Monitoring of virgin olive oil volatile compounds evolution during olive malaxation by an array of metal oxide sensors

In addition to the sanitary aspects of production and the genetic and/or geographic origin of the drupes olive malaxation is a critical control point of virgin olive oil (VOO) production from a qualitative point of view. In particular the sensory peculiarities of malaxation are determined by the presence of C₆ and C₅ aldehydes and alcohols in the VOO head space due to lipoxygenase activity. On-line monitoring of the evolution of these substances during VOO processing could be very useful for defining the operative conditions of malaxation (i.e. time and temperature) in order to improve the VOO sensory quality according to product type.     

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.     

High vacuum applied during malaxation in oil industrial plant: Influence on virgin olive oil extractability and quality

Vacuum technology was applied for the first time at industrial scale to the mechanical extraction processes of virgin olive oil (VOO). The study was carried out using an industrial plant with a working capacity of 4 tons of olives. The use of high vacuum conditions during the malaxation process induced an intense mass transfer into the olive paste that improved the coalescence phenomena of oil droplets with a significant increase in oil extractability for four different cultivars (Arbequina, Arbosana, Koroneiki and Picual). The evaluation of the quality characteristics of the Picual VOO showed an enhancement in the hydrophilic phenol fraction mainly related to the oleacein content. The low temperature set during the vacuum treatment (16 ± 1 °C for 30 min of malaxation) limited the stripping process of the main aldehydes, alcohols and esters. In contrast, other negative volatile compounds related to off-flavoured VOO (ethanol, 3-methyl-1-butanol, ethyl acetate and acetic acid) were significantly reduced.     

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.     

Contribution of olive seed to the phenolic profile and related quality parameters of virgin olive oil

BACKGROUND: Conflicting results have been reported about the effect of fruit de‐stoning on the virgin olive oil (VOO) phenolic profile. The aim of the present study was to determine whether olive seed plays any role in the synthesis of this oil phenolic fraction. RESULTS: Increases of around 25% of total phenolic compounds were observed in oils obtained from de‐stoned olive fruits in three main Spanish cultivars. To investigate the involvement of olive seed in determining the phenolic profile of VOO, whole intact olive fruits were added with up to 400% olive stones. Excellent regression coefficients were found in general for the decrease of total phenolic compounds and, particularly, of o‐diphenolics in the resulting oils. On the other hand, it was found that olive seed contains a high level of peroxidase (POX) activity (72.4 U g^?1 FW), accounting for more than 98% of total POX activity in the whole fruit. This activity is able to modify VOO phenolics in vitro, similar to the effect of adding stones during VOO extraction. CONCLUSION: Olive seed plays an important role in determining VOO phenolic profile during the process to obtain an oil that seems to be associated with a high level of POX activity. Copyright © 2007 Society of Chemical Industry     

Influence of O2 on the quality of virgin olive oil during malaxation

The aim of this work was to investigate the effect of malaxation operating conditions on virgin olive oil quality. Legal, sensory and nutritional parameters of olive oil were evaluated by identifying the role played by enzymes. A comparison was made between oil obtained from a traditional malaxation plant and oil obtained from malaxation equipment (LOM) able to work at low oxygen level and temperature. Research results showed that, during malaxation, oxygen had an effect on both phenolic compounds and fatty acids, mainly favouring enzyme phenomena. Malaxation at a low oxygen level was found to be selective for the formation of both phenolic and C₆ compounds. Oil obtained from malaxation LOM equipment was shown to be richer in both aldehydes such as trans‐2‐hexenal and phenolic compounds than oil obtained from traditional processing. Copyright © 2006 Society of Chemical Industry     

Influence of olive paste preparation conditions on virgin olive oil triterpenic compounds at laboratory-scale

