2.15. Emulsion Stability Index (ESI) and Emulsifying Activity Index (EAI)

The determination of ESI and EAI was conducted following the method of Zhang et al. [31] with minor modification. Protein solution (8 mL; 1 mg/mL) and soybean oil (2 mL) were mixed using homogenizer (20,000 r/min for 1 min). The bottom emulsion (20 μL) was diluted to 5 mL with SDS (Sodium dodecyl sulfate) (0.1%); after vertexing vigorously for 10 s, the absorbance (A₀) was measured at 500 nm. Again, after 10 min, the bottom emulsion (20 μL) was diluted to 5 mL with SDS (0.1%) and the absorbance (A₁₀) was determined following the same procedure. The blank control was SDS solution (0.1%). Equations (7) and (8) were used to calculate ESI and EAI, respectively.

where C is the pre-emulsification protein content (g/mL); φ is the volume fraction of oil phase in emulsion (v/v); and di is dilution factor.