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 t he levels and variation of total protein as well as the individual ami no acids in three northern adapted (latitude >45 degrees N) cultivars of common maize, namely a typical Dent CO251, a Flint CO255 inbred lin e, and commercial hybrid maize Pioneer 3953 with the new quality prote in maize inbred (QPM-C13), and to assess their nutritive value from th eir FAG/WHO amino acid scoring pattern. The total protein content was variable among these cultivars ranging from 7.95% in QPM to 8.2% (Pion eer), 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 t ryptophan and cysteine, and no change in other amino acids except lowe r levels of leucine. As a result, the QPM amino acid profile gives a g ood balance of total essential amino acids, limited only in lysine, an d has an amino acid score, adjusted for digestibility, of 67%, compare d to 28.5, 31.0, and 33.0% values found for Pioneer, Dent, and Flint, respectively. In common maize the primary essential amino acid deficie ncies include lysine, threonine, and tryptophan. These results indicat e that breeding maize for high protein quality can be very effective a nd that a very useful method for evaluating the protein quality of cer eals is calculating their protein quality from their amino acid compos ition.