Okra fruit: LC-ESI/LTQOrbitrap/MS/MSn based deep insight on polar lipids and specialized metabolites with evaluation of anti-hyperglycemic activity

Okra (Abelmoschus esculentus L. Moench.) is a vegetable crop very popular in North-Eastern African countries for its edible fruits. Nowadays, this species can be easily found in European local markets, as a basic ingredient in many local and traditional dishes. Although its extensive and spread use, there is no comprehensive literature about its chemical composition. Thereby, the analysis of the polar extract of okra fruits by high-performance liquid chromatography coupled to multiple-stage linear ion-trap and orbitrap high-resolution mass spectrometry in negative electrospray ionization mode (LC-ESI/LTQOrbitrap/MS/MSn) was carried out. By this approach, 39 metabolites belonging to different polar lipid classes, such as oxylipins, phospholipids, glycolipids, and sphingolipids, were putatively identified for the first time in A. esculentus. Moreover, LC-HRMS/MS analyses guided the isolation and characterization by NMR experiments of 19 specialized metabolites belonging to phenolic acid and flavonoid classes, 8 of them never reported before in A. esculentus. Finally, inhibition of α-glucosidase activity was assayed, suggesting a good anti-hyperglycemic activity for okra fruit.