Crystallization and Melting Profiles
The thermograms of the vegetable oils and MY are shown in Figure 2. The
temperatures of the different exotherms and endotherms of each component
were determined. CA presented a crystallization and melting temperature
at -55.66±0.17°C and -18.91±0.12°C, respectively. CN presented two
crystallization signals, one -3.11±0.27°C and the other at 7.26±0.29°C,
this probably due to the composition of triglycerides in CN, which are
formed by a lower percentage of PFA that crystallize at lower
temperature (Table 1). The melting temperature of CN was at 23.08±0.13°C
(Ghosh & Rousseau, 2009). Two exotherms were observed in MY, one from
the lamellar state crystallization Lα (63.58±0.03°C) and one from
the solid-solid transition Lα ⇔ Sub-α (11.47±0.16°C).
Correspondingly, during heating, Sub-α ⇔ Lα (12.93±0.15°C) and meltingLα (65.52±0.13°C) temperatures were identified. These values are
similar to those reported by other authors for commercial
monoglycerides, where polymorphic states were identified by X-ray
diffraction (López-Martínez et al., 2014). According to some authors
(Vereecken et al., 2009), by employing pure compounds individually, the
main components of MY have different crystallization and melting points,
however, possessing a similar structure palmitic (C16:0) and stearic
(C18:0) acid, they can generate a mixed Lα crystallization
(López-Martínez et al., 2014), so the proportion in which these are
found in Myverol gelator can result in differences in thermal and
microstructural properties.
Since MY is the component responsible for gel structuring and formation,
an analysis of the changes that its endotherms can present in oleogels
with formulation and concentration variables was performed. Changes in
the crystallization of Lα were monitored (Fig. 3). In oleogels
with MGC it was possible to find MY TC values at 31.30±0.10°C in CA and
28.96±0.19°C in CN (Table 2), these values are very similar to those
reported by other authors, in a mixture used of commercial monoglyceride
with lecithin (Aguilar-Zárate et al., 2019). However, unlike the
exotherm with two peak maxima reported by Aguilar-Zárate et al. (2019),
in these systems a single peak maximum is observed, albeit in a more
robust exotherm. While these differences may be due to the temperature
ramp, it is also due to the difference in the proportions of palmitic
and stearic acid. Similarly, a single exotherm was found in the SAT
systems (Fig. 3). However, the crystallization of Lα was at a
higher temperature ~49°C (Table 2).