Use of chlorophyll and carotenoid pigment composition to determine authenticity of virgin olive oil

The chlorophyll and carotenoid pigment profile of 50 mono-variety virgin olive oils was used to develop an index of authenticity for the product. The presence of carotenoids other than those described, or chlorophyll derivatives at another level of degradation, were found to be determing elements of this index for “virgin” olive oil quality. In addition, the ratio of chlorophyll/carotenoid should be around 1, and the ratio of minor carotenoids/lutein should be about 0.5, with a limited variability. These characteristics may be expected of virgin olive oil in general and are independent of variety. Finally, the percentage of lutein, violaxanthin, and total pigment content may be used to distinguish between mono-variety virgin olive oils.     

Effect of storage on the original pigment profile of spanish virgin olive oil

The present study was carried out on 12 virgin olive oils to determine whether one year's storage under mild conditions of 15°C and darkness affected the initial pigment composition of recently extracted virgin olive oil. Although the total pigment content remained constant, the individual contribution of each pigment changed. The acid compounds liberated from the fruits during the oil extraction process promote the beginning of chlorophyll pheophytinization and the isomerization of the 5,6-epoxide groups of the minor xanthophylls. During the first 3 mon of storage, there was a generalized increase in pheophytinization that was different for each oil (P<0.01, Duncan test) but was not correlated with the free acidity measured in them. At the same time, isomerized xanthophylls and allomerized pheophytins increased slightly. Following this stage, pyropheophytin a (a pigment not present in the initial oils), was detected; its concentration increased during storage. There were no significant differences in the final percentages of pyropheophytin a among the 12 oils, and the concentration of this new compound represented around 3% of the chlorophyll fraction. The pheophytin a/pyropheophytin a ratio always exceeded 20. All these small pigment transformations were signs that the oil had been stored. The content and class of pigments present in virgin olive oil are authentic indicators of its history prior to marketing.     

Use of nitrogen to improve stability of virgin olive oil during storage

Experiments were carried out to study the possibility of improving the stability of extra virgin olive oil by using nitrogen as a conditioner gas during storage. With this aim, virgin olive oil samples, obtained from Leccino and Coratina cultivars, were stored in the dark, in closed bottles conditioned with air or nitrogen at 12–20 and 40°C. Results indicated that the FFA percentage increased over 1% only when oils were stored at 40°C. The PV and the K ₂₃₂ value (light absorbance at 232 nm) of oils increased over the limit value allowed by European Union law when the bottles were only partly filled and air was the conditioner gas. The use of nitrogen as conditioner gas helped to avoid this risk during 24 mon of storage at 12–20°C. The total phenolic content of both cultivars oils decreased during storage because their oxidation protected the oils from autoxidation. The content of total volatile compounds in oils decreased continuously during storage at 12–20°C, whereas it increased over 10 (Coratina cv.) and 15 (Leccino cv.) mon and then diminished when the storage temperature was 40°C. The same behavior, i.e., increase then decrease, was ascertained for trans-2-hexenal. The hexanal content of oils increased continuously during storage because this compound is formed by the decomposition of the 13-hydroperoxide of linoleic acid.     

Changes in virgin olive oil characteristics during different storage conditions

In this study we have examined the effect of olive oil storage outdoors on a comprehensive series of quality measures. The conditions used were at the extreme of those encountered during the production of bottle oil. Filtered and unfiltered oils were compared as was the influence of inert gas (nitrogen) in the headspace. Increases in K₂₃₂, K₂₇₀ and peroxides over time were very much reduced by inert headspace gas, which also reduced losses of total phenols and oxidative stability. Headspace nitrogen also reduced the rise in unconjugated phenolics as secoiridoid derivatives declined and minimised losses in polyunsaturated fatty acids. The pattern of volatile compounds detected in olive oils stored indoors or outdoors showed subtle differences. Moreover, when stored with air exposure the levels of some negative sensory components such as penten‐3‐ol and hexanal increased while other positives, like trans‐2‐hexenal were reduced. These changes would be expected to reduce quality. Finally, Panel tests were used. All oils lost perceived quality on storage and this was accelerated outdoors while headspace nitrogen slowed the deterioration significantly. Our data show that storage outdoors for 4 months in winter does not reduce olive oil quality significantly and that an inert gas in the headspace is beneficial. Practical applications : The storage of olive oil for bottling is carried out under a variety of conditions. Here we assess the effects of storage outdoors for oils from the main Greek cultivar (Koroneiki) of olive. Detailed analyses of quality (standard measures, different phenolics, lipids and volatiles) as well as Panel tests were used for evaluation. Our data show that, although storage outdoors causes deterioration quicker than indoors, changes are not serious up to 4 months. Furthermore, the use of an inert headspace gas significantly preserved quality both indoors and outdoors. Thus we would strongly recommend the latter measure to producers.     

