Concentrations Of Ethyl Esters Research Articles

Determination of Total Biodiesel Fatty Acid Methyl, Ethyl Esters, and Hydrocarbon Types in Diesel Fuels by Supercritical Fluid Chromatography-Flame Ionization Detection

A method for determining total biodiesel methyl and ethyl ester content in diesel fuels by supercritical fluid chromatography-flame ionization detection (SFC-FID) is developed. A silica column typically used for determining aromatics in conventional diesel fuels by ASTM D5186 is back-flushed after separation of the hydrocarbons to allow elution of the various esters as a single "total biodiesel" distinct peak. The modification concurrently allows the determination of total aromatic hydrocarbons and their distribution as mono- and polynuclear compounds, as described in the current version of D5186. The instrument response is linear from 1.0% to 50% biodiesel esters with a signal-to-noise ratio of 25 at the 0.1% level. The short-term relative standard is 0.8%. Normalized percent quantitation using a hydrocarbon response factor of 1.00 and an ester response factor of 1.19 provide an average percentage error of 1.8% when measuring actual biodiesel/hydrocarbon fuel blends. The ester response factor is the average of the response factors of 10 pure ester compounds. These responses are calculated from respective solutions of each ester and the four compounds, hexadecane, toluene, tetralin, and naphthalene, as used for the D5186 response factor mixture.

Protection of Volatiles in a Wine with Low Sulfur Dioxide by Caffeic Acid or Glutathione

Concentrations of aromatic volatiles during storage of white wine with reduced (35 mg/L) or typical (55 mg/L) free sulfur dioxide for up to 210 days (7 months) were measured to evaluate how decreased SO₂ affects wine volatiles. Additions of caffeic acid (60 mg/L), glutathione (20 mg/L), or their mixture (30 mg/L + 10 mg/L, respectively) to wine with reduced SO₂ were also examined. In control and treated wines, concentrations of acetate esters, ethyl esters, terpenes, and fatty acids decreased during wine storage, while concentrations of higher alcohols remained constant. Wine samples with reduced or typical SO₂ had statistically equal concentrations of volatiles, with the exception of ethyl acetate, which was higher in the latter. Caffeic acid, glutathione, or their mixture slowed the decrease of several volatile esters and terpenes such as ethyl acetate, isoamyl acetate, ethyl caproate, ethyl caprylate, ethyl caprate, and linalool. Results suggest that SO₂ gives only limited protection to wine volatiles but that caffeic acid, glutathione, or their mixture protect several aromatic volatiles of white wine with reduced SO₂.

Selectivity of Supercritical CO2 in the Fractionation of Hake Liver Oil Ethyl Esters

AbstractThe solubility of different ethyl esters derivatized from hake liver oil in supercritical carbon dioxide was studied. A selectivity factor was used to determine optimal conditions to fractionate the ethyl ester mixture. A strong influence of solvent pressure and temperature was observed within 8.63–18.04 MPa and 40–70 °C. The lowest total solubility of the ethyl ester mixture was obtained when using supercritical carbon dioxide at the lowest density (the lowest pressure and the highest temperatures value tested). The highest discrimination against long‐chain polyunsaturated fatty acids (e.g. EPA and DHA) was also obtained at these above conditions. Conversely, higher solubility and lower selectivity were obtained when solvent density increased. Considering this inverse correlation between selectivity and solubility, a single‐step batch‐fractionation process was designed to increase the 22:6 ethyl ester content from an initial value of 17.5% in the starting material to 55% in the final extract.

Controlling for Serum Albumin Level Improves the Correlation Between Serum Fatty Acid Ethyl Esters and Blood Ethanol Level

