Characterization of aescin as a biosurfactant for environmental remediation

Surface-tension-lowering capacity and emulsion-forming ability of aescin biosurfactant in pure water, seawater, 3 M urea, and 3 M glucose were investigated. Oils used in the emulsification tests were liquid paraffin, ethylbenzene, kerosene, 1-decene, and heavy oils A and C. Volumetric ratios of oil phase to aqueous (water) phase (O/W) were 0.5:4.5, 2.5:2.5, 3.0:2.0, and 4.5:0.5. Concentration of aescin was changed from 0.16 to 27.3 mM. The critical micelle concentration of aescin in water and its surface tension effectiveness were shown to be 0.78 mM and 28.5 mN/m, respectively. Surface-tension effectiveness of aescin was found to be highest in seawater (33.5 mN/m). The emulsifying action of aescin was compared with that of decaglyceryl-monolaurylester (DGML). The performance of aescin was found to be as good as that of DGML and, depending on the O/W ratio and the concentration, aescin could yield emulsification efficiencies as high as 100%. These results indicated that aescin could be classified as a mild surfactant safe for living organisms. Because the surface activity of aqueous aescin solution was not satisfactorily good, attempts were made to improve the situation by addition of alcohols as cosurfactants. Ethanol, isoamyl alcohol, 2-ethylhexanol, n-hexanol, and n-octanol were used. They were added to the solutions at a concentration equimolar to aescin. These cosurfactants improved surface-tension effectiveness of aescin by as much as 53% and its emulsification efficiency by 67%.