3.4.1. Pure fats and oils
Figure 2 shows crystallization and melting curves, while Table S1 in Supplementary material shows a complete table for melting and crystallization peaks of pure fats and oils. Multiple and overlapped peaks were observed in crystallization and melting curves of Brazil nut oil, pracaxi oil, and bacuri fat. This behavior is probably due to the variety of TAGs present in the composition of these lipids, including differences in the carbon length and saturation grade. Multiple endothermic events were also reported by Pardauil et al.(2017), who studied thermal profiles of vegetable oils from Amazon region.
In fact, the crystallization curve of these three lipids exhibited two distinct exothermic peaks. The first probably occurred due to presence of TAGs composed of SFA, and the second due to crystallization of TAGs containing MUFA and PUFA. For pracaxi oil these two fractions might correspond to a fraction rich in behenic and lignoceric acids (crystallization at 5.55 ºC), and other rich in tri-unsaturated TAGs with oleic and linoleic acids (crystallization at -43.22 ºC). For Bacuri oil, these two fractions might correspond to a fraction rich in palmitic acid (crystallization at 25.80 ºC) (PPP/PPoP/POP), and another fraction rich in oleic acid (crystallization at 1.23 ºC) (PPoO/OOP). In case of Brazil nut oil, one fraction is probably rich in TAGs with palmitic and stearic acids (crystallization at -0.38 ºC) (POLi/SOLi) and the other fraction might correspond to tri-unsaturated TAGs with oleic and linoleic acids (crystallization at -60.78 ºC). Such fractions might present particular physical properties that should be investigated more carefully in order to improve the use of these fats and oils in technological applications.
According to the heating curves obtained, pracaxi and Brazil nut oils were fully melted close to 25 °C. This value is close to the melting point of OOBe and OOP (Wesdorp et al., 2005), TAGs with the highest melting temperature in these oils.
Concerning bacuri fat, the melting curve presented a clear recrystallization event (exothermic transition) between the melting of the two main TAG factions. The presence of both endo- and exothermic peaks in the DSC melting indicates that TAG molecules have transitioned from one crystal form into another (Tolstorebrov, Eikevik, & Bantle, 2014). Bacuri fat’s last solid fraction melted at 56.79 °C, which is consistent to the melting point of the β’-modification of PPP (Wesdorp et al., 2005).
On the other hand, patawa oil, tucuma kernel oil and murumuru fat presented sharper and more defined crystallization and melting events. This is probably due to their more homogeneous FA content. Patawa has a high content of oleic acid, while tucuma kernel oil and murumuru fat are rich in lauric and myristic acids.