Fatty acid ethyl esters (FAEEs) are generated by the nonoxidative metabolism of alcohol and correlate positively with blood alcohol levels (BAL). As FAEEs are produced predominantly in the liver and bind to albumin in plasma, blood FAEE concentrations may be affected by serum albumin levels. The aim of this exploratory study was to define the relationship of FAEE levels with BAL after adjustment for serum albumin concentration. Fatty acid ethyl ester, BAL, and albumin concentrations were measured from de-identified, ethanol-containing serum samples (N=18). The assay focused on 3 FAEE species ethyl palmitate, ethyl stearate, and ethyl oleate. The relationships of individual and total FAEE concentrations with BAL using albumin as a covariate were analyzed. Values for Pearson's r between the BAL and the natural log-transformed FAEE (ln FAEE) levels were calculated, and then compared with partial correlation coefficients when controlling for albumin. The impact of serum albumin levels on the relationship between ln FAEE and BAL was evaluated by simple linear regression analysis. Concentrations of total FAEE ranged from 632 to 20,166 nM, and BAL ranged from 9 to 375 mg/dL. In the 18 samples, the Pearson correlation coefficient between BAL and total FAEE levels was 0.868, and increased to 0.909 when controlling for albumin (p<0.0001). Similar statistically significant increases in the partial correlation coefficient occurred for each of the individual species of FAEE when controlling for albumin. In simple linear regression, albumin significantly reduced the variability in the model correlating BAL and FAEE for each of the individual species, as well as for total FAEE. The association between FAEE levels and BAL is enhanced by consideration of serum albumin concentrations. Our findings suggest that serum albumin should be included in any model attempting to define the relationship between BAL and FAEE.

Ambient and low temperature winemaking by immobilized cells on brewer’s spent grains: Effect on volatile composition

Repeated batch wine fermentations were conducted using immobilized yeast cells on brewer’s spent grains as well as free cells, at 25, 20, 15 and 10 °C. The operational stability of the biocatalyst was good and no decrease of its activity was observed, even at 10 °C. Ethanol and wine productivities were high, showing the suitability of the biocatalyst for low temperature winemaking. The interaction effect of immobilization and temperature was statistically significant in most cases. Immobilized cells produced wines with a higher content of ethyl and acetate esters as well as volatile fatty acids, at temperatures of 15 and 10 °C, whereas the opposite was observed for free cells at higher temperatures. Same amounts of higher alcohols were produced by both immobilized and free cells. These amounts decreased dramatically with temperature drop. Wines produced by immobilized cells at low fermentation temperatures (10–15 °C) were characterized by a potentially better flavour due to a better ratio of esters to alcohols.

Transesterificação de óleos vegetais: caracterização por cromatografia em camada delgada e densidade

We studied the transesterification of two vegetable oils: soybean and waste frying oil. The main problem of transesterification is related to the measurement of the ethyl ester content. In this work we used a quick analytical method for assessing the ethyl ester fraction of the purified fuel-grade transesterification products by applying a simple correlation with density. If the ester content is higher than 85% by weight the correlation allows the determination by a single density measurement. This method is suitable for control and determines the ethyl ester quickly and simply.

Repercussion of the clarification treatment agents before the alcoholic fermentation on volatile composition of white wines

Albarino must was clarified with two fining agents, as bentonite and silica gel. Alcoholic fermentation was carried out at semi-industrial scale, and the concentration of free monoterpenes, norisoprenoids, C6-alcohols, higher alcohols, fatty acids, ethyl esters, and acetates was then investigated. The use of bentonite allows loss of several volatile compounds compared to wine control. In a second step, the effect of clarification–stabilization treatments with silica gel on aromatic substances was compared in order to study this influence in white wines elaborated from different aromatic varieties (Albarino and Loureira). The results showed that the use of these fining agent plays a significant role in the wine volatile composition.

The bioavailability and pharmacodynamics of different concentrations of omega-3 acid ethyl esters

Omega-3 fatty acids have a long history of use as dietary supplements and more recently for therapeutic applications as prescription pharmaceuticals. Achieving a high concentration is critical for developing convenient, practical therapeutic formulations. The objective of the study was to explore the uptake and effects of different concentrations of omega-3 acid ethyl esters. Three different omega-3 concentrations were investigated in a clinical study with 101 subjects. All participants were dosed for 14 days with 5.1 g per day of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) ethyl esters provided in three concentrations: 62.5%, 80% and 85% of total fatty acids. Key endpoints of the study were serum phospholipids and standard fasting lipid panels at day 14. Although administered the same quantity of omega-3 fatty acids, the patients taking the more concentrated formulations had higher levels of EPA/DHA in serum phospholipids and greater reductions in serum triglyceride and VLDL cholesterol levels. Total and non-HDL cholesterol were significantly reduced from baseline with all three formulations. In conclusion the concentration of omega-3 fatty acids of the formulations studied had independent effects on the uptake and effect outcomes during short-term administration. Very high concentrations of omega-3 acid ethyl esters (⩾80%) appear to have higher uptake and are more potent for reducing triglycerides (TGs) and VLDL-cholesterol than formulations with lower concentrations.

