W. E. Neff

Effect of triacylglycerol composition and structures on oxidative stability of oils from selected soybean germplasm

The oxidative stability of soybean oil triacylglycerols was studied with respect to composition and structure. Crude soybean oils of various fatty acid and triacylglycerol composition, hexane-extracted from ground beans, were chromatographed to remove non-triacylglycerol components. Purified triacylglycerols were oxidized at 60°C, in air, in the dark. The oxidative stability or resistance of the substrate to reaction with oxygen was measured by determination of peroxide value and headspace analysis of volatiles of the oxidized triacylglycerols (at less than 1% oxidation). The correlation coefficients (r) for rates of peroxide formation (r=0.85) and total headspace volatiles (r=0.87) were related positively to oxidizability. Rate of peroxide formation showed a positive correlation with average number of double bonds (r=0.81), linoleic acid (r=0.63), linolenic acid (r=0.85). Rate of peroxide formation also showed a positive correlation with linoleic acid (r=0.72) at the 2-position of the glycerol moiety. A negative correlation was observed between rate of peroxide formation and oleic acid (r=−0.82). Resistance of soybean triacylglycerols to reaction with oxygen was decreased by linolenic (r=0.87) and increased by oleic acid (r=−0.76)-containing triacylglycerols. Volatile formation was increased by increased concentration of linolenic acid at exterior glycerol carbons 1,3 and by linoleic acid at the interior carbon 2. Headspace analysis of voltiles and high-performance liquid chromatography of hydroperoxides indicated that as oxidation proceeded there was a slight decrease in the linolenic acid-derived hydroperoxides and an increase in the linoleic acid-derived hydroperoxides. The oxidative stability of soybean oil triacylclycerols with respect to composition and structure is of interest to the development of soybean varieties with oils of improved odor and flavor stability.

Physical Properties of Interesterified Fat Blends

Fat blends, formulated by mixing fully hydrogenated soybean oil with nine different commonly used vegetable oils in a ratio of 1:1 (w/w), were subjected to interesterification (also commonly referred to as rearrangement or randomization) with sodium methoxide catalyst. Fatty acid composition and triacylglycerol molecular species of each fat blend and the interesterified product were determined and correlated with the following physical properties: melting, crystallization characteristics and solid fat content. The differences in the endothermic and exothermic peak temperatures, total heat of fusion and crystallization (β and β′ crystalline content) and solid fat content among the fat blends clearly showed the effect of the composition of each oil on the physical properties. Oils that contained a considerable amount of palmitic acid had a favorable influence on the crystallization and polymorphic form of interesterified fat blends.

Characterization of model triacylglycerol (triolein, trilinolein and trilinolenin) autoxidation products via high-performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry

Abstract Oxidation products from the autoxidation of three triacylglycerol standards have been analyzed using reversed-phase high-performance liquid chromatography (RP-HPLC) coupled to mass spectrometry via an atmospheric pressure chemical ionization (APCI) source. Triolein, trilinolein and trilinolenin were autoxidized in the dark at 50–60°C until the oxidation products represented approximately 30% of the starting material. These oxidation product mixtures were then analyzed using RP-HPLC–APCI-MS. Several classes of oxidation products were directly detected and identified. Monohydroperoxides were present in the largest amounts in the oxidation products mixtures. The hydroperoxides were found to provide several structurally useful fragments: epoxide intermediates were formed which then underwent further fragmentation, and other fragments were formed from concerted loss of the hydroperoxide group to form a site of unsaturation. Fragments formed by intra-annular cleavage of epoxide intermediates allowed identification of several hydroperoxide isomers. Bishydroperoxides were observed which underwent similar fragmentation pathways. Mono- and diepoxides were also formed by the autoxidation reaction. Two classes of epoxides were observed: those in which an epoxide formed in place of an existing double bond, and those in which an epoxide formed away from a double bond. Two distinct fragmentation mechanisms were observed for epoxides which were not formed across a double bond. Other oxidation products which were observed included hydroxy trilinolenin, epidioxy trilinolenin and hydroperoxy, epidioxy trilinolenin.

