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Kinetics of quality degradation during storage of monovarietal extra virgin olive oils
No full textIntroduction. Lipophilic derivatives of olive secoiridois (namely, the dialdehydic form of decarboxymethyl oleuropein aglycone, the isomer of oleuropein aglycone, the dialdehydic form of decarboxymethyl ligstroside aglycone, and the isomer of ligstroside aglycone) are present in extra virgin olive oil (EVOO) due to the hydrolysis of their glycosidic precursor catalysed by endogenous glycosidases during the crushing of olive fruit. These compounds as well as alpha-tocopherol have received considerable interest due to their potential health effects, and could be used as indices to evaluate EVOO quality in addition to those established by the EU Regulations (1). Here we report on the kinetics of autoxidation and hydrolytic processes that occur during storage of EVOO, and their effects on the antioxidant content. The aim of this study was to determine whether the potential properties of EVOO antioxidants are maintained or lost during the commercial life of the product.
Materials and methods. EVOOs of the Picual, Arbequina, Taggiasca, and Colombaia cultivars were obtained from industrial oil mills. EVOOs were stored under dark, in closed-bottles (10% head-space), at 25-40oC for a period of 8 months. For each cultivar six bottles were taken from the incubator at scheduled times (monthly) for the analysis of acidity, peroxide number, spectroscopic indices K232 and K270, alpha-tocopherol, phenolics, and antioxidant activity (2).
Results. Four monovarietal EVOOs with different fatty acid compositions and antioxidant contents were chosen to define the extent of antioxidant degradation during storage. Secoiridoids, alpha-tocopherol, and the antioxidant activity decreased in all EVOOs following pseudo-first order kinetics. Oleuropein derivatives were less stable than the corresponding ligstroside derivatives and alpha-tocopherol. Hydroxytyrosol and tyrosol increased during storage as a result of secoiridoid hydrolysis. However, the increase of simple phenolics was lower than the decrease of their precursors, indicating that degradation occurred via both hydrolysis and oxidation. Free acidity, peroxide value, and the spectroscopic indices in the UV region increased following pseudo-zero order kinetics.
The rate constants for quality indices degradation were obtained, and the time to reach the limits established by EU Regulation was calculated. In all EVOOs K232 was the first parameter that exceeded the legal limit. It was found that when EVOOs attained the this latter threshold the residual antioxidant activity was more than 60% with respect to the initial value. These data led to the conclusion that the beneficial properties of EVOOs due to antioxidant activity can be maintained throughout their commercial lives.
References
1. V. Lavelli (2002) J Agric. Food Chem. 50, 26, 7704-7708.
2. V. Lavelli, G. Fregapane, M.D. Salvador (2006), J Agric. Food Chem. 54, 8, 3002-3007
Effect of storage on secoiridoid and tocopherol contents and antioxidant activity of monovarietal extra virgin olive oil
No full textThe degradation of secoiridoid, tocopherol, and antioxidant activity in extra virgin olive oils (EVOOs)
was studied during 8 months of storage in closed bottles in the dark, at 40 and 25 °C. Picual, Arbequina, Taggiasca, and Colombaia monovarietal EVOOs possessing quite different fatty acid and antioxidant contents were used. The secoiridoid aglycones, namely, the oleuropein and ligstroside derivatives, and alpha-tocopherol decreased following pseudo-first-order kinetics. In all EVOOs oleuropein derivatives were less stable than the corresponding ligstroside derivatives and R-tocopherol.
