Indian agricultural researcher Pooja Bhatnagar-Mathur, a Principal Scientist at CIMMYT, says aflatoxin, a toxin produced from soil fungus and found in groundnuts like peanuts, is a serious public health and food safety problem around the globe.
For centuries, people across Mexico and Central America have been using a traditional method, known as nixtamalization, to process their maize.
Now carried out both at household and industrial levels, this technique offers a range of nutritional and processing benefits. It could easily be adopted by farmers and consumers in other parts of the world.
What is nixtamalization?
Nixtamalization is a traditional maize preparation process in which dried kernels are cooked and steeped in an alkaline solution, usually water and food-grade lime (calcium hydroxide).
After that, the maize is drained and rinsed to remove the outer kernel cover (pericarp) and milled to produce dough that forms the base of numerous food products, including tortillas and tamales.
How does it work?
What happens when maize kernels are nixtamalized?
The cooking (heat treatment) and steeping in the alkaline solution induce changes in the kernel structure, chemical composition, functional properties and nutritional value.
For example, the removal of the pericarp leads to a reduction in soluble fiber, while the lime cooking process leads to an increase in calcium content. The process also leads to partial starch gelatinization, partial protein denaturation — in which proteins present in the kernel become insoluble — and a partial decrease in phytic acid.
What are the benefits of processing maize in this way?
In addition to altering the smell, flavor and color of maize products, nixtamalization provides several nutritional benefits including:
These nutritional and health benefits are especially important in areas where maize is the dietary staple and the risk of aflatoxins is high, as removal of the pericarp is thought to help reduce aflatoxin contamination levels in maize kernels by up to 60% when a load is not highly contaminated.
Additionally, nixtamalization helps to control microbiological activity and thus increases the shelf life of processed maize food products, which generates income and market opportunities for agricultural communities in non-industrialized areas.
Where did the practice originate?
The word itself comes from the Aztec language Nahuatl, in which the word nextli means ashes and tamali means unformed maize dough.
Populations in Mexico and Central America have used this traditional maize processing method for centuries. Although heat treatments and soaking periods may vary between communities, the overall process remains largely unchanged.
Today nixtamalized flour is also produced industrially and it is estimated that more than 300 food products commonly consumed in Mexico alone are derived from nixtamalized maize.
Can farmers and consumers in other regions benefit from nixtamalization?
Nixtamalization can certainly be adapted and adopted by all consumers of maize, bringing nutritional benefits particularly to those living in areas with low dietary diversity.
Additionally, the partial removal of the pericarp can contribute to reduced intake of mycotoxins. Aflatoxin contamination is a problem in maize producing regions across the world, with countries as diverse as China, Guatemala and Kenya all suffering heavy maize production losses as a result. While training farmers in grain drying and storage techniques has a significant impact on reducing post-harvest losses, nixtamalization technology could also have the potential to prevent toxin contamination and significantly increase food safety when used appropriately.
If adapted, modern nixtamalization technology could also help increase the diversity of uses for maize in food products that combine other food sources like vegetables.
Cover photo: Guatemalan corn tortillas. (Photo: Marco Verch, CC BY 2.0 DE)
B.M. Prasanna, Director of CIMMYT’s Global Maize Program and the CGIAR Research Program on Maize, is interviewed by France 24 on the aflatoxin crisis in Kenya. Watch here.
New research evidence could have significant implications for breeding approaches to combat harmful aflatoxin contamination in maize while simultaneously contributing to alleviate vitamin A deficiency. The study “Provitamin A Carotenoids in Grain Reduce Aflatoxin Contamination of Maize While Combating Vitamin A Deficiency” is the first published report to document how biofortification with provitamin A can contribute to reduce aflatoxin contamination in maize.
Aflatoxins are harmful compounds that are produced by the fungus Aspergillus flavus, which can be found in the soil, plants and grain of a variety of legumes and cereals including maize. Toxic to humans and animals, aflatoxins are associated with liver and other types of cancer, as well as with weakened immune systems that result in increased burden of disease, micronutrient deficiencies, and stunting or underweight development in children.