The influence of olive paste preparation conditions on the triterpenic content of virgin olive oils from Arbequina and Picual cultivars was investigated. For this purpose, three sieve diameters of the hammer mill (4, 5, and 6 mm), two malaxation temperatures (20 and 30 °C), and two malaxation times (20 and 40 min) were tested. Results obtained showed that for Arbequina oils, a finer crushing level resulted in higher maslinic acid and erythrodiol content. Increasing malaxing temperature and time lead to a rise in both oleanolic and maslinic acid concentration, whereas erythrodiol content increased only for the longer malaxation time. For Picual oils, higher concentrations of oleanolic acid, maslinic acid, and uvaol were obtained by prolonging the paste malaxation time. A finer crushing level resulted also in an increase of maslinic acid content. These findings suggest that virgin olive oil triterpenic composition can be improved by regulating olive paste preparation conditions.     

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.     

Role of polyphenol oxidase and peroxidase in shaping the phenolic profile of virgin olive oil

The main objective of this study was to assess the ability of polyphenol oxidase (PPO) and peroxidase (POX) enzymatic activities present in olive fruit tissues to oxidize main phenolic compounds related to the process to obtain virgin olive oil (VOO) in order to ascertain their involvement in shaping the phenolic profile of this product. In the two olive cultivars under study, Arbequina and Picual, olive PPO activity was found to be largely present in the fruit mesocarp whereas most olive POX activity is in the seed. Moreover, both enzymatic activities display relatively constant values after the onset of fruit ripening when the fruit is harvested for VOO production. Results showed that both PPO and POX activities present in olive fruit at ripening stages are able to oxidize main phenolic glycosides present in the fruit as well as those phenolic compounds arising during the industrial process to obtain the oil, especially secoiridoid compounds derived from oleuropein that mainly determine VOO nutritional and sensorial properties. Experimental data suggest a key role for endogenous olive PPO and POX enzymatic activities in determining the phenolic profile of VOO.     

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.     

DNA diversity in olive (Olea europaea L.) and its relationships with fatty acid,biophenol and sensory profiles of extra virgin olive oils

Olive (Olea europaea L.) is gaining importance worldwide primarily for the production of virgin olive oil (VOO), the main lipid source of the Mediterranean diet.We evaluated the genetic diversity of 20 traditional varieties of Southern Italy using 10 SSR markers. We also produced 382 monovarietal extra virgin olive oils (EVOOs) from the same varieties and studied their chemical profiles by analysing 13 fatty acids (FAs) and 6 olive biophenols (OBPs). In addition, the sensory profile of EVOOs was also assessed.Significant differences among the 20 varieties were found in terms of DNA polymorphism, chemical composition and sensory profile of the EVOOs, highlighting that the genetic variability in olive is detected also in different EVOO features. The chemical variation of EVOOs throughout different years suggested a genotype-specific level of environmental stability and adaptation. The comparison of pairwise distances between varieties obtained by genetic, chemical and sensory data indicated a significant correlation of sensory attributes with the other parameters.The genetic and EVOO composition data underlined the significant diversity present in the varieties under investigation, suggesting that traditional varieties specialized to particular environmental conditions have distinctive, unexplored features. Our work also shows the efficacy of establishing integrated compositional databases as a means to make evident differences among VOOs from traditional varieties. This multidisciplinary information is highly useful to differentiate origin-linked products from others of the same category.     

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.     

Effect of standard phenolic compounds and olive oil phenolic extracts on acrylamide formation in an emulsion system

In this work the effect of standard phenolic compounds such as trolox, phenolic acids (ferulic, gallic, protocatechuic and caffeic acid) and secoiridoids, extracted from virgin olive oil (VOO), on acrylamide formation in an emulsion system was investigated. The emulsion system was heated in an oil bath at different temperatures and for different periods of time. At 105 and 115 °C the generated amounts of acrylamide were negligible during the monitoring time. At 125 °C addition of standard phenolic compounds reduced acrylamide formation which was more pronounced at initial time of heating (20 min) reaching up to 70%. Protocatechuic and gallic acid were more effective than trolox, caffeic and ferulic acid in acrylamide reduction at the final time intervals of heating (30–60 min). On the contrary, addition of VOO extract in the emulsion system resulted in a remarkable increase of acrylamide level, which was ascribed to secoiridoids’ structure containing aldehydic groups.     

