The tryptophan content in protein of cereal grains and legume seeds as a function of nitrogen content. A reappraisal of tryptophan score.
The tryptophan content ([Trp]) in the dry matter (DM) of wheat, maize, barley, sorghum, rice, pearl millet grains, pea and broad bean seeds is evaluated from samples, with various nitrogen contents ([N]DM) and genotypes, using a procedure that has been shown to be strictly quantitative. The determination of linear correlations between [Trp]DM and [N]DM, and between the tryptophan content in protein ([Trp]N) and [N]DM or 1/[N]DM for every species leads to the following observations: (1) [Trp]DM and [N]DM are linearly related. The data show that previous reports of similar relationships underestimate tryptophan by 10 +/- 5% owing to tryptophan degradation during alkaline hydrolysis preparatory to analysis; (2) the linear correlations between [Trp]N and 1/[N]DM, resulting from linear relationships [Trp]DM and [N]DM display coefficients of determination (r2) far lower than 1 and similar to those found for linear correlations between [Trp]N and [N]DM; (3) [Trp]N increases with [N]DM increasing for rice and pearl millet while it decreases for all other species.


CONCLUSIONS
(1) linear relationships between tryptophan and nitrogen have a low predictive value; (2) the nutritional score of tryptophan of foods and feeds, as calculated from the determination of tryptophan using a procedure involving alkaline hydrolysis, is generally underestimated by 10%.
Delhaye
S
S
Laboratoire de Chimie Biologique, INRA, INA-PG, Thiverval Grignon, France.
Landry
J
J
D002523:Edible Grain; D007887:Fabaceae; D006801:Humans; D009584:Nitrogen / Q000032:analysis*; D009747:Nutritional Physiological Phenomena; D014674:Plant Proteins, Dietary / Q000737:chemistry*; D010946:Plants, Medicinal; D012639:Seeds; D014364:Tryptophan / Q000032:analysis*
D014674:Plant Proteins, Dietary; D014364:Tryptophan; D009584:Nitrogen