Comparative study on volatile compounds from Tunisian and Sicilian monovarietal virgin olive oils

The effects of ripening degree of olives on volatile profile of monovarietal virgin olive oils (VOO) from Tunisian and Sicilian cultivars were investigated. Fruits obtained from Tunisia (Chétoui and Chemlali) and Italy (Nocellara del Belice, Biancolilla and Cerasuola) were picked at three different stages of ripeness and then immediately processed. Moreover, the changes in volatile composition were evaluated in Chétoui variety as a function of the irrigation regime versus the rain-fed control. Using headspace–solid-phase microextraction (HS–SPME) technique coupled to GC–MS and GC–FID, the volatile compounds of the monovarietal virgin olive oils were identified and quantitatively analyzed. The proportions of different classes of volatiles of oils showed significant differences throughout the maturity process. The results suggest that adding to the genetic factor; agronomic conditions affect the volatile formation and therefore the organoleptic properties of VOO.     

Effect of the growing area conditions on differentiation between Chemlali and Chétoui olive oils

This paper reports a discrimination study based on the antioxidant compounds, oxidative stability, aroma and sensory profiles of virgin olive oils from the main Tunisian cultivars, Chemlali and Chétoui, grown in two different locations, north and south Tunisia, with important differences in altitude, latitude and climatic conditions. There were significant differences between the oils from both cultivars when grown in the different environments. At higher altitude, the oils showed a greater amount of oleic acid, phenols and a higher stability, whilst in the open the oils had higher saturated and linoleic acid content. Aroma profiles were also influenced by the pedoclimatic conditions; hence, oils from the South had the highest level of (E)-2-hexenal and 1-hexanol, whereas varieties from the North were higher in (E)-3-hexenyl acetate and hexyl acetate. In general, and independently of the growing area conditions, oils from Chétoui olives had higher levels of antioxidants, greater oxidative stability, higher antiradical activities and more marked intensity of bitterness. These results can be used to discriminate and to characterise the Chemlali and Chétoui olive oils from each region.     

Sterolic composition of Chétoui virgin olive oil: Influence of geographical origin

The sterol profile of Tunisian virgin olive oils produced from Chétoui cultivar, the second main variety cultivated in the north of the country, grown under different environmental conditions, was established by gas chromatography using a flame ionisation detector. More than ten compounds were identified and characterised. As expected for virgin olive oil, the main sterols found in all Chétoui olive oils were β-sitosterol, Δ5-avenasterol, campesterol and stigmasterol. Cholesterol, 24-methylenecholesterol, clerosterol, campestanol, sitostanol, Δ7-stigmastenol, Δ5,24-stigmastadienol, and Δ7-avenasterol were also found in all samples, but in lower amounts. Most of these compounds are significantly affected by the geographical origin. The majority of the Chétoui virgin olive oils analysed respected EC Regulation No. 2568, and in all cases total sterol amounts were higher than the minimum limit set by legislation, ranging from 1017 to 1522 mg/kg.     

Chemical composition and oxidative stability of Tunisian monovarietal virgin olive oils with regard to fruit ripening

The chemical composition of virgin olive oil may be influenced by genotype and different agronomic (i.e. fruit ripeness degree, water supply) and technological factors. This article reports the evaluation of the influence of the olive ripening stage on the quality indices, the major and the minor components and the oxidative stability of the two main monovarietal Tunisian cultivars (cvv. Chétoui and Chemlali) virgin olive oils. Moreover, the olives cv. Chétoui were tested in a rain-fed control and an irrigation regime. The oils sampled at five different ripeness stages were submitted to liquid chromatographic determination (HPLC-DAD/MSD) of their quali-quantitative phenolic and tocopherolic profiles. Moreover, the triacylglycerol and fatty acid compositions, and minor components such as squalene, pigments and their relation with the oil oxidative stability were evaluated. The tested oils showed very good correlation between the oxidative stability and the concentrations of total phenols, practically secoiridoids and α-tocopherol.     

