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.