Composition of protein of sorghum grain grown in Botswana

Abstract

The amino acid composition of the total protein in three samples of sorghum grain, grown in Botswana, was determined. The results are considered in relation to local nutritional problems and the occurrence of pellagra.The nutritional value of sorghum is of considerable importance in view of its wide use as a staple food. The average values for the overall composition of total protein of 65 samples of sorghum grain have been summarised by the Food and Agriculture Organisation of the United Nations' and values are also given for other samples, analysed for essential amino acids only, by microbiological methods.' The object of the present investigation was to obtain a picture of the amino acid composition of the total protein of three samples of sorghum, grown in Botswana, to compare with that of sorghum grown elsewhere, as a guide to its comparative nutritional value. In Botswana, sorgum is pounded to a dry powder in a wooden mortar, winnowed to remove husks and cooked with water to a porridge.Pellagra has been attributed2* to the high content of the amino acid leucine in the protein of maize and sorghum. The mechanism of this detrimental effect of excess leucine is not clear, but it apparently increases the need for tryptophan and isol e~c i n e .~ High intakes of leucine bring about alterations in the excretion of N-methylnicotinamide,2 which presumably, in people on low-protein diets of minimal tryptophan content, result in depleting the tissues of nicotinamide, thus causing pellagra.