Determination of essential amino-acids in some Ceylon vegetables.

Until recently methods of amino-acid analysis had been applicable only to purified proteins. In a few instances the effects of impurities have been partly ascertained, noteworthy being the work of Chibnall and his colleagues (Chibnall, 1939) and of Lugg (1938a) on the crude proteins of grasses. The development of the microbiological method in recent years has led to an extension of analysis to relatively crude proteins and even to whole foods. In 1946, I began at the Biochemical Laboratory, Cambridge, and at the Human Nutrition Unit, Medical Research Council, London, a study of the applicability of some recent developments in amino-acid analysis (Macpherson, 1946; Rees, 1946; Tristram, 1946; Stokes, Gunness, Dwyer & Caswell, 1945) to dried foodstuffs from which the fat and water-soluble components had been removed. Latterly I have resorted largely to the microbiological method, owing to its greater applicability to the hydrolysates of crude proteins. The main difficulty of doing amino-acid estimations on crude proteins is in evaluating the destruction of amino-acids brought about by strong acid at high temperatures in the presence of contaminating carbohydrate. I have attempted this evaluation by comparing the essential amino-acid values obtained after (I) direct hydrolysis of the crude proteins in the presence of the associated water-insoluble carbohydrate; and (2) hydrolysis of the acid-soluble material extracted from the crude protein. By also determining several amino-acids in some of the unextracted foodstuff preparations, an attempt has been made to ascertain how far the crude proteins as prepared are representative of the total protein of the foodstuffs, The vegetables used in this study have a complex chemical composition, and it was considered that methods applicable to them could probably be extended to other foodstuffs. This paper reports the results so obtained and evaluates their usefulness for estimating the essential amino-acids in crude proteins.