Three procedures, commonly used for the determination of tryptophan, were found to be unsatisfactory for the assay of cereals. A method using p‐dimethylaminobenzaldehyde was unsatisfactory because cereals dissolved slowly in the sulphuric acid reagent, produced turbid solutions and gave high blank values. Racemisation of L‐tryptophan was found to be incomplete on hydrolysis with barium hydroxide; therefore, microbiological assays are invalidated. Neutralisation of the barium hydroxide with sulphuric acid or carbon dioxide resulted in considerable loss of tryptophan.
A method is described based on hydrolysis with barium hydroxide, precipitation of barium sulphate from an acid solution and colorimetric analysis using p‐dimethylaminobenzaldehyde. The procedure has proved useful for the routine analysis of cereals and other feedingstuffs.