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.     

Effect of extraction conditions on sensory quality of virgin olive oil

The extraction conditions of virgin olive oil have a great influence on its sensory quality. During the centrifugation process, temperature and time of malaxing can be altered to potentially affect quality. Malaxing times (15, 30, 45, 60, and 90 min) and temperatures (25 and 35°C) were studied in an experimental oil mill. Volatile compounds, produced through the lipoxygenase pathway (hexanal, Z-3-hexenal, E-2-hexenal, hexyl acetate, Z-3-hexenyl acetate, hexan-1-ol, E-3-hexen-1-ol, Z-3-hexen-1-ol, and E-2-hexen-1-ol), were analyzed by dynamic headspace gas chromatography, gas chromatographymass spectrometry, and gas chromatography-olfactometry. Different amounts of volatiles responsible for positive attributes of green aroma and negative attributes of astringent mouthfeel of virgin olive oil were determined. The results, after applying mathematical procedures, showed that a temperature of 25°C and a malaxing time between 30 and 45 min produced volatile compounds that contribute to the best sensory quality. High temperature (T≥35°C) with minimum values of time (t<30 min) could also be useful as an alternative way to obtain pleasant green virgin olive oils.     

Purity,quality and stability of Argentinean virgin olive oils

In this paper we evaluate the stability, purity and regulated quality composition of fatty acids and sterols (both physico‐chemical and sensory) of commercial Argentinean virgin olive oils in order to evaluate their acceptance on the world market. For this purpose, samples of the best known and most widely distributed oils in supermarkets located in Buenos Aires (Argentina) were acquired. After thoroughly analysing these samples, only 20% were considered to have an acceptable quality. However, some were excluded because of their high campesterol content, which could be an intrinsic characteristic of these oils. The most useful analytical parameter used to confirm authenticity was ECN‐42 R – ECN‐42 T, followed by wax content and 3.5 stigmastadienes. Only 24% of the extra‐virgin olive oil samples were classified as ‘extra‐virgin’ from the regulated quality viewpoint. The low oleic and high linolenic acid contents of the Argentinean virgin olive oils stand out when compared with European virgin olive oils. The oxidative stability values may be considered very low, indeed even lower than those obtained in Spanish virgin olive oils.     

Relationship between volatile compounds and sensory attributes of olive oils by the sensory wheel

Sixty-five volatile compounds and 103 sensory attributes were evaluated in 32 virgin olive oil samples from three different Mediterranean countries. Volatile compounds were analyzed with a dynamic headspace gas-chromatographic technique by using a thermal desorption cold-trap injector. The sensory analysis was conducted by six panels composed of assessors from the United Kingdom, Spain, the Netherlands, Greece and Italy. Principal-components analysis of sensory attributes was used to construct a statistical sensory wheel that represents the whole virgin olive oil flavor matrix. This wheel is composed of seven sectors that show the basic perceptions produced by the oil: green, bitter-pungent, undesirable, ripe olives, ripe fruit, fruity and sweet. The boundaries of each sector were calculated from the circular standard deviation of its sensory attributes. The relationship between sensory and instrumental analysis was determined by projecting volatiles onto the sensory wheel. Correlations of each volatile with the first two components of the principal-components analysis were taken as its coordinates (x, y) in the sensory wheel. Volatiles took up the most appropriate place within the sector that corresponded with their perception, and often close to the sensory attributes that explained their sensory properties. A gas-chromatographic/sniffing method was applied to virgin olive oil samples to assess the aroma notes that corresponded to olive oil volatile compounds and to verify the relationships found by the sensory wheel procedure. Most (89%) of the volatiles were well classified. Use of the statistical sensory wheel as an appropriate method to relate volatile and sensory data was clearly demonstrated.     

