β-Cyclodextrin-Mediated Removal of Soy Phospholipids from the Air-Water Interface

Binding of soy phosphatidylcholine (PC) and phosphatidylinositol (PI) with beta-cyclodextrin (beta CD) was studied using a spread monolayer technique at the air-water interface. First, surface pressure (pi) versus surface concentration (Gamma) isotherms of both PC and PI were characterized by forming spread monolayers on an aqueous subphase. PC and PI monolayers reached saturation at Gamma of 1.98 and 3.24 mu mol/m(2), respectively, at 25 A degrees C. Subsequently, desorption of PC or PI from the spread monolayer in the presence of 2-14 mM beta CD in the subphase was studied by measuring changes in pi of monolayer. This desorption was indicative of a complex formation between beta CD and PC or PI. The amount of PC or PI bound to beta CD was determined by converting the net change in pi to Gamma by using pi-Gamma isotherms. From the saturated monolayers at the air water-interface, approximately 30% of PC and 50% of PI could be removed by 14 mM beta CD. It was calculated that the free energy change required to transfer a PL from the monolayer at air-water interface to the aqueous phase in presence of beta CD was decreased by 6-7 kcal/mol. Hydrolysis of PC in the monolayer by phospholipase A(2) (PLA(2)) improved extraction efficiency of beta CD. By incorporating 2.29 mu M PLA(2) and 10 mM beta CD in subphase, up to 80% of PC monolayer could be desorbed from the air-water interface. These results are discussed in terms of the potential use of beta CD to remove PLs bound to soy protein.