Volatile compounds in heated oleic acid-esterified propoxylated glycerol

Static headspace and capillary gas chromatography, in combination with infrared and mass spectrometry, were used to collect, separate, identify, and quantitate the oxidative and thermal decomposition products in two heated model compound triacylglycerols, oleic acid-esterified propoxylated glycerol (EPG-08 oleate) and triolein. The EPG-08 oleate and triolein were each heated in a deep-fat fryer at 192±8°C for 12 h each day until the oil contained ≥20% polymeric material. Most of the volatile compounds identified in heated triolein and EPG-08 oleate were associated with the oxidative and thermal decomposition of oleates, such as short-chain alkanes, aldehydes, and alcohols. The major volatile compounds (concentration >20 ppm) in heated EPG-08 oleate and triolein were heptane, octane, heptanal, octanal, trans-2-decenal, nonanal, and trans-2-undecenal. However, a few minor volatile compounds, not previously found in heated fats and oils, were identified in the heated EPG-08 oleate samples. These compounds included 1,2-propanediol, 1-hydroxy-2-propanone (hydroxyacetone), 1-acetoxy-2-propanone (acetoxyacetone), 2-ethyl-4-methyl-1,3-dioxolane, 2,2,4-trimethyl-1,3-dioxolane, 2-heptyl-4-methyl-1,3-dioxolane, and 4-methyl-2-octyl-1,3-dioxolane. Alkyl-substituted dioxolanes have been found in heated methyl linoleate.     

Influence of the position of unsaturated fatty acid esterified glycerol on the oxidation rate of triglyceride

The influence of the position of unsaturated fatty acid esterified glycerol on the oxidation rate of triglyceride was investigated at 50 C. Randomized triglycerides used were prepared by random interesterification between saturated and unsaturated monoacid triglycerides using sodium methoxide as catalyst. The monoacid triglycerides used were tripalmitin, tristearin, triolein and trilinolein. The molecular species of the randomized triglycerides were analyzed by high performance liquid chromatography (HPLC) in combination with gas liquid chromatography (GLC) and enzymatic hydrolysis. From the results of oxygen absorption measurement by GLC, the randomized triglycerides were more stable towards oxidation than the triglyceride mixtures which were prepared by mixing the equivalent quantities of the same monoacid triglycerides as used in the random interesterification. This may be due to the decrease in the contents of most unstable unsaturated monoacid triglycerides by random interesterification with saturated monoacid triglycerides. Furthermore, from the results obtained with the detailed analysis of the randomized triglycerides at different stages of oxidation, it became clear that the triglycerides having unsaturated fatty acids linked at the 2-position of glycerol are more stable towards oxidation than those linked at the 1(or 3)-position. The carbon chain length of saturated fatty acids has essentially no influence on the oxidation rates of unsaturated fatty acids esterified in the same glycerol.     

Odor significance of undesirable degradation compounds in heated triolein and trilinolein

To better understand production of undesirable or negative odors such as fruity, plastic, and waxy that are characteristic of higher oleic acid-containing oils, model heated oil systems of triolein and trilinolein were studied. Identification of the odor significance of volatile compounds produced by fractionated and nonfractionated triolein and trilinolein was done by purge and trap-gas chromatography-ion trap mass spectrometry-olfactometry. The predominant odors of the triolein heated 1, 3, and 6 h at 190°C were fruity and plastic, with other negative odors of acrid and grassy. Some of the volatile compounds that produced negative odors in heated triolein, in order of increasing concentration, were hexanal (grassy), octanal (fruity), (E)-2-decenal (plastic), nonanal (fruity), and (E)-2-undecenal (plastic). Some of the negative odor compounds in trilinolein heated for 1, 3 and 6 h, in order of increasing concentration, included (E)-2-nonenal (plastic), pentanal (grassy), and hexanal (grassy). However, the amount of volatile compounds produced and the intensity levels of the odors were lower in trilinolein than in triolein. Formation of many of the volatiles was explained after identification of the volatile precursors, including epoxy, keto, and dimer oxidation products that were produced during heating. Presented at the American Oil Chemists’ Society 90th Annual Meeting & Expo, Orlando, FL, May 9–12, 1999.     

