Antioxidant effect of phenolic compounds, alpha-tocopherol, and other minor components in virgin olive oil

The effect of acidity, squalene, hydroxytyrosol, aldehydic form of oleuropein aglycon, hydroxytyrosyl acetate, tyrosol, homovanillic acid, luteolin, apigenin, alpha-tocopherol, and the mixtures hydroxytyrosol/hydroxytyrosyl acetate, hydroxytyrosol/tyrosol, and hydroxytyrosol/alpha-tocopherol on the oxidative stability of an olive oil matrix was evaluated. A purified olive oil was spiked with several concentrations of these compounds and, then, subjected to an accelerated oxidation in a Rancimat apparatus at 100 degrees C. Acidity, squalene, homovanillic acid, and apigenin showed negligible effect. At the same millimolar concentrations, the different o-diphenolic compounds yielded similar and significant increases of the induction time, alpha-tocopherol a lesser increase, and tyrosol a scarce one. At low concentrations of o-diphenols and alpha-tocopherol, a linear relationship between induction time and concentration was found, but at high concentrations the induction time tended toward constant values. To explain this behavior, a kinetic model was applied. The effect of the mixtures hydroxytyrosol/hydroxytyrosyl acetate was similar to that of a single o-diphenol at millimolar concentration equal to the sum of millimolar concentrations of both compounds. Concentrations of tyrosol >0.3 mmol/kg increase the induction time by 3 h. The mixtures hydroxytyrosol/alpha-tocopherol showed opposite effects depending on the relative concentrations of both antioxidants; so, at hydroxytyrosol concentrations <0.2 mmol/kg, the addition of alpha-tocopherol increased the induction time, whereas at higher hydroxytyrosol concentrations, the alpha-tocopherol diminished the stability.     

Influence of crystallization on the oxidative stability of extra virgin olive oil

The aim of this study was to evaluate the influence of the extra virgin olive oil (EVOO) physical state on the kinetics of oxidative reactions. To this purpose, EVOO was stored at increasing temperatures from 3 to 60 degrees C and the oxidation was followed by measuring both primary and secondary oxidation products. Results highlighted that crystallization plays an important role in determining EVOO stability. Below the melting point, the oxidation rate was found to be higher than that expected on the basis of the Arrhenius equation. The observed deviation from the Arrhenius equation was attributed to the physicochemical changes occurring as a consequence of phase transitions. In particular, the increase in unsaturated triacylglycerol concentration and the decrease of polyphenol content in the liquid phase surrounding fat crystals were indicated as the main factors causing the deviation. By taking into account these changes it was possible to describe the temperature dependence of the oxidation rate in the entire range of temperatures considered. This model appears to be promising in the challenge to find mathematical models able to predict the stability and, hence, the shelf life of lipid-containing foods.     

Solid-phase microextraction in the analysis of virgin olive oil volatile fraction: characterization of virgin olive oils from two distinct geographical areas of northern Italy

SPME was employed to characterize the volatile profile of virgin olive oils produced in two geographical areas of northern Italy: the region of the Gulf of Trieste and the area near Lake Garda. There are as yet no data on the headspace composition of virgin olive oils from these regions, characterized by particular conditions of growth for Olea europaea. Using the SPME technique coupled to GC-MS and GC-FID, the volatile components of 42 industrially produced virgin olive oil samples were identified and the principal compounds quantitatively analyzed. Significant differences in the proportion of volatile constituents from oils of different varieties and geographical origins were detected. The results suggest that besides the genetic factor, environmental conditions influence the volatile formation.     

Soil water availability in rainfed cultivation affects more than cultivar some nutraceutical components and the sensory profile of virgin olive oil

This research considered the varieties 'Frantoio' and 'Moraiolo' growing in rainfed olive trees (Olea europaea) and took place in Tuscany, central Italy. Soil moisture was monitored during the very meteorologically contrasting years 2002 and 2003 in two nearby olive groves. The plots had the same morphological and climatic conditions, but different soil types. Monocultivar oil samples were analyzed to determine fatty acids, minor polar compounds, and tocopherols content and were submitted to organoleptic analysis by a panel of trained tasters. The results highlighted that soil water regimen affects some nutraceutical components and the sensory evaluation of olive oil. Cultivar also affected yield components, polyphenols, and tocopherols content, but less than soil water availability. The plants on the soil inducing a relatively more intense and longer water deficit during summer (a Skeleti Calcaric Regosol) had an early ripening and gave the best results in terms of phenolic compounds and, consequently, antioxidant properties of the olive oil. The sensorial properties of the oil obtained from both cultivars on the Regosol were superior in both years of the trial.     

