Gianluca Veneziani

Biological Activities of Phenolic Compounds of Extra Virgin Olive Oil

Over the last few decades, multiple biological properties, providing antioxidant, anti-inflammatory, chemopreventive and anti-cancer benefits, as well as the characteristic pungent and bitter taste, have been attributed to Extra Virgin Olive Oil (EVOO) phenols. In particular, growing efforts have been devoted to the study of the antioxidants of EVOO, due to their importance from health, biological and sensory points of view. Hydrophilic and lipophilic phenols represent the main antioxidants of EVOO, and they include a large variety of compounds. Among them, the most concentrated phenols are lignans and secoiridoids, with the latter found exclusively in the Oleaceae family, of which the drupe is the only edible fruit. In recent years, therefore, we have tackled the study of the main properties of phenols, including the relationships between their biological activity and the related chemical structure. This review, in fact, focuses on the phenolic compounds of EVOO, and, in particular, on their biological properties, sensory aspects and antioxidant capacity, with a particular emphasis on the extension of the product shelf-life.

Olive phenolic compounds: metabolic and transcriptional profiling during fruit development

BackgroundOlive (Olea europaea L.) fruits contain numerous secondary metabolites, primarily phenolics, terpenes and sterols, some of which are particularly interesting for their nutraceutical properties. This study will attempt to provide further insight into the profile of olive phenolic compounds during fruit development and to identify the major genetic determinants of phenolic metabolism.ResultsThe concentration of the major phenolic compounds, such as oleuropein, demethyloleuropein, 3–4 DHPEA-EDA, ligstroside, tyrosol, hydroxytyrosol, verbascoside and lignans, were measured in the developing fruits of 12 olive cultivars. The content of these compounds varied significantly among the cultivars and decreased during fruit development and maturation, with some compounds showing specificity for certain cultivars. Thirty-five olive transcripts homologous to genes involved in the pathways of the main secondary metabolites were identified from the massive sequencing data of the olive fruit transcriptome or from cDNA-AFLP analysis. Their mRNA levels were determined using RT-qPCR analysis on fruits of high- and low-phenolic varieties (Coratina and Dolce d’Andria, respectively) during three different fruit developmental stages. A strong correlation was observed between phenolic compound concentrations and transcripts putatively involved in their biosynthesis, suggesting a transcriptional regulation of the corresponding pathways. OeDXS, OeGES, OeGE10H and OeADH, encoding putative 1-deoxy-D-xylulose-5-P synthase, geraniol synthase, geraniol 10-hydroxylase and arogenate dehydrogenase, respectively, were almost exclusively present at 45 days after flowering (DAF), suggesting that these compounds might play a key role in regulating secoiridoid accumulation during fruit development.ConclusionsMetabolic and transcriptional profiling led to the identification of some major players putatively involved in biosynthesis of secondary compounds in the olive tree. Our data represent the first step towards the functional characterisation of important genes for the determination of olive fruit quality.

The influence of the malaxation temperature on the activity of polyphenoloxidase and peroxidase and on the phenolic composition of virgin olive oil.

The effect of the malaxation temperature under sealed conditions on the qualitative and quantitative composition of the phenolic compounds in virgin olive oils produced from four Italian cultivars was assessed for two atmospheric conditions. In both cases, the results show a positive relationship between temperature and the concentration of the derivatives of the secoiridoid aglycones; the effect of the temperature on the oxidoreductases that promote oxidation (polyphenoloxidase and peroxidase) was investigated to determine their optimal temperatures and thermal stability. While olive peroxidase (POD) showed the highest activity at 37°C and high stability in the temperature range tested, polyphenoloxidase (PPO) exhibited the optimum activity at approximately 50°C, but showed low stability at 40°C, with a large variation in stability according to the olive cultivar. These results may contribute to an understanding of the increase in the phenol concentration found in virgin olive oils obtained following higher temperatures of malaxation.

Flash Thermal Conditioning of Olive Pastes during the Olive Oil Mechanical Extraction Process: Impact on the Structural Modifications of Pastes and Oil Quality

The quality of virgin olive oil (VOO) is strictly related to the concentrations of phenolic and volatile compounds, which are strongly affected by the operative conditions of the VOO mechanical extraction process. The aim of this work is to study the impact of a new technology such as flash thermal conditioning (FTC) on olive paste structural modification and on VOO quality. The evaluation of olive paste structure modification by cryo-scanning electron microscopy (cryo-SEM) showed that the application of FTC after crushing produces significant differences in terms of the breaking of the parenchyma cells and aggregation of oil droplets in comparison to the crushed pastes. The virgin olive oil flash thermal conditioning (VOO-FTC) featured a higher concentration of volatile compounds compared to that in the control, particularly of all saturated and unsaturated aldehydes and esters, whereas the phenolic concentration was higher in VOO obtained from the traditional process (VOO-C).

Effect of an olive phenolic extract on the quality of vegetable oils during frying

The potential of a phenolic extract (PE) from olive vegetation water (OVW) to limit the negative effects of frying was tested after adding it at different concentrations to a refined olive oil (RO). Its efficacy was also compared to ROs containing butylated hydroxytoluene (BHT) and an extra virgin olive oil (EVOO) with a high polyphenol content. Analyses of the oils collected after 30min, 1, 2, 4, 6, 8, 10 and 12h of frying at 180°C, demonstrated that degradation of the polyphenols was proportional to the original content; at a concentration of at least 400mg/kg of polyphenols, PE was able to reduce oxidation of the tocopherols and the emission of low-molecular-weight aldehydes better than BHT and with similar results to the EVOO. In addition, secoiridoid oxidative compounds were examined by high-performance liquid chromatography/triple quadrupole tandem mass spectrometry with electrospray ionisation.