Triacylglycerol assembly from binary mixtures of fatty acids byApiotrichum curvatum

To observe how the stereospecific distribution of acyl groups in triglycerides is affected by the composition of fatty acids available for esterification, the oleaginous yeastApiotrichum curvatum was grown on various binary mixture of palmitic, stearic, oleic and linoleic acids as carbon sources, and the yeast triglycerides were analyzed. When oleic acid-linoleic acid mixtures in various ratios were used as substrates, the yeast grew well, and the composition of the intracellular triglycerides reflected the substrate composition, but more linoleate than oleate was deposited in the triglycerides. Oleate was favored over linoleate at thesn-2 position of the glycerol. With substrates containing palmitic and stearic acids, the yeast accumulated less oil, and incorporation of stearic acid into the triglycerides also was very limited. When mixtures of palmitic acid-oleic acid and palmitic acid-linoleic acid were used as substrates, the yeast triglyceride composition did not reflect that of the substrate, and the accumulation in the yeast of the unsaturated acid in the substrate was favored. Possibly, the yeast had more limited access to solid than to liquid substrates. For oleic acid-linoleic acid substrates, when the percentages of oleate and linoleate at the three glycerol positions were plottedvs. the percentage of these acyl groups in the total triglyceride, apparent linear relations were observed for most of the range, and the sums of the intercepts and slopes of the three lines for each acyl group were 0 and 3, respectively. Two mathematical models of triglyceride assembly are proposed, both of which fit the experimental data. One model assumes that for a certain proportion of the glycerol molecules, the acyl composition of the threesn positions is rigidly controlled independently of the substrate concentration. The other assumes that the various acyl groups are distributed on the threesn positions of glycerol with different affinities.     

Chemical Investigations on Celastrus paniculatus Seed Oil I

Fatty acid compositions of four lipid fractions of Celastrus paniculatus seed namely normal triglycerides (20.2%), polar triglycerides (44.4%), polar nonglyceridic ester (23.5%), and nonpolar nonglyceridic ester (11.9%), have been determined by gas liquid chromatography. Percentage contents of major component acids in these fractions are: palmitic, 25.1, 42.0, 12.7, 58.2; stearic, 6.7, 4.5, 15.8; oleic, 46.1, 24.8, 4.7, 14.2; linoleic, 15.4, 14.7, 10.0; and linolenic, 3.0, 13.1, 43.0, respectively. The major molecular species constituting the normal triglycerides are: palmitooleopalmitin, 6.8%; palmitooleostearin, 5.6%; palmitodiolein, 14.7; palmitooleolinolein, 7.0%; stearodiolein, 6.1%; triolein, 8.0% and dioleolinolein 7.6%. Lipolysis of the polar triglyceride indicated as high as 59.6% of saturated acids linked to the 2-position of glycerol.     

Limitations of periodate-permanganate oxidation in determination of glyceride composition: Nonquantitative oxidation and hydrolysis of azelaoglycerides

Oleic acid, methyl oleate, mono- and diunsaturated triglyceride concentrates, triolein,Garcinia indica fat and saffower oil were oxidized with periodate-permanganate reagent in aqueous 60%tert-butanol at 80 C (reflux temperature), 65 C and 28 to 30 C under different conditions. Significant proportions of unoxidized and partially oxidized compounds, mainly ketohydroxy compounds, were found in oxidation products. Hydrolysis of azelaoglycerides, particularly triazelain also occurred. The di- and trisaturated glyceride contents are therefore likely to be higher than the actual for all fats when determined by Youngs and Subbaram's method and for fats containing high proportions of triunsaturated glycerides by Youngs' method.     

