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Thermal degradation of single 7-cholesteryl acetate hydroproxide
No full textThe thermal degradation products of the 7α- and 7β-cholesteryl 3β-acetate hydroperoxides obtained by thermal oxidation of cholesteryl 3β-acetate are reported and discussed. The hydroperoxides were degraded in both the vapour and condensed phases. The main components identified were 7-ketocholesteryl 3β-acetate, 7α- and 7β-hydroxycholesteryl 3β-acetates and the products generated from the loss of the hydroperoxide group and/or of acetic acid. Remarkable is the finding of the epoxy-hydroxy derivatives of cholesteryl acetate among the degradation products
Chromatographic determination of position and configuration isomers of methyl oleate hydroxides from corresponding hydroperoxides
No full textStudies of lipid oxidation usually employ such model systems as purified fatty-acid methyl ester. While methyl oleate hydroperoxides (MOHPs) can only be readily separated from the matrix by HPLC, because of their heat-susceptibility and relative instability, these same techniques are unable to separate cis MOHP from trans isomers. The present study reports an enhanced, rapid separation method for cis and trans isomers of methyl oleate hydroxides, as well as HPLC determination of positional isomers per fraction of configuration isomer and isomer identification by gas chromatography-mass spectrometry
CHROMATOGRAPHIC DETERMINATION OF THE POSITION AND CONFIGURATION OF ISOMERS OF METHYL OLEATE HYDROPEROXIDES
No full textOxygen can react with organic substrates (RH) to yield hydroperoxides, which in many instances are the first products of oxidation to be analytically isolated. A study of the structure of hydroperoxides could elucidate the reaction mechanisms activated during the first steps of oxidation processes. The simplest structural model used in the study of oxidation mechanisms of fats is methyl oleate. In this work the structures of methyl oleate hydroperoxides (MOHPs) were determined by gas chromatography-ion-trap detector mass spectrometry (GC-ITD-MS) of the corresponding hydroxystearates (MSHs). The hydroperoxides were reduced to methyl hydroxyoctadecenoates (MOHs), which were separated into the cis and trans fractions by argentation thin-layer chromatography. By hydrogenation of the double bond the cis- and trans-MOHs were reduced to MSHs for GC-ITD-MS analysis. Methods to isolate and determine the positional isomers of MOHPs were tested. The analytical techniques used were preparative high-performance liquid chromatography and GC-ITD-MS, solid-phase extraction-GC-ITD-MS and direct GC-ITD-MS
Stereospecific distribution of fatty acids in triacylglycerols of olive oils
No full textThe positional distribution of fatty acids (FA) in triacylglycerols (TAG) of 47 virgin olive oils from diverse cultivars grown in distinct areas of North-Eastern Italy was studied. Few data were previously available on oils from these geographical areas. The effects of climatic and geographical conditions on the stereospecific distribution of TAG in olive oil were confirmed. Moreover, the results of the stereospecific analysis were used to evaluate the preferential esterification position of each FA on the basis of the degree of unsaturation and the chain length. The data of the stereospecific analysis of olive oil TAG can contribute to the determination of the selectivity of olive fruit acyltransferases for distinct FA
The advancement of the assessment of food quality control as stressed by recent development in analytical chemistry
No full textSeveral aspects of food quality control (identity and quality) are discussed in this paper. Besides official and traditional methods, which are often time consuming and not always suitable to obtain an adequate description of the analysed food, a number of new methods have been developed within the last few years. The development of analytical methods depends on the development of analytical instrumentation and more accurate knowledge about food composition. Recent trends in food analysis control are to limitate at minimum sample manipulation and to reduce solvent utilisation. Thus, Supercritical Fluid Extraction, Solid Phase and Solid Phase Micro Extraction advantages are discussed, as well as a new analytical approach such as Hyphenated Techniques in Chromatography (LC-GC, LC-LC-GC) applied to trace analysis (PAHs), or volatile compounds stripping and GC-MS analysis applied to honey classification, aided by chemometric methods
Detection of Hazelnut Oil in Virgin Olive Oil by Assessment of Free Sterols and Triacylglycerols
