Isolation and determination of saponin hydrolysis products from Medicago sativa using supercritical fluid extraction, solid-phase extraction and liquid chromatography with evaporative light scattering detection

Saponins are widespread secondary metabolites with various beneficial properties: fungicidal, antibacterial, antiviral, and anticancer. Alfalfa saponin molecules contain mainly: medicagenic acid, hederagenin, bayogenin, and soyasapogenol B. Structural diversity of saponins makes their determination in Medicago sativa extracts very difficult. The most popular determination technique is high-performance liquid chromatography applied with evaporative light scattering detection. Qualitative and quantitative analysis of sapogenins from Medicago sativa by high-performance liquid chromatography with evaporative light scattering detection required hydrolysis and purification of extracts obtained by supercritical fluid extraction. Hydrolysis of saponins with concentrated hydrochloric acid provided high concentration of medicagenic acid. In the purification process, satisfactory results were obtained for solid-phase extraction using octadecyl. Recoveries were from 71 to 99% with a standard deviation from 2 to 8. Hydrolysis with concentrated hydrochloric acid was the only method that allowed identification of all four analyzed sapogenins. Moreover, it is characterized by a short time of preparation, simplicity of execution, a small amount of the sample and solvents. The hydrolysis and purification methods coupled with high-performance liquid chromatography and evaporative light scattering detection can be successfully used for qualitative and quantitative analysis of the main saponins present in Medicago sativa plant extracts obtained by supercritical fluid extraction.