Malawians have a popular saying ‘chimanga ndi moyo’ which translates to ‘maize is life’, and indeed it is particularly in the African continent where it’s milled to make flour for the renowned ugali in both Kenya and Tanzania, nsima in Malawi or pap as South Africans term it.

Maize was introduced to Africa from the Americas between the 16th and 17th century. Before this, sorghum and millet were the staple cereals in most of Sub-Saharan Africa. Maize was readily accepted by African farmers as its cultivation was very similar to that of sorghum but with significantly higher yields. Eventually, maize displaced sorghum as the primary cereal in all but the drier regions.

Since maize is the primary cereal in most African countries, it is vital that any food safety concerns are identified so that appropriate control steps can be taken to thwart human health hazards. Thus far, the major health concerns related to milled maize are contamination with pesticide residues and aflatoxins.

Few Codex MRLs exacerbate pesticide menace

Farmers worldwide rely on pesticides to protect their crops against plant pests and increase yields, which is essential for livelihoods and food security. However, these pesticides often cause trade issues for developing countries agri-food exports since the local Maximum Residue Limits (MRLs) differ from international food safety standards set by the FAO/WHO Codex Alimentarius Commission. When importing countries set their own lower limits, it greatly increases the costs and complexity of trade.

In 2010 a consignment of maize imported to Kenya was found to contain high levels of Aluminum phosphide, a fumigant used to control fungal growth during shipping. The maize was rejected and reshipped back to the country of origin. This incident did underscore the need to monitor maize for chemical contaminants to safeguard human health.

As developed countries phase out second and third-generation pesticides, farmers in Africa have little choice but to use older chemicals because there are few Codex MRLs for newer, less toxic pesticides for their specialty crops. Residue data to establish MRLs and support new product registrations are very rarely generated in developing countries because of increased costs and expected lower profit margins.

The commonest storage pesticides applied as dusting powders are pirimiphosmethyl, an organophosphate (OP) compound mixed with Permethrin, a pyrethroid also known as Actellic. Other dusts powders include malathion (OP), permethrin (pyrethrin), fenitrothion (0p) and fenvalerate (pyrethrin). While these pesticides are used to prolong storage and control pest infestation during storage, no data is available of the residue levels of these pesticides.

It is possible to use most of the approved agricultural chemicals with little food safety impact, provided good practices are used. Nevertheless, investigations need to be undertaken to ascertain if these practices are being actively followed in the production chain.

Mycotoxins a huge economic and health hazard

Maize is susceptible to fungal growth and mycotoxin contamination and this is favored by high temperatures, high humidity as well as other factors such as grain damage by birds or insects, poor postharvest handling, and storage.

The International Food Policy Research Institute reports that on average, 26,000 people in Sub-Saharan Africa die of liver cancer every year through chronic aflatoxin exposure.

Mycotoxins are toxic secondary metabolites of fungi that contaminate food with far-reaching consequences on human and animal health in addition to causing huge economic losses. Regulatory limits offer a guarantee to consumers that the food will not contain toxins in concentrations that are harmful to their health. The first mycotoxin regulations were set in the late 1960s.

As stated by Carlos A. Campabadal, PhD, IGP Institute, Kansas State University, currently there are only two mycotoxins that are known to be produced during grain storage. These two mycotoxins are aflatoxins and ochratoxins that are produced by molds from the Aspergillus family. The rest of the known mycotoxins are produced in the field during the growing phase of grain.

In 2004 aflatoxin contamination of maize occurred in Kenya resulting in 125 deaths. It was observed that the concentration of aflatoxin B1 in maize was as high as 4400 parts per billion (ppb) while the total aflatoxins ranged from 1 ppb to 46,400 ppb which is far greater than the acceptable limit of 5 ppb for aflatoxin B1 (AFB1) and 10 ppb total aflatoxins set by East African Community (EAC) countries.

Kenya’s regulatory watchdog, the Kenya Bureau of Standards (KEBS) has in the past recalled several maize flour brands over contamination with aflatoxin. The country earlier in March 2021 banned the importation of maize from its neighboring countries, Tanzania and Uganda citing high levels of aflatoxin.

Codex has not been able to formulate an internationally acceptable maximum level (ML) for aflatoxin in maize since there is a huge difference in perceived risks, food consumption patterns and the levels of aflatoxin contamination in food produced from different agro-ecological regions.

Countries or regions have been left to formulate their own national or regional MLs. The United States has a 20 ppb and EU a more stringent ML of 4 ppb for total aflatoxins in food.

In developing countries, MLs for total aflatoxins range from 10 to 20 ppb, with 10 ppb being the most frequent. The East African Community (EAC) partner states use an ML of 10 ppb for total aflatoxins in selected foods, cereals, and pulses, which is an EAC-adopted standard as no risk assessment has been done to ascertain the safe level of aflatoxin.

