Biosensor analysis for the kinetic study of polyphenols deterioration during the forced thermal oxidation of extra-virgin olive oil (original) (raw)
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Four samples of olive oil were oxidized under polythermal (dynamic) conditions in the cell of a normalpressure differential scanning calorimeter (DSC) and in the Metrohm Rancimat apparatus. The DSC experiments were carried out in an oxygen flow atmosphere using different linearly programmed heating rates in the range of 4-20 7C/min. Through DSC exotherms, the extrapolated onset temperatures were determined and used for the assessment of the thermal-oxidative stabilities of the samples. Using the Ozawa-Flynn-Wall method and the Arrhenius equation, the activation energies (E a ), pre-exponential factors (Z) and reaction rate constants (k) for oil oxidation under DSC conditions were calculated. The Rancimat measurements of oxidation induction times were carried out under isothermal conditions in an air atmosphere at temperatures from 100 to 140 7C with intervals of 10 7C. Using the Arrhenius-type correlation between the inverse of the induction times and the absolute temperature of the measurements, E a , Z, and k for oil oxidation under Rancimat conditions were calculated. The primary kinetic parameters derived from both methods were qualitatively consistent and they help to evaluate the oxidative stabilities of oils at increased temperatures.
Thermal and chemical evaluation of naturally auto-oxidised virgin olive oils: a correlation study
Journal of the Science of Food and Agriculture, 2013
BACKGROUND: The nature of the relationship between differential scanning calorimetry thermal properties and the oxidation and hydrolysis compounds formed during a real auto-oxidation process in virgin olive oils has not been evaluated so far, as these samples are difficult to find. In this work, 21 samples of virgin olive oil, stored under ideal conditions since their years of production (production range 1991-2005) to develop the natural auto-oxidation process, were analysed in order to evaluate this relationship.
Evaluation of phenolic compound degradation in virgin olive oil during storage and heating
Journal of food and nutrition research
Virgin olive oil is oil with a high biological value, due to its polyphenol content. Virgin olive oils were subjected to heat treatment simulating common domestic processing, including boiling, frying and storage. These processes can affect the phenolic compounds content of oils to a certain degree, depending on each one treatment. Thermal oxidation of oils at 180 °C (frying) caused a significant decrease (p < 0.005) in hydroxytyrosol derivatives (60% reduction after 30 min and 90% reduction after 60 min) and, to a lower degree, in tyrosol derivatives. No changes were observed in the content of lignans (p > 0.005). On the other hand, thermal oxidation of oils at 100 °C (boiling) for 2 h caused a decrease by less than 20% in all classes of phenolic compounds. The reduction of phenolic compounds during storage under environmental conditions was correlated with the peroxide value. When the peroxide value did not exceed the level of 20 meq.kg -1 , as was recorded for low linoleic acid oils and low oxygen availability at the bottles' headspace, a degree of reduction of approximately 30% in hydroxytyrosol derivatives and 10% in tyrosol derivatives was observed, while lignans remained unchanged. Finally, during both heating and storage under environmental conditions, the evolution of oxidized phenolic compounds was observed. The structures of these oxidized products were confirmed by HPLC-MS.
Effects of polyphenol enzymatic-oxidation on the oxidative stability of virgin olive oil
Food Research International, 2013
Activity of laccase from Trametes versicolor was assayed directly in virgin olive oil (VOO) samples. Laccase-treated oils led to the formation of insoluble precipitate and to significant qualitative and quantitative changes of their polyphenol composition. At the extreme condition of oil/laccase incubation (60°C for 1 h) depletion of oleuropein and o-diphenols was estimated up to 90% and 77%, respectively. Results of Rancimat test (130°C and 20 L h −1 ) and oven-test (60°C) evidenced controversial effects on the VOO oxidative stability. At high temperature, induction time of laccase-treated oils was found to be similar or even lower than the one recorded in the chemically-dephenolized oils; therefore, enzyme treatment induced a pro-oxidant effect. Conversely, during the storage at 60°C, all the laccase-treated oils showed an improvement on their oxidative stability compared to the fresh oil counterparts. Experimental data suggest that polyphenol enzymatic-oxidation generated oil by-products which manifest higher radical scavenging or conversely pro-oxidant property, depending on the treatment temperature and storage conditions of the oils.