Volatile compounds after spontaneous fermentation of musts from Vitis vinifera cv. Albariño grapes cultivated in different origins from Rías Baixas AOC, Spain

AbstractWhite wines experimentally produced from the white grape variety Albariño from three different areas from Rias Baixas AOC, north‐western Spain, have been analysed in this study. The contents of terpenes, C13‐norisoprenoids, alcohols, acetates and ethyl esters were determined by GC–MS. The Albariño wines from O Rosal are characterized by a high content of higher alcohols, while wines from Val do Salnés show the highest concentrations of free terpenes, acetates and ethyl esters; and wines of Condado do Tea show the highest concentrations of C13‐norisoprenids, principally due to the α‐ionone. Two principal components accounting for 90.7% of the total variance were calculated by means of a principal components analysis (PCA), and the graphical representation of these two components allows grouping the wines according their respective origins. Volatile compounds with fruity and floral odours showed the highest odour activity values, contributing in a great measure to the aroma of Albariño wines. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Chronic Prenatal Ethanol Exposure and Increased Concentration of Fatty Acid Ethyl Esters in Meconium of Term Fetal Guinea Pig

In humans, the occurrence of prenatal exposure to ethanol is difficult to validate objectively. Increased concentration of fatty acid ethyl esters (FAEE) in the meconium of the newborn may be a biomarker of prenatal ethanol exposure. The validity of this proposed biomarker was tested in pregnant guinea pigs that received chronic oral administration of 4 g ethanol/kg maternal body weight/day (n=8), isocaloric-sucrose/pair-feeding (n=8) or water (n=2) throughout gestation. At gestational day 65 (term, gestational day 66 to 69), each dam and her offspring were euthanized, and meconium was collected from the term fetal large intestine. Eight individual FAEE (lauric, myristic, palmitic, palmitoleic, stearic, oleic, linolenic and arachidonic AEE) were measured by gas chromatography--flame ionization detection and confirmed by gas chromatography--mass spectrometry. The chronic maternal ethanol regimen decreased fetal body weight and brain weight. There was virtually no measurable FAEE in the meconium for the water group (n=3 fetuses). For meconium of the ethanol offspring (n=25 fetuses) compared with the sucrose offspring (n=23 fetuses), the total FAEE concentration was 8-fold higher; and lauric, palmitic, stearic and oleic AEE concentrations were at least 5-fold higher for the ethanol group. The data indicate that fetal meconium FAEE constitute a biomarker of prenatal ethanol exposure for a maternal ethanol regimen that restricts fetal development, with an inverse relationship between meconium total FAEE concentration and both body weight and brain weight.

Chemical composition of volatiles from coconut sap ( neera) and effect of processing

Volatiles from (i) fresh, (ii) clarified and (iii) fermented coconut sap neera were isolated by a simultaneous distillation and solvent extraction method using a Likens-Nikerson apparatus and subjected to GC–MS analysis for identification of chemical constituents. Twenty-one compounds (5.33 ppm), constituting more than 98% of the volatiles from fresh neera, were characterised. Typical major flavour compounds found in volatiles of fresh neera were ethyl lactate, phenyl ethyl alcohol, ethyl lactate, 3-hydroxy-2-pentanone, farnesol, 2-methyl tetrahydrofuran, and tetradecanone. Clarified neera contained lower quantities of volatiles, in which 13 compounds (1.31 ppm), constituting more than 97%, were identified. However, the typical flavour components retained were ethyl lactate, phenyl ethyl alcohol, 1-hexanol, 2-methyl tetrahydrofuran, 3-hydroxy-2-pentanone and 2-hydroxy-3-pentanone. Fermented neera contained a greater quantity of volatiles, in which 12 compounds (37.4 ppm), representing more than 95% of the volatiles, were characterised. Ethyl lactate, phenyl ethyl alcohol and farnesol were among the seven compounds retained from fresh neera. The astringency and harsh note of the fermented neera could be due to the increased amounts of acids (19.0 mg/l), such as palmitoleic acid and dodecanoic acid, along with higher concentrations of ethyl alcohol and ethyl esters.