Quality control and storage studies of virgin olive oil: Exploiting UV spectrophotometry potential

The present work was undertaken in order to examine whether K₂₃₂ values and other UV absorbance characteristics could replace the determination of peroxide value (PV) in routine quality control and also in storage studies of virgin olive oil (VOO). For this reason, PV and extinction coefficients were determined for a large number of VOO samples (n = 40). The samples were then stored at 45 °C for several weeks. Changes in the lipid matrices were monitored by periodic measurements of the same quality indices. UV absorption spectra and the respective derivative ones were obtained before and during storage. Regression data showed that the PV is correlated with the K₂₃₂ value not only at time zero but also during storage. Evidence derived from the first derivative spectrum is strongly related to the oxidative status of the oil. The findings may be used (a) to simplify the decision tree suggested for “the verification of consistency of a VOO sample with commercial category declared” in the EEC Regulation N^o 1989 (2003), which takes into account acidity measurement, PV and absorbance values (K₂₇₀, ΔK, K₂₃₂), and (b) to collect qualitative and quantitative information about the oxidation process during storage.     

Effect of filtration on virgin olive oil stability during storage

The effect of filtration and dehydration on the stability and quality of virgin olive oil during storage at room temperature (25 °C) and under accelerated conditions (40 °C) was studied. Different types of monovarietal olive oil, namely unfiltered (UF), filtered (F) and filtered‐dehydrated (FD), were obtained from Arbequina, Colombaia, Cornicabra, Picual and Taggiasca cultivars. Results showed that filtration and dehydration decreased the rate of hydrolysis of the triacylglycerol matrix, especially at the higher temperature and in oils with a higher initial free acidity (e.g. free acidity of 0.82% and 0.63% in UF and FD Colombaia samples, respectively, after 8 months of storage), and delayed the appearance of rancid defects (e.g. UF and FD Arbequina samples lost extra‐virgin grade after 10 and 12 months of storage, respectively). The formation of simple phenols due to the hydrolysis rate of their secoiridoid derivatives was also greater in unfiltered olive oils (e.g. 174 μmol/kg and 137 μmol/kg in UF and FD Picual samples, respectively, after 8 months of storage). Thus, filtration and especially dehydration could help to prolong the shelf life of high‐quality and less stable olive oils like those obtained from the Arbequina and Colombaia varieties.     

Evolution of phenolic compounds in virgin olive oil during storage

Phenolic compounds are of fundamental importance to the shelf life of virgin olive oils because of their antioxidative properties. In this paper, the evolution of simple and complex olive oil phenols during 18 mon of storage is studied by high-performance liquid chromatography (HPLC) analysis. The olive oils under examination were from various olive cultivars, harvested in two sectors in the same region at different stages of ripeness. The findings indicate that it is not the variety but rather the ripeness of the olives and the soil and climate that influence the phenol composition of virgin olive oil. In addition, a positive correlation was found between the age of the oils and the tyrosol to total phenols ratio. Lastly, gas chromatography-mass spectrometry analysis confirmed that the unidentified peaks detected by HPLC were of a phenolic nature.     

Evolution of thermograph parameters during the oxidation of extra virgin olive oil

The modulated differential scanning calorimetry (M‐DSC) was used as a rapid and effective method to characterize the olive oil at different levels of oxidation. Thermograph parameters have been related to oxidative degradation of the triglycerides. In this study, their relation to the characteristic off‐flavor compounds, correlated to the oxidative degradation of the oil, was also investigated. Extra virgin olive oil samples were subjected to the following oxidation treatments: a) purged with air using glass washing bottles at two flow rate values, b) heated in a conventional oven at two area/oil mass ratios, and c) heated in a microwave oven also at two area/oil mass ratios. Samples were withdrawn and analyzed at predetermined intervals. Flavor and off‐flavor compounds were isolated using a dynamic thermal stripping apparatus and transferred into a gas chromatograph by using a thermal desorption unit. All oil samples were analyzed by M‐DSC during cooling from 25 °C to ?60 °C at 7 °C/min, and heating back to 40 °C at 10 °C/min. High correlation values were obtained between various M‐DSC thermograph parameters and certain volatile compounds. Results showed that M‐DSC could be used as a simple method to indicate compositional changes in olive oil during oxidation.     

