Rapid and simple method for the determination of tryptophan in cereal grains.

Alkaline extracts of cereal proteins are treated in the prescribed sequence: Glacial acetic acid-ferric chloride and 25.8 n H₂SO₄ solutions. Specified amounts of these solutions and the sample are added in order to obtain the required sulfuric acid concentration in the reaction mixture. The reaction mixture is heated at 60°C for 45 min (cereal proteins) or 110 min (standard tryptophan). The absorbance of the resulting violet solution is read at 545 nm. Results are highly precise and agree quite favorably with those of the modified Spies and Chambers method using Pronase hydrolyzates. As little as 6–7 μg of tryptophan in cereal proteins may be determined reliably in samples with negligible blank corrections.The factors affecting color development and the accuracy and precision of the method are discussed.