Alkyl Tail Segments Mobility as a Marker for Omega-3 PUFA-rich Linseed
Oil Oxidative Aging
Abstract
The goal of the present study is to demonstrate 1H LF-NMR time
relaxation measurements for efficient and rapid evaluation of Omega-3
polyunsaturated fatty acids (PUFA)-rich linseed oil (LSO) oxidative
aging mechanisms, by monitoring primary chemical and structural changes
occurring during thermal oxidative stress. The LF NMR monitors the
different proton spin-spin coupling energy relaxation times, T2 within
LSO molecular segments, from the initiation of free radical generation
and hydroperoxide formation to the propagation of alkoxy radicals, and
alpha, beta-unsaturated aldehydes formation, and a termination phase of
crosslinked polymerization end products. The 1H LF NMR T2 values
monitors both the covalent and secondary bonding interactions (e.g.,
electrostatic and hydrogen bonding) during the different oxidation
phases. The present paper shows that LSO tail segments mobility in terms
of T2 multi-exponential relaxation decays, generated by data
reconstructing of 1H transversal relaxation components are providing a
clear, sharp and informative understanding of LSO sample’s autoxidation
aging processes. This is supported by high field band selective 1H NMR
pulse excitation for hydroperoxide and aldehydes quantification of the
same LSO samples at 25, 40, 60, 80, 100, and 120oC with pumped air for
168 h. Peroxide value, viscosity and self-diffusion, as well as fatty
acids profile and by- products determined by GC-MS were also carried
out, and correlated with the LSO tail T2 relaxation results. In
conclusion the selective determination of LSO alkyl tail T2 energy
relaxation time domain values was demonstrated as a rapid evaluation
marker for following omega-3 PUFA-rich oils oxidative aging.