Seeds of Citrullus lanatus (Thunb.) Matsum. & Nakai, Vigna unguiculata (L.) Walp. and Zea mays L.: Chemical Characterization of the Coagulating Solutions

The aim of this study was to characterize the amino acids in the seeds of Citrullus lanatus, Vigna unguiculata and Zea mays; and the proteins in the coagulating solutions of the seed powders of these 3 plants. Amino acids were separated by ion exchange chromatography and determined by ninhydrin reaction with photometric detection. Proteins were characterized by steric exclusion high-performance liquid chromatography (SE-HPLC) on a Superdex column in the range of 10 kDa to 500 kDa and on a Shodex column in the range of 204 Da to 35000 Da. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) was also performed. The results obtained showed that the most abundant amino acid in the seeds of the 3 plant species is glutamic acid, a negatively charged side chain amino acid at neutral pH. The respective contents are 6150 mg/100 g in Citrullus lanatus seeds; 4030 mg/100 g in Vigna unguiculata seeds and 1820 mg/100 g in Zea mays seeds. The percentage of protein constituents with a molecular weight less than 10 kDa is 87.3%; 74.1% and 61.6%; for Citrullus lanatus, Zea mays and Vigna unguiculata coagulant solutions respectively. The percentage of protein constituents with a molecular weight between 1000 Da and 1500 Da is 24.9%;20.4% and 29.2%; respectively for the coagulant solutions of Vigna unguiculata, Zea mays and Citrullus lanatus. A percentage of 25.8%, between 800 and 1000 Da, is also noted for Citrullus lanatus. The study of the coagulant activity showed percentages of turbidity reduction higher than 80%.