Saponin inventory from Argania spinosa kernel cakes by liquid chromatography and mass spectrometry.

Introduction: Argania spinosa kernel cakes, obtained from argan oil extraction process, are known to contain large amounts of saponins. Only a few have been characterised previously, due to the use of pure ethanol as extracting solvent. The use of aqueous 50% ethanol improved the extraction of more polar saponins.

Objective: Identification of polar saponins in kernel cakes of Argania spinosa by liquid chromatography-mass spectrometry and NMR techniques.

Methods: Defatted kernel cakes were first extracted with ethanol and then twice with 50% aqueous ethanol. Individual crude extracts were analysed with an ion-trap mass spectrometer in negative mode electrospray MS and MS/MS modes. NMR experiments were run under standard conditions at 300 K on a Bruker DRX-600 spectrometer.

Results: The LC-MS base peak chromatogram of saponins from pure ethanol extract was dominated by 11 large and several small peaks but the UV chromatogram showed only two peaks, corresponding to the main neutral saponins found previously in Argania: arganine A and B. In 50% aqueous ethanol extracts, numerous other saponins were detected. Many of them were glucuronide oleanane-type triterpene carboxylic acid 3,28-O-bidesmosides (GOTCAB saponins). The assignments of (1) H- and (13) C-NMR spectra of the four most abundant GOTCAB saponins confirmed the MS results.

Conclusion: Four GOTCAB saponins were structurally identified by NMR analysis in the 50% aqueous ethanol extract. Furthermore, LC-MS analyses showed the presence of at least 19 additional polar saponins in these kernel cakes.