Maize consists of three main parts- the hull or bran coat with high fibre content, germ rich in oil and starchy endosperm. The normal maize grain under Indian conditions on an average, contains 14.9 % moisture, 11.1 % protein, 3.6 % fat, 2.7 % fibre, 66.2 % other carbohydrates and 1.5% minerals (National Institute of Nutrition, 2002). Maize kernel protein is made up of five different fractions. The percentage of different fractions to total nitrogen in maize kernel is albumin 7 %, globulin 5 %, non-protein nitrogen 6 %, prolamine 52 % and glutelin 25 % and the left over 5 % is residual nitrogen (Landry and Moureaux, 1982). Protein being the primary structural and functional component of every living cell is one of the most important ingredients that determine the quality of food and feed.

In normal maize grain the quality of protein is poor due to the presence of largest concentration of an alcohol soluble protein fraction ‘prolamine’ also known as ‘Zein’ in the endosperm. The amount of this alcohol soluble protein fraction zein is low in immature maize. They increase as the grain matures. Zein is very low in lysine and tryptophan content.

Since this fraction contributes more than 50 per cent of the total protein, due to this obvious reason the protein of normal maize grain is low in lysine and tryptophan content. On the other hand, zein fractions contain very high amount of leucine and imbalanced proportion of isoleucine (Patterson et al 1980). On the whole, the ill proportion of all these four essential amino acids in maize due the high content of zein results into the poor quality of protein in normal maize. The high quality of protein in other fractions in other parts of maize kernel become recessive due to the dominance of zein in normal maize. The poor quality of protein in normal maize affects its ‘Biological value’ i.e. the availability of protein in the body.

The majority of the population depends on cereals for their livelihood in most of the countries and maize is the staple cereal food throughout the world. Therefore it was realized to improve the biological value of protein in maize genotypes. For this purpose, a new corn type known as ‘Quality Protein Maize’ (QPM) was developed by lowering the concentration of zein by 30 %. As a result, the concentration of two essential amino acids viz., lysine and tryptophan in grain was increased in QPM genotypes as compared to normal grain maize genotypes. The lower content of leucine in QPM further balances the ratio of leucine to isoleucine content (Table 1). The balanced proportion of all these essential amino acid in Quality Protein Maize (QPM) enhanced the biological value of protein.

The True Protein Digestibility of normal maize and Quality Protein Maize is almost same, but the biological value of normal maize is just half as compared to that of QPM varieties (Young et al 1971). Rather, the biological value of QPM is highest among all the food grains (Figure 1) owing to the reason that all cereals except QPM are deficient in lysine, an essential amino acid and all pulses are deficient in methionine, the other essential amino acid (Yadavn et al, 2008). The quality parameters viz., protein content, lysine & tryptophan content of QPM hybrids released for their cultivation in India are given in Table 3.