Accordingly, overall antioxidant activity decreased following pseudo-first-order kinetics, with rate constants ranging from 0.85 10-3 to 4.1 10-3 days-1 at 40 °C and from 0.8 10-3 to 1.5 10-3 days-1 at 25 °C . According to both the antioxidant activity and the hydrolysis and oxidation indices established by EU regulation to assess EVOO quality, Colombaia oil was the least stable, followed by Taggiasca, Arbequina, and Picual oils. Despite antioxidant degradation, EVOOs with high antioxidant contents were still “excellent” after 240 days of storage at 40 °C. These data led to the conclusion that the beneficial properties of EVOOs due to antioxidant activity can be maintained throughout their commercial lives
Relationship Between Sensory Evaluation Performed by Italian and Spanish Official Panels and Volatile and Phenolic Profiles of Virgin Olive Oils
No full textVirgin olive oil (VOO) is typified by characteristic, pleasant sensory notes that differentiate it from other edible oils. Sensory taste, together with nutritional aspects, is the main reason for the increase in consumption of VOO in recent years. Sensory analysis is required by European Official Regulations for olive oil in order to classify the product in commercial categories. In this study, the
relationship between sensory and chemical composition has been investigated. In particular, 16 VOO samples (15 from a single variety of olives), produced in Italy and Spain (eight from each country), were analyzed. Sensory attributes were valued by four panels (three officially recognized both by IOOC and National Ministry: two Italian and two Spanish) employing a total of 59 tasters. Volatile and phenolic compounds were related to olfactory and gustative notes, respectively. Volatile compounds were then separated, identified, and quantified, starting from oil samples, by
solid phase microextraction and capillary gas chromatographic
analysis using a mass spectrometry detector (SPME/cGC-MSD). Furthermore, the phenolic profile was examined by high-performance liquid chromatography with diode-array and mass spectrometry detectors (HPLC-DAD/MSD). Correlations were found between the major volatile compounds (sum of aldehydes C6) and orthonasal perception of olive fruity and retronasal odor of almond.
Additional correlations with bitterness and pungency were
observed for tyrosol and oleuropein aglycon, respectively
Effect of filtration on virgin olive oil stability during storage
No full textThe 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 mmol/kg and 137 mmol/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
STABILITY OF THE SENSORY QUALITY OF VIRGIN OLIVE OIL DURING STORAGE: AN OVERVIEW
No full textThe storage conditions of bottled or tank-stored virgin olive oil, as well as all the agronomical and technological variables of the processing stages, are particularly relevant for preserving the highly valued organoleptic quality of this product. All the efforts made in the olive grove and in the oil mill to produce virgin olive oil with good sensory characteristics can be undermined if improper storage conditions are used. In particular, it is necessary to protect the oil against lipid oxidation which can have many deleterious effects on the quality of virgin olive oil, including the formation of unpleasant organoleptic characteristics, the drastic reduction
of the bouquet and taste notes as well as the reduction of naturally-occurring antioxidant compounds and therefore
shortening of its the shelf life. The oxidation process during storage is known and involves changes to both the major and minor components of virgin olive oil. To slow down the oxidation rate during storage, certain factors such as the presence of oxygen and traces of metals, exposure to light and the binomial storage time/temperature, must be kept under control. This overview will present the importance of reducing these pro-oxidizing effects, as well as the main changes which may occur during the storage of virgin olive oil at the expense of the minor constituents that are more relevant for the olfactive and gustative characteristics and its
impact on the aroma and taste of the oil, particularly the phenolic and volatile compounds
Retention effects of oxidized polyphenols during analytical extraction of phenolic compounds of virgin olive oil
No full textThe hydrophilic extract of virgin olive oil contains several phenolic compounds such as simple phenols, lignans, and secoiridoids that have been widely studied in recent years. Interest in the hydrophilic extract has also been extended to the fraction
of oxidized phenols that form during storage as a consequence of oxidative stress. The present investigation compares the two most commonly used extraction methods, namely liquid–liquid extraction and SPE, on fresh virgin olive oil and that kept at different temperatures in the presence of oxygen to promote the formation
of oxidative products. The selective retention of these natural and oxidized phenolic compounds in relation to the extraction method was assessed. Quantification of eight identified phenolic molecules and 11 unknown peaks was performed by HPLC-DAD/MSD
Chemical, sensory, and chemiometric analysis of Italian and Spain virgin olive oils
No full textVirgin olive oil (VOO) is usually characterised by peculiar pleasant sensory notes, contributing to differentiate it from other edible oils. Sensory taste, together with the nutritional aspects, are the main reasons of the increment in the VOO consumption observed in last years. Sensory analysis is required by olive oil official regulations to classify the product.
The first aim of this work was to evaluate the inter-panel reproducibility of the sensory method by analysing by 16 samples of VOOs, produced in Italy and Spain (8 from Italy and 8 from Spain). The sensory analyses were carried out by different panels located in Italy and Spain.
The second aim of this research was the study of the correlations between sensory and chemical parameters, in particular volatile compounds were related with olfactive, and phenolic compounds with gustative notes. For this aim volatile compounds were separated, identified and quantified, starting from the oil samples, by solid phase micro-extraction and capillary gas chromatographic analysis with mass spectrometry detector (SPME/CGC-MSD). Similarly, the phenolic profile was carried out by high-performance liquid chromatography with diode array and mass spectrometry detectors (HPLC-DAD-MSD)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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