2.3. Characterization of Emulsion

Emulsion morphology was observed by a digital optical microscope (DMBA400, Motic China Group Co., Ltd., Xiamen, China) at 400× magnification and took photos to record observations.

Fluorescence microscopy was carried out using an automatic fluorescence microscope (LECIA DM6 B, Lecia, Wetzlar, Germany). Nile red (1 mg) was dissolved in 1 mL of DMSO to prepare a fluorescent dye solution. The fleshly prepared emulsion and dye solution was mixed evenly and dropped on the slide, covered with a coverslip, and left to dry naturally for 2 h. The distribution of the two phases was observed using a fluorescence microscope.

The rheological property of lutein emulsion was determined using a rotational rheometer (DHR-1, Waters, Milford, MA, USA). The model chosen was flow scanning. Each measurement was carried out using parallel plates with a 40-mm gap. The temperature was set at 25 °C and 50 °C, respectively. Dynamic viscosity values were obtained at shear rates in the range of 0.01–100 s⁻¹. The flow measurement data were evaluated by Herschel–Bulkley:

where τ is the shear stress (Pa); τ₀ is the yield stress (Pa); K is the consistency coefficient (Pa·sⁿ); γ is the shear rate (s⁻¹); n is the flow behavior index.