Enhancement of Amino Acid Availability in Corn Grain
As modern corn hybrids were bred for higher yields, the composition of the grain has inadvertently trended to higher starch content at the expense of protein (Scott et al. 2006). Moreover since corn grain protein is deficient in certain nutritionally essential amino acids, this reduction in grain protein level has further reduced the nutritional quality of the grain. One approach to address this problem is to increase the nutritional quality of corn grain protein, particularly by enhancing the content of essential amino acids, such as lysine and tryptophan.
The most limiting amino acid in corn grain, with respect to the dietary needs of monogastric animals, is lysine. Therefore, enhancement of lysine content is a primary target for improving grain quality. The poor nutritional quality of corn protein is mostly caused by the amino acid composition of endosperm proteins. Corn protein has a lysine content of 2.7%, which is well below the recommendation by FAO (FAO/WHO/UNU 1985) for human nutrition. Although the germ protein has an adequate lysine content (5.4%) in whole grain, this is diluted by the much more abundant endosperm proteins, which have an average lysine content of only about 1.9%. This is because 60–70% of endosperm protein consists of zeins, which contain few or no lysine residues (Coleman and Larkins 1999). Similarly, the absence of tryptophan residues in zein proteins is the reason for the low tryptophan content of corn protein. Therefore, modification of the grain protein profile through approaches such as zein reduction and expression of lysine-rich proteins could significantly improve the balance of amino acids. Alternatively, the lysine content of the grain could be increased by elevating the level of free lysine in the kernel.
KeywordsLysine Content Quality Protein Maize Maize Endosperm Endosperm Protein Amino Acid Availability
Unable to display preview. Download preview PDF.
- Coleman CE, Larkins BA (1999) The prolamins of maize. In: Shewry PR, Casey R (eds) Seed proteins. Kluwer, Dordrecht, pp 109–139Google Scholar
- FAO (1992) Maize in human nutrition. FAO, RomeGoogle Scholar
- FAO/WHO/UNU (1985) Energy and protein requirements. Report of a joint FAO/WHO/UNU expert consultation. WHO, GenevaGoogle Scholar
- Galili G (2004) New insights into the regulation and functional significance of lysine metabolism in plants. Ann Rev Plant Physiol Plant Mol Biol 53:27–43Google Scholar
- Gentinetta E, Maggiore T, Salamini F, Lorenzoni C, Piole F, Soave C (1975) Protein studies in 46 opaque-2 strains with modified endosperm texture. Maydica 20:145–164Google Scholar
- Hadjinov MI, Zima KI, Normov AA (1972) Changes in weight, protein and lysine content in opaque-2 kernels of corn during backcrossing. Maize Genet Coop Newsl 46:101–104Google Scholar
- Johnson LA, Hardy CL, Baumel CP, Yu T-H, Sell JL (2001) Identifying valuable corn quality traits for livestock feed. Iowa State University, Ames Kemper EL, Cord-Neto G, Capella AN, Goncalves-Butruile M, Azevedo RA, Arruda P (1998) Structure and regulation of the bifunctional enzyme lysine-oxoglutarate reductase-saccharopine dehydrogenase in maize. Eur J Biochem 253:720–729Google Scholar
- Landry J, Moreaux T (1982) Distribution and amino acid composition of protein fractions in opaque-2 maize grains. Biochemistry 21:1865–1869Google Scholar
- Landry J, Delhaye S, Damerval C (2002) Effect of the opaque-2 gene on accumulation of protein fractions in maize endosperm. Maydica 47:59–66Google Scholar
- Lopes MA, Larkins BA (1991) Gamma-zein content is related to endosperm modification in quality protein maize. Crop Sci 31:1655–1662Google Scholar
- Lucas DM, Glenn KC, Bu J-Y (2004) Petition for determination of nonregulated status for lysine maize LY038. http://www.aphis.usda.gov/brs/aphisdocs/04 22901p.pdf
- Paez AV, Helm JL, Zuber MS (1969) Lysine content of opaque-2 maize kernels having different phenotypes. Crop Sci 9:251–252Google Scholar
- Prasanna BM, Vasal SK, Kassahun B, Singh NN (2001) Quality protein maize. Curr Sci 81:1308–1319Google Scholar
- Puckett JL, Kriz AL (1991) Globulin gene expression in opaque-2 and floury-2 mutant maize embryos. Maydica 36:161–167Google Scholar
- Scott MP, Edwards JW, Bell CP, Schussler JR, Smith JS (2006) Grain composition and amino acid content in maize cultivars representing 80 years of commercial maize varieties. Maydica 51:417–423Google Scholar
- Wall JS, Paulis JW (1978) Corn and sorghum grain proteins. Adv Cereal Sci Technol 2:135–219Google Scholar