Application of 1H and 13C NMR Fingerprinting as a Tool for the Authentication of Maltese Extra Virgin Olive Oil

Abstract

The application of 1H and 13C nuclear magnetic resonance (NMR) in conjunction with chemometric methods was applied for the discrimination and authentication of Maltese extra virgin olive oils (EVOOs). A total of 65 extra virgin olive oil samples, consisting of 30 Maltese and 35 foreign samples, were collected and analysed over four harvest seasons between 2013 and 2016. A preliminary examination of 1H NMR spectra using unsupervised principle component analysis (PCA) models revealed no significant clustering reflecting the geographical origin. In comparison, PCA carried out on 13C NMR spectra revealed clustering approximating the geographical origin. The application of supervised methods, namely partial least squares discriminate analysis (PLS-DA) and artificial neural network (ANN), on 1H and 13C NMR spectra proved to be effective in discriminating Maltese and non-Maltese EVOO samples. The application of variable selection methods significantly increased the effectiveness of the different classification models. The application of 13C NMR was found to be more effective in the discrimination of Maltese EVOOs when compared to 1H NMR. Furthermore, results showed that different 1H NMR pulse methods can greatly affect the discrimination of EVOOs. In the case of 1H NMR, the Nuclear Overhauser Effect (NOESY) pulse sequence was more informative when compared to the zg30 pulse sequence, since the latter required extensive spectral manipulation for the models to reach a satisfactory level of discrimination.

Seeking a Fast Screening Method of the Varietal Origin of Olive Oil: The Usefulness of an NMR-Based Approach

“…The triacylglycerol fraction (TAG) was analyzed using 1D multinuclear NMR spectroscopy ( 1 H NMR, 13 C NMR DEPT 45). The NMR experiments were conducted on a Bruker Advance III 400 MHz spectrometer (Madrid, Spain), equipped with a wide-band (BBO) observation probe at a temperature of 303K.…”

“…In a 5mm diameter NMR tube, 100 μL of olive oil and 10 μL of mesitylene (internal standard) were dissolved in 500 μL of deuterated chloroform. Each sample was analyzed by means of the two 1D-NMR experiments that encompass 1 H NMR ( Figure S1) and 13 C NMR DEPT 45 ( Figure S2). The pulse sequences used in these experiments were installed in the Bruker TOPSPIN 3.2 pl 6 suite.…”

“…Thus, the 13 C NMR technique was attempted in this work in order to provide fast screening for the discrimination of the olive oils under study according to their varietal origin. In fact, at the outset, we looked at the common broadband 13 C decoupling method and some of the DEPT editing techniques, such as DEPT 90 and DEPT 45. The broadband method was quickly discarded due to the longer accumulation times and lower sensitivity as compared to the DEPT techniques.…”

“…Despite the low relative abundance of the 13 C isotope, 13 C NMR is another very powerful NMR technique that allows the assignment of different carbons within the organic molecule. In particular, the use of 13 C NMR to discriminate the variety of extra virgin olive oils using multivariate statistical analysis has already proven to be a useful tool [16,21].…”

“…Thus, aiming to assess the varietal origin of olive oils produced from nine different varieties (Galega Vulgar, Cobrançosa, Cordovil de Serpa, Blanqueta, Madural, Verdeal Alentejana, Arbequina, Picual and Carrasquenha), an NMR-based approach was applied in this study, and its usefulness in the fast screening of OO varietal origin discrimination was investigated. Since the 1 H NMR spectrum allows one to have information about major and minor olive oil components, whereas 13 C NMR can provide valuable information about the acyl distribution and the acyl positional distribution of glycerol tri-esters of different oils, in this work, two experiments were applied due to their complementary data. Concretely, this study uses the resonance intensities of triacylglycerols obtained by 1 H NMR spectroscopy and a 13 C NMR DEPT45 pulse sequence to classify olive oils according to varietal origin by applying a linear discriminant analysis (LDA).…”