Accurate and detailed amino acid determinations were carried out on nine northern adapted soybean cultivars to ascertain whether their amino acid profiles could be used as potentially useful indices for assessing their protein quality. The cultivars were Maple Amber, Maple Donovan, Maple Glen, Maple Isle, Maple Presto, Maple Ridge, and three brown seed coat near-isogenic lines, Maple Presto Brown, Maple Ridge Brown, and Maple Arrow Brown. Their total protein and amino acid composition were compared with those of an established cultivar, Maple Arrow. Mean protein values for the new cultivars ranged from 30.1 to 33.1% compared to Maple Arrow, which was 33.2%. The total nitrogen content was also variable among these cultivars, ranging from 5.0 to 5.4%. All nine Maple series soybean cultivars were higher in their essential amino acid (EAA) content, that is, EAA(9) = 45.2-46.5%, than the FAO/WHO reference protein pattern value of EAA(9) = 33.9%, for a 2-5-year-old child. Each of the nine new soybean cultivars was limited only in methionine and to a lesser extent in valine and isoleucine and had a protein digestibility corrected amino acid score of 91% for all cultivars, compared to the value of egg protein (97%). These results suggest that the most accurate evaluation of protein quality in soybeans, and possibly other legumes and cereals, is by the protein digestibility-corrected amino acid score.

Amino acid determinations were carried out on 15 new northern adapted cultivars of quality protein maize (QPM) containing opaque-2 modifier genes to ascertain whether their amino acid scoring patterns could be used to select high-lysine QPM genotypes and to assess their protein quality. Total protein in these cultivars ranged from 8.0 to 10.2% compared to two commercial maize 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 levels of lysine (4.43-4.58 g of 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 protein, respectively. Although lysine is the first limiting amino acid in QPM inbreds, the high-lysine QPM genotypes may supply approximately 70.2-72.6% of 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 adapted QPM genotypes may have the potential to increase their lysine content even 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 genotypes with improved protein quality and quantity.

The total protein and amino acid compositions of five newly released northern adapted natto soybean cultivars, namely Canatto, TNS, Nattosan, AC T2653, AC Pinson, and their recurrent parent, Nattawa, have been determined. Mean protein values ranged from 30.4% in AC T2653 to 31.0% (AC Pinson), 31.0% (Nattawa), 32.1% (TNS), and 32.3% (Canatto), compared to the protein content of Nattosan, which was 34.2%. The total nitrogen content was also variable among these cultivars, ranging from 5.15% to 5.92%. All five new natto soybean cultivars were similar in their essential amino acid (EAA) content, i.e., EAA9 = 45.0−47.0%, compared to the FAO/WHO reference protein pattern value of EAA9 = 33.9% for a 2−5-year-old child. Each of the six soybean cultivars was limited only in methionine and, to a lesser extent, in valine and isoleucine and had a protein digestibility corrected amino acid score of 91% for all cultivars, compared to the value of egg protein (97%). These results suggest that the most accurate evaluation of protein quality in natto soybeans, and possibly other legumes and cereals, is by the protein digestibility corrected amino acid score. Keywords: Natto soybeans; assessment; protein quality; amino acids; composition; amino acid score