Thin‐layer Chromatography of Cysteine Derivatives of Onion Flavor Compounds and the Lacrimatory Factor

SUMMARY A technique was developed for evaluating the flavor of freshly crushed onion. The method consisted of grinding the onion and extracting the juice with solvent. The solvent extract was reacted with cysteine to form an amino acid derivative of the flavor compound and finally the derivatives were separated by thin‐layer chromatography with solvents containing large amounts of hydrochloric acid. The principal advantage of the method is that it can measure the relative concentration of the lacrimator and other products of the action of alliinase on the flavor precursor, S‐propenyl‐L‐cysteine sulfoxide. Apparently, this is not measurable by the usual gas‐liquid chromatography technique because of decomposition in the column.