Tryptophan Content of Casein as Determined by a Rat Growth Method.

The tryptophan content of casein has been estimated using a rat growth assay method. Whether the results were calculated on the basis of the percentage of tryptophan in the diet or by using food consumption data to calculate the daily intake of tryptophan, essentially the same results were obtained. These animal assays indicate that casein (14.64% N) contains 1.25% tryptophan which is in good agreement with many reports based on microbioassays of alkaline and enzyme hydrolysates of this protein, but much lower than many commonly accepted figures obtained with chemical methods.