A. Characterization of PUFA-rich Linseed oil (LSO) and Fish oil
(FO) susceptibility to thermal autoxidation using 1H
LF-NMR energy relaxation Time Domain (TD) graphical peak fingerprint
material analysis.
To understand the LF 1H NMR analysis of emulsions we
first characterized the pure linseed and fish oil. Linseed oil and fish
oil are both PUFA-rich materials. Linseed oil is composed mainly of
linolenic acid (18:3, n-3; ALA), linoleic acid (18:2, n-6; LA) and oleic
acid (18:1, n-9; OA). Fish oil is rich in the omega-3 long chain PUFAs
docosahexaenoic acid (22:6, n-3; DHA) and eicosapentaenoic acid (20:5,
n3; EPA) (Azuma et al., 2009). PUFAs have biochemical and physiological
effects on human health enhancement, but the presence of multiple double
bonds and bisallylic carbons affects their oxidative susceptibility, and
generation of toxic oxidative products, directly proportional to their
degree of unsaturation (Miyashita et al., 1993; 2018).
In the liquid oil phase, fatty acids are self-associated as
hydrogen-bonded head to head dimers that are further aggregate as
quasi-liquid crystal clusters alternating head to tail arrangement. The
cluster aggregates determine the fatty acids liquid properties (Iwahashi
and Kasahara, 2011; Berman et al., 2015; Resende et al., 2019b). The
dimer fatty acid assembly is characterized by four different segmental
motions. The ionic head to head groups are the most rigid
microstructure, followed by the double bonds, then aliphatic chain, and
the tail chain is the most mobile segment. In the triacylglycerol(TAG)
structure, a glycerol bridges 3 FA chains, and is also characterized by
four different segmental motions (Resende et al., 2019a)
The 1H LF-NMR energy relaxation TD graphical peak
fingerprinting analysis of LSO and FO are shown on Fig. 1 LSO and FO TAG
structure is characterized by four different rigidity-mobility segments
and each one of these segments have characteristic T1(spin-lattice) and T2 (spin-spin) energy relaxation
times. Analysis of the one-dimensional T1 and
T2 spectra of LSO and FO, shows the presence of fours
characteristic peaks. From previous studies (Berman et al., 2015;
Resende et al., 2019b), peak 1 is assigned to glycerol since the most
rigid microstructure and therefore corresponds to the lowest energy
relaxation times. Peak 2 is assigned as double bonds as the second most
rigid microstructure. Peak 3 is assigned to the aliphatic chains that
have less rigidity and peak 4 is assigned as the tail chain as the most
mobile segment, corresponding to the longest energy relaxation time.
Thus as described in the above paragraph and shown in Fig. 1 and Table 1
the basic molecular segment pattern analysis by 1H
LF-NMR is based on the glycerol segment as the most rigid moiety,
followed by the double bonds of the FA chains, the aliphatic chains and
aliphatic tails, respectively. In the cases of linseed oil (LSO) and
fish oil (FO) of the present study a similar
T1-T2 TD (59-55 ms) was assigned to the
triacylglycerols head groups of the two oils. Additional three
relatively rigid TDs with low mobility peaks were assigned to double
bonds (mono-, di- and polyunsaturated fatty acids) with increasing
mobility for the two oils (Table 1), in agreement with previous reports
(Berman et al., 2015, Meiri at., al 2015). Two peaks assigned to the
long and short aliphatic chains were also assigned as well as two peaks
assigned to the longer tails of omega-6 and short tail of omega-3 were
identified for the two oils.