Preparative chromatographic purification and surfactant properties of individual soyasaponins from soy hypocotyls

The amphipathic character of soyasaponins and their consequent biological and technological properties are well-recognised. However, mainly due to the absence of purified compounds, no data are available on the amphiphilic surfactant properties of individual soyasaponins. In this study we developed a preparative method for the purification of the main soyasaponins species from soy germ. Reversed-phase chromatography (Source 15 RPC) gave a good resolution of the various soyasaponins, and was used for the purification of non- and fully-acetylated soyasaponin Ab, DDMP-conjugated and unconjugated soyasaponins Ba and Bb. For these compounds, the critical micelle concentration (CMC), the minimal attainable surface tension (γ_CMC) and the surface density (Γ_max) were determined using the Wilhelmy plate method. The order of CMC values was as follows: soyasaponin Bb < Ba < βg < αg < Ab < non-acetylated Ab, and the CMC was found to range from 0.56 and to 3.2 g/L. It was concluded that the number of sugar side chains, the presence of acetyl groups and the presence of a DDMP-group are the main factors influencing the CMC of soyasaponins.