Quality Evaluation of Edible Oils by Proton Nuclear Magnetic Resonance Measurement

抄録

¹H-nuclear magnetic resonance (NMR) method using dioxane as the external proton standard was established to evaluate the quality of edible oils. The number of olefinic protons (OP) in oil was determined by the ratio of the integral value of olefinic protons (δ_H 5.33-5.47) versus that of methylene protons of dioxane (δ_H 3.4-3.5) using the solvent system of benzene-d₆-30% MeOD (60°C). In this solvent system, good separation between the olefinic and methine protons from the triglyceride backbone was achieved. As a result, for various UV-irradiated oxidized rapeseed oils, the plots of the OP versus the iodine value and the plots of the number of divinylmethylene protons versus the 2-thiobarbituric acid value gave excellent linearity. In addition, the iodine values calculated by the proposed ¹H-NMR method for five commercially available edible oils agreed with the experimental ones within ±3 iodine value error.