Estimation of Tryptophan Content of Wool by Barium Hydroxide (Baryta) Hydrolysis Method

Abstract

Various factors affecting the estimation of the tryptophan content of wool, by methods based on acid hydrolysis, are discussed. It has been shown that when wool is hydrolyzed in a strong acid medium in presence of p-dimethylaminobenzaldehyde, the tryptophan-aldehyde complex formed decomposes with time and, thus, a correct estimation of tryptophan content is difhcult. When wool is hydrolyzed with barium hydroxide, tryptophan is liberated without decomposition and can be estimated in the hydrolyzate when barium ions and H2S (which is formed as a result of degradation of cystine and its derivatives) are both removed. A method of estimating tryptophan content of wool by baryta hydrolysis is described and has been found to be accurate and reliable. Tryptophan contents of various wools, estimated by the baryta hydrolysis method are reported. Tryptophan content of Australian Merino 70° wool was found to be 0.82 ± 0.01%.

Methods of tryptophan analysis

“…Intense light, oxidizing and reducing agents, including H2S, bisulfite ions, hydrogen peroxide in low concentrations, and chloride ions, interfere in the Spies dimethylaminobenzaldehyde method Chambers, 1948, 1949;Lesuk, 1948;Junéja et al, 1968;DasGupta, 1969). Spies has eliminated interference by H2S, chloride, and bisulfite ions by appropriate use of silver sulfate, which does not interfere (Spies and Chambers, 1950).…”

The Chemistry of Tryptophan in Peptides and Proteins

“…FRIEDMAN et al (136) eliminate interference due to cysteine and cystine residues by reducing the protein disulfide bonds and alkylating the native and generated-SH groups with vinyl derivatives. JUNEJA et al (219) evaluated in detail the interference by sulfur amino acids; they estimated the tryptophan content of wool colorimetrically after hydrolysis with 6N Ba(OH)2 for 5 hours at 125° C followed by removal of liberated H2S and barium with silver sulfate and sulfuric acid respectively.…”