Extraction and characterisation of fonio (Digitaria exilis Stapf) proteins | [Extraction et caracterisation des proteines de petit mil: (Digitaria exilis Stapf)]
1999
Carcea, M. (National Institute of Nutrition, Rome (Italie). Unit of Studies on Cereals) | Salvatorelli, S.
With the aim of contributing to widening the general knowledge on proteins of fonio, a small seeded cereal indigenous to West Africa, and, in particular, to assessing which protein fraction could be responsible for the unusually high methionine content of its kernels, a study was undertaken during which proteins were extracted from grains belonging to two different cultivars with different morphological characteristics, denominated Hothia and Koulli. Hothia had much bigger kernels than Koulli. The grains of the two cultivars had a total protein content of 10.4 and 11.0 % (d.m.). They were ground and defatted with petroleum ether. Fractionation of the seed proteins was carried out on defatted sarnples according to the selective extraction method of Landry and Moureaux (1970) to obtain 3 fractions (albumin plus globulin, prolamin, glutenin) and a residue. The protein content of each fraction and residue was determined by a Microkjeldhal method: in both cultivars the residue showed a protein content of about 7%, whereas the highest content was present in the glutelin fraction (about 60%). The amino acid analysis of each fraction was performed on a Beckman System Gold 126 analyser following the method of Spackman et al.(l958). Both cultivars showed a high methionine content (about 5% g aa/g protein) in the prolamin. However, the highest content of all fractions was found in the Koulli glutelin fraction (about 7%): on the contrary, the Hothia gave 2%. In both cultivars the glutelin fraction also had a high lysine content (more than 5%). This study will continue in the future with the electrophoretic characterisation of the isolated fractions
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