Determination of three major triterpenoids in epicuticular wax of cabbage (Brassica oleracea L.) by high-performance liquid chromatography with UV and mass spectrometric detection

Lupeol, together with α- and β-amyrins in smaller quantities, has been found for the first time in the epicuticular wax of white cabbage (Brassica oleracea L. convar. capitata (L.) Alef. var. alba DC) leaf surface extract. The three triterpenoids were identified by a new high-performance liquid chromatographic (HPLC) method with UV and mass spectrometric (MS) detection using atmospheric pressure chemical ionization (APCI). All three isomeric compounds gave a parent ion peak at m/z 409 [M + H-18]+ and the relative intensities of some characteristic fragment ion peaks in tandem mass spectrometric (MS–MS) spectra of this parent ion enabled differentiation between the isomers. An additional peak at m/z 439 [M + H]+, which could be oleanonic or ursonic aldehyde, was detected by HPLC–APCI–MS. Saponification of cabbage leaf surface extract with 20% NaOH in methanol at 65 °C for 2 h had no influence on lupeol, or α- or β-amyrins, but lead to the formation of three additional compounds, which were not identified.