The promise and challenge of corn masa flour fortification

by Emily Buckley
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Increasing use of commercially produced corn masa flour offers a promising means of addressing the problem of iron deficiency anemia in Mexico and Central America


Iron deficiency anemia (IDA) is one of the most prevalent public health problems in the developing world, with the burden falling most heavily on women and children. In Mexico and Central America a significant percentage of people suffer from anemia, in a large part due to diets that are low in bioavailable iron.

Iron deficiency anemia and its adverse health effects can potentially be reduced by fortifying food staples with iron.

In Mexico, consumption of maize is five times that of wheat. The diets of low-income populations in Mexico and most of Central America consist primarily of corn (tortillas) and beans: average per-capita consumption of tortillas is approximately 5 to 8 per day.

Access to meat products that contain high quality bio-absorbable "heme" iron is beyond the means of most of these people. While tortillas are considered an excellent source of calories due to their high starch content, they are a poor source of good quality protein and of many vitamins (A, D, E, B12, and C) and minerals (iron and zinc). Further, tortilla-based diets are rich in iron absorption inhibitors such as phytic acid and polyphenols.

The development of a centralized industrial process for producing corn masa flour (CMF) and the growing popularity of the product provide a good opportunity for fortifying a key staple in the region. Given the product’s rapid acceptance over its relatively brief lifetime, potentially widespread public health benefits could be realized from using CMF as a fortificant vehicle. Ready-made CMF is especially popular in urban and urbanizing areas. Further, CMF mixes readily with other dry ingredients (i.e. micronutrient fortificants, preservatives, gums, etc.).


The success of iron fortification depends on a number of complex and inter-related factors including the fortificant compound, the food vehicle, the diet consumed in combination with the food vehicle, and the iron status of the consumer.

Effective iron fortification of cereal staples is a challenge in part because of components in the product that inhibit iron absorption, such as phytic acid. These components can reduce absorption of both product-intrinsic and added fortification iron. While corn masa flour contains relatively high levels of intrinsic iron (39mg/kg) relative to wheat flour (11.2mg/kg), most of this iron is not well absorbed during digestion.

The central challenge to any strategy for iron fortification of CMF is to select an iron additive that is highly absorbable (bioavailable), affordable and "opaque" to consumers. The bioavailability of fortificant iron primarily depends on its solubility in gastric juice. Water-soluble compounds like ferrous sulfate are highly soluble in gastric acid; whereas commonly used elemental iron powders rarely dissolve completely. Unfortunately, the more soluble (hence bioavailable) forms of iron tend to be more chemically reactive and can produce undesirable organoleptic effects when added. Iron is a catalyst for lipid oxidation and peroxidation in cereals during storage, and consequently can reduce shelf life.

Some forms of iron also react strongly with sulfur compounds; corn is high in sulfur-containing amino acids. The result may be off-coloration in the product. Therefore, the selection of iron compound for the fortification of CMF is both critical and complex.


The fortification of wheat flour was introduced in Central America in the 1960s. The addition of iron, folic acid, thiamin, niacin and riboflavin in wheat flour is now mandatory in all Central American countries.

In Mexico, a proposed requirement for the fortification of wheat flour with iron and folic acid was introduced in 1996. This requirement was approved by the government and issued in 1999. However, due to lack of resources for monitoring and enforcement, the extent of compliance is not known.

Fortification of the more widely consumed CMF with iron is likely to have a much more significant impact on the general nutritional status of the population than fortification of wheat flour. Recognizing this, governments and industries in Mexico and Central America have expressed interest in, and in some cases made recommendations for the fortification of CMF.

Unlike wheat flour, it is interesting to note that no standards were ever established in the U.S. for the enrichment of corn masa flour. There is interest in this issue among some people in the public health community in part because the anemia rates among low-income populations in the U.S. are highest for Mexican American populations. Presumably, this population would be an ample consumer of tortillas. In addition, representatives from the Coconino County Department of Health Services and the Arizona March of Dimes contacted SUSTAIN to express their interest in the enrichment of corn masa flour (particularly with folic acid) because of the high prevalence of neural-tube birth defects among Native Americans and Hispanic populations in the U.S.

Research indicates that folic acid can significantly reduce the incidence of Neural Tube Defects (NTDs) only when taken during the weeks prior to conception through the first 6 weeks of pregnancy). The U.S. Public Health Service (PHS) first recommended in 1992 that all women of childbearing age consume 400 micrograms (mcg) of folic acid to reduce their risk of having a NTD-affected pregnancy.

In September 1998, industry and government representatives in Mexico, signed an agreement to fortify wheat and corn masa flour, as well as corn nixtamal (dough) with iron, folic acid and zinc, and to restore the thiamin, niacin and riboflavin lost during processing.

The Agreement — the first attempt to establish standards for the fortification of CMF — is widely regarded to be a model for the region. However, efforts have been hindered by uncertainty over the selection and use of iron fortificants. Some CMF and wheat flour producers in Mexico have pledged to voluntarily fortify their products based on the new guidelines. To date, however, the only mandatory requirements for the fortification of CMF exist in Costa Rica; these were established in 1999.


Elemental iron powders are the most commonly used iron fortificants worldwide, but little is known about the extent to which these fortificants are absorbed by the body. Studies conducted over the last 45 years have reported highly variable results, from 5% to 145% relative bioavailability in comparison to the standard, ferrous sulfate.

To help address these concerns, the U.S.-based organization, SUSTAIN, convened a panel of world-renowned research scientists, physicians and industry specialists in Monterrey, Mexico, to review nearly 45 years of research on the bioavailability of elemental iron fortificants.

