Pseudo Malonaldehyde Activity in the Thiobarbituric Acid Test*

In the thiobarbituric acid test for malonaldehyde, 2-hexenal, 2,4-hexadienal and 13-hydroperoxy-9Z,11E-octadecadienoic acid are found to form the characteristic 532 nm chromogen, at pH = 2.7 and at elevated iron(III) levels, faster than malonaldehyde itself. Under the same conditions, but in the presence of EDTA, the chromogen formation is dramatically suppressed. The findings show that malonaldehyde cannot be generated in situ and are interpreted in terms of chromogen formation via an iron catalysed fragmentation of TBA-aldehyde intermediates.