Hydrophilic antioxidants of virgin olive oil. Part 2: Biosynthesis and biotransformation of phenolic compounds in virgin olive oil as affected by agronomic and processing factors

The biosynthesis of the phenolic fraction of olive fruits during ripening and the transformations occurring in this moiety during virgin olive oil (VOO) extraction are discussed in this paper. The influence of agronomical factors that can significantly affect the phenolic profile of VOO is also discussed. Particularly, it is worth emphasizing the role of genetic factors, cultivation and climatic conditions such as water availability, atmospheric temperature, altitude, health status of the fruits, alternate bearing in the olive, and some processing factors such as crushing, malaxation time and temperature or volume of water added during milling. Among these parameters, special attention has been paid to genetic factors due to the high variability observed among Olea europaea genotypes for all recorded traits. In this context, interesting experimental results have been obtained with cultivated and wild olive trees, and also with segregating populations resulting from olive breeding programs. To the authors' knowledge, reviews evaluating the influence of the main factors that contribute to the profile of hydrophilic phenols have not been previously published. The discussion concerning olive breeding programs is a major and novel aspect to be emphasized considering recent trends to obtain new olive cultivars that confer better organoleptic properties and better quality to VOO.     

Evaluation of virgin olive oil bitterness by quantification of secoiridoid derivatives

The bitterness of the main compounds identified in the phenolic extract of virgin olive (Olea europaea L.) oils has been sensory-tested. The aldehydic form of oleuropein aglycone (AOA) was responsible for this attribute. Correlations between the sensory bitterness and concentrations of secoiridoid derivatives, analyzed separately or in different combinations, were obtained for olive oils from different olive varieties. The best correlation obtained corresponds to AOA content (r=0.96; P=1.83×10⁻¹⁷) in the concentration range of 0.03 to 0.5 mmol/kg. AOA concentrations ≥0.5 mmol/kg produce sensory saturation of this attribute. The correlation with AOA concentration was better than that with the absorbance of the phenolic extract at 225 nm. Therefore, the equation obtained allows the evaluation of the bitterness in virgin olive oils by HPLC analysis of the phenolic extract using detection at 280 nm.     

Pinoresinol and 1-acetoxypinoresinol, two new phenolic compounds identified in olive oil

Polyphenols of olive oil show autoprotective, sensory, and nutritional-therapeutic effects. Two new phenolic compounds have been isolated from virgin olive oils by preparative high-performance liquid chromatography and their structures established on the basis of their mass spectra and nuclear magnetic resonance spectral data. The compounds identified are the lignans pinoresinol and 1-acetoxypinoresinol. Both have been found in all the commercial virgin olive oils analyzed. Pinoresinol concentration was rather similar in all the oils. In contrast, 1-acetoxypinoresinol concentration was higher in oils of the Arbequina and Empeltre cultivars than in Picual or Picudo cultivars. Pinoresinol and 1-acetoxypinoresinol may represent the major phenolic compounds in some Arbequina and Empeltre oils. Lignans possess biological and pharmacological properties and, therefore, the two new compounds identified in olive oils may contribute to the reported beneficial effects which are attributed to polyphenols on human health of a diet rich in olive oil.     

Effect of natural antioxidants in virgin olive oil on oxidative stability of refined,bleached, and deodorized olive oil

