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Limiting Amino Acids in Noog (Guizottia abyssinca) as Determined by Amino Acid Composition, Plasma Amino Acid Concentrations, and Growth of the Rat¹

Department of Agricultural Biochemistry, University of Arizona, Tucson, Arizona 85721

The growth-limiting amino acids of noog (Guizottia abyssinca) were determined by amino acid composition, plasma amino acid (PAA) ratio and score, and growth response of weanling rats to amino acid supplements. Compositional studies (percent deficit) revealed that lysine was the most limiting amino acid. However, the results of biological studies (PAA ratio and score, and growth response) suggested threonine and lysine, about equally limiting, as the most limiting amino acids. Protein efficiency ratio of noog meal and noog seed fed at a dietary level of 10% protein improved from 2.6 to 3.9 and from 2.1 to 3.6, respectively, by supplementing the diets with threonine and lysine. An FAO report, based on chemical scores of compositional studies, indicated that valine and the sulfur-containing amino acids were the first- and the second-limiting amino acids, respectively. The results of our growth experiments indirectly disproved this, although the difference might result from comparing different samples. The different predictions of the limiting amino acids by the chemical and biological methods could be due to the inaccuracy of some of the values for the amino acid composition and the inadequate information about the biological availability of amino acids.

KEY WORDS: • noog meal • protein quality • limiting amino acids • amino acid supplementation

¹ The University of Arizona Experiment Station Journal paper no. 2063.

² Present address: HSIU, College of Agriculture, P. O. Box 138, Dire Dawa, Ethiopia.

³ To whom requests for reprints should be addressed.

Manuscript received 25 May 1973.