Non-volatile products of triolein produced at frying temperatures characterized using liquid chromatography with online mass spectrometric detection

Oxidation products from triolein under model heated frying conditions have been analyzed using liquid chromatography with an evaporative light scattering detector and atmospheric pressure chemical ionization (APCI) mass spectrometric detection. Triolein was heated at 190 degrees C with 2% water added each hour, to simulate the moisture of a frozen product, until polar components reached approximately 30%. The samples were separated using reversed-phase high-performance liquid chromatography with APCI-MS detection. Triolein oxidation products included hydroperoxides, epoxides and a ketone. Other products were formed by shortening of an acyl chain on the intact triolein. Normal and oxygen-containing products formed by the dimerization of triolein were also observed. Other products included chain addition products formed by addition of acyl chain subunits to intact triolein to form higher molecular weight products.

Autoxidation products of normal and genetically modified canola oil varieties determined using liquid chromatography with mass spectrometric detection

Normal, high stearic acid and high lauric acid canola oil varieties were heated in the presence of air to allow autoxidation to occur. After the reaction, the oils were analyzed using a non-aqueous reversed-phase high-performance liquid chromatographic separation followed by detection using atmospheric pressure chemical ionization mass spectrometry. Oxidized products were separated and identified. The major autoxidation products which remained intact were epoxides and hydroperoxides. Two classes of epoxy triacylglycerols (TAGs) were formed. One class with the epoxy group replacing a site of unsaturation and one class adjacent to a site of unsaturation, as was previously reported for model TAGs. Intact oxidation products resulted mostly from oxidation of oleic acid, while oxidation products of linoleic and linolenic acid chains decomposed to yield chain-shortened species. Both neutral and polar chain-shortened products were observed. Polar chain-shortened decomposition products eluted at very short retention times and required a different chromatographic gradient to separate the molecules. This class of molecules was tentatively identified as core aldehydes. The high stearic acid canola oil yielded more intact oxidation products containing stearic acid, as expected. The high lauric acid oil produced intact oxidation products which contained lauric acid.

Analyses of vegetable oil triglyceride molecular species by reversed phase high performance liquid chromatography

Abstract Triglyceride molecular species (TGMS) of 10 vegetable oils (olive, soybean, sunflower, corn, cottonseed, pumpkin seed, peanut, safflower, canola and palm oil) were separated and analyzed quantitatively by gradient, reversed phase high performance liquid chromatography with a flame ionization detector (FID). Identification of TGMS was made by comparison of experimental and calculated theoretical carbon numbers (TCN). The relationship between elution time and calculated TCN of each TGMS was linear. The FID response (area percent) was determined to be linear or proportional to weight percent. Nine of the oils showed significant differences between observed TGMS composition and

Triacylglycerol Analysis by High Performance Liquid Chromatography-Atmospheric Pressure Chemical Ionization Mass Spectrometry: Crepis Alpina and Vernonia Galamensis Seed Oils

Abstract Unusual seed oils having significance for chemical synthesis, Crepis alpina, or with fatty acids which contain functional groups important in the preparation of plastics, Vernonia galamensis, were analyzed by a new reversed-phase high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry technique. Using this method, we have identified 16 triacylglycerols in the Crepis alpina oil and 18 triacylglycerols in Vernonia galamensis oil and showed greater sensitivity for detection of and improved identification of triacylglycerols compared to previous analyses using the techniques of reversed-phase and silver ion high performance liquid chromatography with a flame ionization detector. The most abundant Crepis alpina triacylglycerols were: linoleoyldicrepenynoylglycerol (33.0%), tricrepenynoyl (32.3%), palmitoyldicrepenynoyl (11.5%), dilinoleoylcrepenynoyl (6.7%) glycerols. The remaining triacylglycerols occurred at five or less mole percent abundance. The most abun...