The factors influencing the oxidative stability of different commercial olive oils were evaluated. Comparisons were made of (i) the oxidative stability of commercial olive oils with that of a refined, bleached, and deodorized (RBD) olive oil, and (ii) the antioxidant activity of a mixture of phenolic compounds extracted from virgin olive oil with that of pure compounds andα-tocopherol added to RBD olive oil. The progress of oxidation at 60°C was followed by measuring both the formation (peroxide value, PV) and the decomposition (hexanal and volatiles) of hydroperoxides. The trends in antioxidant activity were different according to whether PV or hexanal were measured. Although the virgin olive oils contained higher levels of phenolic compounds than did the refined and RBD oils, their oxidative stability was significantly decreased by their high initial PV. Phenolic compounds extracted from virgin olive oils increased the oxidative stability of RBD olive oil. On the basis of PV, the phenol extract had the best antioxidant activity at 50 ppm, as gallic acid equivalents, but on the basis of hexanal formation, better antioxidant activity was observed at 100 and 200 ppm.α-Tocopherol behaved as a prooxidant at high concentrations (>250 ppm) on the basis of PV, but was more effective than the other antioxidants in inhibiting hexanal formation in RBD olive oil.o-Diphenols (caffeic acid) and, to a lesser extent, substitutedo-diphenols (ferulic and vanillic acids), showed better antioxidant activity than monophenols (p- ando-coumaric), based on both PV and hexanal formation. This study emphasizes the need to measure at least two oxidation parameters to better evaluate antioxidants and the oxidative stability of olive oils. The antioxidant effectiveness of phenolic compounds in virgin olive oils can be significantly diminished in oils if their initial PV are too high.     

Effect of extraction systems on the phenolic composition of virgin olive oils

The effect of extraction systems on the phenolic composition of virgin olive oils obtained from two different Italian cultivars (Coratina and Oliarola) was determined. The oils extracted using two-phase centrifugation showed in all cases higher phenolic concentration in comparison to oils obtained from three-phase centrifugation. In particular, the highest differences were observed for aglykone derivatives of oleuropein (3,4-DHPEA-EDA and 3,4-DHPEA-EA) that are the most concentrated antioxidant phenolic compounds of virgin olive oil. These results were confirmed by the autoxidation stability of the oils examined.     

Stability of a phenol‐enriched olive oil during storage

The use of an emulsifier to stabilize the phenolic compounds added in the preparation of an enriched olive oil was evaluated. Two emulsifiers, lecithin and monoglyceride, were studied. The results showed lecithin to be the most convenient, due to the increase in the value of the oxidative stability of the phenol‐enriched oils in relation to the enrichments prepared with monoglycerides. After that, the shelf life of the prepared oils was evaluated during a period of 256 days of storage at 25°C in the dark. Oil quality parameters, total phenolic content, bitterness index and oxidative stability were studied during the storage period. Additionally, the phenolic composition and antioxidant capacity (by using the ORAC assay) were evaluated at the end of the storage. The phenolic enrichment of the oils allowed the shelf life of the oils to be extended compared with the control (virgin olive oil without phenol addition), delaying the appearance of peroxides and improving their oxidative stability. In addition, the higher content of phenolic compounds in the oils at all stages of storage is desirable in order to increase the intake of these beneficial compounds. Practical applications : The preparation of phenol‐enriched olive oils with a higher phenolic content than the commercial virgin olive oils is of special interest to increase the ingestion of these healthy compounds the daily intake of which is limited due to the high caloric value of olive oil. There are two key points in the development of this product: (i) the dispersion and stabilization of the phenol extract in the oil matrix and (ii) the stability of the phenols in the prepared oils to guarantee the phenol concentration during their shelf life. It is important to study the use of emulsifiers to determine if they allow an improvement in the dispersion of the phenolic extract, and their stabilization in the final product. In addition, the emulsifiers could mask the bitter taste of the enriched oils, which is desirable to increase consumer acceptance of the enriched oil.     

Phenolic composition and antioxidant activity of Southern Italian monovarietal virgin olive oils

The phenolic composition and antioxidant activity of several monovarietal extra virgin olive oils used as blenders for the production of Collina di Brindisi protected designation of origin (PDO) oil, produced between December 2008 and January 2009 using two‐phases or three‐phases extraction system, were evaluated and compared with other manufacturer products designated as PDO. Oils were taken from the most representative ones industrial oil mills in the PDO geographical area. The parameters assessed were free acidity, peroxide value, K₂₃₂ and K₂₇₀ indices, organoleptic characteristics, total phenolic content (TPC), phenolic profile, and antioxidant activity coefficient (AAC). The phenolic contents and profiles of the monovarietal oils showed remarkable differences with respect to PDO oils. The variables that exerted a major influence on phenols concentration were the maturity degree of olives (December>January), followed by the extraction system (two‐phase>three‐phase), and place of growing. The Pearson r correlation index showed that AAC was positively correlated with TPC, p‐coumarate, and 3,4‐DHPEA‐EA, and negatively correlated with peroxide value. Practical applications: The results provide detailed information about: (i) the phenolic composition and the AAC of several monovarietal extra virgin olive oils used as blenders for the production of a PDO oil; (ii) the impact of genetic variability, place of growing, olive maturity degree, and extraction technology on oil phenol compounds; and (iii) the relationships among each phenolic compound and AAC, and their potential utilization as analytical index of antioxidant activity. It is important to study the phenolic compounds and antioxidant activity of monovarietal extra virgin olive oils used to produce PDO oil and to compare with the relative PDO samples in order to define a possible analytical tool able to verify what is stated in the label for consumer information and protection.     

