Characterisation of virgin olive oils from European olive cultivars introduced in Tunisia

The behaviour of three European olive varieties, Ascolana Tenera, Koroneiki and Picholine, cultivated in the north of Tunisia, was compared to an autochthonous variety, Chétoui. Most of the quality indices and the fatty acid composition showed significant variations between the olive oils. Among the introduced varieties, the Picholine cultivar had the highest value of oleic acid (61%) whereas the Ascolana Tenera cultivar was noteworthy for its lowest content of phenolic compounds (175 mg/kg) and presented the highest level of palmitic acid. The Chétoui variety presented a high content of oleic and linoleic acids. But all samples, both the autochthonous Chétoui and the introduced cultivars, have similar levels of antioxidant compounds, with the exception of phenols. The aroma composition showed significant differences between the oils from the foreign cultivars. The major volatile component was the C‐6 aldehyde fraction whose content varied greatly between the different varieties studied: The E‐2‐hexenal content ranged from 1.6 mg/kg of oil in the Ascolana Tenera variety to >5 mg/kg for the Picholine and Koroneiki cultivars, whereas the Chétoui variety had the lowest levels of volatile compounds, with the exception of the hexanal level which was tenfold higher than in the foreign cultivars. Therefore, our results showed that two of the introduced varieties, Koroneiki and Picholine, showed good adaptation to the Tunisian cultivation conditions. So far, we claim the possibility to develop the successful cultivation of these latter imported varieties in the country.     

Phenolic composition of virgin olive oils from cross breeding segregating populations

The evaluation and characterization of segregating populations is a critical step in olive breeding programs. In this work, phenolic profiles of virgin olive oils (VOOs) from segregating populations obtained by cross breeding in Cordoba (Spain) have been evaluated. Genotypes obtained from open pollination of the cultivar Manzanilla de Sevilla, and from crosses between the cultivars Arbequina × Arbosana, Picual × Koroneiki and Sikitita × Arbosana were tested. The phenolic composition was determined after liquid–liquid extraction with 60:40 v/v methanol–water and subsequent chromatographic analysis with ultraviolet (UV) detection of both absorption and fluorescence in a sequential configuration. Results for all studied compounds showed high degree of variability between genotypes, with a higher range of variation than the observed for the genitors. Most of the observed variability was attributable to differences in genotypes within crosses rather than among crosses. Some issues related to breeding strategies are discussed. Practical applications: Phenolic compounds are considered to be of paramount importance for the assessment of virgin olive oil quality due to their contribution to the nutraceutical and sensory profile of this natural food. This study focuses on the evaluation of the content of phenolic compounds in olive oils originated from cross breeding in an olive breeding program (Cordoba, Spain). This step is crucial to determine the range of variation of phenolic compounds and the selection of interesting genotypes with higher composition in total phenols or in an individual phenol targeted at a breeding program.     

Olive Oil from “Sikitita” under Super-High-Density Planting System in California: Impact of Harvest Time and Crop Season

“Sikitita” is a relatively new olive cultivar obtained from crossbreeding between “Picual” and “Arbequina” that can be trained into the super-high-density orchard system. The impact of harvest time and crop season (2017 and 2018) on fruit parameters, oil quality, and minor compounds was assessed for super-high-density “Sikitita” in California, USA. Maximum olive fruit oil content (~49% on a dry basis) was reached between the first and second weeks of November. Quality parameters were within limits for extra virgin classification for all harvest times during both crop seasons. While total phenols were affected by harvest time, crop year, and their interaction, total volatile content was mainly influenced by harvest time. Both phenolic and volatile compounds reached a maximum concentration by the first week of October, suggesting that harvesting at the beginning of October would lead to a richer oil in terms of minor components. However, oil yield can be maximized if the harvest takes place in November. Our results demonstrated fruit parameters, oil quality, and minor compounds of super-high-density “Sikitita” followed a similar pattern and reached comparable values in both years, despite an earlier maturation in 2018. “Sikitita” has potential as a viable cultivar for growers and processors who are looking to expand on the traditional super-high-density cultivars.     

