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1.
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.  相似文献   

2.
Olive stoning during the virgin olive oil (VOO) mechanical extraction process was studied to show the effect on the phenolic and volatile composition of the oil. To study the impact of the constitutive parts of the fruit in the composition of olive pastes during processing, the phenolic compounds and several enzymatic activities such as polyphenoloxidase (PPO), peroxidase (POD), and lipoxygenase (LPO) of the olive pulp, stone, and seed were also studied. The olive pulp showed large amounts of oleuropein, demethyloleuropein, and lignans, while the contribution of the stone and the seed in the overall phenolic composition of the fruit was very low. The occurrence of crushed stone in the pastes, during malaxation, increased the peroxidase activity in the pastes, reducing the phenolic concentration in VOO and, at the same time, modifying the composition of volatile compounds produced by the lipoxygenase pathway. The oil obtained from stoned olive pastes contained higher amounts of secoiridoid derivatives such as the dialdehydic forms of elenolic acid linked to (3,4-dihydroxyphenyl)ethanol and (p-hydroxyphenyl)ethanol (3,4-DHPEA-EDA and p-HPEA-EDA, respectively) and the isomer of the oleuropein aglycon (3,4-DHPEA-EA) and, at the same time, did not show significant variations of lignans. The stoning process modified the volatile profile of VOO by increasing the C6 unsaturated aldehydes that are strictly related to the cut-grass sensory notes of the oil.  相似文献   

3.
Virgin olive oil is valued for its flavor, but unacceptable off-flavors may develop on storage in food products containing this oil due to oxidation. The oxidative stability of oil-in-water emulsions containing bovine serum albumin (BSA) and virgin olive oil phenolic compounds was studied. Four oil-in-water emulsions with and without BSA and phenols isolated from virgin olive oil were prepared. These model systems were stored at 60 degrees C to speed up lipid oxidation. Primary and secondary oxidation products were monitored every three days. Peroxide values and conjugated diene contents were determined as measures of the primary oxidation products. p-Anisidine values and volatile compounds were determined as measures of the secondary oxidation products. This latter determination was carried out by headspace solid-phase microextraction coupled with gas chromatography. Although olive oil phenolic compounds and BSA contributed some antioxidant activity when present as individual additives, the combination of BSA with phenols in an emulsion showed 58-127% synergy, depending on which analytical method was used in the calculation. The emulsion containing phenolic compounds and BSA showed a low level of deterioration after 45 days of storage at 60 degrees C.  相似文献   

4.
Virgin olive oils produced at wide ranges of malaxation temperatures (15, 30, 45, and 60 degrees C) and times (30, 60, 90, and 120 min) in a complete factorial experimental design were discriminated with stepwise linear discriminant analysis (SLDA) revealing differences with processing conditions. Virgin olive oils produced at 15 and 60 degrees C for 30 min showed the most significant (p < 0.01) differences. Discrimination was based upon volatile and phenolic compounds detected in olive oils, peroxide value (PV), free fatty acids (FFA), ultraviolet (UV) absorbances, and oil yield. There were different discriminating variables for processing conditions illustrating the dependence of virgin olive oil quality on malaxation time and temperature. Volatile compounds were the dominant discriminating variables. Common oxidation indicators of olive oil (PV, K232, and K270) were not among the variables that significantly (p < 0.01) changed with malaxation time and temperature. Variables that discriminated both malaxation time and temperature were hexanal, 3,4-dihydroxyphenyl ethyl alcohol-decarboxymethyl elenolic acid dialdehyde (3,4-DHPEA-DEDA) and FFA, whereas 1-penten-3-ol, E-2-hexenal, octane, tyrosol, and vanillic acid significantly (p < 0.01) changed with temperature only and Z-2-penten-1-ol, (+)-acetoxypinoresinol, and oil yield changed with time only. Virgin olive oil quality was significantly influenced by malaxation temperature, whereas oil yield discriminated malaxation time. This study demonstrates the two modes of hexanal formation: enzymatic and nonenzymatic during virgin olive oil extraction.  相似文献   

5.
Bitterness and pungency, sensory quality attributes of virgin olive oil, are related to the presence of phenolic compounds. Fast and reliable alternatives for the evaluation of sensory attributes and phenolic content are desirable, as sensory and traditional analytical methods are time-consuming and expensive. In this study, two amperometric enzyme-based biosensors (employing tyrosinase or peroxidase) for rapid measurement of polar phenolics of olive oil were tested. The biosensor was constructed using disposable screen-printed carbon electrodes with the enzyme as biorecognition element. The sensor was coupled with a simple extraction procedure and optimized for use in flow injection analysis. The performance of the biosensor was assessed by measuring a set of virgin olive oils and comparing the results with data obtained by the reference HPLC method and sensory scores. The correlations between the tyrosinase- and peroxidase-based biosensors and phenolic content in the samples were high (r = 0.82 and 0.87, respectively), which, together with a good repeatability (rsd = 6%), suggests that these biosensors may represent a promising tool in the analysis of the total content of phenolics in virgin olive oils. The correlation with sensory quality attributes of virgin olive oil was lower, which illustrates the complexity of sensory perception. The two biosensors possessed different specificities toward different groups of phenolics, affecting bitterness and pungency prediction. The peroxidase-based biosensor showed a significant correlation (r = 0.66) with pungency.  相似文献   

