3.1. Microstructure and water droplet size behavior of the
emulsions
Overall, independent of the water to oleogel ratio and the CW
concentration used we obtained systems with a mayonnaise-like visual
texture, easy to handle that showed no phase separation even after six
months of storage at room temperature. As examples the Figure 1SM
(Supplementary Material) shows pictures, after 20 days of storage at
25°C, of the W/O emulsions with 0.75% and 3% CW concentration
developed at the different water to oleogel ratios studied. Figure 1
shows photographs obtained through polarized light microscopy (PLM) of
W/O emulsions with 0.75% and 3%
CW concentration developed at the different water to oleogel ratios
studied with 0 days of storage (25°C). For comparison purposes the Fig.
1SM shows PLM photographs of the same emulsions as in Fig. 1 but after
20 days of storage at 25°C. From the visual analysis of the photographs,
it was evident that, independent of the storage time, as the water to
oleogel proportion increased the water droplets of the emulsions became
larger (Figs. 1 and 1SM). Similar results were obtained with W/O
emulsions with 1.5% and 2.25% of CW (data not shown). From the visual
comparisons of the PLM photographs obtained with emulsions recently
developed (i.e., 0 days of storage) with those after 20 days of storage,
it was evident that, independent of the water to oleogel ratio, just the
emulsions with 0.75% CW showed an increase in the droplet size after
the 20 days of storage at 25°C (compare Fig. 1 and 1SM). This behavior
indicated that at 0.75% the CW concentration was not enough to achieve
an efficient emulsification of the water, and some coalescence occurred
during the stirring and/or during storage. Nevertheless, none of these
emulsions showed visual phase separation during their storage. In
contrast, the PLM photographs of the W/O emulsions with 1.5%, 2.25%,
and 3% CW at the different water to oleogel ratios studied, did not
show a significant change in the water droplet size after the 20 days of
storage (data not shown). The previous results were corroborated through
the behavior observed by the WDD97.5% in the W/O
emulsions at 0 days and 20 days of storage (Fig. 2). Thus, as observed
in the PLM photographs (Fig. 1), independent of the CW concentration
used as the water to oleogel ratio increased the system developed
emulsions with larger water droplets diameters (i.e., the
WDD97.5% increased). Additionally, the Fig. 2 showed
that for a given CW concentration and water to oleogel ratio, the
WDD97.5% of the emulsions were statistically the same
after 0 and 20 days of storage at 25°C. This WDD97.5%behavior was observed even with the 0.75% CW emulsions at the different
water to oleogel ratios (Fig. 2). Although the PLM of the 0.75% CW’s
emulsions showed an increase in the water droplet after storage (Figs. 1
and 1SM), it seemed that the NMR measurement of the water droplet
diameter (i.e., the WDD97.5%) was not capable of
detecting the tentative coalescence occurring during storage of the
0.75% CW emulsions. The WDD97.5% results (Fig. 2) also
showed that, independent of the CW concentration, we developed emulsions
of larger water droplet diameters as the water to oleogel ratio
increased. We explained this behavior considering that as the water
proportion increased the concentration of surface-active compounds from
the CW became a limiting factor, simply because more water needed to be
emulsified. The overall result was that we developed emulsions with
larger water droplet diameters (i.e., higher WDD97.5%value) as the water to oleogel ratio increased, particularly above the
50:50 water to oleogel ratio (P < 0.05; Fig. 2). A detailed
statistical analysis of the WDD97.5% behavior (Fig. 2)
showed that, independent of the storage time of the emulsions, at the
40:60 water to oleogel proportion we required to increase the CW
concentrations above 0.75% to achieve an additional reduction in the
WDD97.5% (i.e., decreasing the water droplet diameter)
(P < 0.05). However, in the 50:50 emulsions the additional
reduction in the water droplet diameter was achieved using CW
concentrations above 1.5% (P < 0.05), and in the 60:40
emulsion just at a 3% CW (P < 0.07) (Fig. 2). It is important
to note that increasing the CW concentration in the emulsions above
these values did not result in an additional reduction in the
WDD97.5% value (Fig. 2).
Then, the CW effect to decrease
the emulsions’ droplet diameter was lower as the water to oleogel ratio
increased (Fig. 2). Consequently, at the highest proportion of water
studied (i.e., 60:40), where the emulsions had the largest water droplet
diameter, the effect of the CW to achieve lower
WDD97.5% was significant (P < 0.07) just
using the highest CW concentration in the emulsions (i.e., 3%; Fig. 2).
These results corroborate the conclusion that as the water proportion
increased the CW concentration became the limiting factor for water
emulsification. An additional factor that might limit the reduction of
the water droplet diameter was that the shearing efficiency of the
blender could decrease as the olegels’ hardness increased. Previous
studies showed that the work of shear (i.e., the hardness) of 1% CW
oleogels (25°C) increased from 37.18 g/mm (± 4.30 g/mm) up to 1455.54
g/mm (± 102.44 g/mm) in 3% CW oleogels (Toro-Vazquez et al., 2007). The
CW concentration in the oleogels before adding the corresponding water
proportion, had CW concentrations even above 3% (i.e., 4.5% and 6%).
These CW concentrations would result in oleogels with even higher
hardness than the previously reported in 3% CW oleogels (Toro-Vazquez
et al., 2007), tentatively limiting the efficiency of the blender to
reduce the water droplet diameter in the W/O emulsions.