Extraction and characterisation of fonio (Digitaria exilis Stapf) proteins

With the aim of contributing to widening the general knowledge on proteins of fonio, a small seeded cereal indigenous to West Africa, and, in particul ar, to assessing which protein fraction could be responsible for the unusua lly high methionine content of its kernels, a study was undertaken during w hich proteins were extracted from grains belonging to two different cultiva rs with different morphological characteristics, denominated Hothia and Kou lli. Hothia had much bigger kernels than Koulli. The grains of the two cult ivars had a total protein content of 10.4 and 11.0 % (d.m.). They were grou nd and defatted with petroleum ether. Fractionation of the seed proteins wa s carried out on defatted samples according to the selective extraction met hod of Landry and Moureaux (1970) to obtain 3 fractions (albumin plus globu lin, prolamin, glutenin) and a residue. The protein content of each fractio n and residue was determined by a Microkjeldhal method: in both cultivars t he residue showed a protein content of about 7%, whereas the highest conten t was present in the glutelin fraction (about 60%). The amino acid analysis of each fraction was performed on a Beckman System Gold 126 analyser follo wing the method of Spackman et al.(1958). Both cultivars showed a high meth ionine content (about 5% g aa/g protein) in the prolamin. However, the high est content of all fractions was found in the Koulli glutelin fraction (abo ut 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 co ntinue in the future with the electrophoretic characterisation of the isola ted fractions.