Autoxidation of polyunsaturated triacylglycerols. IV : Volatile decomposition products from triacylglycerols containing linoleate and linolenate

Trilinoleoylglycerol (LLL), trilinolenoylglycerol (LnLnLn) and four synthetic triacylglycerols were autoxidized and the volatile products were investigated to determine the effect of fatty acid glyceride position on the mechanism of hydroperoxide decomposition. Capillary gas chromatography provided a sensitive method to follow the volatile oxidation products of mixtures of LLL and LnLnLn and of synthetic triacylglycerols containing linoleate and linolenate in different known positions. The relative amount of linoleate oxidation was determined by analyzing for hexanal, 2-heptenal and 2,4-decadienal, and the relative amount of linolenate oxidation by analyzing for 2,4-heptadienal and 2,4,7-decatrienal. The volatiles from pure monohydroperoxides of LLL and LnLnLn were compared with those of the corresponding triacylglycerols by capillary gas chromatography. Significant differences in the distribution of volatile products were observed depending on the triacylglycerols precursor. A 1∶1 mixture of LLL and LnLnLn autoxidized at 40°C showed an equal contribution of linolenate and linoleate volatiles at a peroxide value of 34. The synthetic triacylglycerols LLnL and LLLn (L, linoleic; Ln, linolenic acid) formed initially about the same total volatiles, whereas LnLnL formed more volatiles than LnLLn. The ratio Ln to L volatile products was the same for the diL triacylglycerols, and higher for LnLnL than for LnLLn. This new information should permit us to better understand the influence of triacylglycerol structure on the relative oxidative stability of unsaturated triacylglycerols.

Silver ion high-performance liquid chromatography of the triacylglycerols ofCrepis alpina seed oil

The triacylglycerols ofCrepis alpina oil were characterized because this oil has a high concentration of crepenynic (cis-9-octadecen-12-ynoic) acid, a fatty acid useful in the chemical synthesis of deuterated fats for human metabolism studies. The triacylglycerols were separated from the crude oil by solid-phase extraction. Resolution, quantitation and isolation of the individual triacylglycerols were performed by silver ion high-performance liquid chromatography on a commercial column, an acetonitrile in hexane isocratic mobile phase and flame-ionization detection. Isolated triacylglycerols were identified by capillary gas chromatography of their fatty acid methyl esters. Of the eleven eluted triacylglycerols ofCrepis alpina oil, 85% included 35% tricrepenynoyl, 34% linoleoyldicrepenynoyl and 16% dilinoleoylcrepenynoyl glycerols. Triacylglycerols eluted according to the numbers of alkene and alkyne bonds. Elution times, resolution and quantitation were reproducible over a three-month period. The flame-ionization detector response required no response factors for quantitation of the triacylglycerols present inCrepis alpina oil. The silver ion chromatography system permitted the identification of 95% of the triacylglycerols compared to 70% of the triacylglycerols previously identified with reversed-phase high-performance liquid chromatography.

Photooxidation of soybean oils as affected by triacylglycerol composition and structure

The photooxidation of soybean oil was determined and correlated with triacylglycerol composition and structure. Purified triacylglycerols were photooxidized at room temperature under fluorescent light. Rates of peroxide formation and total headspace volatiles were related positively (P<0.5 significance) to oxidizability (r=0.75, r=0.76); content of linolenic acid (r=0.80, r=0.85) and linoleic acid (r=0.61, r=0.57); linoleic acid on carbon 2 (r=0.64, r=0.64); and average number of double bonds (r=0.76, r=0.76). Negative correlations were observed with respect to oleic acid (r=−0.70, r=−0.70). Soybean oil stability was decreased by linolenic acid-containing triacylglycerols and increased by oleic acid-containing triacylglycerols. Trilinoleoylglycerol and dilinoleoyl-oleoylglycerol were the most important oxidation product precursors. However, for high-linolenic acid soybean oil, dilinoleoyl-linolenoylglycerol and trilinoleoylglycerol were the most important oxidation product precursors. The most abundant volatile produced from thermal decomposition at 140°C of photooxidized triacylglycerols was 2-heptenal, except for high-linolenic acid oils, where the most abundant volatile was propanal. The photooxidative stability of soybean oil triacylglycerols with respect to composition and structure is of interest for the development of soybean varieties with oils of improved odor and flavor stability.