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.