PRELIMINARY NMR APPROACHES FOR EVALUATING OLIVE OIL AUTHENTICITY: PULSE SEQUENCE COMPARISON AND CHEMOMETRIC ANALYSIS

The most common types of fraud in olive oil involve substitution with lower-value vegetable oils, such as soybean, sunflower, or canola oils¹. These fraudulent practices not only violate consumer rights but also distort markets and create unfair competition among similar products, resulting in both regional and global economic losses². Considering the important role of NMR spectroscopy in investigating various types of olive oil adulteration^3,4, this study employed three NMR pulse sequences combined with chemometric analysis to investigate authentic and suspect olive oil samples, aiming to compare spectral profiles obtained in adulteration studies. The NMR experiments were carried out on a Bruker AVANCE NEO 500 MHz spectrometer (11.75 T), equipped with a 5 mm Smartprobe® and operating at 25 °C. ¹H NMR spectra were acquired using the zg30 and zgig pulse sequences, while ¹³C NMR spectra were obtained using the zgpg30 pulse sequence. A total of 125 samples were analyzed, all diluted in CDCl₃ with TMS for spectrometer adjustment and chemical shift calibration (δ = 0.00 ppm). After NMR spectra acquisition and processing using TopSpin (v. 4.3.2), the spectral binning was performed on a NMRProcFlow software (v. 1.4.28), and principal component analysis (PCA) was carried out using MetaboAnalyst (v. 6.0). The results from all three pulse sequences showed that some suspect samples shared highly similar spectral features with authentic ones, suggesting potential quality issues rather than authenticity fraud. Some of these samples were previously seized by federal authorities (PF and MAPA) due to tax or regulatory violations. On the other hand, a significant number of suspect samples exhibited spectral profiles distinct from the authentic oils, indicating probable adulteration. From PCA, these anomalous olive oils showed olefinic, bis-allylic, and allylic loadings, suggesting a major adulteration with cheaper unsaturated vegetable oils. The preliminary comparison among pulse sequences indicated convergent results; i.e. all three different NMR pulse sequence approaches could generate valid PCA models capable of distinguishing authentic samples from others at first sight, highlighting the cost-effectiveness of ¹H NMR analysis. Nonetheless, ¹³C NMR provided valuable complementary information and may serve as a robust alternative for confirmation or deeper investigation. Overall, our study underscores the potential of NMR to generate chemical signatures of olive oil samples, offering a powerful tool in the fight against fraud and contributing to greater transparency across the production chain – for the benefit of both producers and consumers. These findings support the value of applying NMR pulse sequences and chemometric tools in olive oil authenticity studies.

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(3)    V. MAESTRELLO et al Comprehensive Reviews in Food Science and Food Safety, 2022, 21: 4056–4075.

(4)    F. TANG et al. Food Control, 2022, 137: 108939.

Acknowledgements: The authors acknowledge the financial and/or institutional support from CNPq, CAPES, FUNDECT/MS, MAPA, and UFMS.