Role of olive seed in the biogenesis of virgin olive oil aroma

Results obtained in a set of experiments point to an effective participation of olive seeds in the biosynthesis of olive oil aroma through the lipoxygenase pathway during the extraction process to produce virgin olive oil. Data showed that olive seeds should contain enzymatic activities metabolizing 13-hydroperoxides other than hydroperoxide lyase, giving rise to a net decrease in the content of C6 unsaturated aldehydes during the olive oil extraction process. Olive seeds seem also to supply this process with alcohol dehydrogenase activity, being more specific for saturated C6 aldehydes and not acting on C5 alcohols. Moreover, olive seeds would be responsible for the biosynthesis of 30-50% esters during the olive oil extraction process of intact fruits. Thus, olive seeds would afford a load of alcohol acyltransferase activity that might be quite unspecific in terms of substrate, producing any kind of esters.     

Influence of thermal treatments simulating cooking processes on the polyphenol content in virgin olive oil

Virgin olive oils were subjected to simulated common domestic processing, including frying, microwave heating, and boiling with water in a pressure cooker. The impact of these processes on polyphenol content and physicochemical characteristics of oils was assessed. Thermal oxidation of oils at 180 degrees C caused a significant decrease in hydroxytyrosol- and tyrosol-like substances. In contrast, oils heated for 25 h still retained a high proportion of the lignans 1-acetoxypinoresinol and pinoresinol. Thermal oxidation also resulted in a rapid degradation of alpha-tocopherol and the glyceridic fraction of oils. Microwave heating of oils for 10 min caused only minor losses in polyphenols, and the oil degradation was lower than that in thermoxidation assays. Again, lignans were the least affected polyphenols and did not change during microwave heating. Boiling a mixture of virgin olive oil and water in a pressure cooker for 30 min provoked the hydrolysis of the secoiridoid aglycons and the diffusion of the free phenolics hydroxytyrosol and tyrosol from the oil to the water phase. Losses of polyphenols were detected only at pH lower than 6. Moreover, alpha-tocopherol and the glyceridic fraction of oils were not modified during this process. It is worth noting that all the heating methods assayed resulted in more severe polyphenols losses and oil degradation for Arbequina than for Picual oil, which could be related to the lower content in polyunsaturated fatty acids of the latter olive cultivar. These findings may be relevant to the choice of cooking method and olive oil cultivar to increase the intake of olive polyphenols.     

Effect of olive stoning on the volatile and phenolic composition of virgin olive oil

Olive stoning during the virgin olive oil (VOO) mechanical extraction process was studied to show the effect on the phenolic and volatile composition of the oil. To study the impact of the constitutive parts of the fruit in the composition of olive pastes during processing, the phenolic compounds and several enzymatic activities such as polyphenoloxidase (PPO), peroxidase (POD), and lipoxygenase (LPO) of the olive pulp, stone, and seed were also studied. The olive pulp showed large amounts of oleuropein, demethyloleuropein, and lignans, while the contribution of the stone and the seed in the overall phenolic composition of the fruit was very low. The occurrence of crushed stone in the pastes, during malaxation, increased the peroxidase activity in the pastes, reducing the phenolic concentration in VOO and, at the same time, modifying the composition of volatile compounds produced by the lipoxygenase pathway. The oil obtained from stoned olive pastes contained higher amounts of secoiridoid derivatives such as the dialdehydic forms of elenolic acid linked to (3,4-dihydroxyphenyl)ethanol and (p-hydroxyphenyl)ethanol (3,4-DHPEA-EDA and p-HPEA-EDA, respectively) and the isomer of the oleuropein aglycon (3,4-DHPEA-EA) and, at the same time, did not show significant variations of lignans. The stoning process modified the volatile profile of VOO by increasing the C6 unsaturated aldehydes that are strictly related to the cut-grass sensory notes of the oil.     