Influence of olive crushing methods on the yields and oil characteristics

In the last years, metallic crushers substituted granite stone mill with some variations in the organoleptic oil characteristics. To control the influence of the crushing method on the yield and oil quality, the olive pastes were obtained using three different ways: (i) new metallic crusher at mobile knives; (ii) granite stone mill; (iii) double olive crushing by the metallic crusher and the granite stone mill. With the aim to ascertain the useful use of a new metallic crusher (at mobile knives), experimental tests were carried out in an industrial oil mill. This oil mill is equipped by a centrifugal decanter generating two oil flows: first and second extraction (recovery) oils. The results showed that the yields obtained by different methods were satisfactory. No statistically significant differences have been observed in terms of oil yield and quality when different crushing devices were used. All first extracted oils are extra virgin with similar organoleptic characteristics, especially for the fruity intensity and for the bitter and pungent taste, as confirmed by the composition of volatile substances and the content of phenolic oil compounds. The recovery oils (second extraction oils) showed, in contrast to first extraction oils, a more intense green colour and a higher content of total phenols. Practical applications: Processing of sound olives with the right ripening grade and good quality allows to easily obtain an extra virgin olive oil, with commercial qualitative parameters according to the European Union requirements. However, different olive crushing systems affect the concentrations of some compounds responsible of aroma and taste (phenolic compounds). The use of the more violent metallic crushers facilitates obtaining oils with total phenol content higher than when using a stone mill. Here we used a particular metallic crusher (at knives) that, however, is suitable to replace the granite stone mill when a less pungent and bitter oil is required.     

Influence of a new crushing technique on the composition of the volatile compounds and related sensory quality of virgin olive oil

The influence of a new crusher i.e. blade crusher on the quality of virgin olive oil from two different italian cultivars (Coratina and Oliarola) was determined. In addition the quality of this oil was compared with that of olive oil extracted with the traditional hammer crusher. Tests were performed in an industrial oil mill using the two different crushing instruments. Results obtained showed that quality parameters i.e. free fatty acids, peroxide value, UV absorption and total phenols content as well as the phenolic composition of oils were not significantly affected by the two different crushers used. On the contrary, the use of the blade crusher influenced the composition of the volatile compounds. In particular, the oils obtained using the blade crusher showed significant increases of some aldehydes such as 1‐hexanal and trans‐2‐hexenal, esters such as hexyl acetate and 3‐hexenyl acetate and a reduction of alcohols such as 1‐hexanol. Moreover, the identified pigments of the oils produced using the blade crusher were found at concentrations slightly lower than those in oils obtained after using the hammer crusher. Finally, results of the sensory analysis showed an improved organoleptic quality for the oils obtained using the blade crusher due to an increase of the cut‐grass and floral sensory notes.     

Characterization of virgin olive oil from Southern Tunisia

Fruits from three Tunisian cultivars of Olea europea L. grown in the southeast of Tunisia were harvested at the maturity stage of ripeness and immediately processed with a laboratory mill. There are as yet no data on the chemical composition of virgin olive oils from the southeast of Tunisia, an area characterized by an arid condition of growth for olive trees. Our results showed significant differences in the analytical parameters examined for the three cultivars such as fatty acid composition, total phenols and o‐diphenols, and the content of chlorophylls and carotenoids, confirming the importance of genetic factors in the chemical characteristics of the oil. Headspace solid‐phase microextraction (HS‐SPME) was applied to the analysis of volatile compounds of virgin olive oils. Forty‐eight compounds were isolated and characterized by GC‐RI and GC‐MS, representing 94.1–98.1% of the total amount. (E)‐Hex‐2‐enal, the main compound extracted by SPME, characterized the olive oil headspace for all samples. So, it was clearly shown that there were qualitative and quantitative differences in the proportion of volatile constituents from oils of the various cultivars.     

A high-field1H nuclear magnetic resonance study of the minor components in virgin olive oils

High-field (600 MHz) nuclear magnetic resonance (NMR) spectroscopy was applied to the direct analysis of virgin olive oil. Minor components were studied to assess oil quality and genuineness. Unsaturated and saturated aldehyde resonances, as well as those related to other volatile compounds, were identified in the low-field region of the spectrum by two-dimensional techniques. Unsaturated aldehydes can be related to the sensory quality of oils. Other unidentified peaks are due to volatile components, because they disappear after nitrogen fluxing. The statistical analysis performed on the intensity of these peaks in several oil samples, obtained from different olive varieties, allows clustering and identification of oils arising from the same olive variety. Diacylglycerols, linolenic acid, other volatile components, water, acetic acid, phenols, and sterols can be detected simulteneously, suggesting a useful application of high-field NMR in the authentication and quality assessment of virgin olive oil.     