Studies on the specificity of a lipase system fromGeotrichum candidum

The lipase system fromGeotrichum candidum preferentially hydrolyzed oleic acid, regardless of position, from the four possible racemic triglycerides containing oleate and palmitate. The rate of hydrolysis of these glycerides was most rapid when the substrate contained two moles of oleate. This acid was also preferentially released from a series of triglycerides containing oleate and two moles of a saturated fatty acid. The chain length of the latter did not alter the specificity for oleate. Equimolar quantities of oleic and linoleic acids were released when triolein and trilinolein (equimolar mixture) were hydrolyzed by this lipase. No differentiation between oleate and palmitoleate was observed when racemic glyceryl 1-palmitoleate-2,3-dioleate was the substrate. However, only 7.2 M%cis-vaccenic acid was released from glyceryl 1-cis-vaccenate-2,3-dioleate and 5.4 M% petroselinic acid from glyceryl 1-palmitoleate-2,3-dipetroselinate. It therefore appears that the enzyme may be specific forcis-9-unsaturation as well as forcis-9,cis-12-unsaturation. When specificity was assumed, the fatty acid compositions of the diglycerides obtained from digestions withG. candidum were close to theoretical. Scientific contribution No. 256, Agricultural Experiment Station, University of Connecticut, Storrs.     

Comparison of radiolytic compounds from saturated and unsaturated triglycerides and fatty acids

Formation of certain radiolysis products from palmitic acid, oleic acid, tripalmitin and triolein has provided a means for comparing the radiolytic effects in saturated and unsaturated triglycerides and fatty acids. These substances were chosen to represent the major constituents of fat found in beef. Fractionation and concentration of radiolytic compounds from the irradiated samples was accomplished by the means of size exclusion chromatography. Quantitative and qualitative analyses were performed using a combined GC/MS computer system. In addition to the primary radiolytic compounds, recombination products of relatively high molecular weight and various propanediol diesters from the corresponding glyceryl moities were identified. Quantitative analyses indicated a greater yield of various radiolytic compounds from free fatty acids than from the corresponding triglycerides. Similarly, radiolytic compounds were produced in greater quantities from the saturated fats than the unsaturated fats. Most of the radiolytic compounds identified in this study have not been previously reported.     

Thermal oxidation of model molecules to reveal vegetable oil polymerization studied by NMR spectroscopy and self-diffusion

Oxidative polymerization of plant oils and lipids is poorly understood yet widely encountered. Oils and fats are renewable resources providing biofuels and polymers. Oil oxidation is accelerated at high temperatures, typically above 110°C, where triacylglycerides are converted into toxic compounds and viscous deleterious polymers. Polymerization of mono-unsaturated oil (210°C, 3 h, open to air) was investigated by comparing four similar sized molecules with different functional groups: oleic acid, methyl oleate, trans-7-tetradecene, and stearic acid. Non-volatile products identified by NMR spectroscopy are minor ketones for saturated fatty acid (stearic acid), epoxides for acyl chains without acid groups (methyl oleate, tetradecane) and copious oligomerization, through ester cross-links, for acyl chains with acid, and olefinic groups (oleic acid). Long range C H coupling clearly shows ester (not ether) cross-links, contradicting long-held beliefs. Chain fragmentation also occurs for heated oleic acid as revealed by formation of a species with a methylene group bonded to oxygen of an ester,  CH₂ O C(O) . Large size (slow diffusion) of the first oligomer (trimer) formed from oleic acid, used to represent hydrolyzed vegetable oil, was evidenced by DOSY (diffusion-ordered spectroscopy). Combined NMR results show oligomers found in heated oleic acid are fatty acid estolides. Model oil reactions demonstrate why olefin and carboxylic acid groups are required for polymerization.     

Oxidative stability of natural and randomized high-palmitic-and high-stearic-acid oils from genetically modified soybean varieties

The oxidative stability of soybean oil triacylglycerols (TAG) obtained from genetically modified soybeans was determined before and after chemical randomization. Soybean oil oxidative studies were carried out under static oxygen headspace at 60°C in the dark and oxidative deterioration was monitored by peroxide value, monometric and oligomeric oxidation products, and volatile compounds. Randomization of the soybean oil TAG improved the oxidative stability compared to the natural soybean oil TAG. Oxidative stability was improved by three factors. Factor one was the genetic modification of the fatty acid composition in which polyunsaturated acids (such as linolenic and linoleic acids) were decreased and in which monounsaturated fatty acids (such as oleic) and saturated acids (palmitic and stearic) were increased. Factor two was the TAG compositional modification with a decrease in linolenic and linoleic-containing TAG and an increase in TAG with stearic and palmitic acids in combination with oleic acid. Factor three was the TAG structure modification accomplished by an increase in saturated fatty acids and a decrease in linoleic and linolenic acids at the glycerol moiety carbon 2. Presented at the AOCS Annual Meeting & Expo, Chicago, IL, May 10–13, 1998.     

