Comparative Analysis of Microcapsule Properties between HPH and MF Methods
In Figure 1A, the droplet size distribution of emulsions prepared through two distinct methods, high-pressure homogenization (HPH) and microfluidization (MF), is depicted. It’s worth noting that the curves representing the HPH samples displayed a bimodal distribution, while those of the MF samples exhibited a unimodal pattern. The unimodal distribution observed in the MF samples suggests a more controlled and precise emulsification process. In contrast, the bimodal distribution observed in the HPH samples may indicate a less uniform particle size distribution. The zeta-potential of the emulsion produced via microfluidization, as illustrated in Figure 1B, exhibited a significant increase. This elevated zeta-potential in the MF samples can be ascribed to the effective mixing and minimized particle aggregation facilitated by the microfluidization process. The consistent particle size distribution and reduced aggregation tendencies contribute to a heightened surface charge density, consequently leading to the observed increase in zeta-potential. Scanning electron microscopy (SEM) micrographs, as depicted in Figure 1C, provided valuable insights into the powders generated through spray drying. Notably, the HPH samples exhibited a higher degree of size variability, whereas the MF microcapsules displayed remarkable uniformity in both size and shape. This stark difference can be attributed to the microfluidization process, which subjects the emulsion to intense shear forces, turbulence, and cavitation, resulting in a more consistent droplet breakup and microcapsule formation. Furthermore, the diminished presence of surface oil in MF microcapsules signifies enhanced encapsulation efficiency.
Figure 1D exhibits the X-ray diffractograms of the microcapsules, revealing noteworthy insights. Both microcapsules displayed characteristic peaks at 2θ values of 20°, 27°, 32°, 45°, 57°, and 67°. However, microcapsules produced via microfluidization (MF) exhibited reduced peak intensities at 27°, 32°, 45°, 57°, and 67°, while displaying heightened intensity at 2θ = 20°. These distinctions suggest discernible alterations in the crystalline phases of microcapsules formed through different homogenization methods. The variations in peak intensities signify differences in the crystalline structures of these microcapsules. The increased peak intensity at 2θ = 20° in MF microcapsules hints at a potentially distinct crystal form or arrangement, which may contribute to their enhanced stability and performance.
The Fourier-transform infrared spectra of the microcapsules, as depicted in Figure 1E, displayed prominent peaks in the ranges of 750-1000 cm-1, 1450-1700 cm-1, and 3000-3500 cm-1. Remarkably, microcapsules produced via MF exhibited a shift toward higher wavenumbers. This shift might indicate alterations in chemical bonding or interactions within the microcapsule structure. The increased intensity of peaks in MF microcapsules could be attributed to a more densely packed and structured encapsulation matrix, thereby contributing to enhanced stability.
Figure 1F portrays the differential scanning calorimetry curve of KO microcapsules. It is noteworthy that both microcapsules exhibited an initial absorption peak around 42°C. However, with increasing temperature, the second absorption peak differed between HPH and MF microcapsules. HPH microcapsules showed a peak at 55°C, whereas MF microcapsules exhibited one at 62°C. This distinction suggests that MF microcapsules possess enhanced thermal stability. The higher second absorption peak temperature in MF microcapsules indicates their ability to endure higher temperatures before undergoing structural changes or degradation.
Thence, the comprehensive analysis of these results underscores the effectiveness of MF as a homogenization method for encapsulating KO. The observed advantages in MF-produced microcapsules, including droplet size distribution, zeta-potential, size uniformity, crystalline phase, structural stability, and thermal resistance, can be attributed to the controlled and efficient microfluidization process, establishing MF as the preferred technique for KO encapsulation.