The Saccharomyces cerevisiae EHT1 and EEB1 Genes Encode Novel Enzymes with Medium-chain Fatty Acid Ethyl Ester Synthesis and Hydrolysis Capacity

Fatty acid ethyl esters are secondary metabolites produced by Saccharomyces cerevisiae and many other fungi. Their natural physiological role is not known but in fermentations of alcoholic beverages and other food products they play a key role as flavor compounds. Information about the metabolic pathways and enzymology of fatty acid ethyl ester biosynthesis, however, is very limited. In this work, we have investigated the role of a three-member S. cerevisiae gene family with moderately divergent sequences (YBR177c/EHT1, YPL095c/EEB1, and YMR210w). We demonstrate that two family members encode an acyl-coenzymeA:ethanol O-acyltransferase, an enzyme required for the synthesis of medium-chain fatty acid ethyl esters. Deletion of either one or both of these genes resulted in severely reduced medium-chain fatty acid ethyl ester production. Purified glutathione S-transferase-tagged Eht1 and Eeb1 proteins both exhibited acyl-coenzymeA:ethanol O-acyltransferase activity in vitro, as well as esterase activity. Overexpression of Eht1 and Eeb1 did not enhance medium-chain fatty acid ethyl ester content, which is probably due to the bifunctional synthesis and hydrolysis activity. Molecular modeling of Eht1 and Eeb1 revealed the presence of a alpha/beta-hydrolase fold, which is generally present in the substrate-binding site of esterase enzymes. Hence, our results identify Eht1 and Eeb1 as novel acyl-coenzymeA:ethanol O-acyltransferases/esterases, whereas the third family member, Ymr210w, does not seem to play an important role in medium-chain fatty acid ethyl ester formation.

Changes in volatile composition of Madeira wines during their oxidative ageing

The influence of the age in the volatile composition of Madeira wines made with Boal, Malvazia, Sercial and Verdelho varieties and aged in oak barrel during 1, 11 and 25 years old was been studied. For this purpose, the evolution of volatile compounds: higher alcohols, ethyl esters, fatty acids, furan compounds, enolic compounds, γ-lactones, dioxanes and dioxolanes, of the four most utilised varieties were determined using liquid–liquid extraction with dichloromeihane. Octan-3-ol was used as internal standard. The wines made with these varieties showed great differences in sugar content and small variations on pH and alcoholic degree. The results show that during ageing, the concentration of fatty acids ethyl esters, acetates and fatty acids decrease significantly contrarily to the great increase of ethyl esters of diprotic acids. There is a strong correlation between sotolon, 2-furfural, 5-methyl-2-furfural, 5-hydroxymethyl-2-furfural and 5-ethoxymethyl-2-furfural with wine ageing. These findings indicate that these compounds can be used as ageing wine markers. Among the molecules studied, sotolon [3-hydroxy-4,5-dimethyl-2(5H)-furanone] was one of the few molecules present in concentrations above the perception threshold in Madeira wines. 5-Eihoxymethyl-2-furfural formed from 5-hydroxymethyl-2-furfural and 2-furfural, derived from sugars, are also involved in the aroma of sweet fortified white wines aged in oxidative conditions. The sensory properties change significantly after long periods of conservation.

