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1.
Solid phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS) of the headspace composition of two sunflower oil samples was carried out; both samples were taken from the same original oil, stored for a prolonged time (112 months) in closed containers at room temperature under different air/oil volume ratios. Great differences in the headspace compositions of both samples were found due to the different oxidation levels reached. One of the most significant findings is that both contain monocyclic and light polycyclic aromatic hydrocarbons, the proportions of which are in line with the oxidation level of the sample. The determination of polycyclic aromatic compounds in the oil liquid matrix of both oil samples, carried out by means of a classical scheme of isolation, cleanup, separation, and quantification, showed that the concentrations of these compounds in the oil liquid phase also follow the oxidation degree reached by each sample, proving that this oxidation process at room temperature leads to the formation of these compounds.  相似文献   

2.
Mixtures of either sunflower oil or thermodegraded sunflower oil and a standard meal were submitted to an in vitro digestion model. The same experiment was carried out with fluid deep-frying fat and thermodegraded fluid deep-frying fat. The thermodegradation of the oil and fat was provoked by submitting them to 190 degrees C with aeration in a convection oven, and the presence in the headspace of the thermodegraded oil and fat of oxygenated alpha,beta-unsaturated aldehydes (OalphabetaUAs), such as 4-hydroxy-2-nonenal (HNE), 4-oxo-2-nonenal (ONE), and 4,5-epoxy-2-decenal (EDE), was monitored by solid phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS). The digestion products were separated by centrifugation in a lipidic phase, an aqueous phase, and a pellet phase. The headspace of these three phases was also studied by SPME/GC-MS to check if the toxic and very reactive OalphabetaUAs above-mentioned remained unaltered after the in vitro digestion process or if they had reacted with the various compounds present in the digestion products, so disappearing from the samples. With the same aim the extract in ethyl acetate of the aqueous and pellet phases, and of the lipidic phase after dilution, were studied by GC-MS. All results obtained showed that a certain proportion of the toxic OalphabetaUAs remains unaltered after digestion, dispersed in the three phases above-mentioned, and thus are bioaccessible in the gastrointestinal tract and so could reach the systemic circulation. Compounds that may originate in Maillard type reactions (2-pentylpyridine) are found among digestion products, proving that these reactions are possible in this process if adequate substrates are present. In addition, it has been shown that toxic metabolites from the synthetic antioxidant BHT, present in fat before digestion, remain unaltered after this process and could reach the systemic circulation.  相似文献   

3.
Static headspace (SHS), headspace solid phase microextraction (HS-SPME), headspace sorptive extraction (HSSE), and direct thermal desorption (DTD) were applied to the analysis of four French virgin olive oils from Corsica. More than 60 compounds were isolated and characterized by GC-RI and GC-MS. SHS was not suited to the characterization of olive oil volatile compounds because of low sensitivity. The SPME and HSSE techniques were successfully applied to olive oil headspace analysis. Both methods allow the characterization of volatile compounds (mainly C(6) aldehydes and alcohols), which contribute significantly to the "green" flavor note of virgin olive oils. The PDMS stir bar showed a higher concentration capacity than a DVB/CAR/PDMS SPME fiber due to the higher volume of polymeric coating. DTD was a very good tool for extracting volatile and especially semivolatile compounds, such as sesquiterpenes, but requires a significant investment like that for HSSE. Finally, SPME may be a more appropriate technique for routine quality control due to its operational simplicity, repeatability, and low cost.  相似文献   

4.
Sulfite was determined in a variety of foods by liquid chromatography (LC) after the samples were mixed with a solution containing mannitol, FeSO4, and Na2HPO4, adjusted to pH 11, and left to stand for 15 min at room temperature. An aliquot of the mixture was placed in a headspace vial and mixed with 50% H3PO4. After 15 min, a portion of the headspace was removed with a syringe containing LC mobile phase without acetonitrile. The syringe was shaken and an aliquot of the solution was analyzed on an anion exchange column with a mobile phase of 0.03M methane sulfonate (pH 10.8) containing 5% acetonitrile. Sulfite was detected amperometrically (glassy carbon electrode) at +0.7 V. The method was successfully compared to the FDA-modified Monier-Williams procedure for a variety of foods. Minimum detectable levels were about 1 microgram/g, based on a 15 g sample.  相似文献   