Efforts to breed maize varieties with resistance to aflatoxin contamination have proven difficult and elusive. Contamination of maize grain and products with aflatoxin is especially prevalent in low- and middle-income countries where monitoring and safety standards are inconsistently implemented.
Biofortification also serves to address “hidden hunger,” or micronutrient deficiency. Over two billion people are affected globally — they consume a sufficient amount of calories but lack essential micronutrients such as vitamins and minerals. Vitamin A deficiency specifically compromises the health of millions of maize consumers around the world, including large parts of sub-Saharan Africa.
Provitamin A-enriched maize is developed by increasing the concentration of carotenoids — the precursors of vitamin A — and powerful antioxidants that play important roles in reducing the production of aflatoxin by the fungus Aspergillus flavus. The relative ease of breeding for increased concentrations of carotenoids as compared to breeding for aflatoxin resistance in maize make this finding especially significant as part of a solution to aflatoxin contamination problems.
Breeding of provitamin A-enriched maize varieties is ongoing at the International Maize and Wheat Improvement Center (CIMMYT) and the International Institute of Tropical Agriculture (IITA), with the support of HarvestPlus. Several varieties trialed in sub-Saharan Africa have demonstrated their potential to benefit vitamin-deficient maize consumers.
The researchers highlight the potential in breeding maize with enhanced levels of carotenoids to yield the dual health benefits of reduced aflatoxin concentration in maize and reduced rates of vitamin A deficiency. This result is especially significant for countries where the health burdens of exposure to aflatoxin and prevalence of vitamin A deficiency converge with high rates of maize consumption.
Read the full study here: https://www.frontiersin.org/articles/10.3389/fpls.2019.00030/full
Financial support for this study was partially provided by HarvestPlus, a global alliance of agriculture and nutrition research institutions working to increase the micronutrient density of staple food crops through biofortification. The views expressed do not necessarily reflect those of HarvestPlus. The CGIAR Research Program on Maize (MAIZE) also supported this research.
This research builds on the Ph.D. dissertation of Dr. Pattama Hannok at University of Wisconsin, Madison, WI, United States (Hannok, 2015).
NAIROBI, Kenya (CIMMYT) — Smallholder farmers in sub-Saharan Africa lose up to a third of their grain after harvest because they often use poor grain storage technologies and ineffective drying practices. Staples like maize stored on-farm are exposed to infestation by insects and fungi. These can lead to contamination with mycotoxins, in particular aflatoxins, poisonous food toxins produced by Aspergillus fungi.
At high doses, aflatoxins can kill. Prolonged exposure to aflatoxins can impact consumers’ health, suppressing immune systems, hindering child growth and even causing liver cancer. Kenya is a particular hotspot for aflatoxins, as regular studies show widespread contamination along the food chain, from maize grain to milk and meat.
Preliminary findings of a study by USAID-funded Feed the Future Innovation Lab for Food Processing and Post-Harvest Handling (FPL) suggest that innovative low-cost grain drying and storage technologies such as hermetic bags and hygrometers could prevent post-harvest crop losses and harmful aflatoxin contamination.
The initial results were shared at a workshop in Nairobi on October 25, 2018, as part of the FPL project, which aims to develop and disseminate affordable and effective post-harvest technologies suited to the African smallholder farmer. This project is a collaboration between the International Maize and Wheat Improvement Center (CIMMYT), Kenya Agricultural & Livestock Research Organization (KALRO) and Purdue University.
A study conducted between May 2017 and May 2018 in Kiboko, Kenya, compared the performance of various hermetic storage containers and bags by different manufacturers with farmers’ usual storage practices. Researchers measured maize grain quality parameters such as grain damage, weight loss in storage, fungal growth and mycotoxins, food quality and seed germination. The results showed hermetic bags were highly effective in averting grain loss for up to one year.