Controlled formation of volatile components in cider making using a combination of Saccharomyces cerevisiae and Hanseniaspora valbyensis yeast species

The effect of pure and mixed fermentation by Saccharomyces cerevisiae and Hanseniaspora valbyensis on the formation of major volatile components in cider was investigated. When the interaction between yeast strains of S. cerevisiae and H. valbyensis was studied, it was found that the two strains each affected the cell growth of the other upon inoculation of S. cerevisiae during growth of H. valbyensis. The effects of pure and mixed cultures of S. cerevisiae and H. valbyensis on alcohol fermentation and major volatile compound formation in cider were assessed. S. cerevisiae showed a conversion of sugar to alcohol of 11.5%, while H. valbyensis produced alcohol with a conversion not exceeding 6%. Higher concentrations of ethyl acetate and phenethyl acetate were obtained with H. valbyensis, and higher concentrations of isoamyl alcohol and isobutyl were formed by S. cerevisiae. Consequently, a combination of these two yeast species in sequential fermentation was used to increase the concentration of ethyl esters by 7.41-20.96%, and to decrease the alcohol concentration by 25.06-51.38%. Efficient control of the formation of volatile compounds was achieved by adjusting the inoculation time of the two yeasts.

Analytical characterization of the aroma of Tinta Negra Mole red wine: Identification of the main odorants compounds

A method for the simultaneous determination of major and minor volatiles composition in different types (dry, medium dry, sweet and medium sweet) of a young Tinta Negra Mole (TNM) monovarietal red wine from 2003 harvest has been validated. Wine samples preparation includes a dichloromethane liquid–liquid extraction followed by concentration under a nitrogen atmosphere. The extracted fraction was analysed by gas chromatography–mass spectrometry and give quantitative information for more than 86 analytes whose concentration range from few μg l −1 to 259.1 mg l −1. The method enables high recovery of volatile compounds in wine good linearity with ( r 2) values higher than 0.980 and good sensitivity. The limits of detection range from 0.003 to 0.534 mg l −1 and limits of quantification from 0.009 to 1.170 mg l −1. The method allows satisfactory determination of more than 80 compounds in the TNM red wines. These wines are characterized by a high content of higher alcohols, ethyl esters, fatty acids and lactones. The levels of sulphur compounds in Tinta Negra Mole medium sweet wines are very low, but they have the highest concentration of carbonyl compounds. Quantitative analysis of the main odorants followed by the determination of aroma index allow us elucidate the aroma of these varieties. On the basis of their odour description and odour threshold, the most powerful odorants of Tinta Negra Mole wines were tentatively established.

Effect of yeast and bacterial adjuncts on the CLA content and flavour of a washed-curd, dry-salted cheese

Three strains of Propionibacterium freudenreichii ssp. shermanii that converted free linoleic acid to conjugated linoleic acid (CLA) in laboratory media were used as adjunct strains, together with strains of Geotrichum candidum and Yarrowia lipolytica, to make a dry-salted, washed-curd cheese. Lactobacillus fermentum was included to produce ethanol (from lactose), a potential substrate for ethyl ester synthesis, while Lactobacillus rhamnosus was used to control the adventitious non-starter lactic acid bacteria population. The total (esterified plus free) level of CLA was similar in the control and experimental cheeses and remained unchanged over 4 months of ripening. Addition of linoleic acid-rich safflower oil to the cheese curd increased the concentration of free linoleic acid generated in the cheese but the CLA content did not change. Free linoleic acid was released by the yeast lipase(s) but there was no conversion to CLA. High concentrations of ethyl esters were produced in the cheeses made with added yeast, giving a fruity flavour.

Supercritical CO2 extraction and concentration of n-3 polyunsaturated fatty acid ethyl esters from tuna cooking juice

Cooking is an important step in the tuna canning process; it usually produces functional solubilized proteins and lipids. The objective of this study was to recover and increase the concentration of functional n−3 fatty acids from the lipids in cooking juice. The lipids contained 12.98% eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) after ethyl esterification and increased to 37.4% with subsequent urea adduct fractionation. Supercritical carbon dioxide extraction was further used to increase the concentration of EPA and DHA ethyl esters. The ratio of EPA+DHA ethyl esters (high-molecular-weight components) to that of C16 and C18∶1 fatty acid ethyl esters (low-molecular-weight components) was used as a separation index for evaluating the process variables. Experimental results indicated that a high CO2 density caused a low separation factor. At 1500 psig and 328.2 K, the extraction collected over 600 L CO2, displaying an accepted concentration factor of EPA+DHA ethyl esters herein. About 80% yield of EPA and DHA was obtained and the ethyl esters increased from 37.4% to 54.3%.