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.     

Potential of selected Portuguese cultivars for the production of high quality monovarietal virgin olive oil

The effect of cultivar and ripeness stage on the potential nutritional value of monovarietal extra virgin olive oils (MEVOOs) obtained from Cordovil, Carrasquinha, Verdeal, and Negrinha do Freixo cultivars was investigated. MEVOOs produced were characterized by high oleic acid (72–83%), tocopherol (182–530 mg/kg), and phenolic compounds (326–1110 mg/kg) content and by a similar polyphenolic profile. 1‐Penten‐3‐one was found to be the compound with the highest contribution for the aroma of the four MEVOO, related to bitter, pungent, and leaf attributes. MEVOO from Verdeal cultivar showed the best performance in terms of the composition: the highest yield of oil, the highest content of oleic acid, high tocopherol, polyphenol and sterol content, and the lowest content of linoleic acid. These characteristics give to these MEVOO not only a great oxidative stability but also interesting properties from the health point of view. MEVOO obtained with fruits at the maturity index of around 4 were in general richer in beneficial minor compounds. MEVOO produced were discriminated by variety and ripeness stage, using a stepwise linear discriminant analysis. This discrimination will in the future enable the prevention of adulteration of these monovarietal olive oils with specific nutritional composition with other olive oils. Practical implications: High‐quality MEVOOs have recently been introduced in the market, which for growers is a practical way to differentiate and increase the commercial value of extra virgin olive oil. The quantification of major and minor olive oil compounds in monovarietal olive oils represents an objective way of predicting the sensory characteristics, stability, and potential health benefits of the oils, as well as preventing their adulteration with other olive oils. This study will help in the selection of olive varieties during the maintenance or development of new olive orchards and also to select optimum harvest period for these varieties, in order to obtain MEVOOs with the maximum quality and health benefits for consumers.     

Characterization of Volatile Compounds of Virgin Olive Oil Originating from the USA

The volatile profiles of virgin olive oils originating from the USA were first studied: 71 volatile compounds were identified in 21 monovarietal virgin olive oils using solid‐phase microextraction–gas chromatography/mass spectrometry, representing 100 % of the headspace composition. Principal component analysis (PCA) allowed for the grouping of olive oils based on geographical origin, and also the distinguishing of olive oil varieties by their relative positions in the group; 17 distinguishable volatile compounds that significantly contributed to the olive oil classification were found to be distributed on a PCA plot according to their sensory attributes. Moreover, the major volatile components were compared among varieties and origins to clarify the genetic and geographic influences. Our results indicate the significant effects of both origin and cultivar on the volatile composition of olive oil as well as the dominant role of the geographic effect compared to the genetic effect on applied samples.     

“Arbequina” Olive Oil Composition Is Affected by the Application of Regulated Deficit Irrigation during Pit Hardening Stage

Three new regulated deficit irrigation (RDI) treatments were applied to “Arbequina” olive orchards during pit hardening. Oil quality was determined by measuring analytical parameters for olive oil grading, antioxidant activity, total phenol content, fatty acid profile, volatile compounds profile, and sensory analysis. Oils from RDI were classified as “extra virgin olive oil” and their quality was improved due to their higher antioxidant potential (ABTS⁺ [increased ~75%] and DPPH^˙ [increased ~25%] assays) and phenols (increased ~53%) than control. Concentration of total volatile compounds decreased (~27%) but RDI olive oils showed a more balanced profile (alcohols, aldehydes, and esters). Monounsaturated fatty acid content increased (~5%) and atherogenic and thrombogenic indexes decreased (~8.5%) in RDI olive oil. Regarding sensory analysis, RDI provided more balanced oils with higher fruit aroma than control. Other benefits of RDI olive oil, when compared with oil from full irrigated orchards are reduced use of water and improved functional and sensory quality.     