Microwave heating effects on the chemical composition and the antioxidant capacity of tataouine virgin olive oils from Tunisia

Four Tunisian virgin olive oils (VOOs), derived from varieties (Chemlali Tataouine, Zarrazi Douirat, Fakhari Douirat, and Dhokar Douirat) grown in the harsh pedoclimatic conditions of the region of Tataouine, were evaluated for their responses to microwave heating. Aside from fatty acid composition, all other evaluated parameters were affected by microwave heating, and their variations depend on the genetic factor. Chemlali Tataouine VOO exhibited the slowest biophenol degradation rate and the least diminution in oxidative stability and consequently, its total fraction and both lipidic and methanolic fractions remained unchanged with an exceptional antioxidant potential. In the remaining studied VOOs, the biophenol contents, the oxidative stability, and the antioxidant potential underwent gradual decreases; nevertheless, their levels at the longer treatment time are close to some fresh VOOs. These results should be taken into consideration when Tataouine VOOs are recommended for microwave heating.     

PHENOLIC COMPOUNDS, TOCOPHEROLS AND OTHER MINOR COMPONENTS IN VIRGIN OLIVE OILS OF SOME TUNISIAN VARIETIES

The phenols, α‐tocopherols, fatty acids and oxidative stability of six monovarietal virgin olive oils (VOOs) were determined. Fourteen phenolic compounds were detected and quantified by solid phase extraction and reversed phase‐high performance liquid chromatography. Dialdehydic form of elenolic acid linked to tyrosol and hydroxytyrosol, oleuropein and ligstroside aglycones were the main components in all samples. Pinoresinol was the most abundant component in lignan fraction. The total phenol content of these monovarietal oils varied from 66.82 mg/kg in “Neb Jmel” oil to 662.74 mg/kg in “El Hor” oil. A wide range of α‐tocopherol contents was also noticed; it varied from 141.94 mg/kg in “Semni” variety to 364.23 mg/kg in “Jdallou” variety. With regard to pigments, chlorophylls and carotenoids were found at variable concentrations: with median values of 11.33 and 3.10 mg/kg, respectively. Among the studied varieties, “Oueslati” and El Hor were characterized by the lowest levels of palmitic and linoleic acids and the highest values of oleic acid.     

Improvement of Chemlali olive oil oxidative stability by blending with Chétoui and Rekhami cultivars

In order to improve the quality of Chemlali olive oil, characterised by a very low stability (2.09 h), blending with two different monovarietal oils in various proportions: Chétoui and Rekhami (known by their higher stability 7.79 and 13.99 h, respectively) was carried out. Results showed that blended oils had an improved oil composition compared to that of Chemlali. In fact, the highest percentage of Chétoui and Rekhami olive oils (90% of blending) can reduce the acidity up to 68.79% and 79.61%, respectively. At 50% blending, oleic acid increased from 53% to 59.54%, while palmitic acid decreased from 20.97% to 14.89% with Chétoui olive oil. At the lowest percentage (10–20%), chlorophylls in Chemlali olive oil underwent significant increase (from 0.18 to 0.47 and 0.65 mg kg⁻¹, respectively). The amount of carotenoids was higher when Chemlali was blended by 20–40% with Chétoui olive oil (from 2.23 to 4.13 and 4.33 mg kg⁻¹). Blending can be used in industrial applications to provide oils with improved composition related to stability, nutrition and functionality and endowed with the characteristics requested by consumers' preferences.     

The compositional quality and volatile compounds of samples from the blend of monovarietal olive oils cultivated in Tunisia

Chemlali olive oil has been blended with oils obtained from Oueslati and Chetoui varieties to improve the quality of the former one. Parameters such as acidity, acids compositions, phenol content, oxidative stability and volatile compounds were characterised for various blends Chemlali × Oueslati and Chemlali × Chetoui. The accumulation of volatiles originating from the lipoxygenase pathway in the monovarietal oils was different and closely dependent on the genetic store of each variety. The concentrations appeared to proportionally vary according to the relative proportion of each monovarietal oil in the mixtures. The blending process improved fatty acids by increasing the oleic acid content and decreasing the palmitic and linoleic acids levels of Chemlali oil. At 40% blending, oleic acid increased from 54% to 62%, while palmitic acid decreased from 18.59% to 16% when Oueslati and Chetoui olive oil was used.     