Evolution of minor polar compounds and antioxidant capacity during storage of bottled extra virgin olive oil

We characterized "Olivastra Seggianese" extra virgin olive oil (EVOO) and evaluated its chemical and sensory characteristics and antioxidant and antiradical activities during storage under novel conditions. Two oils (A and B) were analyzed for the commodity characteristics at blending (t0) and after 9, 12, and 18 months; panel tests were performed and minor polar compounds (MPC) content was assessed at blending (t0) and after 6, 9, 12, and 18 months. Antioxidant and antiradical activities in vitro were evaluated at t0 and after 12 months, by human low density lipoprotein (LDL) and 1,1-diphenyl-2-picrylhydrazil radical (DPPH*) tests. Oil A, which had an initially higher MPC content, possessed "harder" organoleptic characteristics than oil B, which had a lower MPC content and was endowed with a "smoother" taste profile. Statistical analyses showed that secoiridoids, particularly deacetoxy-oleuropein aglycone, should be quantified to evaluate EVOO stability during storage. The antioxidant activity toward human LDL was linked to MPC content and to storage time. The tests on the stable free radical DPPH* confirmed the results on human LDL. We propose this as an additional parameter to evaluate olive oil quality and stability over time.     

Effect of olive ripeness on the oxidative stability of virgin olive oil extracted from the varieties picual and hojiblanca and on the different components involved

The initial stability of virgin olive oil depends on various factors, among which are the variety and the degree of fruit ripeness. The former, which genetically determines the composition of the olive and its oil, also marks, to some extent, its stability. However, oil stability changes as the olive ripens, so it is obvious that the degree of ripeness is an important factor. The oils were obtained by the Abencor system. Acidity, peroxide index, UV absorption at 232 and 270 nm, sensory analysis, fatty acid composition, tocopherols, phenolic compounds, orthodiphenolic compounds, sterols, pigments, and oxidative stability were determined, and the results were analyzed statistically. During ripening there was a decrease in all of the parameters studied except linoleic acid, Delta-5-avenasterol, and oil content, which increased. Virgin oils showed very good correlation between stability and the concentrations of total phenols, o-diphenols, tocopherols, chlorophyll pigments and carotenoids, linoleic and linolenic acids, total sterols, beta-sitosterol, and Delta-5-avenasterol.     

Influence of the decrease in oxygen during malaxation of olive paste on the composition of volatiles and phenolic compounds in virgin olive oil

The sensory and health properties of virgin olive oil (VOO) are highly related to its volatile and phenolic composition. Oxygen control in the pastes during malaxation may be a new technological parameter to regulate enzymatic activities, such as polyphenoloxidase, peroxidase, and lipoxygenase, which affect the phenolic and volatile composition of VOO. In this work, we monitored CO2 and O2 concentrations during industrial-scale olive paste malaxation with various initial O2 concentrations within the malaxer headspace. Results show that the O2 concentration in the malaxer headspace did not affect CO2 production during processing, whereas a strong influence was observed on the changes of the phenolic composition of olive pastes and VOOs, with high correlation coefficient for the total phenols (R = 0.94), especially for oleuropein and demethyloleuropein derivatives (R = 0.81). In contrast, aroma production during malaxation was minimally affected by the O2 concentration in the malaxer headspace.     

Discrimination of storage conditions and freshness in virgin olive oil

Virgin olive oil samples stored in the light at ambient temperature, in the dark at ambient temperature, and at low temperature in the dark for 12 months both with and without headspace were separated into recognizable patterns with stepwise linear discriminant analysis. The discrimination with variables volatile and phenolic compounds, free fatty acid (FFA), peroxide values, K232, and K270 revealed a departure of stored oil from freshness and showed significant (p < 0.01) differences between storage conditions. Virgin olive oil stored at low temperature had characteristics closest to fresh oil while oil stored in the light showed the largest departure from freshness. Parameters that exclusively and significantly (p < 0.01) discriminated storage conditions were identified as potential markers of the storage condition. In the presence of oxygen, hexanal was a marker of storage in the light, FFA was a marker for dark storage, and markers of low-temperature storage were acetic acid and pentanal. In the absence of oxygen, octane was the marker for storage in the light whereas tyrosol and hexanol were markers of virgin olive oil stored in the dark, with no marker indicative of low-temperature storage. E-2-Hexenal, K232, and K270 were identified as markers of virgin olive oil freshness.     