5.
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   

6.
Static equilibrium was established between the gas phase (headspace) and an unstirred aqueous phase in a sealed vessel. The headspace was then diluted with air to mimic the situation when a container of food is opened and the volatiles are diluted by the surrounding air. Because this first volatile signal can influence overall flavor perception, the parameters controlling volatile release under these conditions are of interest. A mechanistic model was developed and validated experimentally. Release of compounds depended on the air-water partition coefficient (K(aw)) and the mass transport in both phases. For compounds with K(aw) values <10(-)(3), K(aw) was the factor determining release rate. When K(aw) was >10(-)(3), mass transport in the gas phase became significant and the Reynolds number played a role. Because release from packaged foods occurs at low Reynolds numbers, whereas most experiments are conducted at medium to high Reynolds numbers, the experimentally defined profile may not reflect the real situation.  相似文献   

7.
From the leaves of aloe, a succulent plant, a dried exudate commonly called aloe can be obtained, which is used as a natural drug for its cathartic effect and is widely employed as a bittering agent in alcoholic beverages. This investigation provides a tentative characterization of several commercial aloe exudates carried out both by reversed phase HPLC and by headspace GC-MS analysis. By means of HPLC the derivatives were evaluated, and by GC-MS the volatile fraction was investigated. Qualitative and quantitative differences among the constituents in various samples of different origins were found. In particular, these were evident in the HPLC profile of Kenya aloe and an Aloe barbadensis sample, which exuded a high content of isoaloeresin D and aloins, whereas GC-MS analysis showed the presence of anisole exclusively in Kenya aloe samples. Moreover, the results obtained by means of the latter technique suggested a reason for the prevailing use of Mosselbay and Port Elizabeth aloes in bitter spirits formulation.  相似文献   

8.
Protection against lipid oxidation and formation of unpleasant fishy and rancid off-flavors in oil-in-water food emulsions, such as fish oil enriched mayonnaise, is difficult to achieve. Volatile profiles from stored mayonnaises with different oil phase compositions were collected using a developed dynamic headspace sampling technique, in which interfering acetic acid was removed in situ with potassium hydroxide, and subsequently 148 volatiles were characterized and monitored by gas chromatography/mass spectrometry. Multivariate statistics showed correlation between the concentration of 62 volatiles and the fish oil and storage parameters, indicating the formation of lipid oxidation products, which impose fishy off-flavors. Further verification was obtained by gas chromatography/olfactometry, by which, among 78 odors, cis-4-heptenal and trans,cis-2,4-heptadienal were detected as distinct fishy notes. In total, 27 volatiles, including 1-penten-3-one, cis-2-penten-1-ol, cis-3-hexenal, cis-4-heptenal, 1-octen-3-one, 1,cis-5-octadien-3-one, 1-octen-3-ol, trans,cis-2, 4-heptadienal, and trans,cis-2,6-nonadienal, were suggested to contribute to the developed unpleasant fishy and rancid off-flavors.  相似文献   

9.
The effects of oil content and droplet size distributions of dilute oil-in-water emulsions on release of four esters with different hydrophobicities were studied under in vivo, static headspace, and artificial throat conditions. The effect of oil content on orthonasal and retronasal perceived intensity of ethyl hexanoate was studied using a seven-person panel. With increasing oil content and with a higher hydrophobicity of the aroma compound, a stronger decrease in aroma release was found. This effect was stronger under static headspace conditions than under in vivo and artificial throat conditions, and the sensory intensity of ethyl hexanoate was perceived stronger orthonasally than retronasally. The lowest effective oil content was determined for all systems. Of the compounds tested, droplet size distribution only influenced the in vivo release of geranyl acetate. The artificial throat results correlated well with in vivo release, giving support to the assumption that a thin layer of liquid remaining in the throat after swallowing determines aroma release.  相似文献   

