Nuclear Magnetic Resonance: Methodologies and Applications

Abstract

Extra virgin olive oil is considered a fundamental food constituent traditionally consumed in the Mediterranean area, while its consumption has extended gradually to other countries. This is due to its high sensory and nutritional quality and, most importantly, because of its protective effects against several illnesses. In the last few years intensive research has been conducted on the analysis of olive oil using nuclear magnetic resonance (NMR), giving particular emphasis to the quality assessment and authentication of this commercial commodity. This review presents a short account of the various NMR techniques and methodologies used for the analysis of olive oil. One-dimensional high-resolution multinuclear NMR spectroscopy of 1H, 13C, and 31P nuclei gives complementary information about the major and minor constituents of olive oil, while the employment of two-dimensional NMR techniques offers the possibility of assigning unambiguously the 1H, 13C, and 31P spectra of the various olive oil grades and unravel hidden resonances of complex spectra usually observed in the polar extracts of olive oils, either through bond or through space connectivity. Quantitative aspects of high-resolution NMR are discussed as well. The potential of the hyphenated NMR spectroscopy with a separation technique, such as liquid chromatography, for high-throughput experiments and recent developments and applications of low-resolution NMR in the field of relaxometry and diffusometry are discussed as well. A few recommendations are given about the NMR instrumentation that satisfies the minimum requirements for an efficient analysis of olive oil. Also, importance is placed on sample preparation including sample pretreatment usually needed if minor compounds (e.g., polyphenols) are investigated. The sections on spectral assignments and statistical methods used for metabonomic studies are kept very concise since the analysis of olive oils using NMR spectroscopy has been described in several good review articles mentioned in the introductory section. Two sections of this review are devoted to applications of NMR spectroscopy to quality assessment and authentication, giving emphasis to olive oil adulteration, geographical origin, and varietal classification. Despite the fact that NMR spectroscopy has made considerable inroads in the field of olive oil, several aspects need further consideration. Some of these new directions are discussed in the final section of this report.