Improved liquid chromatography tandem mass spectrometry method for the determination of phenolic compounds in virgin olive oil

The quantification of volatile compounds in virgin olive oil poses several analytical challenges due to the existence of different concentrations, chemical families, and the possible matrix effect. Accurate quantification, using adequate methodological calibration and statistical procedures, is essential for obtaining reliable results. The aim of this work was to develop and validate an analytical-statistical approach for the quantification of volatile compounds in virgin olive oil. Therefore, several analytical parameters were determined for four calibrations. The ordinary least square (OLS) linear adjustment was selected over the weighted least square due to the homoscedasticity of the variable errors. Additionally, standard addition (AC) and AC with an internal standard (IS) exhibited greater variability, whereas external matrix-matched calibration (EC) was identified as the most reliable approach for quantifying volatile compounds in virgin olive oil. The employment of an IS did not improve the performance of the method in any case. Thus, based on the statistical results, the OLS linear adjustment with EC was selected as the best statistical-analytical approach for quantifying volatiles in olive oil matrices. The volatiles of nine virgin olive oil samples were quantified, applying different methodological calibrations, and no differences were detected, underscoring EC as a superior alternative.

Evaluation of phenolics in the analysis of virgin olive oil using near infrared spectroscopy

This study focuses on the quantification of virgin olive oil phenolic compound while using mid-infrared spectroscopy with chemometrics. For that, 100 samples of virgin olive oils in phenolic compounds which varied between 1.04 and 10.33 g/L were picked up in Morocco’s regions and subjected to infrared analysis. The aim was to develop a calibration model for the prediction of phenolic compounds in olive oil by using Fourier transform-infrared spectroscopy. The spectral transmissions of all samples were obtained in the spectral range of 600–4000 cm–1. The values obtained for correlation coefficient and root mean square errors of prediction were 0.99 and 0.11, respectively. These results showed the capability of the Fourier transform-infrared spectroscopy and the chemometric in developing accurate models to predict the phenolic compounds in virgin olive oil.

BackgroundThe effect of the ethephon application at fruit set and veraison on cell maturity of Olea europaea L. olives and on the extractability of phenolic compounds (PC) in virgin olive oil has been studied.MethodsThe ethephon was sprayed on olive trees of the Moroccan Picholine at the fruit set stage and on other olive trees at the veraison stage at a concentration of 100 mg/L. The effect of these treatments was evaluated by the fruit yield and the determination of the period of olives growth and ripening. The extractability of the olive oil and the diffusion of the PCs in the fat as well as the embrittlement of the parietal structures are also monitored.Results and conclusionsA chemical thinning is entrained out by ethephon when applied at fruit set (16%) or veraison (12%). It also results in precocious ripening of fruits treated at fruit set (about 2 weeks) and a precocity of the harvest similar to that induced in olives treated at veraison (estimated at 6 weeks). At this stage, a significant increase in the fat accumulation (more than 26 g/100 g in the olives treated compared to 7.7 g/100 g olive pulp in the control) and quantities of extracted oils (87 and 83%, respectively, in the olives treated at fruit set and those treated at veraison compared to 70% in the control) as well as a significant improvement in the extractability of the diffusible PCs in these oils at maturity (540 and 590 mg/kg, respectively, in the treated olives at fruit set and those treated at veraison compared to 216 mg/kg in the control oil).

Phenolic compounds in Spanish virgin olive oils were characterized by HPLC. Simple phenols such as hydroxytyrosol, tyrosol, vanillic acid, p-coumaric acid, ferulic acid, and vanillin were found in most of the oils. The flavonoids apigenin and luteolin were also found in most of the oils. The dialdehydic form of elenolic acid linked to tyrosol and hydroxytyrosol was also detected, as were oleuropein and ligstroside aglycons. The structure of a new compound was elucidated by MS and NMR as being that of 4-(acetoxyethyl)-1,2-dihydroxybenzene. Changes of phenolic compounds in virgin olive oils with maturation of fruits were also studied. Hydroxytyrosol, tyrosol, and luteolin increased their concentration in oils with maturation of fruits. On the contrary, glucoside aglycons diminished their concentration with maturation. No clear tendency was observed for the rest of the phenolic compounds identified.

The increasing popularity of olive oil is mainly attributed to its high content of oleic acid, which may affect the plasma lipid/lipoprotein profiles, and its richness in phenolic compounds, which act as natural antioxidants and may contribute to the prevention of human disease. An overview of analytical methods for the measurement of polyphenols in olive oil is presented. In principle, the analytical procedure for the determination of individual phenolic compounds in virgin olive oil involves three basic steps: extraction from the oil sample, analytical separation, and quantification. A great number of procedures for the isolation of the polar phenolic fraction of virgin olive oil, utilizing two basic extraction techniques, LLE or SPE, have been included. The reviewed techniques are those based on spectrophotometric methods, as well as analytical separation (gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE)). Many reports in the literature determine the total amount of phenolic compounds in olive oils by spectrophometric analysis and characterize their phenolic patterns by capillary gas chromatography (CGC) and, mainly, by reverse phase high-performance liquid chromatography (RP-HPLC); however, CE has recently been applied to the analysis of phenolic compound of olive oil and has opened up great expectations, especially because of the higher resolution, reduced sample volume, and analysis duration. CE might represent a good compromise between analysis time and satisfactory characterization for some classes of phenolic compounds of virgin olive oils.

