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.