Calorimetry of edible oils: Isothermal freezing curve for assessing extra‐virgin olive oil storage history

The calorimetric method described here investigates the solid‐liquid phase transitions in a Tuscan extra‐virgin olive oil in order to evaluate the changes induced by light exposition. The parameters of the freezing and the melting curves show high sensitivity to oil quality degradation, in agreement with the data from routine tests at disposal. Possible applications of the method are discussed.     

Discriminating power of the hydrocarbon content from virgin olive oil of extremadura cultivars

Samples of virgin olive oils (105) from seven Extremaduran olive varieties (Cacereña, Carrasqueña, Cornezuelo, Corniche, Morisca, Picual, and Verdial de Badajoz) in three stage of maturity (green, semi-ripe, and ripe) were collected and the alkane, alkene, and sesquiterpene contents determined. There were significant differences at the 0.01 probability level in most of the hydrocarbons, both by variety and by state of maturity. Discriminant analysis applied to 70 samples explained 72.3% of the variance between the different groups of varieties and allowed 90% of the samples to be classified according to their variety. The acceptability of the model was verified against the remaining 35 samples, giving a mean level of correct classification of 94%.     

Stability of a phenol‐enriched olive oil during storage

The use of an emulsifier to stabilize the phenolic compounds added in the preparation of an enriched olive oil was evaluated. Two emulsifiers, lecithin and monoglyceride, were studied. The results showed lecithin to be the most convenient, due to the increase in the value of the oxidative stability of the phenol‐enriched oils in relation to the enrichments prepared with monoglycerides. After that, the shelf life of the prepared oils was evaluated during a period of 256 days of storage at 25°C in the dark. Oil quality parameters, total phenolic content, bitterness index and oxidative stability were studied during the storage period. Additionally, the phenolic composition and antioxidant capacity (by using the ORAC assay) were evaluated at the end of the storage. The phenolic enrichment of the oils allowed the shelf life of the oils to be extended compared with the control (virgin olive oil without phenol addition), delaying the appearance of peroxides and improving their oxidative stability. In addition, the higher content of phenolic compounds in the oils at all stages of storage is desirable in order to increase the intake of these beneficial compounds. Practical applications : The preparation of phenol‐enriched olive oils with a higher phenolic content than the commercial virgin olive oils is of special interest to increase the ingestion of these healthy compounds the daily intake of which is limited due to the high caloric value of olive oil. There are two key points in the development of this product: (i) the dispersion and stabilization of the phenol extract in the oil matrix and (ii) the stability of the phenols in the prepared oils to guarantee the phenol concentration during their shelf life. It is important to study the use of emulsifiers to determine if they allow an improvement in the dispersion of the phenolic extract, and their stabilization in the final product. In addition, the emulsifiers could mask the bitter taste of the enriched oils, which is desirable to increase consumer acceptance of the enriched oil.     

Changes in the main components and quality indices of virgin olive oil during oxidation

This work reports on changes in the major and minor components of virgin olive oil during oxidation, details modifications found in the standardized quality indices, and analyzes the most significant relationships between the components of the oil and its oxidative stability. During the induction period or slow phase of oxidation, polyphenols, tocopherols, and pigments undergo the most important alterations. Other compounds, such as FA or volatiles, suffer significant modifications only during the rapid or exponential phase of oxidation when the natural antioxidant systems fall to minimal values. Among the quality indices, PV and the specific extinction coefficients K ₂₃₂ and K ₂₇₀ increase markedly from the earliest stages of oxidation, whereas titratable acidity does not change appreciably during the induction period. The evolution of the different compounds and parameters analyzed suggests that the tocopherol and orthodiphenol contents are the best indices to determine the average life of the oils.     