Enzymatic interesterification of triolein and tristearin: Chemical structure and differential scanning calorimetric analysis of the products

The structural composition and thermal properties of the products of enzymatic interesterification of triolein and tristearin were investigated. The biocatalyst for the reaction was an immobilized Candida antarctica lipase, SP435. Enzyme load of 10% (w/w reactants) produced 72% of desired total products. Oleoyl-distearoyl triglycerides (SSO, OSS) had higher melting points than dioleoyl-stearoyl triglycerides (OOS, SOO) because the sample contained larger amounts of stearic acid than oleic acid residues. SOS and OSO were hardly produced (0.2 to 1.2%), which indicates that SP435 acted as a nonspecific lipase when catalyzing the interesterification of triolein and tristearin. The maximal yield of OSS and SSO (46.9%) was achieved with a 1.2 mole ratio of triolein to tristearin. As the proportion of tristearin was increased, the production of SOO and OOS decreased, the melting profile of the interesterified triglycerides shifted toward higher melting forms, and the solid fat content increased, indicating formation of hard fats.     

Oxidative decomposition of cholesterol in fish products

Cholesterol oxides in fish products popular in Japan, including salted and dried, boiled and dried and smoked products, were qualitatively and quantitatively determined as trimethylsilyl ether derivatives by gas-liquid chromatography and mass spectrometry. The level of total cholesterol oxides ranged widely between 8.3 ppm in boiled and dried shrimp and 188.0 ppm in boiled and dried anchovy. 7β-Hydroxycholesterol and 7-ketocholesterol were the most prominent oxidative decomposition products of cholesterol. The levels of epimeric epoxides, cholestane triol and 25-hydroxycholesterol were relatively low. To elucidate a mechanism of cholesterol oxidation proceeding during fish processing and subsequent preservation, four model systems, consisting of a mixture of purified cod liver triglycerides plus cholesterol, of a mixture of authentic triolein plus cholesterol, of triolein alone and of cholesterol alone, were stored separately at 25°C in dry air for up to 104 d. The residual fatty acids of the triglycerides, and the cholesterol oxides produced, were recovered and determined. Oxygen uptake remained almost unchanged for the mixture of triolein plus cholesterol. No detectable amount of cholesterol oxides was produced, and the fatty acid content of the residual oleic acid, measured by an internal standard, remained almost unchanged. For the mixture of cod liver triglycerides plus cholesterol, a remarkable increase in oxygen uptake was observed. A continuous increase in the amount of cholesterol oxides was observed, accompanied by a remarkable concurrent decrease in polyunsaturated fatty acid residues, as well as of the oleic acid naturally present. These results strongly suggest that cholesterol oxidation in fish products proceeds in conjunction with oxidative decomposition of the coexisting polyunsaturated fatty acids of fish oils.     

Volatile components from tristearin heated in air

Tristearin was heated to 192 C in air, and its volatile oxidation products were collected directly on a cooled (−60 C) gas liquid chromatography column. Subsequently, the volatile products were separated by temperature programing up to 250 C and identified by mass spectrometry. Methyl ketones and aldehydes were the major degradation products along with minor amounts of monobasic acids, n-hydrocarbons, primary alcohols, and γ-lactones. Qualitative results indicated all the fatty acid methylene carbon atoms are susceptible to oxidation. Quantities of aldehydes and ketones were found to be in excess of their taste threshold concentrations, suggesting thermally oxidized saturated fatty acids may be precursors of some odors and flavors associated with heated lipids. Presented at the AOCS Fall Meeting, Philadelphia, September 1974. ARS, USDA.     

