Physicochemical properties of whey protein, lactoferrin and Tween 20 stabilised nanoemulsions: Effect of temperature, pH and salt

• Formation of nanoemulsions using different types and concentrations of emulsifiers.
• Whey protein isolate or lactoferrin produced smaller droplets than Tween 20.
• Lactoferrin nanoemulsions had good stability to heat treatment, pH and salt.
• Tween 20 nanoemulsions were unstable to high temperature at 90 °C for 15 min.
• Whey protein isolate nanoemulsions unstable at pH 4.5–5.5 and at >30 mM CaCl2.

Oil-in-water nanoemulsions were prepared by emulsification and solvent evaporation using whey protein isolate (WPI), lactoferrin and Tween 20 as emulsifiers. Protein-stabilised nanoemulsions showed a decrease in particle size with increasing protein concentration from 0.25% to 1% (w/w) level with Z-average diameter between 70 and 90 nm. However, larger droplets were produced by Tween 20 (120–450 nm) especially at concentration above 0.75% (w/w). The stability of nanoemulsions to temperature (30–90 °C), pH (2–10) and ionic strength (0–500 mM NaCl or 0–90 mM CaCl2) was also tested. Tween 20 nanoemulsions were unstable to heat treatment at 90 °C for 15 min. WPI-stabilised nanoemulsions exhibited droplet aggregation near the isoelectric point at pH 4.5 and 5 and they were also unstable at salt concentration above 30 mM CaCl2. These results indicated that stable nanoemulsions can be prepared by careful selection of emulsifiers.