Metabolite profiling of saponins in Balanites aegyptiaca plant tissues using LC (RI)-ESI/MS and MALDI-TOF/MS

Saponins are a major family of secondary metabolites which consist of a sugar moiety glycosidically linked to a hydrophobic aglycone (sapogenin). In recent years the interest in saponins has increased significantly because of their diverse properties as natural detergents and foaming agents, their cardiac, immunostimulating, and anti-cancer activity, as well as other health promoting functions. This study deals with metabolitic analysis of saponins from methanolic extracts of fruit mesocarp (ME), seed kernel (KE) and root (RE) of Balanites aegyptiaca (L.) Del. (desert date) plant grown in Israel using LC (RI)-ESI/MS and MALDI-TOF/MS. The structural assignment was carried out by fragmentation experiments of LC (RI)-ESI/MS and literature data. The study has revealed that, all together, twenty-four furostanol saponins were found in ME, KE and RE. Of these, four saponins are found only in ME, five only in KE and six only in RE. Diosgenin was found to be the sole aglycone in all the saponins. The smallest saponin (MW 740 Da) was found with two sugar units (glucose) and the largest saponin (MW 1678 Da) was found with eight sugar units (5 glucose, 2 rhamnose and 1 xylose) attached to diosgenin. The results suggest that MALDI-TOF/MS with positive ion mode is particularly effective for determining the metabolites of saponins in B. aegyptiaca plant tissues. MALDI-TOF/MS not only verified the results of the LC (RI)-ESI/MS, but also identified additional saponins that are now systematically organized in a database of B. aegyptiaca saponins.