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A reappraisal of nitrogen-to-protein conversion factors in cassava roots. [S10-05]

Dufour D., Ricci J., Sanchez T., Morante N., Morel G., Reynes M., Hershey C., Ceballos H.. 2012. In : Second Scientific Conference of the Global Cassava Patnership the 21st Century (GCP21-II), Kampala, Uganda, June 18-22, 2012. s.l. : s.n., 5 p.. Scientific Conference of the Global Cassava Partnership for the 21st Century. 2, 2012-06-18/2012-06-22, Kampala (Ouganda).

A study was conducted comparing the amino acid profiles of 10 commercial varieties (COL) and 15 clones with the highest levels of nitrogen (HIN) over two years of harvests. The highest nitrogen values detected in roots to date are close to 1.30%. The conversion factors of total nitrogen into protein calculated from amino acid profiles was 3.6 ± 0.9 for COL and 2.8 ± 0.2 for HIN. 53.7% of the total nitrogen is measured from protein with no difference between COL and HIN. The remaining 46.3% corresponds to ammonium ions, nucleic acids, or other nitrogenous non-protein molecules. Nitrogen content is 15.1 ± 1.2 and 19.1 ± 0.6% of the protein for COL and HIN, respectively. This difference is explained by a high content of arginine (4 nitrogen atoms per arginine molecule) in HIN clones. For COL, the proteins contained, on average: 23.3% glutamic acid, 15.7% proline, 14.3% arginine, 7.9% aspartic acid, while for HIN: 23.5% glutamic acid, 2.3% proline, 35.5% arginine, 7.9% aspartic acid. A linear correlation was found between the total nitrogen content and the level of arginine in cassava roots. Root protein content based on amino acid profile varied between 1.0% and 2.8% in the clones analyzed. Screening of varieties by the total nitrogen content leads to identify clones that are richest in arginine and not necessarily the richest in protein. Nitrogen alone, therefore, is not adequate to predict protein content.

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