Furthermore, the EAC has not developed a food control system and enforcement mechanism.

Millers “unable” to eliminate pathogens

Compounding the challenges for the industry is an inability to “flip a switch” in milling to eliminate pathogens. The unsuited storage facilities of grains, as well as the wet transformation process, including the unnecessary prolonged tempering and the poor hygienic handling of the flours affect the final product.

Furthermore, it has been shown that enterococci and coliforms are considered as hygiene indicators in the manufacturing process of foods.

Therefore, to avoid food borne illnesses due to enterococci and coliforms, milled maize must be prepared with good manufacturing practices and good conditions of storage. Detection of a high microbial count for yeast and moulds points to improper postharvest and storage handling of the maize grains. The residue built up in milling machines as well as the wet process used can be relevant as additional sources of microbial contamination of commercial samples. Therefore, storage conditions such as relative humidity of atmosphere must be critical control points during processing of maize.

Dealing with sector challenges

In line with the International Organization for Standardization (ISO), the basic food safety concept is that food will not harm the consumer so long as the intended user guidelines are followed when it is prepared. Conversely, food is potentially harmful whenever it has been exposed to hazardous agents and the intended use guidelines have not been followed hence the need to come up with interventions to ensure the prevalent safety threats are nipped at the bud.

A global aflatoxin proficiency testing program grew out of the initial work in Kenya through the Aflatoxin Proficiency Testing and Control in Africa (APTECA) program. In 2014, milling companies were approached by AgriLife, a unique education agency that provides programs, tools, and resources that teach people improved agriculture and food production, personnel and asked to run a known maize flour sample and report their results. Unfortunately, only 20% of the initial participants in the program were satisfied with their laboratory’s aflatoxin test results. To address this deficiency, beginning in 2016, AgriLife teamed up with the Food and Agriculture Organization (FAO) of the United Nations to implement the proficiency testing program in laboratories around the world, including Africa. At the moment, over 200 labs from 62 countries are participating in the program which received ISO accreditation in 2017.

When it comes to shelled maize, the moisture and temperature should be monitored as high levels of moisture and temperature, together with damage to kernels, are the chief reasons for the growth of moulds. Mould growth is negligible when maize moisture content is below 13%. Wet maize should be dried to a temperature of 12-14% as the surest way of limiting mould growth.

If  wet maize is held at moisture levels above 20% – without even a little drying, the temperatures should be maintained as low as possible under some form of aeration or maximum ventilation maintained.

Millers should also employ caution in blending lots of maize that differ substantially in either quality or moisture content. They should not blend maize of 20 percent moisture with 10 percent maize in the notion that the mixed batch will equalize overall at 15 percent. It will not unless the mixing is unusually thorough.

After the maize has been dried to a moisture level adequate for storage, sufficient air flow should be provided to bring the maize to a uniform temperature. Millers should check maize regularly for moisture, heat, mold, insects or off odors and adhere to good sanitation practices, good insect control, and disease control practices.

Essential composition and quality factors: Codex specifications

As with any processed food in the continent, there are various standards laid out by the Codex Alimentarius that each maize miller has to adhere to. The Codex Alimentarius or “Food Code” is a collection of internationally adopted food standards, guidelines and codes of practice adopted by the Codex Alimentarius Commission. While being recommendations for voluntary application by members, Codex standards serve in many cases as a basis for national legislation.

International milling standards differentiate maize flour from maize meal by granulation size, with maize meal consisting of larger, less refined particles. As defined by these standards, what is commonly referred to as maize meal in many African countries is actually maize flour.

Codex stipulates that maize meal should be safe and suitable for human consumption: free from abnormal flavours, odours, insects and filth.

The maximum moisture content for  milled maize is 15.0% m/m with lower moisture limit requirements for certain destinations in relation to the climate, duration of transport and storage.

Milled maize should be free from heavy metals in amounts which may represent a hazard to human health and comply with maximum pesticide residue and mycotoxin limits established by the Codex Alimentarius Commission for this commodity. The MRL for Paraquat, Penthiopyrad, and Phorate pesticides is 0.05mg/kg while that for Propargite is 0.2mg/kg and 0.1mg/kg for Sulfuryl Flouride. The milled maize products shall not exceed total aflatoxin of 10 μg/kg and 5 μg/kg for aflatoxin B1 when tested in accordance with ISO 16050.

It is recommended that the product covered by the provisions of this standard be prepared and handled in accordance with the appropriate sections of the General Principles of Food Hygiene (CXC 1-1969) and other Codes of Practice recommended by the Codex Alimentarius Commission which are relevant to this product.

To the extent possible in Good Manufacturing Practice (GMP), the product shall be free from objectionable matter. When tested by appropriate methods of sampling and examination, the product shall be free from micro-organisms or substances originating from micro-organisms and parasites in amounts which may represent a hazard to health.