Nutritional and biological properties of extra virgin olive oil

The nutritional benefits generally recognized for the consumption of extra virgin olive oil (EVOO) are based on a large number of dietary trials of several international populations and intervention studies. Unfortunately, many authors in this field used questionable analytical methods and commercial kits that were not validated scientifically to evaluate the complex bioactive constituents of EVOO and lipid oxidation and decomposition products. Many questionable antiradical methods were commonly used to evaluate natural polyphenolic antioxidants, including an indirect method to determine low-density lipoprotein (LDL) cholesterol. Extensive differences were observed in experimental design, diet control, populations of different ages and problems of compliance intervention, and questionable biomarkers of oxidative stress. Analyses in many nutritional studies were limited by the use of one-dimensional methods to evaluate multifunctional complex bioactive compounds and plasma lipid profiles by the common applications of commercial kits. Although EVOO contains polyphenolic compounds that exhibit significant in vitro antioxidant activity, much more research is needed to understand the absorption and in vivo activity. Many claims of in vivo human beneficial effects by the consumption of EVOO may be overstated. No distinctions were apparently made between in vivo studies based on general health effects in large populations of human subjects and smaller scale well-controlled feeding trials using either pure or mixtures of known phenolic constituents of EVOO. More reliable protocols and testing methods are needed to better validate the complex nutritional properties of EVOO.     

Effectiveness of microsatellite DNA markers in checking the identity of protected designation of origin extra virgin olive oil

Collina di Brindisi is an Italian extra virgin olive oil that obtained the mark of protected designation of origin (PDO) according to EC Regulation 2081/92. The varietal requirements of the official production protocol of this oil foresee that this oil is prepared from cultivar Ogliarola (minimum 70%) and other Olea europaea L. cultivars that are diffused in the production area, accounting for a maximum of 30%. The aim of this work was to verify the effectiveness of microsatellite analysis in verifying the identity of Collina di Brindisi PDO olive oil. A preliminary assessment of product's quality by means of chemical analyses was also carried out. Microsatellite analysis clarified that the generic name Ogliarola, indicated in the technical sheet of this PDO oil, actually corresponded to the Ogliarola salentina cultivar. Furthermore, the obtained results showed that the examination of a limited number of DNA microsatellites enables the identification of the Ogliarola salentina cultivar in this PDO oil.     

Factors limiting the synthesis of virgin olive oil volatile esters

The aim of the present work was to establish the limiting factors affecting the biosynthesis of volatile esters present in virgin olive oil (VOO). Oil volatile fractions of the main Spanish olive cultivars, Arbequina and Picual, were analyzed. It was observed that acetate esters were the most abundant class of volatile esters in the oils, in concordance with the high content of acetyl-CoA found in olive fruit, and that the content of C6 alcohols is limited for the synthesis of volatile esters during the production of VOO. Thus, the increase of C6 alcohol availability during VOO production produced a significant increase of the corresponding ester in the oils in both cultivars at two different maturity stages. However, the increase of acetyl-CoA availability had no effect on the VOO volatile fraction. The low synthesis of these C6 alcohols seems not to be due to a shortage of precursors or cofactors for alcohol dehydrogenase (ADH) activity because their increase during VOO production had no effect on the C6 alcohol levels. The experimental findings are compatible with a deactivation of ADH activity during olive oil production in the cultivars under study. In this sense, a strong inhibition of olive ADH activity by compounds present in the different tissues of olive fruit has been observed.     

Effects of olive fruit quality and oil storage practices on the diacylglycerol content of virgin olive oils

The evolution of 1,3- and 1,2-isomers of diacylglycerols (DGs) in olive oils obtained from healthy olives and the influence of the olive quality was studied. Healthy olive fruits yielded oils containing almost exclusively 1,2-isomers whereas altered olives produced oils with significant amounts of 1,3-isomers. Virgin olive oils obtained from various olive cultivars and stored at different temperatures showed triacylglycerol hydrolysis and diacylglycerol isomerization depending on the acidity and temperature. The results indicated that the relationship between acidity and total diacylglycerol content has scarce utility for detecting mild refined oil in virgin olive oil. On the other hand, the 1,3-/1,2-DG isomers ratio is useful for assessing the genuineness of virgin olive oils with low acidities during the early stages of storage.     

Determination of furan fatty acids in extra virgin olive oil

The presence of 4 different furan fatty acids (F-acids) was detected in 18 samples of transmethylated monovarietal extra virgin olive oil: methyl 10,13-epoxy-11,12-dimethyloctadeca-10,12-dienoate [diMeF(9,5)], methyl 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoate [diMeF(11,5)] and both olefinic derivatives of diMeF(11,5) with one unsaturation on the side chains conjugated with the furan ring. Transmethylated oils were analyzed by normal phase high-performance liquid chromatography coupled on-line with capillary gas chromatography. After the gas chromatographic separation step, a more selective detection of F-acids was achieved by using a photoionization detector mounted in series with a flame ionization detector. The concentration of F-acids ranged between 50 ppb (detection limit of the method) and 2.1 ppm in the oil. The olefinic derivatives of diMeF(11,5) acids detected were not artifacts created during the sample preparation or during the chromatographic analysis.     

