Alkyl Tail Segments Mobility as a Marker for Omega‐3 Polyunsaturated Fatty Acid‐Rich Linseed Oil Oxidative Aging

Abstract

Omega‐3 polyunsaturated fatty acid (PUFA)‐rich linseed oil (LSO) is an important component in biological systems, foods, and many other industrial products. In recent years, LSO has attracted increased attention in the field of functional foods, which has highlighted its facile susceptibility to aging by autoxidation. Common colorimetric and a long list of spectral methodologies have been used to follow after and predict LSO shelf life's quality, especially in regards to aging by autoxidation. These standard methodologies are nevertheless limited, because of the complexity of the LSO's chemical and physical changes. The goal of the present study is to develop a sensorial 1H LF‐NMR energy relaxation time application based on monitoring primary chemical and structural changes occurring with time and temperature during oxidative thermal stress for better and rapid evaluation of LSO's aging process. Using 1H low‐field NMR, the different T2 times of energy relaxations due to spin–spin coupling, and proton motion/mobility of LSO molecular segments were monitored. As previously reported, we characterized the chemical and structural changes in all phases of the autoxidation aging process. Starting from the initiation phase (abstraction of hydrogen radical, fatty acid chain rearrangement, and oxygen uptake yielding hydroperoxides products), through to the propagation phase (chain reactions resulting in tail cleavage to form alkoxy radicals, and alpha, beta‐unsaturated aldehydes formation), and a termination phase (cross linking and production of polymerization end products). The 1H LF NMR transverse relaxation approach, monitors both the covalent bond's strong forces (100–400 kJ mol−1) in LSO oxidative aging decomposition, as well as secondary relatively weak interactive forces by hydrogen bonds (~70 kJ mol−1), and electrostatic bonds (0–50 kJ mol−1) contributing to secondary crosslinking interactions leading to a LSO viscous gel of polymerized products in the termination phase. In the present paper, we show that LSO tail segments mobility in terms of T2 multi‐exponential energy relaxation time decays, generated by data reconstruction of 1H transverse relaxation components are providing a clear, sharp, and informative understanding of LSO sample's autoxidation aging processes. To support T2 time domain data analysis, we used data from high‐field band‐selective 1H NMR pulse excitation for quantification of hydroperoxides and aldehydes of the same LSO samples treated under the same thermal conditions (25, 40, 60, 80, 100, 120 °C) with pumped air for 168 hours. Peroxide value, viscosity, and self‐diffusion analyses, as well as fatty acids profile and by‐products determined by GC–MS on the same samples were carried out, and correlated with the LSO tail T2 energy relaxation time results. From these results, it is postulated that selective determination of LSO tail T2 time domain can be used as a rapid evaluation marker for following omega‐3 PUFA‐rich oils oxidative aging process within industrial and commercial produc...

Sensitivity of Proton NMR Relaxation and Proton NMR Diffusion Measurements to Olive Oil Adulterations with Vegetable Oils

“…In the relaxation data analysis, , the ratio of the two components’ amplitudes, both for the longitudinal and transverse relaxation processes, was left as a free parameter, and it turns out that the weights of components obtained were typically around 2:1 for the long component . The two components were attributed to the more rigid (shorter component) and more flexible parts (longer component) of the trygliceride molecules, as also reported in previous relaxation NMR studies on olive oils , and, similarly, on pistachio oils . Relaxation measurements performed at 100 MHz allowed us to obtain the relaxation times, T 1 and T 2 , for different proton species, by integrating the corresponding areas of the proton NMR spectra of the oil samples.…”

“…The measure of 1 H NMR relaxation times, longitudinal ( T 1 ) and transverse ( T 2 ), at different Larmor frequencies can give indirect information about several chemical and physical properties of edible oils having a variable fatty acids’ composition, and it has been used to study the effect of thermal oxidation and desiccation processes. ,,, The analysis of 1 H NMR T 1 dispersions of EVOOs and the analysis of T 1 at low magnetic fields have been used to investigate supramolecular structural features, such as the occurrence of inverse-micelle-like organization of triglycerides in extra-virgin olive oils, and dynamic information, such as correlation times associated with rotational motions and self-diffusion constants. − , A low-field (LF) 1 H NMR relaxation method based on the reconstruction of 2D and 3D plots to correlate T 1 and T 2 distributions has been applied to check the thermal oxidation of linseed oils and to detect several types of adulterations of vegetable oils. , This rapid and relatively cheap LF NMR relaxation method seems particularly useful to study the effect of oxidation in several vegetable oils, such as the macadamia, , linseed, sunflower , and other blended oils, , which are used not only for consumption but also for painting, energy, and biomass applications.…”

Semi-Autonomic AI LF-NMR Sensor for Industrial Prediction of Edible Oil Oxidation Status

“…In addition to 1 H LF NMR, numerous chemical and physical analytical lab conventional standard methods have been used to assess lipid oxidation. These include peroxide values (PV) and para-anisidine ( p -AV) that are used in previous studies [ 5 , 41 ]. These common methodologies have many drawbacks, such as strict time regimes during individual stages of analyses, the need to control reaction conditions and components including light and atmospheric oxygen exposure, and large amounts of environmentally harmful solvents [ 56 ].…”

“…The oxidation stability of edible oils and lipid-rich foods is a very important issue, especially with foods that contain polyunsaturated fatty acids (PUFAs), an important nutritional component for health such as cardiovascular and neurological health [ 1 , 2 , 3 ]. Paradoxically, however, these lipids are highly susceptible to oxidation into toxic products during food preparation, transportation, storage, and cooking [ 4 , 5 , 6 ], affecting the food’s texture, taste, aroma, and shelf life [ 7 ].…”

“…Low-field NMR relaxation technology is recognized to have significant potential in elucidating the molecular structures of lipid oxidation products and the oxidation mechanisms. It was recently shown that LF-NMR relaxation is highly efficient in rapidly and accurately monitoring oil oxidation [ 4 , 5 , 19 ], as briefly described below.…”