Olive Oil Quality and Authenticity Assessment Aspects Employing FIA-MRMS and LC-Orbitrap MS Metabolomic Approaches

Abstract

Edible vegetable oils comprise integral components of humans' daily diet during the lifetime. Therefore, they constitute a central part of dietary-exposome, which among other factors regulates human health. In particular, the regular consumption of olive oil (OO) has been largely accepted as a healthy dietary pattern. Responsible for its recognition as a superior edible oil is its exceptional aroma and flavor. Its unique composition is characterized by high levels of monounsaturated fatty acids and the presence of minor constituents with important biological properties, such as the so-called OO polyphenols. Being a high added value product, OO suffers from extensive fraud and adulteration phenomena. However, its great chemical complexity, variability, and the plethora of parameters affecting OO composition hamper significantly the selection of the absolute criteria defining quality and authenticity, and a reliable and robust methodology is still unavailable. In the current study, Flow Injection Analysis-Magnetic Resonance Mass Spectrometry (FIA-MRMS) was investigated under a metabolic profiling concept for the analysis of Greek Extra Virgin Olive Oils (EVOO). More than 200 monovarietal (Koroneiki) EVOO samples were collected from the main Greek OO producing regions and investigated. Both intact oil and the corresponding polyphenols were analyzed in fast analysis time of 2 and 8 min, respectively. In parallel, an LC-Orbitrap MS platform was used to verify the efficiency of the method as well as a tool to increase the identification confidence of the proposed markers. Based on the results, with FIA-MRMS, comparable and improved projection and prediction models were generated in comparison to those of the more established LC-MS methodology. With FIA-MRMS more statistically significant compounds and chemical classes were identified as quality and authenticity markers, associated with specific parameters, i.e. geographical region, cultivation practice, and production procedure. Furthermore, it was possible to monitor both lipophilic and hydrophilic compounds with a single analysis. To our knowledge, this approach is among the few studies in which two FT-MS platforms combining LC and FIA methods were integrated to provide solutions to quality control aspects of OO. Moreover, both lipophilic and hydrophilic components are analyzed together, providing a holistic quality control workflow for OO.

Keywords: EVOO; FIA-MRMS; LC-Orbitrap MS; authenticity; olive oil; polyphenols; quality control.

Figure 1

Representative compounds of OO glycerol fraction (upper part) and biophenols fraction (lower part).

Figure 2

Scores plots of EVOOs and their corresponding biophenol extract acquired via FIA-MRMS. Observations are colored coded according to geographical origin. (A) PCA scores plot of EVOOs including all observations (pareto scaling); (B) OPLS scores plot of EVOOs including all observations (pareto scaling); (C) OPLS-DA plot of EVOOs excluding Ionian island samples (pareto scaling); and (D) OPLS-DA scores plot of biophenol extracts including all observations (UV scaling). R2/Q2 model parameters are annotated (bottom-left).

Figure 3

Box-plots of aldehydic form of oleuropein aglycon (44), oleacein (38), and oleocanthal (32) in the three basic geographical regions Crete (red), Peloponnese (blue), and Ionian islands (yellow).

Figure 4

Box-plots of acetoxypinoresinol (51), elenolic acid (13), hydroxytyrosol (6), and apigenin (20) in the three basic geographical regions Crete (red), Peloponnese (blue), and Ionian islands (yellow).

Figure 5

Box-plots representing intensities of statistical significant compounds grouped according to their chemical class; triterpenic acids, flavonoids, lignans, secoiridoids (oleuropein derivatives, oleacein, and oleocanthal), and elenolic acid derivatives as well as phenyl alcohols. Box-plots are presented according to geographical origin: Crete (red), Peloponnese (blue), and Ionian islands (yellow).

Figure 6

Scores plots of EVOOs and their corresponding biophenol extracts acquired via FIA-MRMS. Plots include the total number of observations and are colored coded according to cultivation practice classID; conventional (blue), integrated (light orange), and certified organic practices (magenta). (A) OPLS-DA scores plot of EVOOs with pareto scaling; (B) OPLS-DA scores plot of biophenols with UV scaling. R2/Q2 model parameters are annotated (bottom-left).

Figure 7

Box-plots representing intensities of statistical significant compounds grouped according to their chemical class; triterpenic acids, flavonoids, lignans, secoiridoids (oleuropein derivatives, oleacein, and oleocanthal) (elenolic derivatives), and phenyl alcohols. Box-plots are presented according to cultivation practice: organic (magenta), conventional (blue), and integrated (light yellow).

Figure 8

Plots of EVOOs and their corresponding biophenols extracts acquired via FIA-MRMS. Plots include the total number of observations and are colored according to production procedure classID: three phases (green), two phases (blue). (A) OPLS-DA of EVOOs treated with pareto scaling. (B) OPLS-DA of biophenols treated with UV scaling. R2/Q2 model parameters are annotated (bottom-left).

Figure 9

Box-plots representing intensities of statistical significant compounds grouped according to their chemical class: triterpenic acids, flavonoids, lignans, elenolic derivatives phenyl alcohols, and oleocanthal (32) from secoiridoids class. Box-plots are presented according to production procedure system: two phase (blue) and three phase (green).

Figure 10

(A) OPLS-DA scores plot of the biophenol extract samples acquired via UPLC-HRMS. Plot includes the total number of observations in color scale according to geographical origin ClassID; Peloponnese (blue), Crete (red), Ionian islands (yellow). QC sample are also included (green). R2/Q2 model parameters are annotated (bottom-left). (B) Base peak (BP) chromatogram of the QC (pooled sample). Certain metabolites are annotated.