Study on the Relaxation Characteristics of Sunflower Oil During Thermal Oxidation Using Low-Field Nuclear Magnetic Resonance

Background Overview

 

During processing and storage, edible oils undergo a series of chemical reactions. Among them, thermal oxidation has the greatest impact on oil stability and the shelf life of oil-containing foods. Oxidation products degrade the oil’s nutritional value and flavor while posing potential health risks.
As a result, understanding the mechanisms of thermal oxidation and developing accurate detection methods remain major research focuses in the field of lipid science.
Low-field Nuclear Magnetic Resonance (LF-NMR) has emerged as a promising technique for rapid oil analysis. It offers speed, non-destructive testing, and requires minimal sample preparation. LF-NMR has been successfully applied in lipid studies, including the characterization of T₂ relaxation properties of edible oils.

LF-NMR Relaxation Characteristics of Sunflower Oil During Thermal Oxidation

T₂ relaxation profiles of sunflower oil stored at 65 °C were obtained using LF-NMR, as shown in Figure 9a. Over time, the overall T₂ signals shifted leftward. A more detailed analysis of the S₂₁ signal area (Figure 9b) reveals an exponential correlation with storage duration (R² = 0.99).
This is because the T₂ relaxation peak reflects the accumulation of certain oxidation products that differ from triglycerides. As storage time increases, compounds similar in behavior to T₂₁ species accumulate, enhancing the LF-NMR signal and enlarging the corresponding peak area (S₂₁) in the T₂ spectrum.

In parallel, 1H-NMR fingerprinting was used to study the dynamic changes in typical oxidation products during the thermal oxidation of sunflower oil. Correlation analysis between specific oxidation markers and S₂₁ was conducted to establish a dose-response relationship.
This data serves as a foundation for deeper interpretation of LF-NMR results and supports the mechanistic understanding of using T₂ relaxation to assess oil quality.

Reference: “Study on the 1H-NMR Fingerprint and LF-NMR Relaxation Characteristics During Thermal Oxidation of Sunflower Oil,” Modern Food Science and Technology, 2014, Vol. 30, No. 8