LC–ESI–MS Characterization of Phenolic Profiles Turkish Olive Oils as Influenced by Geographic Origin and Harvest Year

The purpose of this investigation was to evaluate and compare the differences in the phenolic fractions and antioxidant properties of virgin olive oils from the Nizip yaglik and Kilis yaglik olive varieties cultivated in native and different olive growing areas of Turkey. The phenolic composition of olive oils was carried out by HPLC-DAD and identifications were made by LC–MS. Fourteen phenolic compounds were identified and among these compounds elenolic acid, tyrosol and hydroxytyrosol were the most dominant. Based on the results, there was no difference in distribution of phenolic compounds, but the total phenolic content in oil from native regions was higher than in oil from Bornova regions. The antioxidant capacity of olive oil extracts was determined by two different methods, including DPPH and ABTS. In both methods, antioxidant capacity values were higher in oil from native regions.     

Oil composition of advanced selections from an olive breeding program

Fifteen genotypes coming from crosses between the cultivars Arbequina, Frantoio and Picual were selected on the basis of their agronomic characteristics in a breeding program initiated in 1991. In the present work, the main components of the olive oil of these 15 advances selections have been characterized and compared to their genitors. A wide range of variation was observed for all the fatty acids, minor components and related characteristics evaluated, with significant differences between genotypes for all of them except for β‐tocopherol content. These results confirm the strong genetic influence on olive oil quality previously reported on olive oil cultivar evaluations. The values obtained in the selections have extended the range of variation of their three genitors for all the characters evaluated, except for γ‐tocopherol. Selections UC‐I 7‐8, UC‐I 5‐44 and UC‐I 2‐68 showed the highest average values for tocopherols, polyphenol and C18:1 contents, respectively. Finally, multivariate analysis allowed the classification of genotypes in four groups according to their olive oil composition. Practical applications: Olive oil composition is considered one of the most important objectives in breeding programs aiming at obtaining new olive cultivars. In the last decades olive breeding programs are being carried out in the main olive‐producing countries and several new cultivars and advanced selections have been described. The results of this work provide an initial characterization of virgin olive oils of advanced selections coming from crosses between the cultivars Arbequina, Frantoio and Picual and suggest a strong genetic influence on fatty acid composition, several minor components and related characteristics. These results, together with the agronomic characterization of these selections previously reported, will be used for the final selection of the best genotypes to be registered as new cultivars.     