Stability of virgin olive oil and behaviour of its natural antioxidants under medium temperature accelerated storage conditions

The aim of the present research is to advance the study of virgin olive oil stability, in particular the behaviour of its natural antioxidants during long term storage. The changes undergone by tocopherols and complex and simple phenolic compounds and their antioxidant activity were studied under medium temperature (50 °C) accelerated oxidation conditions over a storage period of 8 months. Different oxygen availability (open and closed bottles, OB and CB) and four different monovarietal Tunisian virgin olive oils (VOO; Chemlali, Chétoui, El Hor and Oueslati) which vary in their fatty acid profile and content of natural antioxidants were employed. Oueslati VOO showed the lowest initial oxidation rate (4.6 PV/week) and as a consequence the highest induction period (IP; 16 days) as compared to the other VOOs studied (initial rate from 7.7 to 12.1 PV/week and IP from 9 to 12 days for El Hor and Chemlali, respectively, in both cases). In all cases the complete depletion of α-tocopherol corresponded with the observed induction period. Since the oxidation rate in the varieties studied is not sufficiently different to explain the great differences in the initial degradation rate observed in the phenolic compounds (mainly between Chétoui VOO, 163 μmol/kg/week, as compared to the other VOO oils, e.g. 6.1 and 2.5 μmol/kg/week, respectively, in Chemlali and El Hor VOOs), a concentration dependent degradation rate of complex phenols is suggested.     

The influence of the malaxation temperature on the activity of polyphenoloxidase and peroxidase and on the phenolic composition of virgin olive oil

The effect of the malaxation temperature under sealed conditions on the qualitative and quantitative composition of the phenolic compounds in virgin olive oils produced from four Italian cultivars was assessed for two atmospheric conditions. In both cases, the results show a positive relationship between temperature and the concentration of the derivatives of the secoiridoid aglycones; the effect of the temperature on the oxidoreductases that promote oxidation (polyphenoloxidase and peroxidase) was investigated to determine their optimal temperatures and thermal stability. While olive peroxidase (POD) showed the highest activity at 37 °C and high stability in the temperature range tested, polyphenoloxidase (PPO) exhibited the optimum activity at approximately 50 °C, but showed low stability at 40 °C, with a large variation in stability according to the olive cultivar. These results may contribute to an understanding of the increase in the phenol concentration found in virgin olive oils obtained following higher temperatures of malaxation.     

Discussion on the objective evaluation of virgin olive oil bitterness

The study aims at investigating the suitability of absorbance at 225 nm as an objective means to evaluate virgin olive oil (VOO) bitterness. Calculation of oleuropein score (OLS) using a standard curve instead of the so far employed K₂₂₅ value is proposed and a “taste index” based on the total phenol content determined by fluorimetry is examined as a complementary tool. Data from sensory evaluation of a series of VOO samples and RP-HPLC determination of phenolic compounds using diode array, fluorimetric or MS detection supported the applicability and merits of the introduced criteria. Phenol profiling using fluorescence detection (280 nm_excitation/320 nm_emission) became useful regarding oil bitterness. The presence of the non-fluorescent elenolic acid at 225 nm, indicated that the K₂₂₅ value is influenced by the presence of this non-bitter compound found at significant levels even in fresh oils. Our finding offers further ground to our proposal for the calculation of the “taste index”.     