Metal oxide semiconductor sensors for monitoring of oxidative status evolution and sensory analysis of virgin olive oils with different phenolic content

An electronic nose based on an array of six metal oxide semiconductor sensors was used to monitor the oxidative status of virgin olive oils (VOO) during storage. VOO samples, with and without phenolic compounds, were stored at 60 °C for 7 weeks. Once a week, absorbance at 232 and 270 nm, oxidized stability index, electronic nose, and sensory analysis were evaluated. Linear discriminant analysis models were constructed in order to classify samples according to oxidative levels. Based on these models, VOO samples with and without phenolic compounds at different storage times, divided in eight categories, were correctly classified also achieving a good correlation for sensory analysis. The method is a fast and economical tool for on-line monitoring of VOO oxidation status.     

Monitoring the enrichment of virgin olive oil with natural antioxidants by using a new capillary electrophoresis method

The enrichment of virgin olive oil (VOO) with natural antioxidants contained in various herbs (rosemary, thyme and oregano) was studied. Three different enrichment procedures were used for the solid–liquid extraction of antioxidants present in the herbs to VOO. One involved simply bringing the herbs into contact with the VOO for 190 days; another keeping the herb–VOO mixture under stirring at room temperature (25 °C) for 11 days; and the third stirring at temperatures above room level (35–40 °C). The efficiency of each procedure was assessed by using a reproducible, efficient, reliable analytical capillary zone electrophoresis (CZE) method to separate and determine selected phenolic compounds (rosmarinic and caffeic acid) in the oil. Prior to electrophoretic separation, the studied antioxidants were isolated from the VOO matrix by using an optimised preconcentration procedure based on solid phase extraction (SPE). The CZE method was optimised and validated.     

Are virgin olive oils obtained below 27 °C better than those produced at higher temperatures?

Within the European Union, indications of ‘first cold pressing’ and ‘cold extraction’ can only be used for virgin olive oil (VOO) obtained below 27 °C from mechanical processing. Three different malaxing temperatures (25, 35 and 45 °C) are here evaluated for the quality of the VOO obtained in a continuous industrial plant. The oils were stored at room temperature in the dark for 12 months. Initially, oil obtained from a blend of Frantoio/Leccino cultivars (F/L) had higher acidity and peroxide levels and lower phenolic content than a Coratina cultivar (Cor). The oxidative stability of the oils positively correlated with malaxation temperature (F/L, R² = 0.818; Cor, R² = 0.987) as the phenolic content was directly proportional to the temperature (F/L, R² = 0.887; Cor, R² = 0.992). Only oils obtained at 45 °C were rejected because of ‘heated or burnt’ off-flavour. Decarboxymethylation of secoiridoids and further hydrolysis of phenolic esters occurred during storage. The oxidation products of derivatives of tyrosol and hydroxytyrosol were detected after nine months in both the F/L and Cor samples. Thus, VOO obtained at a processing temperature lower than 27 °C does not show higher chemical and sensory qualities than VOO obtained at 35 °C.     

Evolution of major and minor components and oxidation indices of virgin olive oil during 21 months storage at room temperature

This article reports the evolution of major and minor components and oxidation indices of seven samples of virgin olive oil (VOO) which differ in their initial contents of natural antioxidants, during 21 months of storage at room temperature and in darkness. As expected, statistically significant differences in the antioxidant contents were observed, with initial concentrations ranging from 0.33 to 0.55 mmol/kg for α-tocopherol and from 1.08 to 3.88 mmol/kg for total phenols. The quality indices PV, K₂₃₂ and K₂₇₀ increased linearly during the storage time studied (21 months), which should make it possible to predict the shelf-life of a VOO sample by extrapolation from the results obtained during a relatively short period of storage (i.e. several weeks). K₂₃₂ was the first parameter that exceeded the established upper limit for extra VOO and therefore seems to be the most relevant index for analysis and monitoring to determine the commercial category of the olive oil. The reduction of total phenolic compounds ranged from 43% to 73%, and it was remarkable that the decrease was higher in samples whose initial phenol contents were greater. Hydroxytyrosol increased linearly in most samples, whereas its complex forms decreased considerably, with the exception of two in which the hydroxytyrosol content decreased continuously or diminished after an initial increase. This fact was probably due to the low initial concentration of hydroxytyrosol secoiridoid forms: i.e. 0.32 mmol/kg for the sum of 3,4-DHPEA-EDA and 3,4-DHPEA-EA in one of these samples as compared to between 0.65 and 2.06 mmol/kg in the others. Finally, there was a slight and apparently linear fall in the α-tocopherol content of all samples, with a reduction ranging from 0.054 mmol/kg (12%) to 0.127 mmol/kg (23%), although there may be a short lag phase at the beginning of the assay.     