Characterization of Extra Virgin Olive Oil from Southern Brazil

Six olive oils extracted from the cultivars Arbequina, Arbosana, Coratina, Frantoio, Koroneiki, and Picual from 2017 and 2018 harvests, cultivated in Pinheiro Machado, Rio Grande do Sul, Brazil, are evaluated for standard oil composition parameters and bioactive constituents (pigments, tocopherols, and phenolic compounds). Multivariate principal component analysis (PCA) and univariate ANOVA and Fisher's LSD test are used to verify the effect of cultivar and harvest year on oil composition. Olive oil composition met extra virgin olive oil (EVOO) standard parameters and is influenced by both cultivar and harvest year. EVOO produced in 2018 has greater chlorophyll, caffeic acid, ligstroside aglycone, hydroxyoleuropein aglycone, syringic acid, and hydroxytyrosol acetate contents than the EVOOs from 2017. Linoleic acid, ferulic acid, ligstroside aglycone, and hydroxytyrosol acetate are the variables whose contents most contributed to the differentiation of oils by cultivar in both harvest years. Chemical characterization analyses allow for the differentiation of oil composition based on harvest year and cultivar. Metabolic quality data obtained here support the establishment of a local EVOO profile and the compounds that most contributed to treatment differentiation may serve as markers that can be utilized in determining origin, cultivar, and harvest year. Practical Applications: Olive production in Brazil is recent and is based on European cultivars which have not been bred for the local environmental conditions. Therefore, the measurement of olive oil metabolic quality will determine cultivar adaptability to local edaphoclimatic conditions as well as assist in the establishment of a standard of identity for the product and promote the development of its market. Olive oil produced in Southern Brazil shows high quality, and is especially rich in phenolic compounds. Although harvest year influences oil composition, oil from both harvests meet EVOO standards and cultivar specific metabolic markers are observed. This study provides the foundation for olive producers in Southern Brazil to seek authentication of the geographical origin of olive oil.     

Quality and Composition of Virgin Olive Oils from Indigenous and European Cultivars Grown in China

The characteristics of eight varieties of virgin olive oil (Arbosana, Arbequina, Coratina, Cornicabra, Frantoio, Koroneiki, Picual, and Ezhi 8) obtained in two successive crops in the southwest of China (Xichang, Sichuan Province) were investigated. Significant differences (P < 0.05) were observed in physicochemical properties, fatty acid profile, minor component contents, and oxidative stability between different varieties of olive oils. The physicochemical properties of all samples met IOC standards for extra virgin olive oil, while in Koroneiki, olive oils were present the optimum oxidation stability among studied varieties. The results of hierarchical cluster analysis and principal component analysis (PCA) showed a good classification between varieties based on their qualitative characteristics. Koroneiki and Ezhi 8 olive oils were significantly different from other varieties mainly due to color, fatty acid profile, and minor components. PCA result also showed that harvest crop influences the characteristics of samples mainly due to the variance of temperature and rainfall.     

Effect of growing area on pigment and phenolic fractions of virgin olive oils of the arbequina variety in Spain

The purpose of this investigation was to study differences in the chlorophyll, carotenoid, and phenolic fractions of virgin olive oils from the Arbequina variety cultivated in different olive growing areas of Spain. Virgin olive oil from Lleida was less heavily pigmented, and these oils showed more negative values for the ordinate a^* (of the CIELAB colorimetric system). Pheophytin a was the major chlorophyll pigment, and lutein was the major component of the carotenoid fraction in all oils analyzed. The chlorophyll a concentration in virgin olive oils from Lleida was 700 μg kg⁻¹, but was 175 μg kg⁻¹ in oils from Jaén, and 200 μg kg⁻¹ in oils from Tarragona. Finally, the chlorophyll a/chlorophyll b ratio was 9 in oils from Lleida and around 0.6 in the other two Arbequina olive oils. In relation to the phenolic fraction, the hydroxytyrosol and tyrosol contents were significantly higher in olive oils from Jaén (grown at higher altitude and precipitation rates). The secoiridoid derivatives showed a significantly higher concentration in olive oils from Tarragona, probably due to the low altitude where they grow, and finally the ratio of (dialdehydic form of elenolic acid linked to tyrosol)/lignans had a value of 1.4 in olive oils from Lleida, whereas this value was around 0.7 in the other Arbequina olive oils.     

Air exposure time of olive pastes during the extraction process and phenolic and volatile composition of virgin olive oil

The time of exposure of olive pastes to air contact (TEOPAC) during malaxation was studied as a processing parameter that could be used to control endogenous oxidoreductases, such as polyphenoloxidase, peroxidase, and lipoxygenase, which affect virgin olive oil quality. Phenolic and volatile compounds were analyzed in the oils obtained using progressive TEOPAC at three ripening stages of olives. Multivariate statistical analysis was applied to the raw data. The phenolic concentration of virgin olive oil progressively decreased with increasing IEOPAC. On the contrary, a positive relationship was found with the concentration of several volatile compounds responsible for virgin olive oil aroma. The effect of TEOPAC, however, was strictly related to fruit ripening.     

