An isocratic reversed-phase HPLC separation of the stereoisomers of the provitamin A carotenoids (α- and β-carotene) in dark green vegetables

An isocratic reversed phase HPLC assay was developed for monitoring the isomers of α- and β-carotene in dark green leafy vegetables using a mixture of isomers obtained from the light catalysed oxidation of all-trans α- and β-carotene in the presence of iodine. The method was applied to Italian spinach, spring cabbage and cowpea leaves. The isomers were identified by the elution order from thin layer chromatography, the absorption spectral data and comparison with published results. The three main isomers of β-carotene found to be dominant in the samples analysed were all-trans, 9-cis and 13-cis β-carotene, and occurred in average proportions of 85, 11 and 4%, respectively, in fresh samples.