Solid-phase extraction gas chromatography-ion trap-mass spectrometry qualitative method for evaluation of phenolic compounds in virgin olive oil and structural confirmation of oleuropein and ligstroside aglycons and their oxidation products

New reversed phase dispersive liquid–liquid microextraction method for the determination of phenolic compounds in virgin olive oil by rapid resolution liquid chromathography with ultraviolet–visible and mass spectrometry detection

Solid-phase extraction and gas chromatographic analysis of phenolic compounds in virgin olive oil

Characterization of volatile compounds of French and Spanish virgin olive oils by HS-SPME: Identification of quality-freshness markers

The presence of different bioactive compounds in virgin olive oil affects its nutritional, oxidative and sensorial properties. Phenolic compounds are olive endogenous bioactive compounds highly susceptible to degradation. Olive endogenous oxidoreductases, mainly polyphenol oxidases (PPO) and peroxidases (POD), may play an important role on the profile of bioactive compounds in olive oil by promoting oxidation of phenolic compounds. The aim of this study was to evaluate if changes on PPO and POD activities in olive fruits from two Portuguese cultivars (Olea europaea, cv ‘Cobrançosa’ and cv ‘Galega Vulgar’) are related with the composition of their olive oils, especially phenolic compounds. Pattern recognition techniques [principal component analysis (PCA), cluster analysis (CA), and discriminant analysis (DA)] were used for multivariate data analysis. Olive oils characterized by their FA composition were grouped by cultivar. When olive oils were characterized by their phenolic composition, green pigments, and enzymatic activities in fruits, they could be discriminated by olive ripening stage. Along ripening, PPO activity was only detected in the fruit mesocarp of both cultivars and POD activity was mainly detected in the seeds. The POD activity, as well as vanillin and gamma‐tocopherol contents in olive oil increased with the ripening index. Conversely, higher PPO activity in fruits at early ripening stages together with higher levels of total phenols, green pigments, beta‐tocopherol, hydroxytyrosol and p‐coumaric acid in olive oils were observed. The ripening stage of fruits showed to be a key factor on the amount and profile of bioactive compounds of olive oil.

SummaryThe main objective of this study was to evaluate the influence of the malaxation time (Mt) and ripening stage on oil quality and phenolic compounds of Hojiblanca and Picual virgin olive oils. In both varieties of oil, phenolic content and oxidative stability decreased as ripening progressed. The total level of tocopherols diminished by up to 40% as fruit ripened. The compositions of palmitic, stearic, lignoceric, oleic, linoleic and linolenic acids were significantly influenced by the ripening process. The present work shows that an increased Mt promoted the increase of free acidity (up to 13.3%) and tocopherols (up to 11.6%) and negatively affected the oxidative stability and the concentration of phenols. Further research is required to determine ripening stages and malaxation conditions for all olive oil varieties to achieve a satisfactory balance between the improvement of both oil yield and oil quality and composition.

It is well known that olive oils are the only foods whose legal control must also involve sensory evaluation, and that a harmonised protocol is used for this purpose: EEC regulation 2568/91 and an IOOC trade norm of the 1990s introduced a standard method among those used to assess the quality of virgin oils, after which a modified method known as the ‘panel test’ was developed and adopted, firstly by the IOOC and later by the EEC. One problem in applying the panel method often depends on the lack of reference standards for training judges, in addition to, in some cases, a lack of exact knowledge of the origin of some defects; for these reasons, several judges have suggested the unification of some defects, even when these originate from different kinds of problems. In this paper we have applied headspace analyses to a number of samples of oils that were also characterised by a panel. Besides the samples, standard defective oils obtained by the IOOC and used for training sensory judges were also analysed, with the aim of obtaining a model for use in method validation. Seventy‐six peaks were detected and most of them identified by gas chromatography/mass spectrometry; their distribution was different in the samples characterised by different defects as assessed by the panel test. The well‐known compounds of virgin olive oils were detected, including the series of C6 compounds, whose importance in defining positive (‘green’ flavour) and negative (rancid) characteristics of olive oils is well known. No samples classified as extra virgin ever present peaks with magnitudes as great as those found in defective oils. Chemometric data evaluation was carried out and samples were clustered on the basis of the headspace composition; the results were found to agree with those of the panel test, so a number of compounds were related to the presence of particular defects. Copyright © 2005 Society of Chemical Industry

Influence of fruit destoning on bioactive compounds of virgin olive oil

The organoleptic assessment (Panel test) is the only procedure within the official methods for determining the quality of virgin olive oils that involves an expert panel. There is an urgent need for analytical methodology that can reliably measure volatile compounds in virgin olive oils that is capable of supporting and anticipating the official Panel test. For this reason, a new method based on solid‐phase microextraction–gas chromatography with the choice of two possible detectors (FID or MS) was subjected to a large international interlaboratory validation study. The study involved a two‐stage process: first, a pretrial phase in which 7 participants were exposed to the method for the first time to identify any initial problems with the methodology; then, a formal validation stage (trial proper), which involved 20 laboratories from Europe, USA, Japan and China. The performance of the different detectors was investigated. While both methods have advantages, the method using FID provided better results for 11 compounds, in terms of reproducibility, compared to MS. This information will allow to implement the method with accurate information of the method performance depending on the detector used.Practical Applications: This study provides information from an interlaboratory validation of a method for measuring volatile compounds in virgin olive oils conducted with laboratories (from industry and academia) working in the olive oil sector. The information on the expected analytical errors in the determination of each volatile compound is necessary to apply this method for supporting the official Panel test (sensory analysis). The SPME‐GC‐MS/FID methods proposed in this work can be used for the internal quality control of a company/distributor/quality control laboratory and could also be used in cases of difficult/contradictory organoleptic assessment, or to confirm results from sensory panels in cases of disputes/disagreement (Reg. EU 2022/2105).