1,721,152 research outputs found
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
Half-seed analysis: rapid chromatographic determination of the main fatty acids of sunflower seed
No full textThe half seed technique, with some recent modifications of traditional analytic methods, is proposed for selecting sunflower with modified fatty acid composition. A rapid method was used for extracting the oil and for methylating fatty acids (about 3 min per sample). Thin layer chromatography (TLC) plates with activated AgNO3 and / or gas chromatography (GLC) with capillary columns was used to analyze the methylated esters. Half seed, whole seed and meal analysis of sunflower and other oilseed species confirmed the validity of the method with regard to sampling, analytic results and embryo terminability. In addition, GLC using a suitable internal standard can be used to evaluate the percentage oil content of seed. About ten sample per hour can be analysed with GLC versus 20-25 with TLC. These times can be further shortened in practice in the laboratory by partially overlapping some steps
Carbonic maceration and traditional wine making: a quality control procedure using gas chromatographic determination of fixed compounds
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Effect of olive ripening degree on the oxidative stability and organoleptic properties of Nostrana di Brisighella extra-vergin olive oil
No full textThe evaluation of the influence of olive ripening degree on the stability of extra virgin olive oils by the determination of the oxidative stability index, the DPPH• radical test, and the quali-quantitative analysis of phenolic compounds, as well as the study of the variation of their sensory profiles, plays a key role in the assessment of the overall olive oil quality. Olives of the cv. Nostrana di Brisighella grown in the north-central Italian region of Emilia-Romagna were picked at four different stages of ripeness and
immediately processed in an experimental mill. The polar extracts of oil samples were submitted to spectrophotometric analysis of total phenols and o-diphenols and to liquid chromatographic
determination of their quali-quantitative profile (HPLC-DAD/MSD). To attain a complete description of oil samples, fatty acid composition, ultraviolet indices ( K232, K270, and ¢ K), free acidity degree, and peroxide value were also determined according to the European Union methods stated in Regulation 2568/91 ( 1, Off. J. Eur. Communities1991, L248, 1-82). Sensory quantitative descriptive analysis (QDA) and triangular tests were performed to establish the influence of olive ripening degree on the resulting oil’s organoleptic properties. The evolution of the analytical parameters studied shows that the ripeness stage of Nostrana di Brisighella olives that yields the best oil corresponds to a Jae ́n index value between 2.5 and 3.5. Oils produced from olives harvested within this time frame present a superior sensory profile accompanied by the highest possible chemical and nutritional propertie
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