Proposed parameters for monitoring quality of virgin olive oil (Koroneiki cv)

The overall quality of virgin olive oil (VOO) is closely related to its oxidative stability that is usually evaluated through the stability index measured by the Rancimat apparatus. Quality characteristics and also pro‐oxidant and antioxidant content for 52 Greek VOO samples (Koroneiki cv) were used to build up a model capable of predicting stability. Collinearity diagnostics, variable selection, and regression analysis were applied to the experimental data to locate the contribution of each parameter to the keeping quality of the samples. The predictive ability of the model was confirmed for a second VOO ample set of the same cultivar. It was found that except for the peroxide value, which negatively influences the stability, other important parameters were α‐tocopherol, total polar phenol and total chlorophyll content. It is concluded that the colorimetric determination of total polar phenols, the spectrometric determination of total chlorophylls and the high‐performance liquid chromatography analysis of α‐tocopherol, not presently included in the established methods of official analysis, can be used for a better evaluation of VOO quality. These parameters, which can be easily adopted as routine methods by the industry, seem to be of utmost importance for shelf life prediction and expiration dating if applied for the promotion of the most competitive products in the international olive oil market.     

Action of chlorophylls on the stability of virgin olive oil

Virgin olive oil was used as substrate to study the influence of chlorophylls on its oxidative stability in light and in darkness. Chlorophylls a and b were added to this substrate, after which oils were stored at 36 ± 2°C for three months under artificial light (1340 lux) or in darkness. The effect of light was greater than that of the additives. The prooxidant action of chlorophylls in the presence of other pigments of the oil was not observed in this assay. During early storage, the rate of peroxide formation was lower in the samples with added chlorophylls, but later it equalled that of the control. In darkness, stability was greater in the samples containing chlorophylls, indicating a slight antioxidant effect, which was more marked for chlorophyll a.     

High-performance liquid chromatography evaluation of phenols in virgin olive oil during extraction at laboratory and industrial scale

Phenolic compounds are of fundamental importance to the quality and nutritional properties of virgin olive oils. In this paper, the high-performance liquid chromatographic analysis of simple and complex olive oil phenols in the streams generated in the two-phase extraction system was carried out using Arbequina and Picual olives. The malaxation stage reduced the concentration of orthodiphenols in oil ca 50–70%, while the concentration of the nonorthodiphenols remained constant, particularly the recently identified lignans 1-acetoxypinoresinol and pinoresinol. Oxidation of orthodiphenols at laboratory scale was avoided by malaxing the paste under a nitrogen atmosphere. Phenolic compounds in the wash water used in the vertical centrifuge were also identified. Hydroxytyrosol, tyrosol, the dialdehydic form of elenolic acid linked to hydroxytyrosol were the most representative phenols in these waters. Hence, phenolic compounds in the wash waters came from both the aqueous and the lipid phases of the decanter oily must.     

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.     

Pyropheophytin a – Determination of thermal degradation products of chlorophyll a in virgin olive oil

The “Joint Committee for the Analysis of Fats, Oils, Fatty Products, Related Products and Raw Materials (GA Fett)” has developed the following method for the determination of Pyropheophytin a in virgin olive oils to detect a possible thermal treatment. It is intended to include this method in Section C, Chapter VI of the German Standard Methods.*     

Profile of enzyme in drupe of oueslati's cv. olives during ripening phases: A support method implementation in the production of extra virgin olive oil

Quality of virgin olive oil (VOO) depends on phenolic molecules content, which depends on the biochemical characteristics of olive fruits, namely endogenous enzymes. In order to ascertain the influence of olive fruit ripening degree on the phenol content, enzyme activities in olive fruits, and the quality of the corresponding oils were studied during Oueslati olive ripening. In fact, three enzymes were studied: peroxidase (POX) in olive seeds, polyphenoloxidase (PPO), and β-glucosidase (β-GL) in olive fruits mesocarp. Each enzyme showed specific trend: POX activity increased gradually until reaching a maximum (17.061 ± 0.101 U g⁻¹ FW) at ripening index (RI) 3.6 and then decreased slowly at advanced ripening stage. However, the maximum of PPO activity (240.421 ± 0.949 U g⁻¹ FW) was observed earlier at RI of 0.7. Concerning β-glucosidase activity, its maximal was 60.857 ± 1.105 U g⁻¹ FW at RI 2.8, then, it decreased sharply to reach 17.096 ± 0.865 U g⁻¹ FW at RI 3.9. A significant increase of total phenol content as well as the antioxidant activity were observed during Oueslati olive ripening. Moreover, phenolic profile indicated that appropriate harvesting date of Oueslati olives coincided with RI 3.9 given that highest content of most important individuals phenolic compounds responsible for the main VOO biological properties achieved on this date. Furthermore, phenols amount of Oueslati VOO was principally due to PPO enzyme activity as the increase in total phenols coincides with the decrease in PPO activity.