Malnutrition is a worldwide dilemma, particularly in developing nations with low capita where animal protein is scarce and expensive. Consequently, many developing nations are forced to obtain their calorie requirements from cereal crops, which, unfortunately, have poor nutritional value for humans such as the amount of essential amino acids that are required for human growth. As a result, nearly 200 million children five years and younger attain insufficient amounts of protein, leading to several health problems that stunt growth, weaken the immune system, and impair intellectual development.
One such crop is maize. With its high content of carbohydrates along with traces of lipids, proteins, vitamins, and minerals, maize serves as the main source of nutrition for the millions of people in developing countries, accounting for approximately 15 to 56% of the total daily calorie intake. Accordingly, maize is dubbed the “poor man’s nutricreal.” Unfortunately, like other grains, maize is deficient in lysine and tryptophan, two of the eight essential amino acids that the human body cannot synthesize on its own. Both lysine and tryptophan are vital in the production of protein in the body. Therefore, maize’s insufficient amounts of these amino acids are a direct cause for malnutrition in several developing countries.
Help from Genetic Modification
In order to combat maize’s deficiencies, researchers have spent the past 30 years working on isolating a mutant that would allow maize to produce higher concentrations of lysine and tryptophan. Researchers were successful with the introduction of the opaque-2 mutation, a mutation that doubles the lysine content of maize and therefore improves the protein quality of the crop. The opaque-2 mutation encodes a transcriptional activator that regulates the expression of 22-kD alpha zein storage proteins; reducing zein storage protein translates to higher levels of lysine. However the opaque-2 mutant brought along with it lower yields, an undesirable chalky, soft kernel, and higher susceptibility to disease and pest damage – all factors that make opaque-2 maize unattractive for farmers to cultivate.
Birth of Quality Protein Maize
Researchers at the International Maize and Wheat Improvement Center (IMWIC) continued their search for an improved form of maize that would have the traditional taste yet carry sufficient amounts of lysine and tryptophan. Improvements were finally made with the creation of quality protein maize (QPM) through backcrossing opaque-2 modifiers and opaque-2 mutants and several cycles of recurrent selection of maize.
The resulting QPM contained nearly twice as much lysine and tryptophan than regular maize; QPM produced 3.98 grams of lysine for every 100 grams of protein whereas unmodified maize produced only 1.81 grams of lysine for every 100 grams of protein. QPM was very successful because not only did the maize maintain the increased concentrations of lysine and tryptophan form the opaque-2 gene, but it was also able to maintain the original kernel hardness and density, preventing infections and diseases from pests and increasing crop yields. Subsequently, there is now more than one million hectors of quality protein maize grown worldwide.
Benefits of Quality Protein Maize
Millions of infants and small children in the many developing countries of the world can only depend on maize for carbohydrates and their limited proteins, fats, vitamins, and minerals. As stated before, maize does not have all the essential amino acids-lysine and tryptophan-for human growth and will therefore lead to malnutrition without additional supplementary sources. Quality protein maize would be the start in helping those at risk of malnutrition. QPM would be the start in helping those at risk of malnutrition. Studies demonstrated that QPM as the only source of protein and fat in diets of weaned infants and small children can support growth equivalent to that attained from sophisticated cow’s milk-derived formulas.
Gaziola, S., Alessi, E., Guimaraes, P., Damerval, C., Azevedo, R. 1999. Quality protein maize: a biochemical study of enzymes involved in lysine metabolism. J. Agric. Food Chem. 47, 1268-1275.
Graham, G., Lembcke, J., Lancho, E., and Morales, E. 1989. Quality protein maize: digestibility and utilization by recovering malnourished infants. Pediatrics. 83, 416-421.
Prasanna, B., Vasal, S., Kassahun, B., and Singh, N. 2001. Quality protein maize. Current Science. 81, 1308-1319.
Pray, C., Paarlberg, R., and Unnevehr, L. 2007. Patterns of political response to biofortified varieties of crops produced with different breeding techniques and agronomic traits. AgBioForum. 103, 135-143.
Wang, X. and Larkins, B. 2001. Genetic analysis of amino acid accumulation in opaque-2 maize endosperm. Plant Physiology, 125, 1766-1777.
Zarkadas, C., Yu, Z., Hamilton, R., Pattison, P., and Rose, N. 1995. Comparison between the protein quality of northern adapted cultivars of common maize and quality protein maize. J. Agric. Food Chem. 43, 84-93.