Assessment of the protein quality of 15 new northern adapted cultivars of quality protein maize using amino acid analysis

Amino acid determinations were carried out on 15 new northern adapted culti vars of quality protein maize (QPM) containing opaque-2 modifier genes to a scertain whether their amino acid scoring patterns could be used to select high-lysine QPM genotypes and to assess their protein quality. Total protei n in these cultivars ranged from 8.0 to 10.2% compared to two commercial ma ize varieties, Dekalb DK435 (7.9%) and Pioneer 3925 (10.3%). Four of these QPM genotypes, QPM-C26; QPM-C21, QPM-C79, and QPM-C59, contained high level s of lysine (4.43-4.58 g df lysine/100 g of protein), whereas the remaining varied from 3.43 to 4.21 g of lysine/100 g of protein, compared to Dekalb DK435 and Pioneer 3925, which contained 2.9 and 3.1 g of lysine/100 g of pr otein, respectively. Although lysine is the first limiting amino acid in QP M inbreds, the high-lysine QPM genotypes may supply similar to 70.2-72.6% o f human protein requirements, compared to 46.2% for Dekalb DK435 and 50.1% for Pioneer 3925, 55-63% for oats, and 59-60.3% for barley. Northern adapte d QPM genotypes may have the potential to increase their lysine content eve n further, either by an increase in specific high-lysine-containing nonzein proteins, such as the synthesis of factor EF-1a, or by a further reduction in the 19 and 22 kDa alpha -zein in the endosperm or both. This knowledge could assist maize breeders in the selection of new high-performance QPM ge notypes with improved protein quality and quantity.