Evaluation of the 1-methyl-2-phenylindole colorimetric assay for aldehydic lipid peroxidation products in plants: Malondialdehyde and 4-hydroxynonenal

The 1-methyl-2-phenylindole colorimetric assay is considered specific for malondialdehyde (MDA) and 4-hydroxynonenal (HNE) in mammalian systems, but its specificity in plant tissues is unknown. This study demonstrates that the assay produces a purple/blue chromophore with an absorbance peak at 586 nm for a malondialdehyde standard, while aqueous extractions from Ribes spp. Beta vulgaris, and Lycopersicon esculentum tissues produce an orange chromophore with an absorbance maximum at 450 nm and a large shoulder that extends to 700 nm. No distinctive MDA peak was discernable in plant samples at λ = 586 nm and absorbance was attributed to background interference. The reaction between sucrose and 1-methyl-2-phenylindole produced an orange chromophore with a spectrum similar to those obtained from plant extractions, suggesting that simple sugars are the likely source of background interference. This study demonstrates that the 1-methyl-2-phenylindole colorimetric assay is non-specific for detecting MDA and HNE in plants and its use is cautioned due to interference, particularly from sugars.