Comparison between the protein quality of northern adapted cultivars of common maize and quality protein maize

The present study was designed to quantitatively measure and compare the levels and variation of total protein as well as the individual amino acids in three northern adapted (latitude >45 o N) cultivars of common maize, namely a typical Dent CO251, a Mint CO255 inbred line, and commercial hybrid maize Pioneer 3953 with the new quality protein maize inbred (QPM-C13), and to assess their nutritive value from their FAO/WHO amino acid scoring pattern. The total protein content was variable among these cultivars ranging from 7.95% in QPM to 8.2% (Pioneer), 10.5% (Dent), and 11.79% (Flint). The QPM maize protein, however, proved to be of higher quality than common maize protein because it contained double the amount of lysine and arginine, higher levels of tryptophan and cysteine, and no change in other amino acids except lower levels of leucine. As a result, the QPM amino acid profile gives a good balance of total essential amino acids, limited only in lysine, and has an amino acid score, adjusted for digestibility, of 67%, compared to 28.5, 31.0, and 33.0% values found for Pioneer, Dent, and Flint, respectively. In common maize the primary essential amino acid deficiencies include lysine, threonine, and tryptophan. These results indicate that breeding maize for high protein quality can be very effective and that a very useful method for evaluating the protein quality of cereals is calculating their protein quality from their amino acid composition