New hydrothermal treatment of alperujo enhances the content of bioactive minor components in crude pomace olive oil

The application of a new process based on the hydrothermal treatment of olive oil waste (alperujo) led to a final solid rich in pomace olive oil (POO) enriched in minor components with functional activities. The effects of the time (15-90 min) and the temperature (150, 160, and 170 °C) of the thermal processing of alperujo on the yield, quality, and enrichment of minor components of crude POO were evaluated. The final treated solid had an increase in oil yield up to 97%, with a reduction in solids up to 35.6-47.6% by solubilization. Sterols increased up to 33%, aliphatic alcohols increased up to 92%, triterpenic alcohols increased up to 31%, squalene increased up to 43%, tocopherols increased up to 57%, and oleanolic acid increased up to 16% by the new treatment. The increase maintains a high concentration of functional substances probably even in the refining POO.     

Detection of extra virgin olive oil adulteration with lampante olive oil and refined olive oil using nuclear magnetic resonance spectroscopy and multivariate statistical analysis

High-field 31P NMR (202.2 MHz) spectroscopy was applied to the analysis of 59 samples from three grades of olive oils, 34 extra virgin olive oils from various regions of Greece, and from different olive varieties, namely, 13 samples of refined olive oils and 12 samples of lampante olive oils. Classification of the three grades of olive oils was achieved by two multivariate statistical methods applied to five variables, the latter being determined upon analysis of the respective 31P NMR spectra and selected on the basis of one-way ANOVA. The hierarchical clustering statistical procedure was able to classify in a satisfactory manner the three olive oil groups. Subsequent application of discriminant analysis to the five selected variables of oils allowed the grouping of 59 samples according to their quality with no error. Different artificial mixtures of extra virgin olive oil-refined olive oil and extra virgin olive oil-lampante olive oil were prepared and analyzed by 31P NMR spectroscopy. Subsequent discriminant analysis of the data allowed detection of extra virgin olive oil adulteration as low as 5% w/w for refined and lampante olive oils. Further application of the classification/prediction model allowed the estimation of the percent concentration of refined olive oil in six commercial blended olive oils composed of refined and virgin olive oils purchased from supermarkets.     

Detection of rancid defect in virgin olive oil by the electronic nose

A sensor array of 32 conducting polymer sensors has been used to detect the rancid defect in virgin olive oils. A training set, composed of admixtures of a Portuguese virgin olive oil with different percentages (0-100%) of a rancid standard oil, was used for the selection of the best sensors classifying correctly the samples. Information on volatile compounds responsible for rancidity and the sensory evaluation of samples by assessors were used for explaining the mathematical selection of sensors. A tentative calibration, using unsupervised procedures (PCA and MDS) and a nonlinear regression, was carried out, with the training set, and later confirmed with a test set with which rancid commercial samples of different varieties were used to spike a Greek extra virgin olive oil at low levels of rancidity (0.5-6%).     

Analytical evaluation of virgin olive oil of first and second extraction

Virgin olive oils from percolation (first extraction) have been compared with the corresponding oils from centrifugation (second extraction). The former were characterized by (i) higher contents of total phenols, o-diphenols, hydroxytyrosol, tyrosol-aglycons, tocopherols, trans-2-hexenal, total volatiles, and waxes; (ii) higher values of resistance to autoxidation and of turbidity; (iii) higher sensory scores; (iv) higher ratios of campesterol/stigmasterol, trans-2-hexenal/hexanal, and trans-2-hexenal/total volatiles; (v) lower contents of chlorophylls, pheophytins, sterols, and aliphatic and triterpene alcohols; (vi) lower alcoholic index and color indices; (vii) similar values of acidity, peroxide index, and UV (ultraviolet) spectrophotometric indices; (viii) similar percentages of saturated and unsaturated fatty acids, triglycerides, and diglycerides; and (ix) similar values of glyceridic indices. Stigmastadienes, trans-oleic, trans-linoleic, and trans-linolenic acid isomers were not detected in the two genuine oil kinds. Hence, the qualitative level of the first extraction oil was superior to the second extraction one.