Color Measurements in Blue-Tinted Cups for Virgin-Olive-Oil Tasting

Color measurements have been performed using eighteen virgin-olive-oil tasting cups with ten different commercial virgin olive oils, positioned in a color cabinet with a D65 source. Three geometries (spectroradiometer tilted 0°, 30°, and 60°) were employed, simulating different positions of the taster’s eye. Our main goal was to test whether traditional blue-tinted cups effectively conceal the color of virgin olive oils, as desired in sensorial analyses. None of the cups employed had all their geometrical dimensions within the standardized values, despite being cups used in official sensorial analyses. Measuring a magnitude similar to the spectral transmittance, we found substantial differences among the glasses of the eighteen tasting cups. Comparing color variability for one virgin olive oil in different tasting cups, and one tasting cup with different virgin olive oils, we discovered that: (1) variability was higher in the case of one virgin olive oil in different cups; (2) in both cases the variability increased with the tilt of the spectroradiometer; (3) even when the variability was lowest (i.e., 0° measurements for two oils in the same cup), the average color difference was above typical visual thresholds in simultaneous comparison experiments. In the most usual case of a successive comparison between two oils in the same tasting cup, it is expected that in most cases tasters will perceive color differences between the oils when their eyes are tilted 60° with respect to the horizontal, but not when they observe the cup in the horizontal direction. In summary, blue-tinted olive-oil-tasting cups reduce, but do not completely conceal, oil color. The use of opaque tasting cups with black walls is suggested.     

Phenolic Characterization and Geographical Classification of Commercial Extra Virgin Olive Oils Produced in Turkey

The aim of this research was to characterize the extra virgin olive oil samples from different locations in the Aegean coastal area of Turkey in terms of their phenolic compositions for two consecutive years to show the classification of oil samples with respect to harvest year and geography. Forty seven commercial olive oil samples were analyzed with HPLC–DAD, and 17 phenolic compounds were quantified. Hydroxytyrosol, tyrosol, vanillic acid, p-coumaric acid, ferulic acid, cinnamic acid, luteolin and apigenin were the characteristic phenols observed in all oil samples for two harvest years. Syringic acid, vanillin and m-coumaric acid were the phenolic compounds appeared in the olive oil depending on the harvest year. Partial least square-discriminant analysis (PLS-DA) of data revealed that oils from the north Aegean and south Aegean areas had different phenolic profiles. The phenolic compounds, which played significant roles in the discrimination of the olive oils, were tyrosol, oleuropein aglycon, cinnamic acid, apigenin and hydroxytyrosol to tyrosol ratio. The Aegean coastal region is the largest olive oil producer and exporter of Turkey. This study shows that the olive oils from different parts of the region have their own defining characteristics that can be used in the authentication studies and geographical labeling of Turkish olive oils.     

Evolution of phenolic compounds in virgin olive oil during storage

Phenolic compounds are of fundamental importance to the shelf life of virgin olive oils because of their antioxidative properties. In this paper, the evolution of simple and complex olive oil phenols during 18 mon of storage is studied by high-performance liquid chromatography (HPLC) analysis. The olive oils under examination were from various olive cultivars, harvested in two sectors in the same region at different stages of ripeness. The findings indicate that it is not the variety but rather the ripeness of the olives and the soil and climate that influence the phenol composition of virgin olive oil. In addition, a positive correlation was found between the age of the oils and the tyrosol to total phenols ratio. Lastly, gas chromatography-mass spectrometry analysis confirmed that the unidentified peaks detected by HPLC were of a phenolic nature.     

