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VIRGIN OLIVE OIL SHELF LIFE: STUDY OF OIL STABILITY AT ROOM TEMPERATURE AND UNDER ACCELERATED STORAGE CONDITIONS
Abstract
Virgin olive oil stability is very high in comparison with other vegetable oils. Accelerated shelf-life tests (ASLT) using temperatures around 100 degrees C are generally employed to estimate the induction period of the oxidation reaction in a short period of time, but no satisfactory correlation has been found with the VOO shelf-life at room temperature. The main goal of this research is, therefore, to study the chemical stability and the autoxidation process of VOO in the attempt to estimate the shelf-life of this product. A good correlation between the time required to reach EU Regulation upper limits for PV, K-232 and K-270, and the temperatures of the assay, up to 60 degrees C, by a potential equation in all samples studied was found. Moreover, a similar slope was obtained; this makes feasible to establish an ASLT method at a temperature below 60 degrees C to estimate shelf-life at room temperature.
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An experimental investigation was carried out to study the influence that exposure to light has on the quality of extra virgin oil during a 12-month storage period by comparing it with the quality of extra virgin oil stored in the dark. The results showed that the oils stored in the light had significantly lower tocopherol, carotenoid and chlorophyll contents than did the same oils kept in the dark. Moreover, the oils stored in the dark mainly contained primary oxidation products, while the oils kept in the light contained secondary oxidation products as confirmed by the K
270 values which exceeded the legal limits even after purification by means of alumina. Overall, the results obtained showed that the shelf life of the oils exposed to light is shorter than that of oils kept in the dark, and that after only 2 months of exposure to light the oils examined could no longer be considered as extra virgin.
The usefulness of Artificial Neural Network Systems (ANNW) to predict the stability of vegetable oil based on chemical composition
was evaluated. The training set, comprised of a composition of major and minor components of vegetable oil as inputs and as
outputs, induction period and values of slopes for initiation and propagation, was measured by oxygen consumption. The best
predictability was achieved for oils stored at 35°C with light exposure, when the major fatty acids, chlorophylls, tocopherols,
tocotrienols, and metals were used as predictors. For oils stored at 65°C without light, a good predictability was obtained
when composition of the major fatty acids and the amounts of tocopherols and tocotrienols were used. These results suggest
that vegetable oil stability can be successfully predicted by ANNW when partial oil composition is known.
This paper presents an analysis of oxidation in olive oil TAG at different temperatures within a range of 40–60°C in darkness,
as measured by the rate of formation of hydroperoxides, their decomposition products, and sensory and chemical flavor deterioration.
At 60°C, the oxidation process was relatively fast, and all the indexes of the extent of oxidation behaved in a very similar
way. The behaviors of the rate of formation of conjugated dienes (measured as the K
232), of oxidized TAG (determined by HPLC), and of carbonyl compounds (measured as anisidine value) were very similar to that
of the PV. The induction periods (IP) of the four indexes were less than 36 h. Nevertheless, the IP for K
270 and the sum of oxidized TAG dimers and polymers were 5 d. At 50 and 40°C, the rate of formation of secondary oxidation products
was lower. Residual linolenic acid or PUFA as determined by GC showed correlation coefficients higher than 0.999 with the
Totox index at all of the assayed temperatures. The rancid recognition threshold corresponded to lower values of the oxidation
indexes at lower temperature. Moreover, at all assayed temperatures, the rancidity threshold apparently coincided with the
IP for the kinetics of 2,4-decadienal formation.
An investigation was carried out on virgin olive oils of the Gentile (Larino), Gentile (Colletorto), Coratina, and Leccino
varieties, harvested at different times, to assess their oxidation stability. The olive oils were analyzed by means of peroxide,
K232′ and K270 values at 1, 6, 12, and 18 mon of storage in green bottles, in the dark, at temperatures ranging from a mean of 6°C in winter
to 12°C in summer. A subsample was also oven-tested at 75°C and then analyzed on a weekly basis using the same oxidative parameters.
The less ripe the olives (harvested in the same area during 1 mon), the more resistant the olive oils were to forced oxidation.