Phenolic acid content and sensory properties of two Spanish monovarietal virgin olive oils

In recent years, phenolic acids have received considerable attention as they are essential to olive oil quality and nutritional properties. This study aims to validate a rapid and sensitive method based on ultra‐performance liquid chromatography/time‐of‐flight mass spectrometry (UPLC–TOF‐MS) for analyzing the phenolic acid content of olive oil and assessing its impact on virgin olive oil (VOO) sensory attributes. Once this method was validated, we used it to evaluate the phenolic acid composition of several Spanish monovarietal virgin olive oils in relation to nine different olive ripening stages. The results obtained confirm that the methodology developed in this study is valid for extracting and analyzing phenolic acids from VOO. The phenolic acid content of the virgin olive oils sampled was proven to be influenced by the type of cultivar and olive harvest date. Therefore, phenolic acids might be used as potential markers for olive oil cultivar or ripening stage. Finally, the data obtained indicate that the sensory properties of VOO may be differently affected by its phenolic acid content depending on the type of cultivar. Practical applications: The method validated in the present study – based on UPLC‐TOF‐MS – allows experts to assess the phenolic acid content of different VOO cultivars (varieties). This application will probably be very useful to the olive oil industry. The reason is that our study revealed that phenolic acids have an impact on the sensory quality of VOO, which is essential to consumer preferences and choice. In addition, there are phenolic acids that are only found in a particular variety of olive oil obtained from fruits at a specific ripening stage. Consequently, phenolic acids could be used as potential markers for olive oil variety and harvest time.     

Using lipid profiles and genotypes for the characterization of Corsican olive oils

In 2004, the Corsican producers of olive oils obtained a French protected designation of origin (PDO) “huile d'olive de Corse”, but up to now specifications of Corsican oil production do not clearly indicate the oil attributes related to the territory of production. That is why the fatty acid and triacylglycerol (TAG) compositions of olive oils from the nine main cultivars used to produce oils under PDO were determined and related to the olive variety. The results showed (i) that the nine cultivars covered only four olive varieties, as revealed by random‐amplified polymorphic DNA markers, (ii) that the lipid composition of oils is strongly dependent on the variety, and (iii) that the lipid composition of the four varieties is completely discriminated on the basis of the proportions of four TAG (OOO, OOL, PoOO, OOL) and one fatty acid (18:0). These results clearly establish the relationships between some characteristics of oils and the area of production (Corsica) for at least three varieties that are originated from Corsica. For the fourth variety, other investigations on minor compounds and on sensory attributes of oils must be undertaken to link some oil traits to the territory of production.     

Determination of Aroma Profiles of Olive Oils from Turkish Olive Cultivars

This study analyzed volatile aromatic compounds present in the oils of Turkish olive cultivars. The cultivars Gemlik, Ayval?k, Memecik, Domat, Uslu, Halhal?, Kilis ya?l?k, Nizip ya?l?k, Ha?ebi and Karamani were harvested from important Turkish olive‐growing locations, such as Bal?kesir, Bursa, Manisa, Ayd?n, Mu?la, ?zmir, Kilis, Mersin, Hatay and Gaziantep during the 2007–2008 and 2008–2009 growing seasons. Olive samples were collected in two harvest years, at almost the same maturity stage, and processed under the same conditions. Headspace solid‐phase microextraction (HS‐SPME) was used to analyze volatile aroma compounds in the olive oil samples. Forty‐seven compounds were characterized and quantified using gas chromatography‐mass spectrometry/flame ionization detector (GC–MS/FID). The most abundant identified compounds were trans‐2‐hexenal, hexanal and 3‐methyl‐1‐butanol. The trans‐2‐hexenal, hexanal and 3‐methyl‐1‐butanol contents of oil samples varied between 0.86–67.15, 3.93–61.82 and 0.48–84.74 %, respectively.     

Effects of Cultivars and Location on Quality, Phenolic Content and Antioxidant Activity of Extra-Virgin Olive Oils

Quality characteristics of extra-virgin olive oils depend on several factors. In order to study the effects of genotype and growing location on olive oil quality, olives from cv. Coratina, Nocellara, Ogliarola, and Peranzana, picked in four locations of the Apulia region (Italy), were crushed by a three-phase system to produce mono-cultivar extra virgin olive oils that were analyzed for acidity, peroxide value, spectrophotometric indices, total phenolic content, phenolic profile and antioxidant activity. The experimental data concerning peroxide value, spectrophotometric indices, phenolic content and profile and antioxidant activity showed great variability among the cultivars grown in the same location and also among the oils produced with olives of the same cultivar but grown in different locations. For each cultivar, no significant differences were found among locations in terms of acidity and ΔK whereas peroxide value, K₂₃₂, and K₂₇₀ differ significantly among locations for both Ogliarola and Peranzana cv. Concerning the phenolic content of Ogliarola cv., no differences were highlighted between the locations whereas the phenolic contents of Peranzana significantly changed as a function of the place of growing. On the basis of these results, the statistical multivariate analysis did not allow the classification into homogeneous groups neither of the oils belonging to the same cultivar nor of those obtained from olives picked in the same location.     

