Fig. 2 Demonstration of LSO (a) and FO (b) 2D
T1-T2 TD fingerprinting map after 96 h
heating at 55 oC.
The LSO and FO 1H LF NMR energy relaxation time
spectra after undergoing oxidation (Fig. 2) has more peaks than the four
characteristic peaks of the original LSO and FO (Fig. 1). These new
peaks correspond to the oxidation products. The spectrum of a
non-oxidized oil (Fig. 1) is characterized by 4 major peaks with the
T1 and T2 of similar values with the
peaks being aligned in the diagonal of the map. After oxidation the map
of Fig. 2 not only present new peaks related to the oxidation products
but there is also a bending effect in the curve from the diagonal
because of decreasing T2 values, indicating oxidation
(Resende et al., 2019a,b). In order to confirm the oxidation of the LSO
and FO after 96 hours of thermal oxidation observed in the1H LF-NMR energy relaxation time map of Fig. 2, these
material were also analyzed by peroxide value (PV) tests. The PV test
results (Table 2) support the oxidation of the LSO and FO wherein the
fish oil shows a higher PV value, indicating a higher degree of
oxidation than the LSO. This is in agreement with the GC-MS results of
changes of fatty acids profile during thermal heating (not shown) and
previously published literature (Resende et al., 2019), because of the
higher number of double bonds in the fish oil increase its propensity to
oxidation.
Table 2: Peroxide values (PV) of LSO and FO in thermal
conditions (55oC)