Biological Availability of Tryptophan

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Abstract
The availability of tryptophan from beef, pork, casein, egg albumin, beef fibrin, purified soybean protein and from milk powders was determined and was found to be 80 to 100% in all cases, the highest being from beef. When the amount of supplementary tryptophan was increased either by increasing the level of the protein supplement or by adding crystalline L-tryptophan together with the protein supplement, the apparent availability was lowered. Two ways of presenting the data and calculating availability have been discussed. The percentage availability figures arrived at with two different types of calculation did not differ significantly from each other. The unavailable tryptophan in the feces of different experimental groups given beef, pork, egg albumin and fibrin supplements was low, correlating well with the results of the other determinations.