Comparison of fatty acid profiles and mid‐infrared spectral data for classification of olive oils

The composition of olive oils may vary depending on environmental and technological factors. Fatty acid profiles and Fourier‐transform infrared (FT‐IR) spectroscopy data in combination with chemometric methods were used to classify extra‐virgin olive oils according to geographical origin and harvest year. Oils were obtained from 30 different areas of northern and southern parts of the Aegean Region of Turkey for two consecutive harvest years. Fatty acid composition data analyzed with principal component analysis was more successful in distinguishing northern olive oil samples from southern samples compared to spectral data. Both methods have the ability to differentiate olive oil samples with respect to harvest year. Partial least squares (PLS) analysis was also applied to detect a correlation between fatty acid profile and spectral data. Correlation coefficients (R²) of a calibration set for stearic, oleic, linoleic, arachidic and linolenic acids were determined as 0.83, 0.97, 0.97, 0.83 and 0.69, respectively. Fatty acid profiles were very effective in classification of oils with respect to geographic origin and harvest year. On the other hand, FT‐IR spectra in combination with PLS could be a useful and rapid tool for the determination of some of the fatty acids of olive oils.     

The volatile composition of samples from the blend of monovarietal olive oils and from the processing of mixtures of olive fruits

The volatile fraction deriving from the lipoxygenase pathway of samples obtained by processing olive fruits of 2 cultivars in known proportions was compared with that of samples deriving from the blending of oils extracted from the same cultivars and in the same proportions. The varieties considered for the mixtures were Coratina and Koroneiki, Coratina and Frantoio, and Dritta and Bosana, respectively. The results confirmed that the accumulation of each volatile compound from the lipoxygenase pathway in the monovarietal oils was different and closely dependent on the genetic store of each variety. The concentrations of the mentioned compounds appeared to change in a way proportional to the percent of each monovarietal oil in the samples obtained by blending 2 monovarietal oils. Instead, the oils obtained by processing mixtures of fruits from the 2 corresponding cultivars showed a striking accumulation of volatile compounds, especially of C₆‐compounds, which reached higher concentration at different percentages depending on the cultivars processed.     

Chemometric analysis of combined NIR and MIR spectra to characterize French olives

Chemometric treatment of near‐infrared (NIR) and mid‐infrared (MIR) combined spectra was used firstly to predict oil and water contents in fresh olive fruit samples (n = 223) and secondly to classify these samples into five principal French cultivar origins (Aglandau, Cailletier, Olivière, Salonenque, and Tanche). The study was carried out during four crop years (2005/2006 to 2008/2009) to take into account the seasonal variations. The comparison of the results obtained in the combined range (REP = 2.6% for the water content and 3.5% for the oil content) provides an obvious advantage compared to the NIR and MIR techniques used separately. Fresh olive fruit cultivars were satisfactorily classified with the partial least squares‐discriminant analysis (PLS‐DA) method in the combined range. After use of the K‐means clustering on the PLS‐DA scores, all the samples were well classified into their five groups of origin. The use of infrared combined spectra allows a considerable improvement in estimating olive fruit quality (oil and water contents, varietal origins).     

Photometric assay for polyphenol oxidase activity in olives, olive pastes, and virgin olive oils

A photometric method is proposed that allows the determination of phenolase activity in olive fruits, olive pastes, and virgin olive oil. The method can also be used to quantify partially purified phenolase from olives, and is based on the coupling between 4-methyl-o-benzoquinone, the reaction product of phenolase toward its substrate 4-methylcatechol, and the aromatic amine 4-amino-N,N-diethylaniline. The deep-blue adduct arising from this reaction has been characterized by means of nuclear magnetic resonance and mass spectrometric techniques and identified as 4-(4′-diethylaminophenylimino)-2-hydroxy-5-methyl-cyclohexa-2,5-dienone. This compound shows an absorption band, centered (in dichloromethane) at 617 nm, with an ε of 11,080 M⁻¹cm⁻¹. The main advantage of the proposed method resides in the high absorption coefficient of the adduct and its ultraviolet/visible absorption pattern, with a λ_max in a spectral region void of significant interferences by the pigments that ultimately will probably be present in the extracts to be tested by this proposed method. The method has proven to be sensitive, specific, and reliable. This paper is dedicated to the memory of Professor Francesco Corongiu, Dean of the Faculty of Sciences, University of Cagliari, prematurely deceased one year ago.