The product should be packaged in containers which will safeguard the hygienic, nutritional, technological, and organoleptic qualities of the product. The containers, including packaging material, should be made of substances which are safe and suitable for their intended use. They should not impart any toxic substance or undesirable odour or flavour to the product.



Contaminant And Toxin


Heavy Metal


Arsenic (As)

0.10 ppm max


Copper (Cu)

2.0 ppm max


Lead (Pb)

0.10 ppm max


Cadmium (Cd)

0.02 ppm max


Mercury (Hg)

0.01 ppm max

Pesticide Residues



< 10ppb



< 10ppb



< 10ppb



< 10ppb

Toxic Or Noxious Seeds


Crotolaria (Crotolaria spp.)



Corn cockle (Agrostemma githago L.)



Castor bean (Ricinus com- munis L.)



Jimson Weed (Datura spp.)





10 Bq/Kg max.



Aflatoxin (total B1+B2+G1+G2)

20 ppb max.

Though maize flour is the primary cereal consumed in many African countries, less than 30% of the industrially milled maize on the continent is fortified.

World Food Programme


Micronutrient deficiencies: An unfinished agenda

Micronutrient deficiencies constitute a heavy disease burden that is shouldered disproportionately by a highly vulnerable group in the most vulnerable countries in the world: children under 5 years in Sub-Saharan Africa (SSA). SSA with 11% of the world’s population accounts for more than half of the deaths and half of U5 disability-adjusted life years (DALYs) lost to deficiencies of vitamin A, iron, zinc, and iodine.

Food fortification which is the addition of one or more micronutrients to foods consumed by a large proportion of the general population, has been demonstrated to be an effective public health intervention to improve micronutrient intakes and micronutrient status.

Though maize flour is the primary cereal consumed in many African countries, less than 30% of the industrially milled maize on the continent is fortified.

In 2016, representatives of government, grain milling, and development sectors from 14 countries in Africa met to deliberate the need to scale up maize flour fortification programs. Their work resulted in an Africa Maize Fortification Strategy for 2017-2026. The maize strategy is used as a reference to develop national fortification strategies for implementation by maize consuming countries. The Strategy has been aligned with World Health Organization (WHO); Eastern and Central African Health Secretariat (ECSA), East African Community (EAC), Common Market for Eastern and Southern Africa (COMESA) regulations and guidelines regarding maize fortification.

Maize flour fortification in most African countries is still on voluntary basis. A few countries such as South Africa, Uganda, Kenya, Tanzania, Zimbabwe, Burundi, Nigeria, Malawi and Mozambique have mandatory maize flour fortification legislation. Through the voluntary food fortification programs, the countries and partners have put a lot of efforts to start and scaleup maize flour fortification in Africa. However, even where there is mandatory legislation for maize flour fortification, fortification by millers has been lagging due to the lack of or inadequate industry infrastructure, lack of technology for small commercially packaging mills, the absence of premix distribution mechanism and effective Quality Assurance and Quality Control (QAQC) systems.

The concentration of vitamins and minerals to be added must be calculated based on nutritional requirements and consumption patterns, after which losses during storage and cooking must also be considered. Venezuela, for example, fortifies maize flour with a vitamin-mineral premix containing vitamin A, thiamin, riboflavin, niacin, and iron. Also, certain producers in Zimbabwe and Namibia fortify maize meal with a vitamin–mineral premix containing vitamin A, thiamin, riboflavin, niacin, folate, pyridoxine and iron.

In line with the World Food Program (WFP) specifications, fortified milled maize should comprise of 99.98% maize and vitamin/mineral premix of 0.025% (250g/ton) by weight. It must be fortified to provide the following net micro nutrient supplement per kilogram of finished product:


However, variable levels of micronutrients naturally present in maize may lead to variable amounts of micronutrients in finished product.

Quality control a key aspect in maize milling

Quality control plays a vital part in every stage of the production of milled maize from intake to packing. When it comes to testing, larger mills are at an advantage as they have fully equipped labs where routine checks can be carried out, as opposed to the small millers who cannot afford to equip and run such labs. Some of the basic tests that need to be conducted are moisture content, speck tests (black specks appear when the tip cap of the maize is not removed on the degerminator and ground up on the roller mill) and cooking test where maize meal products are cooked, tested and qualities such as taste and texture are noted.

The moisture content of the flour is important to ensure that the flour will be stable during storage. Flour containing more than 14.5% moisture is prone to mold and bacterial growth. It is also necessary to know the moisture content of the flour in order to adjust flour test data to a constant moisture basis. Commonly used moisture basis varies by country so the basis used should also be reported. Protein content is the basis by which flour is bought and sold and is one of the main factors controlling the price.