Thermal decomposition of methyl oleate hydroperoxides and identification of volatile components by gas chromatography-mass spectrometry

The role of methyl oleate hydroperoxides as precursors of volatile compounds was investigated by thermal decomposition in the injector port of a gas chromatograph attached to a computerized mass spectrometer. The major volatile compounds identified correspond to those formed from triolein heated in air at 192 C.     

Hydrolysis of triglycerides in the isolated perfused rat lung

The purpose of this study was to investigate the hydrolysis of saturated and unsaturated triglycerides by lung lipoprotein lipase and to measure the incorporation of triglyceride fatty acids into lung tissue lipids. Lipolytic activity was studied in the isolated ventilated rat lung, perfused for 100 min in a recycling system with Krebs Ringer bicarbonate containing bovine serum albumin, 5.6 mM glucose, and 1.5 or 10 mM triglyceride. Saturated triglycerides were hydrolyzed at significantly (p<0.05) lower rates than unsaturated triglycerides; tricaprylin, trimyristin and tripalmitin were hydrolyzed at 8.1+1.8, 5.4+1.5 and 9.5+1.8 μmol free fatty acids/g dry wt/100 min, respectively, whereas triolein and trilinolein were hydrolyzed at 20.2+1.8 and 20.6+0.3 μmol free fatty acids/g dry wt/100 min, respectively. The polyunsaturated triglycerides, trilinolein and triarachidonin were hydrolyzed at even higher rates (44.3+3.0 and 50.9+5.4 μmol free fatty acids/g dry wt/100 min, respectively). Intralipid infused at a concentration of 10 mM triglyceride was hydrolyzed at a significantly higher rate than at 1.5 mM triglyceride (58+6.3 μmol free fatty acids/g dry wt/100 min vs 16.6+1.7 μmol free fatty acids/g dry wt/100 min, respectively). Labeled unsaturated triglycerides were broken down at significantly higher rates than labeled saturated triglycerides. Incorporation of triglyceride-fatty acid into lung lipid was greater into neutral lipids than into phospholipids. The data suggest that (a) the factors that appear to affect lung lipoprotein lipase activity are composition and concentration of circulating triglyceride, (b) uptake of fatty acids into the tissue was proportional to the rate of hydrolysis of the emulsion, and (c) triglyceride-fatty acids could therefore be used by the lung for metabolic needs. The data presented in part at the Annual Meetings of the American Physiological Society, Atlanta, GA, April 1981, and the American Thoracic Society, Detroit, MI, May 1981, and published in abstract form-Fed. Proc. 40, 621 (1981), andAm. Rev. Respir. Dis. 123, 219 (1981).     

Changes in the structure of soybean triglycerides during maturation

Soybeans of the Hawkeye variety were picked at eleven periods from 30 to 111 days after flowering and extracted with chloroform-methanol. The triglyceride fraction of five pickings, selected 35 to 91 days after flowering (when synthesis of lipid was most active), were isolated by silicic acid thin layer chromatography (TLC) and species composition determined using argentation TLC and lipase hydrolysis. The triglyceride content of the total lipid increased from 6.5% at 30 days after flowering to 85% in the mature bean (111 days). The major changes in fatty acid composition of the triglycerides occurred during the first 52 days after flowering. During this period linolenic acid decreased from 34.2% to 11.7%, the percentages of linoleic and oleic acids increased, stearic remained fairly constant and palmitic decreased slightly. Large quantitative changes occurred in the molecular species of the triglycerides of the bean during maturation; some triglycerides containing linolenic acid could not be detected approximately 66 days after flowering. Although changes occurred in the percentage and amount of each triglyceride species, the positional distribution of fatty acids remained virtually unchanged throughout maturation. Linolenic acid was distributed fairly uniformly between the β-position and the α-positions, linoleate favored esterification in the β-position, and oleate the α-positions. Most of the stearic and palmitic acids were esterified in the α-positions. The consistency of the positional arrangement of the fatty acids indicated that the mode of glyceride synthesis was established very early during maturation and molecular species composition was controlled by the fatty acids available for synthesis.     

