2D and 3D Spectrum Graphics of the Chemical-Morphological Domains of Complex Biomass by Low Field Proton NMR Energy Relaxation Signal Analysis

Euro J Lipid Sci & Tech

Wiesman

2019

A major stability issue of food and other products containing lipids is their susceptibility to oxidation and the efficacy of endogenous or exogenous antioxidants that are sensitive to internal morphological and chemical structures which are difficult to characterize with current analytical methods. This work develops signal reconstruction of 1H LF‐NMR spin‐lattice (T1) and spin‐spin (T2) energy relaxation times into 2D T2 versus T1 peak graphs of the internal chemical and morphological arrangements within lipid materials, with the potential for efficient structural studies of lipid oxidation and antioxidant efficacy in complex foods. This novel NMR inverse Laplace transformation (ILT) signal processing reconstruction is now applied in a PUFA‐rich linseed oil's thermal autoxidation and antioxidant efficacy study. To characterize antioxidant efficacy, it is important to understand the mechanism of oxidation and the chemical and morphological structural aspects. The initial steps of oxidation show a clear peak shift to shorter T2 versus T1 peak values, for the different poly‐unsaturated fatty acids (PUFA), which for mono‐unsaturated and saturated FAs remain unchanged. These peak shifts are within an oxidation time period needed for hydroperoxides formation. For longer oxidation times a new set of T2 versus T1 peaks are generated with shorter T2 and stable and/or increased T1 values, suggesting formation of aldehydes and polymerized oxidation end products. The chemical changes of the fatty acids of linseed oil are confirmed by their gas chromatography analysis during the studied time interval. Similarly peroxides and aldehydes formation trends are confirmed by PV and p‐ansidine tests, respectively for the same time points. Based on the oxidation study the control of T1 and T2 relaxation times by α tocopherol antioxidant is characterized. In effect α tocopherol antioxidant maintains peak stability during linseed oil's thermal autoxidation, in a 2D T2 versus T1 relaxation time graph of peaks assigned to chemical morphological structures, demonstrating α tocopherol's ability to minimize linseed oil's oxidation. Practical Application: Monitoring of food products oxidation and quality control. 1H LF‐NMR T1 and T2 energy relaxation times reconstructed with PDCO into 2D spectra of material analysis has proven to be an advantageous tool to monitor complex chemical and morphological structural changes during the autoxidation of PUFA‐rich linseed oil. It is suggested that an initial oxidation phase generates a shift, of the original linseed peaks along the T1 = T2 diagonal due to hydroperoxide formation. At longer oxidation times there is an accumulation of peaks below the diagonal line assigned to oligomeric/polymeric termination products, generating a significant “bending effect.” α tocopherol addition at effective concentrations is able to change this pattern of PUFA‐rich linseed oil oxidation by blocking early peaks shift and late bending effect.

“…We demonstrated an improved reconstruction program if a l 2 regularization term is added to the objective function, through

λ

, of a common regularization, as seen in Equation :

\begin{array}{l} center & \min λ {true∥ F true∥}_{F}^{2} + {true∥ R true∥}_{F}^{2} \\ center & s . t . K_{1} F K_{2} + R = S \end{array}

where R is the residuals matrix and

λ

l_{1}

norm of the solution resulted in relatively sparse results .…”

Section: Methodsmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 97%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

¹H LF‐NMR Energy Relaxation Time Characterization of the Chemical and Morphological Structure of PUFA‐Rich Linseed Oil During Oxidation With and Without Antioxidants

Euro J Lipid Sci & Tech

Wiesman

2019

Multidimensional Proton Nuclear Magnetic Resonance Relaxation Morphological and Chemical Spectrum Graphics for Monitoring and Characterization of Polyunsaturated Fatty‐Acid Oxidation

Campisi-Pinto

et al. 2019

J Americ Oil Chem Soc

Polyunsaturated fatty acids (PUFA) are components of many commercial products such as edible oils, foods, cosmetics, medication, and in biological systems such as phospholipids of cellular membranes. Although PUFA aggregates are important functional components, they are also related to system degradation, because PUFA are susceptible to oxidation via their multiple double bonds and allylic carbons. Current technologies are not effective in characterizing the morphological and chemical structural domains of saturated, monounsaturated fatty acids (MUFA) and PUFA materials, or how the morphological structures of fatty acids, at the mesomolecular, nanomolecular, and molecular levels, affect their oxidation mechanisms. In this article, the 1 H low-field (LF) NMR energy relaxation time technology is proposed as a tool to analyze PUFA oils undergoing thermal oxidation. This technology generates two-dimensional (2D) chemical and morphological spectra using a primal-dual interior method for the convex objectives (PDCO) optimization solver for computational processing of the energy relaxation time signals T 1 (spinlattice) and T 2 (spin-spin). The 2D graphical maps of T 1 vs. T 2 generated for butter, rapeseed oil, soybean oil, and linseed oil show that the different degrees of unsaturation of fatty-acid oils affect their chemical and morphological domains, which influences their oxidative propensity. The technology of the 1 H LF-NMR energy relaxation time proved to be an effective tool to characterize and monitor PUFA oxidation.

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

Wiesman

2020

J Americ Oil Chem Soc

Self Cite

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...