Compositional and Tissue Modifications Induced by the Natural Fermentation Process in Table Olives

Olive fruits contain high concentrations of phenols that include phenolic acids, phenolic alcohols, flavonoids, and secoiridoids. The final concentration of phenols is strongly affected by brine conditions. The factors involved in modification by brine are still partially unknown and can include hydrolysis of secoiridoid glucosides and the release of hydrolyzed products. In this study olives from various Italian cultivars were processed by natural fermentation (e.g., without a preliminary treatment of olives with NaOH) using a selected Lactobacillus strain. Processed olives are characterized by a low phenolic concentration of phenols, consisting mainly of phenyl alcohols, verbascoside, and the dialdehydic form of decarboxymethylelenolic acid linked to (3,4-dihydroxyphenyl)ethanol (3,4-DHPEA-EDA), whereas a high level of phenols occurs in olive brine from all the cultivars studied. Olives of the Coratina cultivar, control and with fermentation by Lactobacillus pentosus 1MO, were analyzed in a frozen hydrated state by cryo scanning electron microscopy and energy-dispersive X-ray microanalysis, on both surface and transversal freeze-fracture planes. Structural modifications, found in olives after fermentation, may explain the phenol release in brine.

Optimization of the Temperature and Oxygen Concentration Conditions in the Malaxation during the Oil Mechanical Extraction Process of Four Italian Olive Cultivars

Response surface modeling (RSM) was used to optimize temperature and oxygen concentration during malaxation for obtaining high quality extra virgin olive oils (EVOOs). With this aim, those chemical variables closely related to EVOO quality, such as the phenolic and the volatile compounds, have been previously analyzed and selected. It is widely known that the presence of these substances in EVOOs is highly dependent on genetic, agronomic, and technological aspects. Based on these data, the two parameters were optimized during malaxation of olive pastes of four important Italian cultivars using some phenols and volatile compounds as markers; the optimal temperatures and oxygen levels, obtained by RSM, were as follows for each cultivar: 33.5 °C and 54 kPa of oxygen (Peranzana), 32 °C and 21.3 kPa (Ogliarola), 25 °C and 21.3 kPa (Coratina), and 33 °C and 21.3 kPa (Itrana). These results indicate the necessity to optimize these malaxing parameters for other olive cultivars.

Candida adriatica sp. nov. and Candida molendinolei sp. nov., two yeast species isolated from olive oil and its by-products.

Thirteen strains isolated from virgin olive oil or its by-products in several Mediterranean countries were found to be phenotypically and genetically divergent from currently recognized yeast species. Sequence analysis of the large subunit (LSU) rDNA D1/D2 domain and internal transcribed spacer regions/5.8S rDNA revealed that the strains represented two novel species described as Candida adriatica sp. nov. (type strain ZIM 2334(T) = CBS 12504(T) = NCAIM Y.02001(T)) and Candida molendinolei sp. nov. (type strain DBVPG 5508(T) = CBS 12508(T) = NCAIM Y.02000(T)). Phylogenetic analysis based on concatenated sequences of the small subunit rRNA gene, the D1/D2 region of the LSU rDNA and the translation elongation factor-1α gene suggested that C. adriatica sp. nov. and C. molendinolei sp. nov. should be placed within the Lindnera and Nakazawaea clades, respectively.

Characterization of 3,4-DHPEA-EDA oxidation products in virgin olive oil by high performance liquid chromatography coupled with mass spectrometry.

Secoiridoid derivatives are the most important antioxidants of virgin olive oil (VOO), and their oxidation products could be used as molecular markers of VOO freshness to define the VOO autoxidation state. The aim of this research was to characterise the dialdehydic form of decarboxymethyl elenolic acid linked to hydroxytyrosol (3,4-DHPEA-EDA) oxidation products to find analytical indicators that could be used as early evaluation index of the VOO autoxidation state. 3,4-DHPEA-EDA was oxidised by enzymatic and Fenton reactions. Terpenic structure oxidation products accumulated in VOO during the autoxidation process, thus they may be used as early evaluation index of the VOO autoxidation state before fatty acids oxidation.

Flash Thermal Conditioning of Olive Pastes during the Oil Mechanical Extraction Process: Cultivar Impact on the Phenolic and Volatile Composition of Virgin Olive Oil

The concentration of phenolic and volatile compounds in virgin olive oil (VOO) is closely related to the different operative conditions applied to the mechanical extraction process of the olive oil. However, the great qualitative and quantitative variability of these compounds indicates an important role played by genetic and agronomic aspects. A heat exchanger was placed in front of a traditional, covered malaxer to study the impact of flash thermal conditioning (FTC) of olive paste on the quality of VOO, which is highly influenced by phenolic release and aroma generation. The VOO flash thermal conditioning of five major Italian cultivars showed a higher concentration of phenols (range of increase percentage, 9.9-37.3%) compared to the control trials, whereas the FTC treatment featured a differentiated impact on the volatile fractions, associated with the genetic origins of the olives.