6.
The phenolic fraction of virgin olive oil influences both its quality and oxidative stability. One of the principal threats of the quality of olive fruit is the olive fly ( Bactrocera oleae) as it alters the chemical composition. The attack of this olive pest has been studied in order to evaluate its influence on the quality of virgin olive oil (free acidity, peroxide value, fatty acid composition, water content, oxidative stability, phenols, and antioxidant power of phenolic fraction). The study was performed using several virgin olive oils obtained from olives with different degrees of fly infestation. They were acquired in different Italian industrial mills from the Abruzzo region. Qualitative and quantitative analyses of phenolic profiles were performed by capillary electrophoresis-diode array detection, and electrochemical evaluation of the antioxidant power of the phenolic fraction was also carried out. These analyses demonstrated that the degree of fly attack was positively correlated with free acidity ( r = 0.77, p < 0.05) and oxidized products ( r = 0.58, p < 0.05), and negatively related to the oxidative stability index ( r = -0.54, p < 0.05) and phenolic content ( r = -0.50, p < 0.05), mainly with secoiridoid compounds. However, it has been confirmed that the phenolic fraction of olive oil depends on several parameters and that a clear correlation does not exist between the percentages of fly attack and phenolic content.  相似文献   

7.
The operative conditions of malaxation such as temperature and time of exposure of olive pastes to air contact (TEOPAC) affect volatile and phenolic composition of virgin olive oil (VOO) and, as a consequence, its sensory and healthy qualities. In this paper, optimal temperature and TEOPAC during malaxation were studied, in lab scale, in two Italian cultivars using phenolic compounds, volatile composition, and sensory analysis of VOO as markers. The optimal temperature and TEOPAC, selected by response surface modeling,were cultivar-dependent being 30 min of TEOPAC at the lowest temperature investigated (22 degrees C) and 0 min of TEOPAC at 26 degrees C for Frantoio and Moraiolo cultivars, respectively.  相似文献   

8.
This work studies the changes in the quality indices standardized by the European Union, together with the evolution of the oxidative stability and sterols, polyphenols, alpha-tocopherol, pigments, and fatty acids contents throughout the storage of Picual and Hojiblanca olive cultivar "extra" virgin olive oils at 2 degrees C + darkness and 30 degrees C + illumination. Only two quality indices (K(270) and sensory evaluation) indicate the loss of the extra quality of the oil during storage, and there is an excellent correlation between initial stability and the time to reach the limit of K(270) > 0.25 (after which the oil quality is no longer of "extra" quality). This time can be predicted with an error of <10%, which is of great commercial interest and previously unknown. Also unknown until now is that the changes in polyphenols, pigments, and alpha-tocopherol with storage time follow first-order kinetics.  相似文献   

9.
Capillary electrophoresis (CE) can be effectively used as a fast screening tool to obtain qualitative and semiquantitative information about simple and complex phenolic compounds of extra virgin olive oil. Three simple phenols (tyrosol, hydroxytyrosol, and vanillic acid), a secoiridoid derivative (deacetoxy oleuropein aglycon), and two lignans (pinoresinol and acetoxypinoresinol) were detected as the main compounds in extra virgin olive oils by high-performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE). Spectrophotometric indices, radical scavenging activity, and oxidative stability of extra virgin olive oil samples obtained from olives hand-picked at different ripening degrees were statistically correlated with the CZE and HPLC quantification. The concentration of phenols in extra virgin olive oil decreased with ripeness of olive fruits. The high correlations found between CZE and the other analytical results indicate that CE can be applied as a rapid and reliable tool to routinely determine phenolic compounds in extra virgin olive oils.  相似文献   

