Factors controlling the turbidity of submicron emulsions stabilized by food biopolymers and natural surfactant

• Submicron emulsions were prepared with mean droplet diameter of 70–450 nm.
• Modified starch, whey protein isolate and Quillaja saponins were used as emulsifier.
• Lipid phase and interface composition on turbidity were droplet size dependent.
• When droplet size <100 nm, turbidity is independent of lipid phase and interface.
• A polynomial relationship was established between droplet size and turbidity.

There is a market need of emulsion-based beverages to delivery insoluble materials and yet provide desirable appearance (cloudy or transparent). Submicron emulsions (70–450 nm) stabilized by modified starch (MS), whey protein isolate (WPI), and Quillaja saponins (QS) were prepared using microfluidization. Emulsions were characterized by dynamic light scattering, cryogenic scanning electron microscopy, and turbidimeter. Factors influencing the formation and turbidity of prepared emulsions were evaluated. Results showed that mean droplet diameter (MDD) of prepared emulsions decreased with increasing emulsifier concentration, homogenization pressure (41, 96 and 152 MPa), and number of passes (1–6) through a Microfluidizer®. When MDD >100 nm, lipid phase with higher refractive index imparted higher turbidity. WPI and QS interface imparted higher turbidity than MS interface. As MDD decreased to about 100 nm, turbidity was independent of lipid phase and interface composition. Turbidity and MDD showed polynomial correlation with maximum turbidity achieved at MDD of around 500 nm. Turbidity increased linearly with dispersed phase concentration (0.1–1 mg/g) and decreased with increasing refractive index of continuous phase (1.333–1.442). This study provides valuable information for the formulation of emulsion-based beverages with specified turbidity.