Machines for olive paste preparation producing quality virgin olive oil

Polyphenolic substances enhance the resistance to oxidation of virgin olive oils, but an excess of polyphenols determines a marked bitter, somewhat tannic taste of the oil, similar to the taste of unripe olives. Tests have been carried out on drupes of different cultivars in industrial productions to evaluate the effect of the machines used to prepare olive pastes on the contents of polyphenols in the oils. Notably greater amounts of polyphenols were found in the oils extracted from hammer-crushed pastes than in the oils extracted from milled pastes. The kneading process which follows, especially if it is long, often reduces the amounts of total polyphenols. Therefore, in order to obtain the best organoleptic and chemical quality in extra virgin olive oils, two systems are suggested for the processing procedures. For olives of certain cultivars (Coratina) and for not-blackened or slightly blackened drupes yielding oils with a very high content of total polyphenols, it is most expedient to use the stone-mill together with a kneader system. But it is more suitable to utilize the hammercrusher together with a kneader system in processing olives (such as the Ogiiarola Salentina or Leccino cultivars) yielding normally “sweet” oils with a low content of total polyphenols.     

Cherry leafroll virus: Impact on olive fruit and virgin olive oil quality

We performed a survey on the yield, quality, and chemical characteristics of virgin olive oils from two olive varieties in Croatian Istria: Frantoio and Ascolana tenera, on Cherry leafroll virus‐infected and virus‐noninfected trees and on two harvest dates. Free acidity, peroxide value, specific spectrophotometric absorptions at 232 and 270 nm, fatty acid composition, total phenols, o‐diphenols, oil color, and pigments were determined. Infected olives had lower oil yield and maturity index versus healthy ones. Oils from infected fruits had significant lower value of K₂₃₂ and K₂₇₀ and very elevated total phenols content compared to those obtained from healthy olives. Infected Frantoio gave a lower content of o‐diphenols than the healthy ones, which is in contrast to infected Ascolana that had higher values. The aim of this study is to determine the chemical changes in virgin olive oils from healthy and infected trees related to virus influence. According to our knowledge, this is the first survey on the possible influence of viruses on olive fruits, oil yield, and virgin olive oil quality. Practical applications : There are only few papers which analyze the influence of viruses on crops (especially influence on wine quality) and their effects on yield or other agronomic parameters. This work evaluates for the first time the impact of Cherry leafroll virus on the quality of virgin olive oil obtained from Frantoio and A. tenera varieties in terms of basic parameters related to the hydrolitic and oxidative status, content in antioxidant compounds, and in pigments as well as in fatty acid composition.     

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.     

Natural antioxidants and volatile compounds of virgin olive oils obtained by two or three‐phases centrifugal decanters

Research has been carried out to ascertain the influence of different centrifugal decanters employed in olive process on oil yields and qualitative characteristics and composition of volatile compounds of virgin olive oil. Tests were performed in an olive oil mill equipped with centrifugal decanters at two or three‐phases. Results show that oil yields were similar and oils extracted from good‐quality olives do not differ in free fatty acids, peroxide value, UV absorptions and organoleptic assessment. Total phenols and o‐diphenols content as well as induction time values are higher in oils obtained by the centrifugal decanter at two‐phases, because it requires less quantity of water added to olive paste in comparison to the three‐phases centrifugal decanter. The amount of water added determines the dilution of the aqueous phase and lowers the concentration of the phenolic substances more soluble in vegetable waste water. Due to the partition equilibrium law the concentration of the same substances consequently diminishes in the oil. In this research, the coefficient of the partition equilibrium of total phenols between oil and vegetable water has been calculated and discussed. No significant difference occurred, due to the different decanters employed, in the average values of the volatile components of the head‐space of oils.     

Aroma‐Relevant Volatile Compounds as Markers for the Sensory Quality of Argan Oil