Control labs grapple to detect minute levels of mycotoxin

Across the world, the occurrence of mycotoxins in foods and feeds is actively monitored by food and feed business operators, official control laboratories and research organizations either to determine the regulatory compliance or the quality of foods and feeds. Analytical methods are generally well established for many mycotoxins; currently liquid chromatography (LC) based methods coupled to tandem mass spectrometry (MS) are probably the most widely applied and preferred.

The current trend in mycotoxin analysis seems to be on the one hand to reach ever lower concentration levels and multi-mycotoxin and full metabolite profiles, and on the other hand to determine the compliance at the statutory levels by fast on-site techniques. The current multi-analyte and multi-class analytical methods are capable of a high throughput of samples making larger amounts of results available than ever before in a short period of time.

The analysis at the low concentrations requires not only advanced and expensive techniques but also experienced human resources and time. These reasons typically limit the routine control laboratories to analyze mycotoxins at their lowest possible limits of detection/limits of quantification (LODs/LOQs) the method is capable to. They rather operate with pragmatic fit-for-purpose methods in the region of the legal mycotoxin maximum levels (MLs).

Large scale processors and contract analytical laboratories can utilize end-to-end automated ELISA workflows which provide high throughput solutions for economical and accurate screening up to 1ppb in grains. Where confirmatory tests are needed, advanced LC/MS/MS technologies provide a sensitive tool to screen multiple mycotoxins simultaneously at high parts per trillion (ppt) concentrations.

Combustion Analysis and Near-infrared spectroscopy for protein analysis

Combustion analysis is an automated and rapid method which is replacing the Kjeldahl method as the standard method of analysis for protein content in food and animal feeds.

There are many different protein combustion instruments which all have the same basic operating principle. A sample of known mass is combusted in a high temperature chamber (about 900°C) in the presence of oxygen which causes the release of carbon dioxide, water and nitrogen gases. The carbon dioxide and water are absorbed and the nitrogen is separated out and quantified using special columns. Nitrogen content is then used to calculate crude protein content using conversion factors.

Near-infrared spectroscopy (NIR) can also be used to directly measure protein content. It is the fastest and easiest method to run. An advantage of NIR is that the moisture and protein contents as well as many other properties of the flour can be measured simultaneously.

PerkinElmer takes lead with new state-of-art innovations

To make first-pass testing easier at the grain elevator to the lab bench and for small-scale labs, many in the industry are utilizing rapid lateral flow testing strips given their intuitive methodology and reliability. The cost-effective lateral flow strips require little user training and the simplicity of the design contributes to the speed of testing making it the ideal solution for ingredient intake monitoring. With this the manufacturers can verify whether they are sourcing quality ingredients from trusted suppliers or if further testing needs to be done.

In 2018, PerkinElmer debuted QSight Triple Quad 400 Series (a LC/MS/MS system) which provides advanced confirmation testing and analyzes multiple types of mycotoxins — like aflatoxin, vomitoxin, zearalenone, fumonisin, T-2 and Ochratoxin A. Come 2019, the company introduced a lateral flow test named, AuroFlow AQ Afla strip test with QuickSTAR Horizon strip reader to help lab professionals, technicians and farmers conduct first-round screening for aflatoxins in corn (including B1, B2, G1, and G2) down to 2-300 ppb detection levels, in six minutes. This solution features a single-step, water-based extraction method with lateral flow testing at room temperature — enabling safe and easy sampling without incubators and centrifuges. The handheld reader is battery operated and rugged, supporting flexible in-field testing. Results are easy to view on the reader’s menu-driven color touchscreen and then stored and archived for further reference and audit trails.

Ash content is often used as a measure of the grade or type of flour because it shows how much bran is present in the flour. Flours milled using a low extraction rate are premium products with low ash contents that can be sold for a higher price than flours milled with a high extraction rate that includes more bran and higher ash. The Perten Inframatic 86 series NIR with ash kit (AACCI Approved Method 08-21.01), one of PerkinElmer’s inventions, is the only NIR currently specified in an approved method to measure ash content. This instrument allows the user to adjust the bias and slope in the NIR calibration so the measured values are more accurate. The adjustments are calculated by analyzing a reference set of flours using both the NIR and the muffle furnace ash method.




Chemical Form

Vitamin A

1.0 mg/kg

Dry Vitamin palmimate 250 n.s

Vitamin B1

4.4 mg/kg

Thiamine monomitrate

Vitamin B2

2.6 mg/kg


Vitamin B3

35.0 mg/kg


Folic Acid

1.0 mg/kg

Folic acid

Vitamin B12

0.008 mg/kg



15 mg/lg



30 mg/kg

Zinc Oxide

This feature appeared in the March/April 2022 issue of Food Safety Africa. You can read the magazine HERE