RESUMO
BACKGROUND: Thylakoid-stabilised emulsions have been reported to possess satiety-promoting effects and inhibit pancreatic lipase-colipase activity in vitro, which prompted the investigation of their interfacial properties. RESULTS: Thylakoid membranes isolated from spinach were used as an emulsifier/stabiliser in oil (triglyceride)-in-water emulsions. Emulsions were characterised with respect to droplet size, interfacial tension, creaming, surface load and electron microscopy. The effects of pH and thylakoid concentration were also considered. Droplet size decreased with increasing thylakoid concentration, reaching a plateau around 15 microm beyond concentrations of 2 mg protein mL(-1) oil. The resulting emulsions were stable against coalescence but were subject to creaming. The surface pressure (air/water interface) of the thylakoid isolate was 44 mN m(-1) and the surface load 13 mg m(-2) at 10 mg protein mL(-1) oil. Electron micrographs showed thylakoids adsorbed as bunched vesicles on the drop surfaces. The stabilisation mechanism can be described as a combined effect of surface-active molecules, mainly membrane proteins but also membrane lipids, exposed on surfaces of thylakoid membrane vesicles adsorbed as particles. CONCLUSION: Thylakoid membranes effectively stabilise oil-in-water emulsions, which should facilitate their incorporation in food with satiety-promoting effects. To the authors' knowledge, this is the first study on the emulsifying properties of an isolated biological membrane as a functional ingredient.