Discussions during the workshop revealed that inconsistent and incomplete information exists on food-grade elemental iron powders evaluated in past absorption studies and in use by industry today. This is due, in part, to the inherent technical difficulty of measuring the bioavailability of elemental iron powders. Furthermore, past research, in most cases, failed to adequately identify the particular type of elemental iron powder studied or to ensure that the experimental form resembled the commercial forms. Nevertheless, based on a review of available data, workshop participants concluded that one of the powders could be recommended for use in fortification programs on an interim basis. Key findings and recommendations from the workshop included that electrolytic iron (325 mesh) appears to be about half as bioavailable as ferrous sulfate, which is the standard against which iron fortificants are typically compared.

Based on the current state of knowledge, there is insufficient information about the bioavailability of the other elemental iron powders to offer specific recommendations

Given the high prevalence of iron deficiency anemia in developing countries and the wide use of elemental iron powders in food fortification programs, a thorough evaluation of iron powders in current use is highly recommended.

Workshop participants determined that the pool of commercially available iron powders that would need to be evaluated is actually fairly small. They further agreed that it would be inadvisable to rely in the future on problematic and inconsistent radioisotopic studies of iron powders. They recommended that the bioavailabilities of elemental iron powders might best be evaluated through in-vivo studies designed to monitor improved iron status among mildly iron-deficient volunteers.

Following the Monterrey Workshop and subsequent briefing meetings, SUSTAIN drafted and published a set of "Guidelines for Iron Fortification of Cereal Food Staples." The guidelines are designed as an interim tool to help program planners select and use iron fortificants in public health programs and will change as more information becomes available. These guidelines have been widely disseminated among international agencies, NGOs, donors and the private sector. (See page 62 for a summary of the key recommendations).

SUSTAIN currently is sponsoring a comprehensive evaluation of the bioavailability of each of the iron powder fortificants in use today. Following a series of preliminary screening tests to identify the most promising candidates, a human study will be conducted in mildly iron deficient individuals. Results from the human study are expected in 2003. The outcome of these studies will provide a solid basis for making recommendations on the use of elemental iron powders in food fortification.


Table 1. Anemia Rates for Women of Childbearing Age
and Children in Central America.




Pregnant Women

Non-pregnant Women

Mexico (1999)

A) 48.0% B) 27.2%




Costa Rica (1996)

A) 36.0% B) 26.0%




Guatemala (1995)

A) 50.0% B) 26.0%




El Salvador (1998)

A) 49.0% B) 30.0%




Honduras (1996)

A) 52.0% B) 28.0%




Nicaragua (2000)

A) 56.0% B) 36.0%





A) Pre-school children ages 12-24 months old;
B) Pre-school children ages 2-5 years old.
* No significance in urban/rural differences.


Industrialization of corn masa flour

Industrial production of corn masa flour for tortilla making had its origin in Mexico in the late 1940s; before then all tortillas were made only from fresh masa (dough), a labor-intensive traditional process that dates back to the ancient Maya and Aztec civilizations, and which is still used today.

Looking for a more streamlined means of producing tortillas, Mexican entrepreneurs Don Roberto Gonzáles and his son Roberto Gonzáles Barrera developed a method for processing the fresh masa into flour, which could then be used to make tortillas. In 1949 they then established the first corn masa flour plant in their hometown of Cerralvo, N.L. (Mexico). Several other companies in Mexico, Central America and the U.S. have since entered the market as well. Mexico has more than twenty CMF manufacturing plants, whose end product is used to make almost half of the over 11 million metric tonnes of tortillas sold each year in that country. Central America hosts eight more plants located in Guatemala, Costa Rica, El Salvador and Honduras.

The demand for corn masa flour accelerated rapidly in the 1990s, and today an estimated 40-50% of all tortillas in Mexico are made with the flour.




Guidelines for Iron Fortification

Ferrous sulfate: Because of its high bioavailability and low cost, FCC-grade dried ferrous sulfate is often the best choice. It can be used in bakery flour, semolina and other types of low extraction wheat flours, which are normally used within one month after production. Only dry powders with a fine particle size should be used, because large particle sizes and hydrated ferrous sulfate can cause color and spotting problems.

Ferrous fumarate: FCC-grade ferrous fumarate has a bioavailability similar to that of ferrous sulfate. It is insoluble in water and therefore causes fewer organoleptic problems than the more soluble ferrous sulfate. However, it usually costs more than ferrous sulfate.

Elemental iron: Elemental iron powders may be considered as potential iron sources if unacceptable changes in color, flavor or storage properties of the fortified food prevent use of either ferrous sulfate or ferrous fumarate. At the current state of knowledge, electrolytic iron is the best choice among the elemental iron powders. It is about half as bioavailable as ferrous sulfate.

Foods with high levels of inhibitory factors (phytic acid or polyphenols) significantly reduce iron absorption, limiting the impact of fortification. In such cases, it may be necessary to add an iron absorption enhancer or reduce the amount of inhibitor in the food. Where permitted, use of sodium iron-EDTA or disodium EDTA plus ferrous sulfate as fortificants should be considered. Other options include dietary change, fortification of a food that is consumed separately from the main inhibitory meals, and iron supplementation.

In planning a fortification strategy, the optimal level of iron fortification will depend on a number of factors, including the prevalence of iron deficiency, the nature of the diet, the distribution of cereal foods, and the bioavailability of the added iron.


SUSTAIN (Sharing U.S. Technology to Aid in the Improvement of Nutrition) engages industry in public health efforts to improve nutrition in developing countries. The organization links industry specialists with local counterparts to transfer know-how, improve manufacturing and widen distribution networks. SUSTAIN’ research and activities mentioned in this article have been funded in part through the generosity of the Bill and Melinda Gates Foundation.

For reference for this article, or more information on the work of SUSTAIN, visit or contact SUSTAIN directly by phone 1.202.457.0168 or email