The amount of total phenols in the oils was found to be directly related, even if to a low degree, to the oleuropein content
in the olives and inversely related, to the same degree, to (3,4-dihydroxyphenyl)ethanol. The latter is a derivative of oleuropein;
(3,4-dihydroxyphenyl)ethanol content increases as the olives ripen, but it is very low in fresh virgin olive oils, owing to
the hydrophilic nature of the phenolic alcohol, which goes mainly into the waste-water during processing. Among the varieties
considered, Coratina oils showed the highest resistance to forced oxidation because of their high total phenol content.
The effect of free fatty acid (FFA) content on the susceptibility to thermooxidative degeneration of vegetable oils was determined
by Rancimat analysis. A prooxidant effect of FFA was observed in all filtered oils, independently of lipidic substrate and
of its state of hydrolytic and oxidative alteration. The intensity of this effect was related to FFA concentration, but regression
analysis of the experimental data did not show a general correlation law between FFA concentration and induction time (I
t). Different results were obtained for freshly processed virgin olive oils, characterized by postpressing natural suspension-dispersion:
opposite behavior was observed of FFA content as regards oxidative stability, depending on the presence of suspended-dispersed
material. This fact is of interest because the dispersed particles play a double stabilizing effect on both oxidative and
hydrolytic degradation. These results showed that avoidance of oil filtration is highly desirable to extend olive oil’s shelf
life.
The experimentally defined oxidative alterations taking place in packaged olive oil stored in various packaging materials and storage conditions, were used as basic evidence in order to develop and support a descriptive mathematically expressed theory, and eventually to conclude on a predictive model. Hexanal was experimentally quantified for extra virgin olive oil packaged in 0.5 L glass, PET, and PVC bottles, and stored at 15 °C, 30 °C and 40 °C under fluorescent light or dark conditions for 12 months. A set of mass transport equations describing the chemical reactions occurring in the oil phase as well as the diffusion of oxygen in the oil phase and through the packaging material, was numerically solved for various combinations of temperatures, light conditions and packaging materials. In addition, the probability of the packaged olive oil not to reach the end of its shelf life during a certain time period, was estimated and proposed as a quality reduction indicator. The suggested model could be used as a tool for an accurate forecast of the quality issues for packaged olive oil.
Virgin olive oil has a high resistance to oxidative deterioration due to both a triacylglycerol composition low in polyunsaturated fatty acids and a group of phenolic antioxidants composed mainly of polyphenols and tocopherols. Polyphenols are of greater importance to virgin olive oil stability as compared with other refined oils which are eliminated or drastically reduced during the refining process.This paper covers the main aspects related to the oxidative stability of virgin olive oil during storage as well as at the high temperatures of the main processes of food preparation, i.e., frying and baking. Differences between oxidation pathways at low and high temperature are explained and the general methods for the measurement of stability are commented on. The compounds contributing to the oxidative stability of virgin olive oils are defined with special emphasis on the antioxidative activity of phenolic compounds. Finally, the variables and parameters influencing the composition of virgin olive oils before, during and after extraction are discussed.
Olive oil is the fat of choice in the Mediterranean area, where the diet has been associated with a lower incidence of coronary heart disease and certain cancers. Phenols in extra virgin olive oil are responsible for its peculiar pungent taste and for its high stability. Recent findings demonstrate that olive oil phenolics inhibit oxidation of low-density lipoproteins (the most atherogenic ones) and possess other potent biological activities that if demonstrated in vivo, could partially account for the observed healthful effects of diets that include high-quality olive oil and other foods rich in flavonoids and phenols. Keywords: Olive oil; phenols; atherosclerosis; Mediterranean diet; antioxidants; free radicals
Extra virgin olive oil is considered to be a high quality oil for health and nutrition and is widely consumed by the Mediterranean population. Presence of natural photosensitizers in olive oil may compromise its nutritional quality if stored in clear plastic or glass container under fluorescent light. In this study, the oxidative stability of commercial extra virgin olive oil (EVOO) and its chlorophyll and tocopherol stripped counterpart (SEVOO) stored at 60C in the dark and under fluorescent light (2650 lux) was evaluated. A column chromatographic procedure using silicic acid, Celite 545, activated charcoal and powdered sugar (sucrose), and eluted with hexane, provide an effective means for stripping extra virgin olive oil from its minor components. Minor components, mainly tocopherol and other phenolic compounds as well as carotenoids in SEVOO, influenced their oxidative stability in the dark. Meanwhile, natural pigments such as chlorophyll played a major role in the photooxidation of EVOO. Therefore, commercial extra virgin oil should be protected from direct light exposure in order to protect it from the oil from photooxidative deterioration.