10.
This study investigated the effect of both the degree of ripening of the olive fruit and irrigation management-rain-fed, two different regulated deficit irrigations (RDI), the method proposed by the Food and Agriculture Organization of the United Nations (known as FAO), and 125 FAO (125% FAO)-on the phenolic and volatile composition of Cornicabra virgin olive oils obtained during two crop seasons. Secoiridoid phenolic derivatives greatly decreased upon increase of both irrigation and ripening, for example, the 3,4-DHPEA-EDA content decreased from 770 to 450 mg/kg through fruit ripening under rain-fed conditions and from 676 to 388 mg/kg from rain-fed conditions to FAO irrigation treatment (at a ripeness index of approximately 4). Moreover, secoiridoid derivatives of hydroxytyrosol decreased more than those of tyrosol. The levels of major volatile components decreased in the course of ripening but were higher in irrigated olive oils: for example, the E-2-hexenal content ranged between 4.2 and 2.6 mg/kg (expressed as 4-methyl-2-pentanol) over fruit maturation under rain-fed conditions and between 8.0 and 3.5 mg/kg under FAO scheduling. It is important to note that where water was applied only from the beginning of August (RDI-2), when oil begins to accumulate in the fruit, the resulting virgin olive oil presented a phenol and volatile profile similar to those of the FAO and 125 FAO methods, but with a considerable reduction in the amount of water supplied to the olive orchard.  相似文献   

11.
The sensory and health properties of virgin olive oil (VOO) are highly related to its volatile and phenolic composition. Oxygen control in the pastes during malaxation may be a new technological parameter to regulate enzymatic activities, such as polyphenoloxidase, peroxidase, and lipoxygenase, which affect the phenolic and volatile composition of VOO. In this work, we monitored CO2 and O2 concentrations during industrial-scale olive paste malaxation with various initial O2 concentrations within the malaxer headspace. Results show that the O2 concentration in the malaxer headspace did not affect CO2 production during processing, whereas a strong influence was observed on the changes of the phenolic composition of olive pastes and VOOs, with high correlation coefficient for the total phenols (R = 0.94), especially for oleuropein and demethyloleuropein derivatives (R = 0.81). In contrast, aroma production during malaxation was minimally affected by the O2 concentration in the malaxer headspace.  相似文献   

12.
Detection of rancid defect in virgin olive oil by the electronic nose   总被引：1，自引：0，他引：1  
A sensor array of 32 conducting polymer sensors has been used to detect the rancid defect in virgin olive oils. A training set, composed of admixtures of a Portuguese virgin olive oil with different percentages (0-100%) of a rancid standard oil, was used for the selection of the best sensors classifying correctly the samples. Information on volatile compounds responsible for rancidity and the sensory evaluation of samples by assessors were used for explaining the mathematical selection of sensors. A tentative calibration, using unsupervised procedures (PCA and MDS) and a nonlinear regression, was carried out, with the training set, and later confirmed with a test set with which rancid commercial samples of different varieties were used to spike a Greek extra virgin olive oil at low levels of rancidity (0.5-6%).  相似文献   

13.
The effect of O 2 concentration on oil volatile compounds synthesized during the process to obtain virgin olive oil (VOO) was established. The study was carried out either on the whole process or within the main steps (milling and malaxation) of this process with two olive cultivars, Picual and Arbequina, at two ripening stages. Data show that O 2 control during milling has a negative impact on VOO volatile synthesis. This effect seems to depend on cultivar and on the ripening stage in cultivar Picual. Because most VOO volatiles are synthesized during olive fruit crushing at the milling step, O 2 control during malaxation seems to affect just slightly the volatile synthesis. The highest effect was observed when control of O 2 concentration was performed over the whole process. In this case, the content of volatile compounds of oils obtained from both cultivars and ripening stages showed quite similar trends.  相似文献   

14.
Besides affecting the oil's sensorial characteristics, the presence of herbs and spices has an impact on the nutritional value of the flavored oils. The aim of the study was to develop a new product based on the phenol-enrichment of a virgin olive oil with both its own phenolic compounds (secoiridoid derivatives) plus additional complementary phenols from thyme (flavonoids). We studied the effect of the addition of phenolic extracts (olive cake and thyme) on phenolic composition, oxidative stability, antioxidant activity, and bitter sensory attribute of olive oils. Results showed that flavonoids from thyme appeared to have higher transference ratios (average 89.7%) from the phenolic extract to oil, whereas secoiridoids from olive presented lower transference ratios (average 35.3%). The bitter sensory attribute of the phenol-enriched oils diminished with an increase of the concentration of phenols from thyme, which might denote an improvement in the consumer acceptance.  相似文献   

15.
The initial stability of virgin olive oil depends on various factors, among which are the variety and the degree of fruit ripeness. The former, which genetically determines the composition of the olive and its oil, also marks, to some extent, its stability. However, oil stability changes as the olive ripens, so it is obvious that the degree of ripeness is an important factor. The oils were obtained by the Abencor system. Acidity, peroxide index, UV absorption at 232 and 270 nm, sensory analysis, fatty acid composition, tocopherols, phenolic compounds, orthodiphenolic compounds, sterols, pigments, and oxidative stability were determined, and the results were analyzed statistically. During ripening there was a decrease in all of the parameters studied except linoleic acid, Delta-5-avenasterol, and oil content, which increased. Virgin oils showed very good correlation between stability and the concentrations of total phenols, o-diphenols, tocopherols, chlorophyll pigments and carotenoids, linoleic and linolenic acids, total sterols, beta-sitosterol, and Delta-5-avenasterol.  相似文献   