“If these bags are sealed properly, oxygen cannot get in or out. This creates an anaerobic environment that suffocates grain-damaging insects and prevents fungi from growing” says CIMMYT economist Hugo De Groote.
Making hermetic storage more accessible
The Africa Technical Research Center (ATRC) is involved in the development of some of the hermetic bags that were tested during the study. ATRC director Johnson Odera noted that most of the insect infestations start in the field. “When the farmer harvests and transports the maize home, the grain is already infested,” Odera explained. “The damage can be extensive depending on the level of infestation. One of the ways to minimize the losses, while keeping the food safe for consumption is to use hermetic bags”.
These bags, however, remain largely unavailable to smallholder farmers, according to the study. This is mainly due to farmers’ low awareness levels and the high cost of hermetic bags. Unlike normal storage bags that cost about $0.7 each, hermetic bags retail for $2 to $2.5.
A second study, conducted with maize producers and traders in Kakamega, western Kenya, suggests that dropping prices by 20 percent had the potential to increase sales by 88 percent.
This study further suggested that farmers can benefit a lot from using low-cost hygrometers to accurately measure moisture content in maize. Grain is quickly spoiled by fungi contamination if it is not dry enough when stored. One or two percent lower moisture levels can make a big difference in reducing aflatoxin contamination.
“Farmers could put maize grain samples in a plastic bag and insert low-cost hygrometers to read moisture content after temperature is stabilized in 15 minutes,” says Purdue University professor Jacob Ricker-Gilbert. “They then know if their grain is safe enough for storage or not. However, standard hygrometers cost around $100, which is out of reach for many small farmers.”
Purdue University, CIMMYT and KALRO conducted a market survey in 2017 among maize farmers and traders in Kenya to assess their willingness to buy low-cost hygrometers. The survey found that farmers were willing to pay an average price of $1.21 for a hygrometer, while traders said they would buy at $1.16 each. The project was able to get cheap and reliable hygrometers at less than one dollar, opening the door for possible commercialization. One company, Bell Industries, has started to market the devices as a pilot.
Raising farmers and policymakers’ awareness on appropriate storage and drying technologies is now a priority for scientists working on the FPL project, which will hopefully lead to less maize spoiled and better food safety.
Exposure to more frequent and intense climate extremes is threatening to reverse progress towards ending hunger and malnutrition. New evidence points to rising world hunger. A recent FAO report estimated the number of undernourished people worldwide at over 800 million. Severe food insecurity and undernourishment are increasing in almost all sub-regions of Africa, as well as across South America.
“It’s very important to ensure food security,” says CIMMYT maize quality specialist Natalia Palacios. “But we also have to focus on food nutrition, because increasing yields doesn’t always mean that we’re improving food quality.” Food quality, she explained, is affected not only by genetics, but also by crop and postharvest management practices. As head of CIMMYT’s maize nutritional quality laboratory, Palacios’ work combines research on all three.
As she prepares to attend the World Food Prize in Des Moines, Iowa – which this year recognizes the contributions of those working to combat malnutrition and ensure food and nutrition security – Palacios discusses ways in which she and CIMMYT colleagues work to address health and nutrition challenges.
What role can CIMMYT play in addressing global nutrition challenges?
Nutrition is an interdisciplinary issue, so there are several ways for CIMMYT to engage. In breeding, there’s a lot we can do in biofortification—which means to increase grain nutrient content. The CIMMYT germplasm bank, with its more than 175,000 unique collections of maize and wheat seed, is an invaluable source of genetic traits to develop new nutritious and competitive crops.
CIMMYT also addresses household nutrition challenges, including food availability, proper storage, and consumer behavior and choice. In cropping systems, the Center studies and promotes diversification, agroforestry, and improved soil health and farming practices, and at the landscape level it examines the role of agricultural practices. Gender research and foresight allow us to identify our role in the evolving setting of agri-food systems and rural transformation. We are prioritizing areas where CIMMYT can play a key role to address global nutrition challenges and partner effectively with leading nutrition groups worldwide.
