4. Conclusions
A recent publication (Penagos et al., 2023) showed that carnauba wax and
beeswax can develop structured W/O emulsions stabilized through the
Pickering effect and by a network of wax crystal dispersed through the
oil phase. Based on contact angle measurement these authors discarded
the CW as a tentative stabilizer of W/O emulsions, although under the
conditions used (i.e., pre-emulsification step at 90°C followed by a
dynamic crystallization step up to achieving 5°C) no W/O emulsions were
done with the CW (Penagos et al., 2023). The results obtained in the
present study showed that, under the time-temperature conditions used
initially to develop a CW oleogel (i.e., cooling stage from 90°C to
25°C) followed by an emulsification process at 25°C, the CW can develop
structured W/O emulsions with stability to freeze/thaw cycles even after
20 days of storage at 25°C. Under these processing conditions ≈26% of
the CW components remained in the oil phase (i.e., triterpenic alcohols,
esters of triterpenic alcohols, aliphatic alcohols, and fatty acids) and
≈73% of the CW components, mainly n -alkanes and long chain
esters, developed an oleogel. We considered that the CW components
remaining in the oil phase, could act as surface-active agents at the
oil-water interface during the emulsification process stabilizing the
water droplets. An additional stabilizing phenomenon of the CW emulsions
was the hardness (i.e., elasticity) of the oleogel phase surrounding the
water droplets. This oleogel, developed during the cooling stage before
water addition, was structured through the crystallization of the
constitutive n -alkanes and long chain esters of the CW.
Consequently, a great extent of the rheological properties of the
oleogel, essentially determined by the CW concentration, determined the
elasticity (i.e., G’) of the W/O emulsions (Fig. 6). Thus, at a constant
water to oleogel ratio the G’ of the emulsions increased exponentially
as the CW concentration increased. An additional factor that determined
the CW emulsions’ rheology was the reduction in the water droplet
diameter (i.e., decrease in the WDD97.5% of the
emulsions) associated with the emulsifying effect of the surface-active
component of the CW. However, the emulsifying effect of the CW to
decrease the WDD97.5% of the emulsions (Fig. 2) that
subsequently resulted in an increment in the emulsion’s G’, depended on
the water proportion in the emulsions. This was because, as the water
fraction increased the amount of surface-active compounds of the CW
became the limiting factor to achieve an efficient emulsification of the
water phase. Consequently, when compared with the
WDD97.5% observed in the 40:60 and 50:50 emulsions, we
obtained larger water droplet diameters (i.e., higher
WDD97.5% in the emulsions) in the 60:40 emulsions (Fig.
2). Therefore, independent of the CW concentration the emulsions
developed at the higher water to oleogel proportion (i.e., 60:40), were
also the ones showing the lower stability, as assessed by the
freeze-thaw cycles applied by DSC (Fig. 4). The emulsions developed with
the lower CW concentration, which represented the condition of most
limiting concentration of surface-active compounds of the CW, also
showed low emulsion stability that became more evident as the water to
oleogel proportion increased (Fig. 4A). Our results indicated that the
W/O emulsions formulated with water to oleogel ratios of 40:60 and 50:50
and with CW concentrations between 1.5% and 3%, were the most stable
even after two freeze-thaw cycles applied emulsions stored for 20 days
at 25°C. Finally, commercial standard and light mayonnaises observed
similar rheological behavior than several W/O emulsions developed with
the CW. Within this context, Figure 8 shows the time-dependent recovery
profiles of commercial standard mayonnaise (M-1 with 46.4% ± 0.2%
water and 40.3% ± 0.2% vegetal oil; M-2 with 12.0% ± 0.1% water and
85.3% ± 3.2% vegetal oil) (Fig. 8A) and commercial light mayonnaise
(LM-1 with 61.3% ± 1.3% water and 22.4% ± 0.2% vegetal oil; LM-2
with 49.9% ± 0.2% water and 17.4% ± 4.7% vegetal oil) (Fig. 8B). The
rheological profiles of these commercial mayonnaise are shown in
comparison with the recovery profiles of structured W/O emulsions
formulated with 40:60 and 50:50 water to oleogel ratios and 1.5% CW
after 20 days of storage at 25°C. Evidently, the recovery profiles of
the 1.5% CW emulsions formulated with water to oleogel ratios of 40:60
and 50:50 even after 20 days of storage, showed a rheological behavior
closer to the ones observed by the standard mayonnaise (Fig. 8A). This
in spite that, according to the mayonnaises’ manufacturers, the water
emulsification was done using highly efficient industrial homogenizers
and stabilized with a combination of emulsifiers (i.e., egg yolk, whey
protein, ovalbumin/egg white powder) and gelling agents (i.e., xanthan
gum, modified starch). Consequently, when observed under the PLM the
water droplets’ diameter of the commercial mayonnaise was substantially
smaller (data not shown) than the ones obtained with the blender used to
develop the CW emulsions. The results of this study showed that CW is a
multifunctional ingredient suitable for the elaboration of stable edible
structured W/O emulsions. It is important to point out that under
similar processing conditions other vegetable waxes (i.e., rice bran
wax, carnauba wax) developed W/O emulsions. However, the emulsions
developed by these waxes showed poor texture that after a few hours
(i.e., rice bran wax) or after 3 to 4 days (i.e., carnauba) showed phase
separation. In contrast, the mayonnaise-like W/O emulsions developed
with CW concentrations between 1.5% and 3% using water to oleogel
ratios of 40:60 and 50:50 did not have the waxy flavor characteristic of
the CW oleogels, and were stable not showing phase separation even after
6 months at 25°C. Currently we are evaluating the development of CW
emulsions utilizing a tabletop homogenizer under different
time/temperature and shearing rate conditions using vegetable and
mineral oil as the continuous phase.