The aim of the present work is to identify and characterize the most important aroma active compounds of argan oil from unroasted and roasted argan almonds as well as roasted almonds obtained from goat‐digested fruits by dynamic headspace GC and GC‐olfactometry with aroma dilution analysis to classify samples from the market according to their processing. While fresh ground argan almonds are characterized by only seven aroma active compounds, in argan oil from unroasted and roasted almonds, 22 and 35 aroma active compounds are found, respectively. As a result of the roasting process, 14 aroma active compounds with dilution factors >64 are detected in the oil by GC‐olfactometry. 17 aroma active compounds show significant differences between the three different argan oil qualities. These compounds are used to differentiate the quality of argan oil from the market. Practical Application: Argan oil belongs to the high‐price oils on the market but sometimes the sensory quality of the oil contradicts the positive image that has been built up for oil by unpleasant cheese‐like and fusty sensory attributes. Although some information about the composition of the volatile compounds of cold‐pressed argan oil from unroasted and roasted kernels is available, the knowledge about compounds that are typical for the aroma of argan oil is important in order to develop analytical methods for the classification of different argan oil qualities. This reduces the work for a panel group that is often time and labor consuming and sometimes the results are not reliable. The present paper demonstrates which volatile compounds show significant differences between argan oil from unroasted and roasted argan almonds as well as roasted almonds obtained from goat‐digested fruits allowing a differentiation of these oils.     

Evolution of phenols and pigments in extra virgin olive oil from irrigated super‐intensive orchard

Phenolic compounds have a high importance in olive oil because of their effect on shelf life and sensory properties. This study reports on the HPLC profiles of the phenolic compounds of virgin olive oils obtained from Arbequina olives from the harvesting in a super‐intensive orchard under a linear irrigation system. In addition, phenolic content, carotenoid and chlorophyllic pigments, and oxidative stability were analyzed. Total phenol content and 3,4‐DHPEA‐EDA increased up to a maximum throughout the ripening process. The simple phenols tyrosol and hydroxytyrosol acetate increased throughout the ripening process, however, there was not found a clear trend in hydroxytyrosol content. Minor constituents such as vanillic acid and p‐coumaric acid increased up to a maximum and then decreased, since vanillin decreased progressively throughout the time of harvest. 3,4‐DHPEA‐EDA and lignans were present in considerable amounts in the studied samples, while oleuropein aglycone was present in a low amount. Total phenol content and oil stability followed the same trend throughout the study, so a very good correlation was established between them. Total secoiridoids and, specifically, 3,4‐DHPEA‐EDA seemed to be responsible for oil stability. The pigment content decreased during ripening, and not a positive correlation was found between pigments and oil stability. Practical applications : The results can be used to determine the best time for harvesting in order to obtain olive oils with different phenols and pigment contents. This is important for sensory characteristics of the olive oils and also for olive oil stability.     

On the importance of total polar phenols to monitor the stability of Greek virgin olive oil

A large number of virgin olive oil samples obtained from different areas in Greece were analyzed for various quality parameters. The work focuses on the colorimetric determination of total phenols with the Folin‐Ciocalteu reagent and its importance in predicting shelf life of virgin olive oil. The results indicate a good correlation of total polar phenol content with the stability of the oil. Colorimetric determination of ortho‐diphenol content does not seem to be a better means for predicting virgin olive oil stability. RP‐HPLC quantification of hydroxytyrosol and tyrosol in their free form gives poor results in the case of freshly extracted oils. It is concluded that until an easy‐to‐manage HPLC method will be available, which will quantify accurately both free and bound forms of hydroxytyrosol and other phenolics, the colorimetric method for the determination of total polar phenols remains a good practical means to evaluate the stability of virgin olive oil.     

Stability to oxidation of virgin olive oils as related to olive conditions: Study of polar compounds by chemometric methods

Polar compounds of virgin olive oils were analyzed. They influence oil flavor and aroma and improve the shelf-life of the oil. The orthodiphenolic fraction is particularly significant for oil stability because of its antioxidative activity. A relationship between the composition of the whole fraction of polar compounds and the state of health of the olives was established. For this purpose, oil samples were obtained from olives that had reached different degrees of ripeness and that had been affected by Dacus oleae infestation differently. The polar compounds were then analyzed by high-performance liquid chromatography. The data set was studied by means of chemometric methods. Partial least squares regression was used to obtain models that show a significant correlation between composition of the oil’s polar compounds and conditions of the olives sampled. In particular, compounds with antioxidative activity were directly linked with the state of health of the olives. The models obtained allow tracing of the state of health of the olives sampled through analysis of the polar fraction of virgin olive oil with a high degree of accuracy, and thus prediction of the oil’s expected shelf life.