title: Surface activity of saponin from Quillaja bark at the air/water and oil/water interfaces.
abstract: Surface activity of Sigma's Quillaja bark saponin (QBS) was studied by means of dynamic interfacial tension and surface dilational rheology at three fluid/fluid interfaces with the polarity of the non-aqueous phase increasing in the order: air/water, tetradecane/water and olive oil/water. The equilibrium interfacial tension isotherms were fitted to the generalized Frumkin model with surface compressibility for the air/water and tetradecane/water interfaces, whereas the isotherm for the third interface displays a more complex shape. Upon fast compression of a drop of concentrated "Sigma" QBS solution immersed in olive oil, a clearly visible and durable skin was formed. On the other hand, no skin formation was noticed at the air/water interface, and only a little at the tetradecane/water interface. Addition of a fatty acid, however, improved slightly the skin-formation ability of the QBS at the latter interface. The surface behavior of the QBS from Sigma was compared with that from Desert King, Int. ("Supersap"), employed in a recent study by Stanimirova et al. [22]. The two products exhibit different areas per molecule in the saturated adsorbed layer (0.37nm(2) vs. 1.19nm(2) for "Sigma" and "Supersap", respectively). Also their surface rheology is different: although both QBSs form predominantly elastic layers, for "Sigma" the surface storage modulus, εr=103mNm(-1), while for "Supersap" εr=73mNm(-1) at 10(-3)moll(-1) (i.e., around their cmc). The two saponin products exhibit also different ionic character, as proven by the acid-base titration of their aqueous solutions: QBS from Sigma is an ionic surfactant, while the "Supersap" from Desert King is a non-ionic one.
authors.affiliation: Department of Microbioanalytics, Faculty of Chemistry, Warsaw University of Technology, Warsaw, Poland. kamil.wojciechowski@ch.pw.edu.pl
authors.forename: Kamil
authors.initials: K
authors.lastname: Wojciechowski
mesh_terms: D000388:Air; D000473:Alkanes / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D000069463:Olive Oil; D024301:Plant Bark / Q000737:chemistry*; D010938:Plant Oils / Q000737:chemistry*; D031990:Quillaja / Q000737:chemistry*; D062605:Quillaja Saponins / Q000737:chemistry*; D012212:Rheology; D013500:Surface Tension; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D000473:Alkanes; D000069463:Olive Oil; D010938:Plant Oils; D062605:Quillaja Saponins; C024713:n-tetradecane; D014867:Water