Nutritive quality of leaf proteins coagulated at different pH

Leaf proteins obtained by coagulation at different pH were examined for their chemical composition and nutritional quality. Green juice was extracted from alfalfa, red clover, Italian ryegrass and oats and leaf protein was coagulated by heating the juice after adjusting the pH to 4 or 8-8.5, or without any adjustment of the pH (about pH 6). The mild alkaline juice from Italian ryegrass and oats did not cause the satisfactory coagulation but it was achieved with the addition of Ca salt to the juice before heating. There were no important differences in the amino acid compositions of the leaf proteins coagulated at different pH. Crude ash, Ca and Mg contents increased with an increase in pH of coagulation and the protein coagulated at pH 8 had remarkably high contents of crude ash, Ca, Mg, Na and P in each crop. The leaf protein coagulated at pH 6, on the contrary, had a high content of true protein and low contents of nitrogen free extracts and nucleic acid as compared with those at pH 4 and 8. The pH of coagulation of leaf protein from alfalfa and red clover had no effect on the nutritional quality of the respective proteins. In Italian ryegrass and oats, however, the leaf protein coagulated at pH 8 was found to be nutritionally inferior to those coagulated at a lower pH. The data presented in this work support that in general, the leaf protein produced by heating the green juice without any adjustment of pH may be suitable for protein resources because of its desirable properties, i.e. high true protein content and good nutritional quality.