Purified oleosins at air-water interfaces

Oleosins are low molecular mass proteins that are distinguished from other proteins for their extended central hydrophobic domain which covers almost half of its entity. For this work, they were extracted from isolated maize germ oil bodies. The purification steps included washing with diethylether and a chloroform-methanol-water mixture. Their amphipathic terminal domains positioned at the organelle surface, where they strongly interact with the surface polar phospholipids, made the application of a third washing step with acetone essential. Although oleosins are well known for their insolubility in water, we were able to prepare aqueous buffer solutions of 0.008 wt% at pH 8.0. The interfacial behaviour of oleosins was studied, in order to predict their ability to stabilize foams. Even at low concentrations they were capable of decreasing the interfacial tension of air-water interfaces to values similar to those obtained from milk protein or egg yolk apolipoproteins adsorption. Pendant drop profile analysis showed that the dilatational elastic modulus was frequency-dependent, but at the same time the elastic to viscous modulus ratio was frequency-independent and below 0.1. The results indicate that oleosins might have a high potential as foam stabilizers, a fast developing and challenging field.