How does the biofortification of staple crops like maize and wheat help to improve nutrition?
CIMMYT biofortification research has focused on micronutrients such as provitamin A in maize and zinc in both maize and wheat, to benefit consumers whose diets depend on those crops and may lack diversity. Biofortification must be complemented by enhanced dietary diversification and education for better nutrition.
How important are processing and post-harvest storage in terms of ensuring high-nutritional quality?
Research on post-harvest processing and storage is key to our work. A critical topic in maize is monitoring, understanding, and controlling aflatoxins—poisonous toxins produced by molds on the grain. CIMMYT has worked mainly to develop aflatoxin-tolerant maize, but recent funding from the Mexican food industry has enabled us to launch a small, more broadly-focused study.
In the past, aflatoxins showed up every three or four years in Mexico, and even then at fairly low levels. Aflatoxin incidence has lately become more frequent, appearing almost every year or two, as climate changes expose crops to higher temperatures and fungi are more likely to develop in the field or storage, especially when storage conditions are poor.
What are the implications of high aflatoxin incidence for health and nutrition?
The implications for health and nutrition are huge. High consumption can affect the immune system and lead to pancreatic and liver cancers, among other grave illnesses.
How easy is it to tell if a kernel is contaminated?
It’s impossible to tell whether grain is contaminated without doing tests. The chemical structure of the toxin includes a lactone ring that fluoresces under UV-light, but this method only tells you whether or not the toxin is present, and results depend contamination levels and kernel placement under the lamp.
We’re spreading the lamp method among farmers so they can detect contamination in their crops, as well as making other of our other methods more accessible and less expensive, for use by farmers and food processors.
A novel approach allows the detection of aflatoxin-producing fungi in maize fields. A new study explains the technique and how it was tested. “Detection of Aflatoxigenic and Atoxigenic Mexican Aspergillus Strains by the Dichlorvos–Ammonia (DV–AM) Method” was developed in collaboration between scientists from the International Maize and Wheat Improvement Center (CIMMYT), the Japanese National Agriculture and Food Organization (NARO) and Fukui University of Technology, funded in part by the CGIAR Research Program on Maize (MAIZE).
Aflatoxins are harmful compounds produced by the fungi Aspergillus flavus, which can be found in the soil, plants and grain of a variety of cereals and commodities including maize, nuts, cottonseed, spices and dried fruit. The toxic carcinogenic qualities of aflatoxins pose serious health hazards to humans and animals when contaminated crops are ingested. These health risks include cancers of the liver and gallbladder, stunted development in children, premature births and abnormal fetal development.
Not all strains of A. flavus produce aflatoxins however, so it is important to be able to detect and distinguish between A. flavus strains that are benign (atoxigenic) and those that produce dangerous toxins (aflatoxigenic). Current methods of detection are often complicated by the fact that the fungal strains display very similar physiological and molecular traits, thus a new approach is required.
In the study, a novel approach to detect and distinguish A. flavus strains was tested. Using soil samples from a CIMMYT experimental maize field in Mexico, fungal isolates were chemically treated in-line with a method recently developed in Japan, resulting in a color change indicative of toxicity. The method was found to be effective and accurate in the detection of the aflatoxigenic strains of the fungus.
This study is foundational work in the development of a simple, cost-effective and efficient method of detecting aflatoxigenic strains of A. flavus, which will help inform growers about the potential aflatoxin contamination of their crops. This is of particular importance in the developing world, where the resources for effective control of the fungus are often lacking.
To read the original study, “Detection of Aflatoxigenic and Atoxigenic Mexican Aspergillus Strains by the Dichlorvos–Ammonia (DV–AM) Method”, please click here.
Original citation: Kushiro, M.; Hatabayashi, H.; Yabe, K.; Loladze, A. Detection of Aflatoxigenic and Atoxigenic Mexican Aspergillus Strains by the Dichlorvos–Ammonia (DV–AM) Method. Toxins 2018, 10, 263.
