A spectroscopic and chemometric study of virgin olive oils subjected to thermal stress (original) (raw)
Related papers
Journal of Chemistry
The use of olive oil with cooking purposes, as final seasoning or within cooked foods is increasing worldwide due to its numerous nutritional and health benefits. These attributes are mainly determined by olive oil chemical composition, which can be altered after thermal processing, oxidation processes, or incorrect practices. For this reason, and due to the numerous factors which have influence in olive oil quality, the correct chemical characterization is highly relevant. In this study, fatty acid composition of four extra virgin olive oil (EVOO) varieties was studied. The major fatty acid (FA) determined was oleic acid (77.1% on average), followed by palmitic (11.5% on average). In addition, thermal oxidation behaviour of the four EVOO samples was studied as an indicator of their quality and stability during thermal processing. This was performed through differential scanning calorimetry (DSC) from a temperature of 40°C at six different heating rates in the range of 0.5–10°C min−...
Food Chemistry, 2011
With the aim to characterise the antioxidant properties of different extra-virgin olive oils and to understand in more detail the mechanisms of oil degradation, we have made an experimental study on thermal induced oxidative processes of extra-virgin olive oils by using different techniques: Fourier Transform Infrared (FTIR) spectroscopy, rheology and time-resolved luminescence. The oxidation process was followed at three different heating temperatures (30, 60 and 90°C) as a function of time up to 35 days. Thermal treatment induced changes in the FTIR spectra in the wavenumbers region 3100-3600 cm À1 : in particular, the absorption profiles show an initial formation of hydroperoxides and a subsequent increase of alcohols and secondary oxidation products. In agreement with the FTIR data, rheology measurements show that after thermal treatment all examined samples exhibit an increase in the viscosity values with respect to pristine ones, indicating that the heat treatment induces the formation of polar molecules with propensity to form hydrogen bonds, which has as a consequence a viscosity increase. Finally, a lifetime increase of luminescence of chlorophyll is observed in agreement with the viscosity rise. Indeed, the viscosity increase reduces the frequency of collisions between the chromophore and its environment, consequently lowering the non-radiative contribution to the luminescence decay.
Journal of Taibah University for Science, 2015
This paper presents the influence of heating on the content of saturated and unsaturated fatty acids and tocopherols of extra virgin and refined olive oil as well as some parameters describing the oxidative states of these oils. The results show that heat treatment causes a decrease in the nutritional quality of the two types of olive oil. The content of unsaturated fatty acids decreased significantly (p < 0.05) from 87.4% to 84.5% for refined olive oil, while no change was found for extra virgin olive oil. The content of saturated fatty acid did not change substantially for either type of oil. The heat treatment also caused a decrease in the tocopherol content that was more evident for the refined olive oil. This heat treatment results in an increase in free fatty acids that was more pronounced for refined olive oil. A similar result was found for the peroxide value.
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.
Journal of Near Infrared Spectroscopy, 2008
Virgin olive oil quality is the result of complex interactions between olive variety, environment and cultivar practice. Evaluation of its quality is based on chemical and sensory analyses (ECC Regulation) that are time-consuming, expensive and destructive of the sample. Spectroscopic techniques present significant advantages in terms of speed and cost of analysis per sample. Italian extra virgin olive oils from Lombardy, Tuscany and Calabria were analysed by conventional analytical and spectroscopic methods. The sample set was composed of 60 single-cultivar (Casaliva, Leccino and Frantoio) extra virgin olive oils (monovarietal extra virgin olive oils) and 59 extra virgin olive oils produced from a mixture of cultivars from each geographical area (industrial extra virgin olive oils). Free acid content, peroxide value and spectrophotometric indices ( K232, K270 and Δ K) were measured. Olive oils were also analysed by near infrared (NIR) and mid-infrared (MIR) spectroscopy in transmis...
Journal of the American Oil Chemists' Society, 1997
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.