Volatile components from trilinolein heated in air

Pure trilinolein and mixtures of trilinolein-tristearin, trilinolein-triolein, and trilinolein-triolein-tristearin were heated to 192 C in air. Volatiles were collected, separated, and identified by gas chromatography-mass spectrometry. Major volatiles observed from each heated sample produced compounds unique to the autoxidation-decomposition of the trilinolein component and included: pentane, acrolein, pentanal, 1-pentanol, hexanal, 2- and/or 3-hexenal, 2-heptenal, 2-octenal, 2,4-decadienal, and 4,5-epoxydec-2-enal. When samples containing both trilinolein and triolein were heated, volatiles were produced that could be ascribed to each triglyceride. However, heated mixtures containing tristearin produced no observable volatiles that could be related to the oxidized saturated triglyceride. Minor volatiles identified from the heated trilinolein and its mixtures included; aliphatic acids, saturated and unsaturated aldehydes, primary and secondary alcohols, gamma lactones, furans, hydrocarbons, and methyl ketones.     

The variation of triglyceride structure with fatty acid composition in pig adipose tissue

Forty-five triglyceride samples with a wide range of fatty acid compositions were selected from a large number of pig adipose tissue samples (inner and outer back fats and perenephric fat) available from nutritional experiments. These samples were subjected to stereospecific analysis to determine the changes occurring in the positional distribution of the component fatty acids. The oleic acid content of the triglycerides was taken as the standard of comparison and as this increased, the proportions of the other unsaturated fatty acids also increased in a linear manner and the concentrations of the saturated components decreased proportionately. In position 1, the palmitic acid concentration remained constant while the stearic acid concentration decreased linearly and the concentrations of the unsaturated fatty acids increased. In position 2 the stearic acid concentration remained almost constant while the palmitic acid concentration decreased linearly in response to increases in the concentrations of the unsaturated acids. The least change occurred in position 3 where there were slight decreases in the concentrations of saturated acids as the concentrations of unsaturated acids increased. The precise quantitative relationships depended on the tissue examined. Constant proportions of the available myristic and palmitoleic acids were found in all three positions and constant proportions of the available stearic and oleic acids were found in position 1. These results are discussed in relation to possible pathways of triglyceride biosynthesis in pig adipose tissues.     

Alteration of soybean oil composition by plant breeding

Experimental lines selected from the cross PI 90406 × PI 92567 are being used in an attempt to improve soybean (Glycine max [L.] Merr.) oil by altering fatty acid composition through plant breeding. Preliminary evidence shows that the concentration of linolenic acid in soybean oil is reduced by selection for high levels of oleic acid. Levels of poly-unsaturated acids in “high oleic” selections are lower, to various degrees, but the concentration of saturated fatty acids is not different from that of the variety Dare, a representative southern commercial cultivar. In triglyceride from the “high oleic” selection, N70-3436, levels of palmitic, stearic, oleic, linoleic, and linolenic acid are 9.5, 2.0, 40.1, 43.3, and 5.1 mol %, respectively. The types of triglyceride structures observed in the experimental lines which were examined also are changed. The combined level of triolein, monooleyl-dilinolein, and dioleyl-mono-linolein in seed from N70-3436 is doubled and constitutes ca. 50% of the oil.     

Adipose hormone-sensitive lipase preferentially releases polyunsaturated fatty acids from triglycerides

Rat adipose hormone-sensitive lipase-mediated release of fatty acids from triglycerides was studied in three model systems: i) cultured preadipocytes containing polyunsaturated fatty acid-enriched triglyceride; ii) perfused epididymal fat pads; and iii)in vitro incubations of crude preparations of hormone-sensitive lipase with synthetic triglyceride-analogues as substrates. We found that cultured preadipocytes challenged with 10μM norepinephrine tended to release more ω6 and ω3 polyunsaturated fatty acids than saturated fatty acids. Fat pads perfused with 10 μM norepinephrine preferentially released arachidonate and α-linolenate but tended to retain oleate and linoleate. Finally, crude preparations of hormonesensitive lipase released from the triglyceride-analogue substrates α-linolenate twice as fast as oleate. We conclude that rat adipose hormone-sensitive lipase preferentially releases polyunsaturated fatty acids from triglycerides. We suggest that this may be a mechanism by which these fatty acids are kept from being trapped in fat depots and maintained in the circulation.