Effect of the matrix volatile composition in the headspace solid-phase microextraction analysis of extra virgin olive oil

The effectiveness of headspace solid-phase microextraction (HS-SPME) for the quantitative analysis of extra virgin olive oil volatiles was investigated on 44 standard compounds, using an adsorbent polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber. The method’s sensitivity was satisfactory, as was its repeatability. However, when the extraction was carried out on mixtures containing all the standard analytes, phenomena of coating saturation and competition between components caused losses in linearity at lower levels of concentration, thus distorting the quantitative evaluation. Coating saturation or displacement between components was also found to be responsible for the bias in the quantitative determinations when extra virgin olive oil samples were analysed. These limitations were overcome by diluting the oil at concentrations not exceeding the total capacity of the fiber coating and until the quantity of displacing compounds was reduced to sufficiently low levels.     

Effects of olive paste fast preheating on the quality of extra virgin olive oil during storage

The olive paste obtained after crushing was fast preheated under different time/temperature conditions and then malaxed in an industrial oil mill (600 kg Frantoio/Leccino olive blend). Legal parameters (peroxides, free acidity and sensory panel), oil yield, total phenolic content, oxidative stability and phenolic profile were monitored during 12 months of storage of the virgin olive oil (VOO) kept in closed bottles in the dark. A fast preheating not longer than 72 s at 38 °C without malaxation lead to an extra VOO with a shelf-life of at least 12-months, similarly to the traditional EVOO obtained with malaxation. A fast preheating not longer than 72 s at 38 °C followed by 10 min malaxation lead to an EVOO with a ‘mild’ sensory profile and a shelf life of at least 12-months. Thus, the use of a specific designed fast preheater instead or before (a shortened) malaxation allows to obtain an EVOO with a low bitter/pungent attribute from olives which are rich of (sometimes unpleasant) phenolic compounds with the aim to meet the preference of targeted groups of consumers. Time and temperature of fast preheating are the critical parameters of the process.     

Heat-oxidation stability of palm oil blended with extra virgin olive oil

Rancimat induction time of palm oil (PO), several extra virgin olive oils (EV) and their binary blends have been determined at three different temperatures (120, 130 and 140°C). Analytical composition and oxidation stability of PO/EV blends were found to be a linear combination of the oil partners. Induction time of pure PO was always higher than those of EV oils and blends, in which induction time increased proportionally with the percentage of PO. However, induction time of 80% PO blend was similar to that of pure PO. Fatty acid composition appeared to be the most important factor affecting heat-oxidation stability and a saturated/unsaturated ratio near 1 was the optimally stable composition. Conversely, total phenols had a zero or negative role on the oxidative stability of the blends. Finally, in heat-oxidised oils significant losses of polyunsaturated fatty acids and formation of short-chain fatty acids were recorded.     

Lipolytic yeasts distribution in commercial extra virgin olive oil

The olive oil lipase-producing yeasts can lower the quality of the product through the hydrolysis of the triacylglycerols. In this research the olive oil total yeasts were divided into five chromogenic groups, for each group the amount of the lipase-producing yeasts was evaluated and the more active isolates were classed. The trials showed the prevalence of more than three chromogenic yeast groups in the commercial poly-varieties of extra virgin olive oil mixture, whereas in the mono-varieties one, no more than one chromogenic yeast group prevailed according to the olive variety. The ratio of the lipase-producing yeast varied from 33% in the smooth brown chromogenic group to 83% in the wrinkly bluish one. The physiological and genetic analyses of the more active lipase-producing yeast belonging to each chromogenic group allowed us to classify the wrinkly red 1892 strain and the wrinkly bluish 1890 strain as Candida parapsilosis, whereas the smooth white 1885 strain was classed as Candida wickerhamii. The ribosomal (26S) D1/D2 region sequencing results of the wrinkly white 1886 strain and the smooth brown 1887 strain are not identical to that of any known yeast species. They showed 8 substitution and 11 substitution plus 2 indels, respectively, different from Pichia mexicana and Pichia minuta. This is the first report where the human pathogen C. parapsilosis species was found in commercial extra virgin olive oil. The chromogenic group evaluation permitted the rapid preliminary identification of technological and human health important olive oil yeasts.     

Means-end chains analysis of extra virgin olive oil purchase and consumption behavior

Consumption and purchase behavior towards extra virgin olive oil are not well understood in the US. Soft laddering interviews were conducted with 63 Northern California consumers and means-end chains analysis on the interview data revealed common grounds of consumption and buying motivations for three different a priori defined consumer segments. Consumption motivational structures were more similar across the different consumer segments than purchasing ones. Consumers who purchased only local extra virgin olive oil had simpler perceptual orientations than consumers who purchased imported extra virgin olive oils or both imported and local oils. Several different consumer values could be associated with consequences that were linked to just one attribute. On the other hand, one particular value could also be associated with a few different attributes. These findings provide opportunities for the olive oil industry to design products that will better satisfy consumer values and needs.     