10.
Six samples of cod liver oil were studied using Fourier transform infrared (FTIR) spectroscopy and (1)H nuclear magnetic resonance ((1)H NMR). These techniques provide information simply and rapidly about the global features of the cod liver oil main components, showing their potential as routine techniques for evaluating certain parameters of the quality of the cod liver oil. FTIR spectroscopy provides information about the molar percentage of polyunsaturated acyl groups in the sample and also about the ratio between unsaturated and saturated structures. (1)H NMR provides information about the proportions or concentrations of certain acyl groups and also of some minor compounds such as cholesterol. Both techniques are simple and fast. New approaches are presented to evaluate the molar proportions or concentrations of some acyl groups such as the molar percentages of omega-3, docosahexaenoic, and eicosapentaenoic acyl groups; furthermore, some novel approaches for evaluating the molar percentages of unsaturated and saturated acyl groups are also given. Results obtained from both spectroscopic techniques are in total agreement.  相似文献   

11.
A method using solid phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MS) was developed and used to determine the oxidation of freeze-dried chicken myofibrils spiked with methyl linoleate. Freeze-dried chicken myofibrils were found to act as a significant reservoir for hexanal. Recovery of hexanal emissions from the headspace above spiked myofibrils was 95% using a 5 min sampling time, with a total analysis time of approximately 12 min/sample. The SPME-GC/MS working linear response was from 0.01 to 10 mg hexanal/L (r( 2) = 0.995). Freeze-dried chicken myofibrils with added methyl linoleate (0.6 mmol/g of protein) were stored at 50 degrees C at water activities of 0.30 and 0.75 for 0, 12, 27, and 50 h. Lipid oxidation was determined using SPME-GC/MS to measure headspace hexanal concentration, the thiobarbituric acid reactive substances assay (TBARS) to quantify malonaldehyde, and a conjugated diene assay. Lipid oxidation was influenced by storage time and water activity. A strong correlation (r = 0.938) existed between SPME-GC/MS and TBARS. The use of SPME-GC/MS was a sensitive and rapid method for detecting hexanal as an indicator of lipid oxidation in chicken myofibrils.  相似文献   

12.
The changes of headspace flavor compounds of banana during ripening were studied by a solid-phase microextraction (SPME) method. Three temperatures, 20, 25, and 30 degrees C, were used to investigate the temperature effect on the changes of headspace flavor compounds of banana during ripening over a period of 8 days. Banana juice concentration, salt concentration, time, and temperature were investigated for optimizing the SPME method. The most suitable concentrations of banana juice and salt were 33.3 and 20%, respectively. The optimal temperature and time are about 50 degrees C and 48 min, respectively. Increasing ripening temperature could accelerate ripening rate. Ethanol developed most rapidly at 30 degrees C, whereas amounts of the other investigated flavor compounds stored at 25 degrees C were greater than those of the ones stored at 20 or 30 degrees C.  相似文献   

13.
Experiments were conducted to determine the volatile compounds in cooked chicken meat using a static headspace gas chromatographic (GC) technique. Preheating conditions for samples in vials were tested at 70, 80, and 90 degrees C for 20-120 min at each temperature. The majority of the peaks increased in size as the temperature and time increased. Optimum conditions were established as preheating at 80 degrees C for 30 min followed by analysis on a packed column of 8% Poly MPE on Tenax GC with the temperature programmed from 50 to 200 degrees C at 10 degrees/min. Coefficients of variation for major peaks ranged from 8.3 to 14.7%. These results were compared with those obtained with a capillary column analysis of samples preheated at the same conditions. Cooked and stored chicken patties, pretreated with different levels of sodium tripolyphosphate, were analyzed by the thiobarbituric acid (TBA) method and the headspace GC technique. Significant positive correlations were obtained between TBA numbers and the areas of 3 major peaks of the headspace profiles, indicating the applicability of the rapid headspace GC method for the determination of oxidative changes in chicken meat.  相似文献   