16.
Wheat germ is susceptible to oxidation due to its high content of unsaturated oil. Volatile compounds in stored wheat germ were evaluated using dynamic headspace gas chromatography (HS-GC) and sensory analysis. Preliminary comparisons were also made between freshly prepared wheat germ and wheat germ subjected to microwave heating at 45 and 55 degrees C prior to storage at room temperature. The progress of oxidation was followed in untreated wheat germ for 4 weeks and in heat-treated wheat germ for 7 weeks by HS-GC and sensory evaluation. Significant (p < 0.05) changes in rancid odor and flavor were observed in the untreated wheat germ after 3 weeks, whereas no corresponding difference was observed in the microwave-heated wheat germ after 7 weeks of storage. Identification of a total of 36 volatile compounds was performed according to their mass spectra and Kovats indices. The major volatiles were hexanal, alpha-pinene, 1-hexanol, and 3-carene. In addition to analysis of a short period of storage, 30 volatile compounds were identified from the headspace of wheat germ stored for >1 year.  相似文献   

17.
The activity of olive microbiota during the oil extraction process could be a critical point for virgin olive oil quality. With the aim to evaluate the role of microbiological activity during the virgin olive oil extraction process, just before oil extraction freshly collected healthy olive fruits were immersed in contaminated water from an olive mill washing tank. The oils extracted were then compared with control samples from the same batch of hand-picked olives. The presence of lactic and enteric bacteria, fungi and Pseudomonas on the surface of olives was proved to be much higher in washed than in control olives, with increments in cfu/g between 2 and 3 orders of magnitude. The biogenesis of volatile compounds and the extraction of olive polyphenols and pigments were significantly influenced by the microbiological profile of olives even without any previous storage. In most cases the effect of olive microbiota on oil characteristics was greater than the effect exerted by malaxation time and temperature. Oils from microbiologically contaminated olives showed lower amounts of C5 volatiles and higher levels of C6 volatiles from the lipoxygenase pathway and some fermentation products. On the other hand, a decrease of chlorophylls, pheophytins, xanthophylls and the ratio chlorophyll/pheophytin was observed in these oils. Likewise, the microbiological activity during oil extraction led to significantly lower amounts of polyphenols, in particular of oleuropein derivatives. These differences in olive oil chemical composition were reflected in oil sensory characteristics by the decrease of the green and bitter attributes and by the modification of the oil color chromatic ordinates.  相似文献   

18.
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19.
Enzymatic extracts from olive pulp (Olea europea L.) were used to characterize lipoxygenase (LOX) activity in order to determine its role in the biogenesis of the volatile compounds that influence the aroma of extra virgin olive oil. The LOX activity was tested spectrophotometrically at an optimal pH of 6.0 in three olive cultivars, Ascolana Tenera, Kalamata, and FS17. The trend of the LOX activity was determined as a function of pH and temperature; the kinetic constants of the enzyme were also determined. The highest LOX activity was observed in the FS17 fruit, which had the highest concentrations of C(5) and C(6) compounds (aldehydes, alcohols, and ketones), followed by Kalamata and Ascolana T., respectively. Given the direct relationship between enzymatic activity and the quantity of aromas measured in the fruit, it is hypothesized that olive LOX is involved in the formation of C(5) and C(6) volatile compounds. To study the mechanism of the movement of the aromas from the fruit to the oil, which was obtained by simple mechanical extraction, the headspace of the oil for each cultivar was analyzed as well as the aromatic composition in order to compare it with the aromas of the fruit.  相似文献   

20.
The effects of UV radiation on the chemical and sensory characteristics of virgin olive oils (cv. Arbequina and Picual) were assessed. Even small doses of UV radiation induced oxidation of the virgin olive oil samples. Total phenols and fatty acids contents decreased during the process as well as the intensity of the bitter and fruity sensory attributes, while the intensity of the rancid sensory attribute notably increased. Acetaldehyde, 2-butenal, 2-pentenal, octane, octanal, hexanal, nonanal, and 2-decenal were the volatile compounds most affected, showing an important increase during the irradiation process. Nonanal, hexanal, and pentanal showed high correlation with the rancid sensory attribute (90%, 86%, and 86%, respectively). 2-Decenal and nonanal concentrations allowed us to predict the alteration level of the samples by mean of multiple Ridge regression.  相似文献   

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