Virgin olive oil and olive fruit minor constituents as affected by irrigation management based on SWP and TDF as compared to ETc in medium-density young olive orchards (Olea europaea L. cv. Cornicabra and Morisca)

This study investigated the effect of different irrigation managements, based on the measurement of the stem water potential (SWP) and the trunk diameter fluctuations (TDF) of the olive tree, as compared to the ET-FAO methodology, with regard to the minor constituents composition of virgin olive oil (VOO) and olive fruit in two different experimental olive orchards (Olea europaea L. Cornicabra cv. and Morisca cv.). No clear relationships between the water stress integral, both seasonal and from DOY 229–277, and the oleuropein content in the drupes were found. Nevertheless, a good agreement between the content of this biophenol and the minimum SWP of the olive trees, measured from the beginning of August to the end of the irrigation season, were found (r² = 0.88–0.95 and r² = 0.90–0.95 in Cornicabra and Morisca cultivars, respectively). A lower minimum water potential corresponded therefore with a higher biophenol content in the drupe and consequently with a superior phenolic content in VOO. In both cultivars, the volatile compounds most affected by the water status of olive trees were hexanal, E-2-hexenal and hexan-1-ol, showing an inverse relationship with the water stress integral observed. Furthermore, it was observed that the irrigation scheduling based on the SWP measurement, with a threshold of ?1.2 MPa provided VOO in both cultivars with a similar phenolic and volatile composition with regard to those obtained with the FAO treatment.     

Phenolic compounds in olive oil and olive pomace from Cilento (Campania,Italy) and their antioxidant activity

Virgin olive oil (VOO) has nutritional and sensory characteristics that make it unique and a basic component of the Mediterranean diet. Its importance is mainly attributed to its richness in polyphenols, which act as natural antioxidants and may contribute to the prevention of several human diseases. In this paper we report the determination and quantification of oleocanthal, one of the main substances responsible for the bitter taste of olive oil, together with a quali-quantitative analysis by HPLC analytical methods of phenolics from Cilento VOO and olive oil pomace. The total phenolic content was also determined and the in vitro antioxidant and free-radical scavenging activities by DPPH test was evaluated. A superoxide anion enzymatic assay was also carried out and the results were confirmed by the inhibition of xanthine oxidase activity assay. The possible protective role played by VOO secoiridoids on injurious effects of reactive oxygen metabolites on the intestinal epithelium, using Caco-2 human cell line, was investigated.     

Influence of the malaxation time and olive ripening stage on oil quality and phenolic compounds of virgin olive oils

The main objective of this study was to evaluate the influence of the malaxation time (Mt) and ripening stage on oil quality and phenolic compounds of Hojiblanca and Picual virgin olive oils. In both varieties of oil, phenolic content and oxidative stability decreased as ripening progressed. The total level of tocopherols diminished by up to 40% as fruit ripened. The compositions of palmitic, stearic, lignoceric, oleic, linoleic and linolenic acids were significantly influenced by the ripening process. The present work shows that an increased Mt promoted the increase of free acidity (up to 13.3%) and tocopherols (up to 11.6%) and negatively affected the oxidative stability and the concentration of phenols. Further research is required to determine ripening stages and malaxation conditions for all olive oil varieties to achieve a satisfactory balance between the improvement of both oil yield and oil quality and composition.     

Oxidative stability of olive oil and its polyphenolic compounds after boiling vegetable process

The changes in the stability and phenolic content of an extra-virgin olive oil and an olive oil following boiling operation in the presence of vegetables have been studied. After the boiling process, none of the olive oil samples was oxidized, independently of the olive oil quality used. However, in contrast with tocopherols, all polyphenolic components decreased in concentration with the thermal treatment and this decrease was dramatic in the presence of vegetables, probably because of their high content in metals such as iron and copper. The addition of olive oil only 15 min before the end of the boiling process was shown to bring benefits in general for the content of both elenolic acid derivatives, 3,4-DHPEA-EA and 4-HPEA-EA, and hydroxytyrosol acetate in the processed oils. Moreover, less destruction of the vegetables polyphenols was also observed when processing olive oils only 15 min before the end of the boiling process. Interestingly, and besides the use of EVOO instead of OO did not bring benefits to the stability of samples or a higher polyphenolic content in the samples after processing, an higher radical scavenging capacity of phenolic extracts obtained from EVOO samples could be observed.