Virgin Olive Oils from Super-High-Density Orchards in California: Impact of Cultivar,Harvest Time,and Crop Season on Quality and Chemical Composition

The impact of cultivar, harvest time, and crop season on olive fruit characteristics and olive oil quality and minor components composition is assessed for super-high-density “Arbequina”, “Arbosana”, and “Koroneiki” in California, United States, during 2016, 2017, and 2018. Fruit oil content reaches a plateau in November for “Arbequina” and “Arbosana,” while the accumulation rate keeps constant until early December for “Koroneiki.” Free fatty acids, diacylglycerols, pyropheophytins, and ΔK are not affected by any of the considered factors. Peroxide value, K_232, and K₂₇₀ decreases with harvest time. Chlorophylls content decreases with harvest time, more rapidly in “Arbequina” and “Arbosana” than in “Koroneiki”. Cultivar is the main factor affecting the fatty acid profile. “Koroneiki” has the highest oleic acid content, followed by “Arbosana” and “Arbequina.” Phenolic and volatile compounds are profoundly affected by cultivars and crop seasons, suggesting the relevance of these factors on the sensory and nutritional properties of virgin olive oil from super-high-density cultivars. Stepwise linear discriminant analysis allows selecting suitable markers among fatty acids, phenolic, and volatile compounds for cultivar, crop season, and harvest time discrimination. Practical Application: This paper constitutes the first report of a multiyear study considering quality and composition in bioactive compounds of super-high-density “Arbequina,” “Arbosana,” and “Koroneiki,” planted in California, USA. This information helps processors understand the differences in oil made from the most common super-high-density cultivars along harvest times and for growers to make planting and harvesting decisions.     

Effect of crop season on the composition of virgin olive oil with protected designation of origin “Les garrigues”

In recent years a growing demand for agricultural produce with an identifiable geographical origin has developed. The aim of this work was to study differences in quality and composition of virgin olive oils produced over four consecutive crop seasons in the region of the protected designation of origin “Les Garrigues” (Catalonia, Spain), taking the harvesting period and the climatic conditions of the year into consideration. The results obtained in this study indicate that virgin olive oil composition is greatly influenced by climatic conditions, mainly the cumulative rainfall in the case of FA composition and phenolic compounds, and the minimum temperatures during harvest period in the case of chlorophyll, carotenoid pigments, and α-tocopherol content. The harvest period influenced most of the parameters analyzed, apart from the PV and FFA content. Prediction models for carotenoid pigment content, oxidative stability, and bitter index were found.     

Quality Characterization of the Olive Oil from Var. Tosca 07® Grown in a Commercial High Density Orchard

A high density olive orchard represents a new planting system that requires cultivars with low vegetative vigor, such as Arbequina and Arbosana varieties. Different cultivars provide different performances in such orchards. This research was performed in order to determine the behavior of the new olive variety Tosca 07^® in a commercial, high density orchard. The quality of Tosca 07^® olive oils in three different maturity degrees during two crops seasons by physico-chemical and nutritional characterization were compared with Arbequina olive oils obtained from trees grown under the same conditions. Tosca 07^® is a very interesting olive variety for high density orchards. Because of its early ripening, it would be suitable for early harvesting, and this could be interesting for avoiding cold temperatures, frost, etc. Tosca 07^® olive oils have also demonstrated a very suitable chemical composition in comparison with Arbequina olive oils, especially for their high content of antioxidant compounds (α-tocopherol and pigments) present within the oils.     

Evaluation of the polyphenolic content of extra virgin olive oils using an array of voltammetric sensors

A novel system to evaluate the phenolic content of extra virgin olive oils is reported. The method uses an array of voltammetric electrodes. Such electrodes are chemically modified with electroactive materials (five phthalocyanines and six conducting polymers). The voltammetric responses towards the phenolic fractions extracted from extra virgin olive oils consist in complex voltammograms. Curves show redox processes related to the electrochemical activity of the phenolic fraction under study, and redox peaks associated to the electroactive material. In addition the antioxidant activity of polyphenols influences drastically the electrochemical behaviour of the electrodic material. The pattern of responses provided by the array represents the fingerprint of each sample and can be used to discriminate and evaluate the degree of phenolic content of extra virgin olive oils. Principal component analysis (PCA) conducted using kernel functions has demonstrated the capability of the array of electrodes to discriminate olive oils according to their phenolic content and bitterness index. Using partial least square discriminant analysis (PLS-DA) good correlations between the results obtained using the array of sensors and the polyphenol content, the bitterness index (analysed by chemical methods) and the bitterness degree determined by the panel of experts has been obtained.