14.
The majority of fuel ethanol in the United States is produced by using the dry-grind corn ethanol process. The corn oil that is contained in the coproduct, distillers' dried grains with solubles (DDGS), can be recovered for use as a biodiesel feedstock. Oil removal will also improve the feed quality of DDGS. The most economical way to remove oil is considered to be at the centrifugation step for separating thin stillage (liquid) from coarse solids after distilling the ethanol. The more oil there is in the liquid, the more it can be recovered by centrifugation. Therefore, we studied the effects of corn preparation and grinding methods on oil distribution between liquid and solid phases. Grinding the corn to three different particle sizes, flaking, flaking and grinding, and flaking and extruding were used to break up the corn kernel before fermentation, and their effects on oil distribution between the liquid and solid phases were examined by simulating an industrial decanter centrifuge. Total oil contents were measured in the liquid and solids after centrifugation. Dry matter yield and oil partitioning in the thin stillage were highly positively correlated. Flaking slightly reduced bound fat. The flaked and then extruded corn meal released the highest amount of free oil, about 25% compared to 7% for the average of the other treatments. The freed oil from flaking, however, became nonextractable after the flaked corn was ground. Fine grinding alone had little effect on oil partitioning.  相似文献   

15.
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   

16.
The effects of water content and temperature variation on the release of flavor components into the headspace over flavors, encapsulated by an extrusion process, in low water content carbohydrate matrixes is studied. The largest amounts of release occurred when the matrix was above its glass transition temperature, whether this was due to increased water content or elevated temperature. Under these conditions up to 70% of the sucrose in the matrix crystallized over a period of 10 days, as quantified using Fourier transform Raman spectroscopy. Smaller amounts of headspace release occurred when the water content of the encapsulated flavor system was decreased from 3. 5 to 3.1% w/w. Small amounts of release occurred from the "as prepared" materials, which were associated with the presence of small amounts of unencapsulated flavor oil with direct access to the headspace. It was concluded that release due to matrix permeability was relatively slow as compared with the above mechanisms.  相似文献   

17.
Pectin gels consist of polysaccharide networks surrounded by water. The gel networks can prevent release of aroma molecules from the gel to the gas phase above. In this study static headspace measurements were performed to correlate aroma concentration in the gas phase above pectin gels to different amounts of the gel ingredients. As a consequence, aroma concentration in the headspace in relation to gel texture, as characterized by rheology measurements, was also studied. Aroma concentration in the headspace above strong gels was low, due to entrapment of aroma molecules within the gel structure. Viscous solutions generally gave a high aroma concentration in the headspace, but owing to a complex matrix, this was lowered when large amounts of the gel ingredients were added. However, a high correlation between interaction terms and square terms of design variables and rheology parameters with aroma compounds indicated nonlinear and complex relationships.  相似文献   

18.
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.  相似文献   

19.
The oxidation process of 13 edible oil samples with different proportions of oleic, linoleic, and linolenic acyl groups has been studied using Fourier transform infrared spectroscopy. The oxidation experiments were carried out by heating the samples in a convection oven at 70 degrees C. Duplicate spectra were recorded from a film of pure oil between two disks of KBr for each sample every day during the course of the oxidation, and frequency data of each band of the spectrum were collected automatically. Changes in the values of the frequency of most of the bands of the spectra were observed. The shiftings of the frequency value of specific bands allowed one to distinguish between the different stages of the oxidation process and to establish the oxidation degree of each oil sample. This methodology could be useful to evaluate the oxidative stability of edible oils in a simple, fast, and accurate way.  相似文献   

20.
The chemical nature of davanone isolated from natural davana oil via packed column preparative supercritical fluid chromatography with a carbon dioxide-based mobile phase has been defined. Analyses used to characterize davanone included nuclear magnetic resonance spectroscopy, optical rotation, mass spectrometry, headspace solid-phase microextraction, enantiomeric purity via gas chromatography (GC), and GC-coupled olfactometry. For comparison, natural davana oil was subjected to the same types of measurements. The enriched davanone sample was nearly 100% optically pure. This indicates that fractionation of the davana oil with supercritical fluids at near room temperature had little effect on the optical integrity of the sample.  相似文献   

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