Comparison of standard and NMR methodologies for assessment of oxidative stability of canola and soybean oils

The oxidative stability of refined, bleached and deodorized canola and soybean oils was evaluated over a 30-day dark storage period at 65 °C. Peroxide value (PV), conjugated diene (CD) and triene (CT) contents, 2-thiobarbituric acid reactive substances (TBARS) and p-anisidine values were determined. In addition, NMR spectroscopy was used to monitor relative changes in the proton absorption pattern of the fatty acids of oils during storage. Canola oil showed higher PV, CD, CT and TBARS as compared with those for soybean oil. The ratio of aliphatic to olefinic protons in both oils, determined by NMR spectroscopy, increased steadily over the entire length of the storage period, indicating progressive oxidation of unsaturated fatty acids in both oils.