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.