This article was originally published on the website of the CGIAR Research Program on Maize.
Check out other recent publications by CIMMYT researchers below:
NAIROBI, Kenya (CIMMYT) — Although maize is a staple food for millions of Kenyans it is usually consumed in one of five ways: roasted or boiled; mixed with beans, or in ugali (a dough-like dish made from maize flour, millet flour or sorghum flour) and porridge. This is nothing compared to over 600 dishes derived from maize in Mexico, about 300 of them made through a process called nixtamalization or lime-cooking.
The process includes cooking and steeping dried maize grain in water and food-grade lime (calcium hydroxide), rinsing the maize to remove the outer kernel cover (pericarp) and milling it to produce dough that can be consumed in different ways, according to Natalia Palacios, maize quality specialist at the International Maize and Wheat Improvement Center (CIMMYT). This method, first developed in Mesoamerica where the crop was originally cultivated, has existed in the region for thousands of years.
If adapted, modern nixtamalization technology could increase maize uses and offer Kenyans invaluable benefits. Food-grade lime is rich in calcium, providing nutritional and health benefits. Nixtamalized food products such as tortillas (small circular-shaped flatbreads) are said to have same nutritional value as milk. About 94 percent of Mexicans eat tortillas, with 79 kilograms (174 pounds) per capita being consumed in rural areas and 57 kilograms per capita in urban areas every year.
By removing the pericarp, the technology contributes to reduce aflatoxin fungal contamination levels in maize kernels by 30 to 60 percent. Due to aflatoxins, Kenya has suffered maize production losses and, more importantly, a loss of human lives. In 2004, 124 people died due to aflatoxin contamination, and 155,000 90-kilogram bags of maize had to be discarded, according to government reports. Nixtamalization technology may therefore also contribute to increasing food safety for Kenyan consumers, who, according to the U.N. Food and Agriculture Organization, are not fully aware of the harvest, drying and storage techniques necessary to prevent mycotoxin growth and contamination.
The benefits of nixtamalization will soon become a reality for Kenyans following the official presentation of nixtamalized maize mills to the Cabinet Secretary of Kenya’s Ministry of Agriculture, Livestock and Fisheries by Mexico’s ambassador to Kenya, Erasmo Martínez, which took place on 4 April 2016 in Nairobi. This event marked the official launch of a new project titled “Expanding maize utilization as food and enhancing nutrition improved health and development in Kenya through processing technologies from Mexico,” which will contribute to disseminating new technology across the country. The three-year project will be led by the Kenya Agricultural Livestock and Research Organisation (KALRO).
The launch was followed by a week of training of 27 trainers from the public and private sectors led by CIMMYT and its collaborators from the tortilla industry in Mexico City and the National Autonomous University of Mexico. The training focused on building the capacity of partners who will be the major drivers of the commercialization of nixtamalized products.
“Geographically Mexico is very far from Kenya, but we want to bring a technology that is benefiting millions of people in Mexico every day, and it’s my hope that this will go beyond Kenya,” Martínez said, lauding this milestone. The Mexican embassy and the Mexican Agency for International Cooperation and Development played a crucial role in bringing the technology to Kenya.
“This technology is important because of its value addition to our food sector through reduction of aflatoxin exposure, increased market and income opportunities for youth and women, which will attract and improve their involvement in agribusiness,” said Sicily Kariuki, Cabinet Secretary for Public Service and Youth, who played a key role in the initial discussion on transferring this technology to Kenya.
KALRO will support raising awareness of the technology among small- and medium-sized companies, increasing their investment opportunities. KALRO is the custodian of the equipment donated by the Mexican government that is being used for training. CIMMYT will support this work by providing technical and capacity building expertise.
“We will help to evaluate and monitor grain quality besides developing resilient maize to ensure we have improved materials that fit the purpose of an efficient nixtamalization,” Palacios said. CIMMYT will also continue to collaborate with its partners on research aimed at finding further scientific evidence of the use of nixtamalization as a way of decreasing aflatoxin exposure.