Distribution of dimorphic yeast species in commercial extra virgin olive oil

Recent microbiological research has demonstrated the presence of a rich microflora mainly composed of yeasts in the suspended fraction of freshly produced olive oil. Some of the yeasts are considered useful as they improve the organoleptic characteristics of the oil during preservation, whereas others are considered harmful as they can damage the quality of the oil through the hydrolysis of the triglycerides. However, some dimorphic species can also be found among the unwanted yeasts present in the oil, considered to be opportunistic pathogens to man as they have often been isolated from immunocompromised hospital patients. Present research demonstrates the presence of dimorphic yeast forms in 26% of the commercial extra virgin olive oil originating from different geographical areas, where the dimorphic yeasts are represented by 3–99.5% of the total yeasts. The classified isolates belonged to the opportunistic pathogen species Candida parapsilosis and Candida guilliermondii, while among the dimorphic yeasts considered not pathogenic to man, the Candida diddensiae species was highlighted for the first time in olive oil. The majority of the studied yeast strains resulted lipase positive, and can consequently negatively influence the oil quality through the hydrolysis of the triglycerides. Furthermore, all the strains showed a high level of affinity with some organic solvents and a differing production of biofilm in “vitro” corresponded to a greater or lesser hydrophobia of their cells. Laboratory trials indicated that the dimorphic yeasts studied are sensitive towards some components of the oil among which oleic acid, linoleic acid and triolein, whereas a less inhibiting effect was observed with tricaprilin or when the total polyphenols extracted from the oil were used. The observations carried out on a scanning electron microscope (SEM), demonstrated the production of long un-branched pseudohyphae in all the tested dimorphic yeasts when cultivated on nutrient-deficient substrates.     

Diacylglycerol isomers in extra virgin olive oil: Effect of different storage conditions

An experimental investigation was carried out with the aim to investigate on the isomerisation of 1,2-diacylglycerols to 1,3-diacylglycerols as a function of the storage conditions, as well as to identify indices useful to evaluate the freshness of the oils. Two oils derived from two different cultivars (Coratina and Ogliarola barese) were stored for two years as follows: in bottles at dark; in clear glass bottles at light; in green glass bottles at light; in bottles at dark, the latter subjected to repeated opening and samplings to simulate domestic use. The obtained results evinced that during the storage period a significant increase in the 1,3-isomers was observed due to an isomerisation from the 1,2 to the 1,3 isomeric form, consequently the 1,3/1,2 ratio increased in both oils. The covariance analysis of the data showed that the isomerisation of diacylglycerols, taking place during time, was affected by the type of oil, probably due to the different initial hydrolysis level, but was not affected by the storage conditions. Among the parameters considered, the total diacylglycerols/1,3-diacylglycerols ratio could be used as freshness index of extra virgin olive oil, since it is not affected by either oil or storage conditions.     

Differential scanning calorimeter application to the detectionof refined hazelnut oil in extra virgin olive oil

The potential application of differential scanning calorimetry (DSC) to verify adulteration of extra virgin olive oil with refined hazelnut oil was evaluated. Extra virgin olive oil and hazelnut oil were characterised by significantly different cooling and heating DSC thermal profiles. Addition of hazelnut oil significantly enhanced crystallisation enthalpy (at hazelnut oil ?20%) and shifted the transition towards lower temperatures (at hazelnut oil ?5%). Lineshape of heating thermograms of extra virgin olive oil was significantly altered by hazelnut oil addition: a characteristic exothermic event originated at −27 °C in extra virgin olive oil and progressively disappeared with increasing hazelnut oil content, while the major endothermic peak at −3.5 °C broadened (at hazelnut oil ?40%) and the minor endothermic peak at 8 °C shifted toward lower temperatures (at hazelnut oil ?5%). The preliminary results presented in this study suggest that DSC analysis may be a useful tool for detecting adulteration of extra virgin olive oil with refined hazelnut oil.     

A capacitive technique to assess water content in extra virgin olive oils

The present research investigated the correlations between capacitance and water content of extra virgin olive oils (EVOO). A commercial capacitor probe for radio applications and an LCR meter were used for electric tests in the frequency range from 500 Hz to 512 kHz. Seventeen samples of different EVOO with a moisture content ranging from 178 to 1321 mg/kg oil were selected for study. To assess the influence of moisture only, the oil with the maximum water content was filtered down to 288 mg/kg oil and five samples with intermediate water contents were prepared and submitted to electrical measurements. Subsequently, the capacitance of all 17 EVOO samples was measured at selected frequencies.     

