2.7 Accelerated stability analysis
The accelerated storage stability of fresh emulsions was analyzed using an analytical photocentrifuge LUMiSizer® LS650 (LUM GmbH, Berlin, Germany) using the methodology used by Erramreddy et al. (2017). An aliquot of emulsion (400 μL) was added with a syringe into a rectangular polycarbonate cuvette (8 mm x 2 mm) (LUM GmbH, Berlin, Germany) and centrifuged at 4000 rpm (2325xg). The equipment transmits an 865 nm wavelength laser through the cuvettes every 60 s (1000 transmission profiles collected in 16 h 40 min) during the centrifugation. The light intensity transmitted through the emulsion depends on droplet movement under the centrifugal force. Data analysis and calculation of sedimentation velocity (μm/s) from the final transmission profile were processed using the SEPView® software 4.1 (LUM GmbH, Berlin, Germany).
2.8 Rheological properties of W/O emulsions
The apparent viscosity and viscoelasticity of fresh and 7 days old emulsions were measured using an AR-G2 rheometer (TA Instruments, Montreal, QC, Canada) at 25 °C with an acrylic parallel plate (60 mm diameter). For viscosity measurement, a shear rate from 0.01 to 100 s-1 and a loading gap of 1000 µm were used. The oscillatory mode was used at a strain ranging from 0.01 to 1000% to measure storage (G’) and loss moduli (G”) at a constant frequency of 1 Hz. (6.18 rad/s). The apparent viscosity values of emulsions at a shear rate of 0.1 s-1 on day 0 and 7 were used to calculate the viscosity index (Eq. 3) to determine the change in viscosity with time.
\(Viscosity\ index=\ \frac{\text{Apparent\ viscosity\ of\ emulsion\ }on\ day\ 7}{\text{Apparent\ viscosity\ of\ fresh\ emulsion}}\)Eq. 3