A kinetic study of the autoxidation reaction in olive oil triacylglycerols stored in darkness at different temperatures (25, 40, 50, 60 and 75 °C), in absence of pro- and antioxidant compounds to avoid confounding effects, is described. After the induction period (IP) the decrease in the oxidizing substrate and the formation of primary oxidation products followed a pseudo-zero-order kinetic, and the calculated Ea from the Arrhenius equation for the formation of hydroperoxides was 32.1 kJ·mol−1. The formation of secondary oxidation products followed a pseudo-first-order kinetic whose rate reaction constant also increased exponentially with temperature. The first oxidation index to exceed the upper limit in the EU regulations was PV, followed by K232 and K270. The time required reaching these limits and the rancidity threshold showed a potential dependence on temperature, and therefore with accelerated storage at 75 °C, POO shelf-life in ambient conditions (25 °C) can be predicted. Finally, there was a good linear relationship between the time required to reach the rancidity threshold and the IP of the formation of the 2,4-decadienal, and hence this instrumental determination could be useful to measure sensory recognition of the rancid defect in POO.
The aim of this work was to set up a phenomenological model to predict the stability of extra virgin olive oil based on combined stability/instability indices. A screening of stability/instability indices was carried out by multivariate statistical analyses on company data for virgin olive oil. Screened indices were acidity, oleic acid content and bitter taste. The ability of these indices to predict stability was checked by measuring the following degradation parameters on 11 oil samples of different compositions planned by a fractional factorial design (FFD): peroxide value, UV spectroscopic indices, minor polar component content, oxidative status of fatty acids, antioxidant activity and sensory descriptors of aroma, taste and flavour. Experimental data were processed by multivariate statistical analyses. A combination of acidity, oleic acid content and bitter taste values was significantly able to predict oil stability expressed by the peroxide value, the K232 UV index and the oxidative status of fatty acids. Copyright © 2005 Society of Chemical Industry
Predictive microbiology can be used to determine and predict the shelf-life of perishable foods under commercial distribution conditions based on microbial growth kinetics. This paper presents general microbial growth kinetics with the Monod model and the Gompertz function. Additional models are given to describe effects of food composition (e. g.a
w) and environmental conditions (e.g. temperature, gas atmosphere) as well as their interaction on the growth kinetic parameters (lag time and specific growth rate). These models can be used to predict the time to reach a critical level under any constant conditions within the range tested. A combination of microbial kinetics with an engineering accumulation approach can be used to predict the final microbial level in a food, or the loss of shelf-life, for any known time-temperature sequence, if there is no history effect or the history effect is negligible. A time-temperature indicator, could be used for predicting the remaining shelf-life of perishable foods under any distribution condition based on microbial growth kinetics.
Oxidation is the primary cause of virgin olive oil quality deterioration. This paper presents a correlation between oxidative
stability, as determined by the Rancimat method, and some chemical components involved in the oxidation process of a set of
74 Cornicabra virgin olive oils obtained from three successive crop seasons (94/95 to 96/97). Results showed a clear influence
of total polyphenols on virgin olive oil stability, with linear regression coefficients which were similar for the three seasons
studied, and a much lower contribution of α-tocopherol and unsaturated fatty acids, mainly linoleic acid. A significant effect
dependent on the crop season was also observed.
The aim of this work was to study the changes in the lipid substrate and in the minor components and specially in the phenolic fraction of commercial virgin olive oils of Arbequina cultivar after 12 months of storage. An increase of oleic acid percentage was found in the fatty acid composition. Important losses of chlorophyll, carotenoids, and total phenol content of oils occur after the storage period. Significant decreases were observed in secoiridoid derivatives and 3,4-DHPEA-AC after the storage period, while lignans were the more stable phenolic compounds. α-tocopherol disappeared after the storage period, in all oils.
A descriptive model was applied to study the shelf life of packaged olive oil, based on 24 month simulations and for various combinations of storage conditions close to the “real-life” situations. The major factors influencing oxidation (namely light, oxygen permeability of packaging materials and temperature of storage), were combined in various case studies otherwise requiring time-consuming experiments. The time evolution of the possibility for packaged olive oil not to reach the end of its shelf life and the month, after bottling, at which this possibility becomes 70%, 50% and 30%, were presented. It was found that exposure of packaged olive oil to light in continuous or alternating patterns should be avoided since, even for a short time, it could significantly stimulate the oxidative degradation caused only by elevated temperatures and presence of oxygen. In general, all the packaging materials tested could be considered adequate for preserving the quality of olive oil under a variety of storage conditions. Plastic containers had a particularly stronger protective role when oil was stored light, while glass was the most protective material when oil was stored in the dark.