西班牙和意大利进口特级初榨橄榄油品质比较

为了系统研究我国主要进口的特级初榨橄榄油性质,比较分析了我国主要进口的8种西班牙和意大利特级初榨橄榄油的脂肪酸组成、酸值、过氧化值及微量成分含量,并对其进行了挥发性成分分析及感官评价。结果表明：西班牙特级初榨橄榄油的C18∶1（77.22%）和C23∶0（0.94%）含量平均值高于意大利样品（分别为72.46%和0.64%）,西班牙特级初榨橄榄油的酸值、过氧化值低于意大利样品;西班牙特级初榨橄榄油中含有γ-生育酚和δ-生育三烯酚,而意大利样品中未检出这两种,且西班牙特级初榨橄榄油中α-生育酚含量平均值（189.58 mg/kg）高于意大利样品（161.26 mg/kg）,角鲨烯含量平均值（6 127.83 mg/kg）远高于意大利样品（4 083.50 mg/kg）,两者甾醇含量差异很小。虽然西班牙特级初榨橄榄油的醛类含量平均值低于意大利样品,但酯类含量更高。感官评价发现,西班牙特级初榨橄榄油的果味、苦味、辣味评分皆高于意大利样品。综上,西班牙特级初榨橄榄油的酸值、过氧化值较低,α-生育酚、角鲨烯含量高于意大利样品,且感官评分较高。     

Authentication of extra virgin olive oils by Fourier-transform infrared spectroscopy

Fourier-transform infrared spectroscopy (FTIR), followed by multivariate treatment of the spectral data, was used to classify vegetable oils according to their botanical origin, and also to establish the composition of binary mixtures of extra virgin olive oil (EVOO) with other low cost edible oils. Oil samples corresponding to five different botanical origins (EVOO, sunflower, corn, soybean and hazelnut) were used. The wavelength scale of the FTIR spectra of the oils was divided in 26 regions. The normalized absorbance peak areas within these regions were used as predictors. Classification of the oil samples according to their botanical origin was achieved by linear discriminant analysis (LDA). An excellent resolution among all categories was achieved using an LDA model constructed with eight predictors. In addition, multiple linear regression models were used to predict the composition of binary mixtures of EVOO with sunflower, corn, soybean and hazelnut oils. For all the binary mixtures, models capable of detecting a low cost oil content in EVOO as low as 5% were obtained.     

Tocopherol speciation as first screening for the assessment of extra virgin olive oil quality by reversed-phase high-performance liquid chromatography/fluorescence detector

A method based on reversed-phase high-performance liquid chromatography with fluorescence detector has been developed for the determination of tocopherols in vegetable oils. Oils were diluted in acetonitrile/tetrahydrofuran (THF) and injected directly onto HyPurity C₁₈ column. Methanol and THF (90:10) mixture was used as a mobile phase. Tocopherols were detected by fluorescence detector. The method had good limit of detection (LOD) (7 ng/g for α-tocopherol and 6 ng/g for β-, γ- and δ-tocopherols) and reproducibility (CV% < 2.8%).     

Influence of the exposure to light on extra virgin olive oil quality during storage

An experimental investigation was carried out to study the influence that exposure to light has on the quality of extra virgin oil during a 12-month storage period by comparing it with the quality of extra virgin oil stored in the dark. The results showed that the oils stored in the light had significantly lower tocopherol, carotenoid and chlorophyll contents than did the same oils kept in the dark. Moreover, the oils stored in the dark mainly contained primary oxidation products, while the oils kept in the light contained secondary oxidation products as confirmed by the K₂₇₀ values which exceeded the legal limits even after purification by means of alumina. Overall, the results obtained showed that the shelf life of the oils exposed to light is shorter than that of oils kept in the dark, and that after only 2 months of exposure to light the oils examined could no longer be considered as extra virgin.     

