Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2024 Mar 1;29(5):1111.
doi: 10.3390/molecules29051111.

NMR Analysis of Extra Virgin Olive Oil of the Epirus Region of Greece with Emphasis on Selected Phenolic Compounds

Theodoros Tsolis  1 , Dimitra Kyriakou  1 , Evangelia Sifnaiou  1 , Dimitrios Thomos  1 , Dimitrios Glykos  1 , Constantinos G Tsiafoulis  2   3 , Achilleas Garoufis  1   2   4
Affiliations

NMR Analysis of Extra Virgin Olive Oil of the Epirus Region of Greece with Emphasis on Selected Phenolic Compounds

Theodoros Tsolis et al. Molecules. .

Abstract

Extra virgin olive oil (EVOO) is recognized for its numerous health benefits, attributed to its rich phenolic components. NMR has emerged as a prevalent technique for precisely identifying these compounds. Among Mediterranean countries, Greece stands as the third-largest producer of olives, with the Epirus region notably advancing in olive cultivation, contributing significantly to the dynamic growth of the region. In this study, an NMR method was employed based on the acquisition of a 1H NMR spectrum along with multiple resonant suppression in order to increase the sensitivity. Using the above method, 198 samples of extra virgin olive oil, primarily sourced from the Epirus region, were analyzed, and both the qualitative and quantitative aspects of the phenolic compounds were obtained. In addition, we examined the effects of various factors such as variety, harvest month, and region origin on the phenolic compounds' concentration. The results revealed an average total phenolic content of 246 mg/kg, closely approaching the EU health claim limit of 250 mg/kg. Approximately 15% of the samples were confidently characterized as high-phenolic olive oil. The highest concentrations were observed in the Thesprotia samples, with several Lianolia varieties exceeding the total phenolic content of 400 mg/kg. Statistical tests demonstrated a significant influence of the olive variety and the month of fruit harvest on phenolic component concentration, followed by the region of origin. A very strong correlation was noted between the total phenolics content and the levels of oleocanthal and oleacein, with a correlation coefficient (r) of 0.924. Upon optimization of all factors affecting olive oil quality, the majority of the EVOOs from the Epirus region have the potential to be characterized as high in phenolic content.

Keywords: Epirus region; effect factors; health claim; multi-suppression NMR; olive oil; phenolics.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Scheme 1
Scheme 1
The structures of the studied phenolic compounds.
Figure 1
Figure 1
(A) Comparison of SE and MSE spectra of selected Epirus olive oil; (Β) Aldehydic region of the SE and MSE spectra, with assignment of the studied phenolic compounds.
Figure 2
Figure 2
Part of the noesygppr1d spectrum of EVOO from Vlaxerna (Arta), showing the ratio of oleokoronal (7) and oleomissional (8) with 5S,4S ligstrodial (7a) and 5S,4S oleuropeindial (8a) (2:1), respectively; (A) The coupling constants of the peaks in the magnified area; (B) The calculation of oleacein (4) peak integration. Area = Value for the deconvolution results; Int = Integral of each component.
Figure 3
Figure 3
(A) The sum of oleocanthal (3) and oleacein (4) distributions of the analyzed Epirus olive oil samples (N = 178). The red line represents the mean and the brown line the median; (B) The total phenolic distributions of the analyzed Epirus olive oil samples (N = 178). The red line represents the mean and the brown line the median.
Figure 4
Figure 4
Means of total phenolics, oleocanthal (3), and oleacein (4) for the studied olive oils in Epirus, categorized by variety. The mean values are expressed in mg/kg.
Figure 5
Figure 5
Pairwise comparisons between varieties for (A) Average total phenolics; (B) Average oleocanthal (3); and (C) Average oleacein (4). Significance values have been adjusted using the Bonferroni correction for multiple tests.
Figure 6
Figure 6
(A) Means of total phenolics, oleocanthal (3), and oleacein (4) for the studied olive oils of Epirus as a function of harvest month; (B) Difference in concentration of total phenolics, oleocanthal (3), and oleacein (4) in relation to harvest month, with the corresponding means marked by a dashed line. Mean values are expressed in mg/kg.
Figure 7
Figure 7
(A) Pairwise comparisons between harvest months. (A) Average total phenolics; (B) Average oleocanthal (3); (C) Average oleacein (4). Significance values have been adjusted using the Bonferroni correction for multiple tests.
Figure 8
Figure 8
Means of the phenolic compounds and total phenolics for the studied olive oils of Epirus as a function of prefecture. Values of means are expressed in mg/kg.
Figure 9
Figure 9
Means of phenolic compounds and total phenolics for the studied olive oils of Epirus, as a function of rainfall class. Values of means are expressed in mg/kg.
Figure 10
Figure 10
Total phenolics scatter plot versus index D1.
Figure 11
Figure 11
(A) Map of Greece with the Epirus region indicated with red; (Β) Samples collected from the Epirus area are marked with map markers.
See this image and copyright information in PMC

References

    1. Diamantakos P., Giannara T., Skarkou M., Melliou E., Magiatis P. Influence of Harvest Time and Malaxation Conditions on the Concentration of Individual Phenols in Extra Virgin Olive Oil Related to Its Healthy Properties. Molecules. 2020;25:2449. doi: 10.3390/molecules25102449. - DOI - PMC - PubMed
    1. Harwood J.L., Aparicio R. Handbook of Olive Oil: Analysis and Properties. Aspen; Gaithersburg, MD, USA: 2000.
    1. Kiritsakis K., Melliou E., Magiatis P., Gerasopoulos D. Enhancement of Bioactive Phenols and Quality Values of Olive Oil by Recycling Olive Mill Waste Water. JAOCS J. Am. Oil Chem. Soc. 2017;94:1077–1085. doi: 10.1007/s11746-017-3011-1. - DOI
    1. Gimeno E., Castellote A.I., Lamuela-Raventos R.M., De la Torre M.C., Lopez-Sabater M.C. The Effects of Harvest and Extraction Methods on the Antioxidant Content (Phenolics, a-Tocopherol, and b-Carotene) in Virgin Olive Oil. Food Chem. 2002;78:207–211. doi: 10.1016/S0308-8146(01)00399-5. - DOI
    1. European Union Commission Regulation (EU) No 432/2012 of 16 May 2012 Establishing a List of Permitted Health Claims Made on Foods, Other than Those Referring to the Reduction of Disease Risk and to Children’s Development and HealthText with EEA Relevance. Off. J. Eur. Union. 2012;136:1–40.

LinkOut - more resources