1H Nuclear Magnetic Resonance (NMR) Fingerprints and Low-Field- NMR Relaxation Properties of Sunflower Oil during Thermal Oxidation
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Abstract:
1H nuclear magnetic resonance (1H-NMR) was used to study change patterns associated with relative content of oxidation products (conjugated olefins, aldehydes, oxides, aromatic hydrocarbons, and free fatty acids) produced by the process of thermal oxidation during storage of sunflower oil at 65 ℃. Correlation analysis with S21 changes in low-field (LF)-NMR relaxation was conducted. The 1H-NMR results indicated that the amount of primary oxidation products increased initially and then decreased with time, where hydroperoxide- conjugated dienes were preferentially degraded as compared to hydrogen peroxides. The amount of secondary oxidation products and hydrolysates such as aldehydes, epoxides, and free fatty acids increased exponentially with time (R2 > 0.96), whereas the amount of aromatic hydrocarbons also increased and then decreased with time. The LF-NMR peak area S21 for the oil sample increased exponentially (R2 = 0.99) with time. Correlation analysis showed that oxides and free fatty acids had the highest correlation with S21, which was proved reasonable and reliable by model validation. The results could provide a foundation to further explore the characteristic peak S21 such that the quality of edible oil could be improved using the LF-NMR results as reference.