How Heating Affects Extra Virgin Olive Oil Quality Indexes and Chemical Composition
Journal of Agricultural and Food Chemistry, 2007
Two monovarietal extra virgin olive oils from Arbequina and Picual cultivars were subjected to heating at 180°C for 36 h. Oxidation progress was monitored by measuring oil quality changes (peroxide value and conjugated dienes and trienes), fatty acid composition, and minor compound content. Tocopherols and polyphenols were the most affected by the thermal treatment and showed the highest degradation rate although their behavior was different for each cultivar. R-Tocopherol loss was more important in Arbequina oil whereas, total phenol content loss was greater in Picual oil. The later showed an important decrease in hydroxytyrosol (3,4-DHPEA) and its secoiridoid derivatives (3,4-DHPEA-EDA and 3,4-DHPEA-EA), while lignans decrease was lesser. For Arbequina oil these compounds remained stable, and a lowering tendency was observed for tyrosol (p-HPEA) and its derivatives (p-HPEA-EDA and p-HPEA-EA). In general, flavone content showed a decrease during heating, being higher for Arbequina oil. On the other hand, oleic acid, sterols, squalene, and triterpenic alcohols (erythrodiol and uvaol) and acids (oleanolic and maslinic) were quite constant, exhibiting a high stability against oxidation. From these results, we can conclude that despite the heating conditions, VOO maintained most of its minor compounds and, therefore, most of its nutritional properties.
2012
Evoo bottles stored at room temperature, which can develop high levels of oxidation leading to undesirable flavour. Thus, new, simple and fast methods are needed for the evaluation of oxidative status of Evoo, avoiding expensive and time consuming techniques and assuring correct classification among legally defined commercial categories 4. Differential scanning calorimetry DSC is a well known thermoanalytical technique that is used in several applications in the field of vegetable oils 5, 6. In recent years, several publications have emerged on the use of DSC for the assessment of Evoo quality 7 9. These have studied the cooling and heating thermal properties and established the composition of Evoo in terms of triacylglycerols, fatty acids and minor components 10, 11 , also using statistical approaches 12, 13. DSC was also found to be a valuable tool for assessing the oxidative deterioration of vegetable oils 14. Its application to evaluate the degree of thermo-oxidation after conventional heating has been reported for Evoo 15 as well as Abstract: Three extra virgin olive oils having different fatty acid compositions and total phenol contents were submitted to an accelerated storage test at 60 for up to 21 weeks. Their oxidative status, evaluated by peroxide values and total phenolic content, was related to differential scanning calorimetry cooling profi les and thermal properties. Changes in crystallization profi les were consistent starting from 12 weeks for the two oil samples (B and C) that had a higher content of linoleic acid and medium/low amounts of phenols, respectively, whereas they became detectable at the end of the test for the remaining oil (sample A). Decrease of crystallization enthalpy and shift of transition towards lower temperature were also evident at 4 weeks of storage for samples B and C, whereas the same changes in the transition profi le were noticeable at 12 weeks for sample A. Differential scanning calorimetry appears to be suitable for the discrimination of oxidative status of extra virgin olive oils with widely different fatty acid composition.
Grasas y Aceites, 2014
Fourier transform infrared (FTIR) spectroscopy has been proposed to study the degradation of virgin olive oils (VOO) in samples undergoing thermoxidation. The polar and nonpolar fractions of oxidized oils have been analyzed by FTIR to provide further information on the minor spectral changes taking place during thermoxidation. This information assists in the interpretation of the spectra of the samples. For this purpose polar and nonpolar fractions of 47 VOO samples thermoxidized (190 °C) in a fryer were analyzed by FTIR. The time-course change of the band area assigned to single cis double bonds was explained by their correlation with the decrease in oleic acid (adjusted-R 2 =0.93). The bands assigned to the hydroxyl groups and the first overtone of ester groups was better studied in the spectra collected for the polar and nonpolar fractions, respectively. The bands assigned to peroxide, epoxy, tertiary alcohols and fatty acids were clearly observed in the spectra of the polar fraction while they are not noticeable in the spectra of the oils.
Varietal discrimination of extra virgin olive oils by near and mid infrared spectroscopy
Food Research International, 2010
The use of near and mid infrared spectroscopy, combined with chemometric analysis, was explored as a tool to classify samples of Italian extra virgin olive oil on the basis of the cultivar.A total of 82 monovarietal samples (‘Casaliva’, ‘Leccino’ and ‘Frantoio’) of extra virgin olive oils were analysed. Several variables were measured: the free acidity, the peroxide value, spectrophotometric indices,