This article reports the evolution of major and minor components and oxidation indices of seven samples of virgin olive oil (VOO) which differ in their initial contents of natural antioxidants, during 21 months of storage at room temperature and in darkness. As expected, statistically significant differences in the antioxidant contents were observed, with initial concentrations ranging from 0.33 to 0.55 mmol/kg for α-tocopherol and from 1.08 to 3.88 mmol/kg for total phenols. The quality indices PV, K232 and K270 increased linearly during the storage time studied (21 months), which should make it possible to predict the shelf-life of a VOO sample by extrapolation from the results obtained during a relatively short period of storage (i.e. several weeks). K232 was the first parameter that exceeded the established upper limit for extra VOO and therefore seems to be the most relevant index for analysis and monitoring to determine the commercial category of the olive oil. The reduction of total phenolic compounds ranged from 43% to 73%, and it was remarkable that the decrease was higher in samples whose initial phenol contents were greater. Hydroxytyrosol increased linearly in most samples, whereas its complex forms decreased considerably, with the exception of two in which the hydroxytyrosol content decreased continuously or diminished after an initial increase. This fact was probably due to the low initial concentration of hydroxytyrosol secoiridoid forms: i.e. 0.32 mmol/kg for the sum of 3,4-DHPEA-EDA and 3,4-DHPEA-EA in one of these samples as compared to between 0.65 and 2.06 mmol/kg in the others. Finally, there was a slight and apparently linear fall in the α-tocopherol content of all samples, with a reduction ranging from 0.054 mmol/kg (12%) to 0.127 mmol/kg (23%), although there may be a short lag phase at the beginning of the assay.
Industries aim to ensure extra virgin olive oil (EVOO) stability especially during commercial activities up to use by end consumers. The objective of this work was to set up predictive models of EVOO stability during commercial activities. Stability was studied on five lots of a batch of Tuscan virgin olive oil to simulate different commercial activities. Chemical, physical, and sensory analyses were carried out on EVOO samples. Experimental data were processed by multivariate analyses to select significant parameters and by regression analyses to set up kinetic models. A few parameters were found to be significant: hydroxytyrosol and tyrosol contents, carotenoid absorbance at 475 and 448 nm, alpha-tocopherol content, Rancimat induction time, and K(232). It was also shown that the stability of this EVOO was not significantly influenced by different uncontrolled bottling, transport, and storage conditions in supermarkets. Empirical models were set up to predict the time to reach a reference value for K(232).
Changes in the concentration of tocopherol, monophenols, o-diphenols, squalene, and polyunsaturated fatty acids in olive oil were evaluated during 1 year at various storage conditions. Samples of two different extra virgin olive oil (EOO), produced in Calabria (Italy), were stored in dark and in colorless bottles, filled up completely or to half, in order to simulate the domestic storage conditions. The extent of oxidation or photooxidation was monitored by periodic measurements of peroxide values and the rate of degradation of alpha-tocopherol, o-diphenols, squalene, and polyunsaturated fatty acids. The quantitative analysis of the constituents has been performed by HPLC-DAD, HPLC-MS, and GC-MS. The main changes in the concentrations of the analyzed compounds were associated with the major oxygen level in the half-empty glass bottles. alpha-Tocopherol was the first molecule to be oxidized (-20% after 2 months, -92% after 12 months). Squalene and o-diphenols were protected in the first months by the presence of alpha-tocopherol, and their content decreased significantly only after 6 and 8 months, respectively, in the half-empty bottles. The concentration of polyunsaturated fatty acids remained almost constant during 8 months for all four different storage conditions; their oxidation started when the level of the antioxidants decreased.
