Particle Size

The 3-D response surface plots for Z-Ave, D50, and D90 (Figure 2A–C) showed that as the emulsification speed (rpm) increased, the particle size decreased. In contrast, the number of HPH cycles did not cause a direct change in particle size, although a decrease was observed when the emulsification speed and the number of HPH cycles increased together.

The lowest and highest values of Z-Ave (124.80 and 141.90 nm, respectively), D50 (55.90 and 86.70 nm), and D90 (144.00 and 189.40 nm) were observed, respectively, when 14,000 rpm with 18 cycles and 11,000 rpm with 12 and 18 cycles were used. Therefore, it was concluded that higher emulsification speed and number of HPH cycles decrease the NLC size, which can be explained by the kinetic energy used in the high-speed emulsification process required to obtain a stable emulsion of uniform nanoparticle size [11]. In addition, the prolongation of the HPH process with more cycles promoted the breakdown of the emulsion oil droplets, since they suffered higher compression, turbulence, and cavitation within the homogenization gap [79,92,98]. Furthermore, the stability and bioavailability of the NLC dispersion were also improved [78,92]. Thus, 14,000 rpm with 18 homogenization cycles were set as the ideal conditions for the HPH method.