Volatile phenols in virgin olive oils: Influence of olive variety on their formation during fruits storage

The potential significance as odorants and markers of olive fruits degradation has been recently pointed out for volatile phenols in virgin olive oil (VOO) and related to the appearance of VOO sensory defects. The few studies carried out in order to elucidate the factors affecting their formation in olive fruits or VOOs, indicated that they could be considered as analytical indices of olive fruits degradation during storage, likely reflecting the microbiological activity. In the present study, the effect of the olive variety (‘Arbequina’, ‘Arbosana’ and ‘Leccino’) on the production of volatile phenols during twelve days of storage in closed plastic bags was evaluated. The different resistance of each variety to the microbiological attach was observed during olive fruit storage, and it was reflected by the evolution of guaiacol, 4-ethylphenol and 4-ethylguaiacol, and related to free acidity values. On the contrary, a scarce dependence on the microbial growth or varietal factors was observed for 4-vinyl derivatives, which appeared more directly related to the time of olives storage. The evolution of volatile phenols found certain correspondence in the sensory characteristics of the resulting VOOs, while the rest of VOO chemical quality indices did not show major variations during fruits storage.     

High performance size-exclusion chromatography analysis of polar compounds applied to refined, mild deodorized, extra virgin olive oils and their blends: An approach to their differentiation

An investigation was carried out to evaluate the use of High Performance Size-Exclusion Chromatography (HPSEC) of polar compounds of refined, mild deodorized, extra virgin olive oils as well as of their blends, in attempting to reveal significant differences in the amounts of the substance classes constituting polar compounds among these oils. Two sets of blends were prepared by mixing an extra virgin olive oil with both refined and mild deodorized olive oils in increasing amounts. The obtained data highlighted that the triacylglycerol oligopolymers were absent or present in traces in the extra virgin olive oil, while their mean amount was equal to 0.04 g/100 g and 0.72 g/100 g in mild deodorized and refined olive oils, respectively. Oxidized triacylglycerols and diacylglycerols were more abundant in mild deodorized oil and refined oil than in extra virgin olive oil. The Factorial Discriminant Analysis of the data showed that the HPSEC analysis could reveal the presence of refined/mild deodorized oils in extra virgin olive oils. In particular, the classification functions obtained allowed designation of mixtures containing at least 30 g/100 g of mild deodorized oil and all those containing refined olive oil as deodorized oil, therefore as oils subjected to at least a mild refining treatment.     

The role of olive β-glucosidase in shaping the phenolic profile of virgin olive oil

The main objective of this work was to investigate the biochemical factors directly affecting the phenolic profile of virgin olive oil (VOO) such as the content of phenolic glycosides and the β-glucosidase activity present in the olive fruit. The phenolic compositions of VOO from two olive cultivars, Arbequina and Picual, were studied throughout the ripening phase. Picual oils displayed significantly higher phenolic content than Arbequina oils at all ripening stages; however, the total phenolic content of Arbequina fruits was consistently higher than that of Picual fruits. The most abundant phenolic glucosides found in olive fruits were oleuropein, present in both cultivars, and demethyloleuropein, only detected in Arbequina fruits. Nevertheless, the content of phenolic glycosides can hardly be regarded as a limiting factor given that the total secoiridoid content in VOOs represents an average of 1–4% of the secoiridoid glycosides present in the fruits. Although the level of β-glucosidase activity does not seem to be a limiting factor in these two cultivars, experimental data on the selectivity of the enzyme towards olive phenolic glucosides and its product specificity suggest that olive β-glucosidase plays a critical role in shaping the phenolic profile of VOO. A hypothesis on the biochemical formation of the dialdehydic form of decarboxymethyloleuropein (3,4-DHPEA-EDA) from oleuropein is proposed.     

