Determination of the Tryptophan Content of Feed and Feedstuffs by Ion Exchange Liquid Chromatography

Abstract

A method for determining the tryptophan content of feed and feedstuffs was established. This method involved three steps: alkaline hydrolysis, pretreatment of the hydrolysate for chromatography, and measurement of tryptophan by ion exchange liquid chromatography. With this method, the recovery of tryptophan in egg-white lysozyme, which is a pure protein with six tryptophan residues, was 97%. It was shown that co-existing nutrients, such as carbohydrate, fiber, and free or combined ash, did not affect the recovery of tryptophan in lysozyme, but that the recovery of tryptophan was reduced by the presence of fat. Therefore, defatting of feed and feedstuffs is necessary to obtain accurate values for tryptophan analysis by this method. The tryptophan contents of some proteins, feedstuffs, and feeds were determined under the optimum conditions established in this study.