Ultra turrax

The emulsifying activity index (EAI) and the emulsion stability index (ESI) were determined by referring to Meng et al.^{24 (link)} Briefly, SZSP (5%, w/v) was dissolved in 10 mM of PS buffer (pH 7.0). Then, the pH of the solution was adjusted to a value within the range of 2–10 using 1 M HCl or 1 M NaOH. Next, 15 mL of protein solution and 2 mL vegetable oil were mixed using a homogenizer (IKA-T18, ULTRA-TURRAX, GE) at 15 000 rpm for 1 min. The emulsion (50 μL) samples were pipetted at 0 and 30 min from the bottom of the tube and diluted in 5 mL 0.1% SDS solution. The absorbance of the emulsion at 30 min and 0 min were determined using a spectrophotometer (Shimadzu UV-Visible 1800, Tokyo, Japan). The EAI and ESI were calculated using eqn (4) and (5), where A₀ is the absorbance of the emulsion, DF is the dilution factor, C is the concentration of protein solution (mg mL⁻¹) and φ is the oil volume fraction.

The FC and FS of SZSP were determined according to a previous report by Shevkani et al. with some modifications.^{20 (link)} 50 mL SZSP solution (1%, w/v) was prepared, and then adjusted to a pH (2–10) using 1 M HCl or 1 M NaOH. The solution was mixed at 15 000 rpm using a homogenizer (IKA-T18, ULTRA TURRAX, GE) for 1 min. The foam volume was measured at time 0 min and 30 min after homogenization. The FC and FS of SZSP were calculated using eqn (6) and (7), where V₀ (mL) is the foam volume at 0 min, V₃₀ (mL) is the foam volume at 30 min and V (mL) is the initial liquid volume.