In olive oils, relationships between oxidative stability, glyceridic composition, and antioxidant content were investigated. Lipid matrices, obtained by purification of olive and high-oleic sunflower oils, were spiked with hydroxytyrosol, alpha-tocopherol, and mixtures of them and then subjected to oxidation in a Rancimat apparatus at 100 degrees C. At the same concentration of antioxidants, induction time (IT) decreased as the unsaturation rate of the matrix increased, but only fair correlations were found with fatty acid composition. Oxidative susceptibility (OS(TAG)) was calculated as a function of the relative oxidation rate of the triacylglycerols, and a linear relationship-IT (h) = (a + b)OS(TAG)-between induction time and this parameter showed a good correlation coefficient (r > 0.990, p < 0.001). In the case of matrices with a single antioxidant, origin ordinate (a) and slope (b) can be calculated as a function of the antioxidant concentration. In matrices spiked with mixtures of hydroxytyrosol and alpha-tocopherol, a simple relationship between the coefficients a and b and the concentration of antioxidants cannot be established because additive and subtractive effects occur depending on the relative concentrations of both antioxidants. However, approximate values for these coefficients can be obtained, allowing the estimation of the oil stability. In various olive oils, an acceptable agreement was found between the IT experimentally determined and that calculated from the oil composition. These results confirmed that the Rancimat stability of olive oils mainly depends on triacylglycerol composition and concentrations of o-diphenols and alpha-tocopherol.
The aim of this study was to evaluate the influence of the extra virgin olive oil (EVOO) physical state on the kinetics of oxidative reactions. To this purpose, EVOO was stored at increasing temperatures from 3 to 60 degrees C and the oxidation was followed by measuring both primary and secondary oxidation products. Results highlighted that crystallization plays an important role in determining EVOO stability. Below the melting point, the oxidation rate was found to be higher than that expected on the basis of the Arrhenius equation. The observed deviation from the Arrhenius equation was attributed to the physicochemical changes occurring as a consequence of phase transitions. In particular, the increase in unsaturated triacylglycerol concentration and the decrease of polyphenol content in the liquid phase surrounding fat crystals were indicated as the main factors causing the deviation. By taking into account these changes it was possible to describe the temperature dependence of the oxidation rate in the entire range of temperatures considered. This model appears to be promising in the challenge to find mathematical models able to predict the stability and, hence, the shelf life of lipid-containing foods.
Virgin olive oil samples stored in the light at ambient temperature, in the dark at ambient temperature, and at low temperature in the dark for 12 months both with and without headspace were separated into recognizable patterns with stepwise linear discriminant analysis. The discrimination with variables volatile and phenolic compounds, free fatty acid (FFA), peroxide values, K232, and K270 revealed a departure of stored oil from freshness and showed significant (p < 0.01) differences between storage conditions. Virgin olive oil stored at low temperature had characteristics closest to fresh oil while oil stored in the light showed the largest departure from freshness. Parameters that exclusively and significantly (p < 0.01) discriminated storage conditions were identified as potential markers of the storage condition. In the presence of oxygen, hexanal was a marker of storage in the light, FFA was a marker for dark storage, and markers of low-temperature storage were acetic acid and pentanal. In the absence of oxygen, octane was the marker for storage in the light whereas tyrosol and hexanol were markers of virgin olive oil stored in the dark, with no marker indicative of low-temperature storage. E-2-Hexenal, K232, and K270 were identified as markers of virgin olive oil freshness.
Oxidative stability should be one of the most important quality markers of edible oils; nevertheless, it is not recognized as a legal parameter. The results reported in this study highlight the differences in the olive oil oxidation process under Rancimat accelerated conditions with respect to long-term storage at room temperature and clearly show the lack of correlation between shelf life and the Rancimat induction period. A better correlation, although not yet satisfactory, was found when the same oxidation end-point was used in both assays. The parameter K 270, a marker of secondary oxidation products, was the first index to reach the established upper legal limit under Rancimat conditions, whereas at 25 degrees C it was an index of primary oxidation products ( K 232). Furthermore, the ratio of oxidation rate at Rancimat conditions to oxidation rate at 25 degrees C was more than double for secondary oxidation products compared with primary ones. Notable differences were also observed in degradation rates of the different unsaturated fatty acids and in rates of formation of polar oxidation compounds. Moreover, under the Rancimat conditions antioxidants such as o-diphenols and alpha-tocopherol rapidly depleted, and when they had practically disappeared, there was a sharp increase in oxidation indices, such as peroxide value, and in oxidation products. At 25 degrees C, on the other hand, the depletion was much lower.
Two monovarietal extra virgin olive oils from Arbequina and Picual cultivars were subjected to heating at 180 degrees 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. Alpha-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.
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