Electrochemical sensor and biosensor for polyphenols detection in olive oils
Food Chemistry, 2000
The aim of the work was to compare dierent techniques, in evaluating the phenolic content of an extra-virgin olive oil with varying storage time and storage conditions. A disposable screen-printed sensor (SPE) was coupled with dierential pulse voltammetry (DPV) to determine the phenolic fractions after extraction with a glycine buer; DPV parameters were chosen in order to study the oxidation peak of oleuropein, which was used as reference compound. A calibration curve of oleuropein was performed in glycine buer 10 mM, pH=2, NaCl 10 mM (D.L.=0.25 ppm oleuropein, RSD=7%). Moreover a tyrosinase based biosensor operating in organic solvent (hexane) was also assembled, using an amperometric oxygen probe as transducer. The calibration curves were realised using¯ow injection analysis (FIA) with phenol as the substrate (D.L.=4.0 ppm phenol, RSD=2%). Both of these methods are easy to operate, require no extraction (biosensor) or rapid extraction procedure (SPE), and the analysis time is short (min). The results obtained with these two innovative procedures were compared with a classical spectrophotometric assay using Folin±Ciocalteau reagent and HPLC analysis. Other extra-virgin olive oil quality parameters were investigated using classical methods in order to better de®ne the alteration process and results are reported. #
OCL, 2016
The aim of the present investigation is to compare the chemical characterization of four monovarietal virgin olive oils obtained from fruits of olive trees grown in Morocco (Picholine, Picual, Arebiquine, Koroneiki) with kinetic parameters of oxidation based on Rancimat measurements and finally to assess the oxidative stabilities. The examined oils from different varieties showed a chemical composition within the regulatory limits. Rancimat measurements of induction times were carried out under isothermal conditions in an air atmosphere at temperatures from 373 to 423 K with intervals of 10 K. Using the Arrhenius-type correlation between the inverse induction times and the absolute temperature of the measurements, E a , Z, and k values for oil oxidation under Rancimat conditions were calculated. The primary kinetic parameters derived from this method were qualitatively consistent and help to evaluate the oxidative stabilities of oils at increased temperatures. Keywords: Chemical composition / kinetics of oxidation / olive oils / oxidative stability / rancimat Résumé-Caractérisation chimique et la détermination des paramètres cinétiques sous le test Rancimat de quatre huiles d'olive vierges monovariétales cultivées au Maroc. Le but de ce travail est d'abord de comparer les caractéristiques chimiques de quatre huiles d'olive vierges monovariétales obtenues à partir de fruits d'oliviers cultivés au Maroc (Picholine, Picual, Arbequina, Koroneiki) à l'aide des paramètres cinétiques d'oxydation basés sur des mesures Rancimat et ensuite évaluer leur stabilité à l'oxydation. Ainsi les huiles examinées de différentes variétés ont montré une composition chimique dans les limites réglementaires. Les mesures de Rancimat des temps d'induction ont été effectuées dans des conditions isothermiques, dans une atmosphère d'air à des températures de 373 à 423 K. En utilisant la corrélation de type Arrhenius entre les temps d'induction inverse et de la température absolue des mesures, E a , Z et les valeurs de k pour l'oxydation de l'huile dans les conditions de Rancimat ont été calculées. Les paramètres cinétiques primaires dérivés de cette méthode étaient qualitativement cohérents et aident à évaluer la stabilité d'oxydation des huiles à des températures élevées.
European Journal of Lipid Science and Technology, 2013
A mild sample handling method able to minimize polyphenol degradation due to endogenous enzymes during the sample preparation permitted the assessment of polyphenol decay in the oily fraction of the olives during their storage before processing. During 7 days of storage at 15°C, the concentration of polyphenols in the olives was stable in vegetation water, whereas in the oily fraction of the fruits it remained almost constant in the first 3 days and then decreased rapidly. The polyphenol decay of the oily fraction of the stored olives can be attributed to the oxidoreductase enzymes of the fruit as well as those produced by the microbiota grown in the carposphere during storage. The activity of phenoloxidase in the olive pulp decreased drastically in the first 2 days of storage, and then decreased gradually, whereas peroxidase activity showed a gradual reduction throughout the entire storage period. The microbiological analysis showed a rapid increase of bacteria and yeast number during the first 4 days, then the values leveled out during the storage period. Phenoloxidase activity of microbic origin was low during the first 3 days then increased rapidly, whereas peroxidase activity increased during the first 3 days then leveled out to the same values for the duration of the storage time. Practical applications: The mild sample handling method of extraction studied was able to minimize olive oil polyphenol degradation during the sample preparation due to the endogenous enzymes of the olive fruits. The use of this method allows for the improvement of virgin olive oil quality, through the assessment of polyphenol concentration decay during all the stages of olive oil production, including that of fruit storage before processing.
Fluorescence spectroscopy for monitoring deterioration of extra virgin olive oil during heating
Analytical and Bioanalytical Chemistry, 2005
The potential of fluorescence spectroscopy for characterizing the deterioration of extra virgin olive oil (EVOO) during heating was investigated. Two commercial EVOO were analysed by HPLC to determine changes in EVOO vitamin E and polyphenols as a result of heating at 170°C for 3 h. This thermal oxidation of EVOO caused an exponential decrease in hydroxytyrosol and vitamin E (R 2=0.90 and 0.93, respectively) whereas the tyrosol content was relatively stable. At the same time, amounts of preformed hydroperoxides (ROOH), analysed by an indirect colorimetric method, decreased exponentially during the heating process (R 2=0.94), as a result of their degradation into secondary peroxidation products. Fluorescence excitation spectra with emission at 330 and 450 nm were recorded to monitor polyphenols and vitamin E evolution and ROOH degradation, respectively. Partial least-squares calibration models were built to predict these indicators of EVOO quality from oil fluorescence spectra. A global approach was then proposed to monitor the heat charge from the overall fluorescence fingerprint. Different data pretreatment methods were tested. This study indicates that fluorescence spectroscopy is a promising, rapid, and cost-effective approach for evaluating the quality of heat-treated EVOO, and is an alternative to time-consuming conventional analyses. In future work, calibration models will be developed using a wide range of EVOO samples.