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Keywords:

  • glass transition;
  • nanoemulsion;
  • optimization;
  • stability;
  • viscosity

Abstract:  The objective of this study was to determine the effect of changing viscosity and glass transition temperature in the continuous phase of nanoemulsion systems on subsequent stability. Formulations comprising of β-casein (2.5%, 5%, 7.5%, and 10% w/w), lactose (0% to 20% w/w), and trehalose (0% to 20% w/w) were generated from Design of Experiments (DOE) software and tested for glass transition temperature and onset of ice-melting temperature in maximally freeze-concentrated state (Tg′ & Tm′), and viscosity (μ). Increasing β-casein content resulted in significant (P < 0.0001) increases in viscosity and Tm′ (P= 0.0003), and significant (P < 0.0001) decreases in Tg′. A mixture design was used to predict the optimum levels of lactose and trehalose required to attain the minimum and maximum Tg′ and viscosity in solution at fixed protein contents. These mixtures were used to form the continuous phase of β-casein stabilized nanoemulsions (10% w/w sunflower oil) prepared by microfluidization at 70 MPa. Nanoemulsions were analyzed for Tg′ & Tm′, as well as viscosity, mean particle size, and stability. Increasing levels of β-casein (2.5% to 10% w/w) resulted in a significant (P < 0.0001) increase in viscosity (5 to 156 mPa.s), significant increase in particle size (P= 0.0115) from 186 to 199 nm, and significant decrease (P= 0.0001) in Tg′ (−45 to −50 °C). Increasing the protein content resulted in a significant (P < 0.0001) increase in nanoemulsion stability. A mixture DOE was successfully used to predict glass transition and rheological properties for development of a continuous phase for use in nanoemulsions.