No full textFree sterols were evaluated as factors for discriminating between genuine virgin olive oil and hazelnut-mixed virgin olive oil. Numeric analyses of the results amplified the differences between groups. The application of this method to virgin olive oil samples and their mixtures with 10% hazelnut oil distinguished between genuine and nongenuine virgin olive oil with statistical certainty. Triacylglycerol analysis was tested for the same purpose by using parameter ΔECN42, but although it possessed a discriminating capacity, it alone could not distinguish the aforementioned groups with sufficient certainty. Free Δ7-sterols data were combined with ΔECN42 data into a single discriminating function to improve differentiation and bring more ruggedness, and for detection of low amounts (10%) of hazelnut oil in virgin olive oil. In fact, the values obtained by addition of Δ7-sterol data and ΔECN42 data showed a higher discriminating capacity than single parameters. In a single operation the method produced all the oil fractions necessary for analysis of free sterols and triacylglycerols with ECN42. Solid-phase extraction was applied in substitution of traditional chromatography on a silica column
Identification of New steroidal Hydrocarbons in Refined Oils and yhe Role of Hydroxy Sterols as Possible Precursors
No full textThe dehydration of sterols during the refining process of vegetable oils results in the formation of steroidal hydrocarbons (sterenes or steradienes) with two double bonds in the ring system. Other steroidal hydrocarbons whose structures were in agreement with the presence of three double bonds in the ring system were detected in the sterene fractions of refined vegetable oils. The 5α-, 7α-, and 7β-hydroxy derivatives of cholesterol and phytosterols have been dehydrated in n-butanol/H 3PO 4 to form steroidal hydrocarbons with three double bonds at the 2, 4, and 6 positions in the ring system. These hydrocarbons had the same relative retention time and mass spectra as those present in the sterene fractions of refined oils. The dehydration of the hydroxy sterols dissolved in extra virgin olive oil and in the presence of 1% bleaching earths at 80 °C for i h results in the formation of the same steroidal hydrocarbons found in the refined oils
Methods for triacylglycerols analysis in vegetable oils
No full textTriacylglycerols analysis is a powerful tool to assess purity of vegetable oils, mainly applied to olive oils. Official methods by EU and IOC standardized RP-HPLC analysis of triacylglycerols to evaluate the amount of ECN42 terms, even if, in many cases, the obtained separation was not satisfactory, the method was adopted to check for extraneous oils with high amounts of oleic acid. An improvement of the method suitable to check for admixtures with several oils had been proposed by substitute acetone/acetonitrile with propionitrile. Ratios between selected TAGs were then calculated. The ECN42 value obtained by using the two different eluting solvents were compared and some discrepancies were highlighted.
Some peculiar mixtures of seed oils and olive oil, however, cannot be detected even by this approaches, while gas chromatography can be a suitable approach.
Capillary GC on short column coated with non polar stationary phase was applied and results suggested that some limits can be proposed for C48 and C60.
Care must be applied to the injection method, as thermal degradation can easily take place
Mass Spectrometry Characterization of the 5alfa-, 7alfa and 7beta-Hydroxy Derivatives of beta-sitosterol, Campesterol, Stigmasterol and Brassicasterol
No full textThe 5 alpha-hydroperoxides of beta-sitosterol, campesterol, stigmasterol, and brassicasterol were obtained by photooxidation of the respective sterols in pyridine in the presence of hematoporphyrine as sensitizer. The reduction of the hydroperoxides gives the corresponding 5 alpha-hydroxy derivatives. The 7 alpha- and 7 beta-hydroperoxides of the sterols were obtained by allowing an aliquot of the 5 alpha-hydroperoxides to isomerize to 7 alpha-hydroperoxides, which in turn epimerize to 7 beta-hydroperoxides. The reduction gave the corresponding 7 alpha- and 7 beta-hydroxy derivatives. The 5 alpha-, 7 alpha-, and 7 beta-hydroxy derivatives of beta-sitosterol, campesterol, stigmasterol, and brassicasterol were identified by comparing thin-layer chromatography mobilities, specific color reactions, and mass spectral data with those of the corresponding hydroxy derivatives of cholesterol, which were synthesized in the same manner. The phytosterols had the same behavior to photooxidation as cholesterol and, moreover, the different phytosterols photooxidized at about the same rate. The mass spectra of the trimethylsilyl ethers of the hydroxy derivatives of the phytosterols investigated and of the corresponding hydroxy derivatives of cholesterol have the same fragmentation patterns and similar relative ion abundances
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