Comparative study of extra virgin olive oil flavor profile of Koroneiki variety (Olea europaea var. Microcarpa alba) cultivated in Greece and Tunisia during one period of harvesting

The effects of geographical region, irrigation and ripening degree of olives on the profile of volatile compounds isolated by monovarietal virgin olive oils from Crete and Tunisia of Koroneiki variety (Olea europaea var. Microcarpa alba) using the SPME GC/MS technique were investigated. Fruits obtained from Greece (island of Crete) and Tunisia (Sfax region) were picked at three and two different growth stages respectively and then immediately processed. The most important compounds identified were esters, alcohols, carbonyl compounds and hydrocarbons. The main volatile compounds present in the oil samples were C6 derivatives, such as [E]-2-hexenal, [E]-2-hex-1-enol, [Z]-3-hexen-1-ol and 1-hexanol. In addition to C6 compounds, the aroma of the studied samples contained reasonable amounts of various classes of C5 components. The tested oil samples showed different volatile profiles. Specifically, the concentration of total esters, carbonyl, C6 and C5 compounds increased significantly with the ripening degree in Cretan, but not in Tunisian olive oils. Principal component analysis of the results indicated that primary maturity and geographical region rather than irrigation affected significantly the volatile’s profile of olive oil.     

Chemical and thermal characterization of Tunisian extra virgin olive oil from Chetoui and Chemlali cultivars and different geographical origin

Application of differential scanning calorimetry (DSC) to discriminate among extra virgin olive oils on the basis of cultivar–environment interaction was preliminary evaluated on Tunisian samples from two varieties (Chetoui and Chemlali) and different geographical origin relating thermal properties obtained by cooling and heating thermograms to chemical composition. Higher content of triunsaturated triacylglycerols and oleic acid and lower amount of palmitic acid were detected in Chetoui samples in comparison with Chemlali oils. Cooling thermograms exhibited two well distinguishable exothermic peaks in all samples; the major event at lowest temperature was taller and sharper in Chetoui samples whereas the other peaking at highest temperature was more evident for Chemlali oils. Crystallization enthalpy did not account for the differences observed in chemical composition between the two cultivars. On the contrary, T _on and T _off of crystallization were found to significantly differ according to the compositional differences due to cultivars and geographical provenience interaction. Heating profiles exhibited a minor exothermic peak followed by multiple endothermic events and appeared also distinctive of oil samples from two cultivars. All thermal properties obtained by the analysis of heating thermograms significantly differed among oil samples from different geographical provenience. The application of DSC appeared useful to differentiate samples of different cultivars and/or geographical proveniences.     

Effect of oxygen reduction during malaxation on the quality of extra virgin olive oil (Cv. Carboncella) extracted through “two-phase” and “three-phase” centrifugal decanters

Quality and composition of virgin olive oil (VOO) are strictly dependent on complex processes that take place during the olive fruit crushing and malaxation of the olive paste. In this work, modulation of O₂ levels within malaxation chambers (R1: unmodified atmosphere; R2: oxygen: 12.73–4.64 kPa from the beginning to the end of malaxation; R3: 10.46–2.27 kPa; R4: 9.87–0.69 kPa) in two continuous “two-phase” and “three-phase” oil extraction plants was performed. Combined effects on the biosynthesis of nutritionally bioactive molecules and aroma volatiles and on the resulting sensory properties of the produced oils were investigated. Results showed that the type of oil extraction plant markedly affected the level of the phenolic compounds in the oil (and the related sensory attributes of bitter, pungency, astringency and bitter and pungency persistence). Reduction of O₂ concentration in the malaxing chamber, while having a minor impact on the presence of phenolic compounds, significantly affected the formation of all the examined volatiles. Particularly, lowered levels of oxygen hindered the formation of lipoxygenase derived volatiles weakening odours and flavours of artichoke, fresh fruity, and fresh cut grass.     

Optimisation of extra virgin olive oil quality

This study investigated the correlation between total polyphenol content and the stability (ie induction time by Rancimat) of oil samples according to different regions, cultivars, extraction technologies and ripening times of raw material. Results indicate a correlation of oil stability with total polyphenols, (r=0·88), a chemical variable easy to determine. We have set up an oil quality index as a measure of desirability including legal parameters, especially the Council Olive Oil International score (COI Score), stability (phenol content) and process yield into account. The study of the effects of olive ripening and storage prior to processing and olive paste mixing times and temperatures on the quality index using an experimental factorial design (2⁴) were investigated. The process variables selected in the experimental factorial design were studied and the main effects on desirability were identified. Based on this information, the extraction process was optimised for quality index in relation to fruit ripening and olive paste mixing time using a response contour to identify optimal experimental conditions. This innovative procedure shows that process conditions can be optimised as a function of D_tot, evaluated according to scientific determinations. © 1998 SCI.     

初榨橄榄油风味化合物研究进展

阐述了初榨橄榄油风味的主要来源途径即脂氧合酶途径,对影响初榨橄榄油风味特征的若干因素如品种和地理环境,油橄榄果实成熟度,加工工艺,储藏条件等因素进行了讨论和分析.介绍了初榨橄榄油中挥发性化合物的分析检测方法,并且展望了橄榄油风味化合物研究的应用和发展前景.