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