bastak Protein Analyzer!
Maize kernels, especially the germ, contain a significant amount of oil. Whole maize kernels typically contain about 3–5% crude fat. Since most of the oil is concentrated in the germ, whole grain maize flour retains this oil, while degermed flours have significantly lower oil content. Oil content directly affects the energy value, flavor, and shelf life of the product. Determine the highest quality in maize oil content at European standards with the Bastak Fat Analyzer.
Starch is the major fraction of maize on a dry matter basis, usually ranging from 60–75%. It is a fundamental parameter in determining the energy value and industrial usability of maize. Identify maximum quality in dry matter with the Bastak Polarimeter.
In conclusion, chemical and physical analyses used in the quality control of maize grain and flour play a critical role in determining product suitability, nutritional value, and safety. These analyses are essential for optimizing production processes, controlling storage conditions, and enhancing final product quality. Monitoring the defined parameters in accordance with standards ensures effective utilization of maize within sustainable agricultural and food systems. Achieve perfect process optimization with 54 different types of Bastak Quality Control Devices, all certified under ICC Standards 189 and 192.