Quantification of soybean oil ethanolysis with 1H NMR

AbstractIn this study, proton NMR spectroscopy (200 MHz) was used for quantifying the content of ethyl esters in known mixtures of soybean oil and ethyl soyate (biodiesel). For this purpose, the peak areas of ester ethoxy and glycerol methylenic peaks in the region of 4.05–4.40 ppm were measured and a calibration plot of the respective peak areas vs. the known composition of the oil/ethyl ester mixtures was used. The transesterification values determined in this way were compared with viscosity and total glycerol determinations and a good correlation was obtained. Therefore, for routine analysis, the conversion (in %) of oil to ethyl esters was determined. The methodology presented in this work proved to be quicker and simpler than others reported in the literature, such as GC and/or HPLC.

Fatty acid ethyl esters: markers of alcohol abuse and alcoholism

Chronic alcoholism, which is associated with hepatic, pancreatic, and myocardial diseases, is one of the major health problems in the United States with high morbidity and mortality. Many individuals who abuse alcohol chronically die even before reaching the clinical stage of the disease. Reliable biomarkers of the diseases induced by chronic alcohol abuse, as well as for alcoholism, currently are not available. In the current study, we measured plasma concentrations of fatty acid ethyl esters [(FAEEs), nonoxidative metabolites of ethanol] in 39 patients with a detectable concentration of alcohol in their blood samples. In turn, we determined the relation of FAEE concentrations with blood alcohol concentration (BAC). Of 39 patients in whom we evaluated this relation, only five had a history of chronic alcohol abuse, and six had a history of acute alcohol abuse. Patients' age ranged from 25 to 71 years. Within this age range, greater concentrations of FAEEs were found in the plasma samples obtained from patients in the 41- to 50-year age group. There were no sex-related differences in BAC, nor in FAEE concentrations. Thirteen patients had a BAC greater than 300 mg%. For 11 patients, the BAC ranged between 200 and 299 mg%, and, for 12 patients, the BAC ranged between 100 and 199 mg%. In comparison with findings for patients with a BAC that ranged between 100 and 299 mg%, the FAEE concentrations were approximately twofold higher in patients with a BAC greater than 300 mg%. Ethyl palmitate and ethyl oleate were the main FAEEs detected in most patients. In general, FAEE concentrations increased with increasing BAC. However, in comparison with patients with a history of acute alcohol abuse, a greater increase in total FAEE concentrations was observed in patients with a history of chronic alcohol abuse (4,250 ng/ml and 15,086 ng/ml, respectively). Fatty acid ethyl esters were either detected in trace amounts or not detectable in the plasma of control subjects with no known alcohol ingestion. These results support our hypothesis that nonoxidative metabolism of ethanol to FAEEs is an important pathway of ethanol disposition during chronic alcohol abuse, and that FAEE concentrations can be a more reliable biomarker of chronic alcohol abuse than a history of acute alcohol abuse.

Tequila volatile characterization and ethyl ester determination by solid phase microextraction gas chromatography/mass spectrometry analysis.

Solid phase microextraction (SPME) and gas chromatography were used for tequila volatile characterization and ethyl ester quantitation. Several factors determined the differences in tequila volatile profiles obtained by the SPME technique, namely, sampling mode, fiber coating, and fiber exposure time. Each of these factors determined the most suitable conditions for the analysis of volatile profiles in tequila. Volatile extraction consisted of placing 40 mL of tequila in a sealed vial kept at 40 degrees C. A poly(dimethylsiloxane) fiber was immersed in the liquid for 60 min and desorbed for 5 min into the gas chromatograph. The identified volatiles by mass spectrometry were mainly alcohols, esters, and ketones. The calibration curves for ethyl hexanoate, octanoate, and decanoate followed linear relationships with highly significant (p < 0.001) determination coefficients (R2 = 0.99). The coefficients of variation of less than 10% for ethyl ester concentrations indicated that the technique was reproducible. The limits of quantitation for ethyl esters were 0.05 parts per million, which were below the concentration range (0.27-15.03 ppm) found for different tequila samples. Quantitative differences in ethyl esters were found for the four most commonly known tequila types: silver, gold, aged, and extra-aged.