A comparison of fat globule diameters obtained by
using conventional and ultrasonic homogeniser is given in
the Table. As shown in the Table, milk homogenised by
the conventional homogeniser had smaller fat globules
than non-homogenised milk, and milk homogenised by
ultrasound (higher power levels) also had smaller fat
globules than milk homogenised by a conventional
homogeniser. However, the higher the ultrasound
amplitude levels, the smaller the fat globule diameter. The best homogenisation and the smallest fat globule
diameter (0.725 µm) were obtained at a power level of
100 for 10 min.
The fat globule diameters of milk homogenised by
using conventional and ultrasonic homogeniser ranged
between 2.0-3.0 and 0.5-5.0 µm, respectively, while the
fat globule diameters of non-homogenised milk ranged
between 4.0 and 7.0 µm. The fat globule diameters
obtained at a power level of 40 for 10 min (2.375 µm)
were similar to those from (2.625 µm) conventional
homogenisation (Table). Consequently, the fat globule
diamater obtained in conventional homogenisation could
be achieved by using ultrasonic homogenisation at power
level of 40 for 10 min.
Micrographs of milk samples are shown in Figure 1.
As shown in Figures 1a-j, as the ultrasound power levels
and exposure times increased, the distribution of fat
globules was more stable and smaller fat globule
diameters were obtained. It was difficult to observe the
fat globules at a power level of 100 for 10 min (Figure
1j) because of breakage into very small fragments. There
were numerous fat globules smaller than 1 µm at a
power level of 100 for 10 min (Figure 1j). However, the
fat globules in non-homogenised milk could be easily seen
(Figure 1a).A significant correlation was found between the
diameter of fat globules and homogenisation efficiency (P
< 0.01). The homogenisation efficiency of milk samples
versus amplitude levels is plotted in Figure 2.
As shown in Figure 2, as the amplitude levels
increased, the homogenisation efficiency of homogenised
milk samples also increased. However, the exposure
times had an important effect on the homogenisation of
milk.