Whey protein coating increases bilayer rigidity and stability of liposomes in food-like matrices

Liposomes are suitable for encapsulating lipophilic bioactive compounds, enhancing compound solubility, stability and bioavailability. To enhance physical stability of liposomes in food-like matrices they were coated with positively charged whey protein isolate (WPI). WPI concentration, for a successful coating, was optimised by dynamic light scattering (DLS) and zeta potential measurements. Membrane properties of coated and uncoated vesicles were investigated by electron paramagnetic resonance (EPR) with site-directed and non-site-directed spin probes. Coexistence of two or three simulated spin probe populations indicated a less fluid membrane and higher concentration of water molecules in the phosphate/glycerol moiety with WPI coating. This relies on the insertion of WPI into the membrane, which is favoured by the molten globule state under investigated acidic conditions. Physical stability of liposomes benefits from WPI coating, as indicated by prolonged shelf-life, cancellation of osmotic effects in the presence of salts or sugars and a lower sensitivity towards low pH values during in vitro gastric digestion.