Effect of phospholipids on extraction of hydrophilic phenols from virgin olive oils

Three methods, most frequently used in hydrophilic phenols extraction from virgin olive oils (liquid–liquid, solid-phase with C18 and solid phase with diol-bound sorbents), were applied on virgin olive oils enriched with 2.0–10.0 mg/kg of phospholipids (granular de-oiled soy lecithin). Phospholipids addition significantly decreased the total phenols concentration determined colorimetrically. Liquid–liquid extraction showed the best repeatability and recovery, and the lowest decrease of total phenols extracted in the presence of phospholipids. Extraction rate declined with the increase of phospholipids concentration, but showed a kind of saturation behaviour. Addition of phospholipids (5 g/kg) to various commercial extra virgin olive oils resulted in a different degree of total phenols decrease (from 1% to 45%), probably because of different affinity of phospholipids toward different classes of phenolic compounds. During prolonged contact time between phenols and phospholipids (60-days storage), oxidation monitored by K270 and a decrease of total phenols concentration proceeded more rapidly in the presence of phospholipids.     

Influence of olive storage period on volatile compounds and oil quality of two Tunisian cultivars of Olea europea,Chemlali and Chetoui

Olives (Olea europaea cv. Chemlali and Chetoui) used for oil production were stored, in plastic containers, at 5 °C for four different periods (0–3 weeks) before oil extraction. After storage, the oils were extracted from the fruits, and the acidity, peroxide value, coefficients of specific extinction at 232 and 270 nm, stability, pigments, total phenols, fatty acids, and volatile compounds were determined. The results showed that storage of fruits produced losses in the olive oil quality. During storage, a marked decrease in total phenols content was observed. The cultivar richer in phenols (862.16 mg kg^?1 in Chétoui) had a lower loss (25%). On the contrary, in Chemlali olive oil, the starting value of 728.52 mg kg^?1 decreased to 469.25 mg kg^?1, with a loss of 35%. Chétoui and Chemlali olive oils presented the highest oxidative stability before storage (58.76 and 47.05 h, respectively), while the lowest values were recorded using olives stored for 3 weeks (54.46 and 43.43 h, respectively). The changes in the volatile bouquet were determined using headspace solid phase microextraction (HS‐SPME). Thirty compounds were characterised by GC–FID and GC–MS. Compounds belonging mainly to alcohols, esters, aldehydes, ketones and hydrocarbons chemical classes characterised the volatile profiles.     

The antioxidant capacity and oxidative stability of virgin olive oil enriched with phospholipids

Virgin olive oil (VOO) enriched with phospholipids (soy lecithin) up to the levels present in seed oils (from 2.5 to 10.0 g/kg) was studied as a potential functional food. Lecithin addition slightly increased the concentration of tocopherols and considerably increased K270 values. In the fatty acid composition, an increase of linoleic and a slight decrease of oleic acid were observed, as the decrease of monounsaturated/polyunsaturated fatty acid ratio. The radical-scavenging activity was evaluated by two methods: electron spin resonance spectroscopy using galvinoxyl free radical and VIS spectroscopy measurement of the disappearance of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical. Results indicate that lecithin addition retards the scavenging activity of VOO that is ascribed to the bipolar character of lecithin and its ability to entrap hydrophilic antioxidants. The effect of lecithin addition on the oxidative stability of VOO was evaluated by the Rancimat method, and a positive linear correlation (r = 0.9849) with induction time was found.     

Discrimination of five Tunisian cultivars by Mid InfraRed spectroscopy combined with chemometric analyses of olive Olea europaea leaves

The high biodiversity of olive tree and the economic needs require tools for the correct classification and identification of the different cultivars. Simple and rapid methods are in increasing demand. In the present work, FT-MIR spectroscopy associated to chemometric treatment is proposed as a direct and rapid tool to discriminate cultivars according to their olive leaves, a persistent tissue the whole year. A set of 75 samples of olive leaves representative of five Tunisian cultivars (Chemlali, Sayali, Meski, Zarrazi and Chétoui) cultivated in the same geographical area was analysed. Discrimination between the five Tunisian cultivars was performed by the chemometric approach, principal component analysis (PCA), based on the FT-MIR spectral data provided by olive leaves. Furthermore, a correct classification (100%) of the five Tunisian cultivars was obtained by the Partial Least Square Discriminate Analysis (PLS-DA) method.