Determination of Unsaturated Fatty Acids Composition in Walnut (Juglans regia L.) Oil Using NMR Spectroscopy

Walnut is a precious marketed nut characterised by kernels containing more than 60% of oil. Gas chromatography (GC) is the most used method to analyse oils; nonetheless, polyunsaturated (PUFA)s and monounsaturated fatty acids (MUFA)s were not separated sufficiently. Therefore, our study is based on the employment of two GC systems with different columns. However, for determination of PUFAs and MUFAs composition, 13 C nuclear magnetic resonance (NMR) seems to be a promising technique by showing the resonance for each unsaturated fatty acids (UFA)s in olefinic region, and also for saturated fatty acids (SFA) in the aliphatic region. 13 C NMR was able to distinguish between fatty acid isomers such as oleic (C18:1 Δ9) and vaccenic (C18:1 Δ11) acid. In addition, different fatty acid length with same position of unsaturated carbon were distinguished and determined by 13 C NMR, for instance between vaccenic (C18:1 Δ11) and eicosenoic (C20:1 Δ11) acid. NMR quantification takes the advantages of chemical shifts to accurately calculate fatty acid contents for both saturated and unsaturated one. Besides providing the full profile of fatty acids, this study adds information regarding quantitative and qualitative composition of walnut oil. This can expand the analytical methods used to improve the knowledge of nutritional values of oil and food products. Graphical abstract