Quantification of oleacein and oleuropein aglycone in olive oil using deuterated surrogates by normal-phase ultra high performance liquid chromatography with quadrupole time-of-flight mass spectrometry

Studies on the Detection of Oleuropein from Extra Virgin Olive Oils Using Enzymatic Biosensors

Oleuropein (OLEU) is an important indicator of the quality and authenticity of extra virgin olive oils (EVOO). Electrochemical sensors and biosensors for the detection of oleuropein can be used to test the adulteration of extra virgin olive oils. The present study aimed at the qualitative and quantitative determination of oleuropein in commercial EVOO samples by applying electrochemical techniques, cyclic voltammetry (CV) and square wave voltammetry (SWV). The sensing devices used were two newly constructed enzyme biosensors, supported on single-layer carbon-nanotube-modified carbon screen-printed electrode (SPE/SWCNT) on whose surface tyrosinase (SPE/SWCNT/Tyr) and laccase (SPE/SWCNT/Lac) were immobilized, respectively. The active surfaces of the two biosensors were analyzed and characterized by different methods, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR) and the results confirmed the efficient immobilization of the enzymes. SPE/SWCNT/Tyr was characterized by a low detection limit (LOD = 9.53 × 10⁻⁸ M) and a very good sensitivity (0.0718 μA·μM⁻¹·cm⁻²) over a wide linearity range from 0.49 to 11.22 μM. The process occurring at the biosensor surface corresponds to kinetics (h = 0.90), and tyrosinase showed a high affinity towards OLEU. The tyrosinase-based biosensor was shown to have superior sensitive properties to the laccase-based one. Quantitative determination of OLEU in EVOOs was performed using SPE/SWCNT/Tyr and the results confirmed the presence of the compound in close amounts in the EVOOs analysed, proving that they have very good sensory properties.

Semi-synthesis as a tool for broadening the health applications of bioactive olive secoiridoids: a critical review

Covering: 2005 up to 2020Olive bioactive secoiridoids are recognized as natural antioxidants with multiple beneficial effects on human health. Nevertheless, the study of their biological activity has also disclosed some critical aspects associated with their application. Firstly, only a few of them can be extracted in large amounts from their natural matrix, namely olive leaves, drupes, oil and olive mill wastewater. Secondly, their application as preventive agents and drugs is limited by their low membrane permeability. Thirdly, the study of their biological fate after administration is complicated by the absence of pure analytical standards. Accordingly, efficient synthetic methods to obtain natural and non-natural bioactive phenol derivatives have been developed. Among them, semi-synthetic protocols represent efficient and economical alternatives to total synthesis, combining efficient extraction protocols with efficient catalytic conversions to achieve reasonable amounts of active molecules. The aim of this review is to summarize the semi-synthetic protocols published in the last fifteen years, covering 2005 up to 2020, which can produce natural olive bioactive phenols scarcely available by extractive procedures, and new biophenol derivatives with enhanced biological activity. Moreover, the semi-synthetic protocols to produce olive bioactive phenol derivatives as analytical standards are also discussed. A critical analysis of the advantages offered by semi-synthesis compared to classical extraction methods or total synthesis protocols is also performed.

Direct determination of phenolic secoiridoids in olive oil by ultra-high performance liquid chromatography-triple quadruple mass spectrometry analysis

In recent years, a large number of biological properties and an important role in the organoleptic characteristics of olive oil have been attributed to phenolic secoiridoids, such as oleacein, oleocanthal, oleuropein aglycone and ligstroside aglycone. Consequently, quantifying them is of great interest for the olive oil sector. Currently, there is no consensus in which analytical method must be use to accurately determine these compounds in olive oil, mainly owing to the lack of reference standards for calibration. In this work, analytical standards of phenolic secoiridoids have been used to develop a quantitative and rapid analytical method by UHPLC-MS/MS, in which sample extraction is not carried out. Simple dilutions of the sample with dry tetrahydrofuran and dry acetonitrile were performed before analysing them. It is worth noting that under these conditions the generation of artefacts such as acetals and hemiacetals of the aldehydic forms is highly reduced. The detection and quantification was performed with a Xevo TQS tandem quadrupole mass spectrometer. The method was validated at four concentration levels and finally applied to six samples of extra virgin olive oil.

Extraction, Analysis, and Antioxidant Activity Evaluation of Phenolic Compounds in Different Italian Extra-Virgin Olive Oils

The analysis of phenolic compounds in extra virgin olive oils was carried out by high-performance liquid chromatography utilizing photodiode array and mass spectrometry detectors. The chromatographic profile of thirty samples from four Italian Regions highlighted the presence of secoiridoids, phenolic alcohols, flavonoids, and phenolic acid classes. A similar qualitative profile was observed with some differences in peak area and fifteen compounds were tentatively identified. Quantitative analysis was performed by UV detection considering eight standard phenolic compounds. The chromatographic method, after optimization, was validated studying some parameters, e.g., intra-day and inter-day retention time precision, limit of detection, limit of quantification, and linearity. Recovery of the method was performed achieving good results (10 and 50 g·g^-1 with recovery of 72.9⁻92.1% (w/w) and 79.1⁻102.8% (w/w), respectively). In all samples secoiridoids were the main compounds ranging from 85 to more than 99% (w/w) of the total concentration of detected phenolic compounds while phenolic acids accounted for the lowest percentage (0.1⁻0.6%, w/w). Finally, total concentration of phenolic compounds and antioxidant activity were determined with different chemical assays. A good and significant correlation among total phenolic compound concentration and antioxidant activity was observed. A significant different phenolic compound concentration and antioxidant activity was determined between samples from Puglia and Sicily. This was studied performing statistical analysis by one-way analysis of variance (ANOVA) followed by Bonferroni post-hoc test.