Analysis of molecular species of peroxide adducts of triacylglycerols following treatment of corn oil with tert-butyl hydroperoxide

We recently demonstrated that exposure of synthetic mono- and diunsaturated triacylglycerols to tert-butylhydroperoxide (TBHP) leads to formation of stable adducts of the oxidizing agent and the unsaturated esters (Sjövall, O., Kuksis, A., and Kallio, H., Reversed Phase High-Performance Liquid Chromatographic Separation of tert-Butyl Hydroperoxide Oxidation Products of Unsaturated Triacylglycerols, J. Chromatogr. A 905, 119-132, 2001). In the present study we isolated and identified the TBHP adducts of corn oil triacylglycerols. The much wider range of molecular species available in the corn oil permitted us to demonstrate that the yield of the adducts varies with the degree of unsaturation of the triacylglycerol. The highest yields were obtained for the linoleate (20%, of linoleoyl-containing residual triacylglycerols) and the lowest ones for the oleate (5% of oleoyl-containing residual triacylglycerols) triacylglycerols, whereas the saturated triacylglycerols did not give TBHP adducts in readily detectable amounts. Normal-phase thin-layer chromatography along with reversed-phase high-performance liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization was used to isolate and separate the major molecular species of polyunsaturated triacylglycerols and corresponding TBHP adducts. As an extreme example, the dilinoleoylmonooleoylglycerol was identified as the mono-, di-, tri-, tetra-, and penta-TBHP adduct. LC/MS with electrospray ionization at elevated capillary exit voltage (pseudo tandem mass spectrometry) was used to confirm structures of the [M-RCOOH]+ ions and the absence of TBHP adducts of [M-RCOOH]+. It is concluded that stable adduct formation is an unavoidable complication of preparation of oxotriacylglycerols by oxidation with concentrated TBHP solutions and care must be taken to resolve the adducts from the desired oxidation product.

Regioisomerism of triacylglycerols in lard, tallow, yolk, chicken skin, palm oil, palm olein, palm stearin, and a transesterified blend of palm stearin and coconut oil analyzed by tandem mass spectrometry

Triacylglycerols (TAG) of lard, tallow, egg yolk, chicken skin, palm oil, palm olein, palm stearin, and a transesterified blend of palm stearin and coconut oil (82:18) were investigated by chemical ionization and collision-induced dissociation tandem mass spectrometry. Accurate molecular level information of the regioisomeric structures of individual TAGs was achieved. When existing in a TAG molecule of lard, palmitic acid occupied 90-100% of the sn-2 position. Within the major fatty acid combinations in tallow TAGs, the secondary position sn-2 was preferentially occupied in the decreasing order by oleoyl > palmitoyl > stearoyl residues, the order in saturated TAGs being myristoyl > stearoyl = palmitoyl. TAGs in egg yolk were more asymmetric than in chicken skin, with linoleic acid highly specifically attached in the yolk sn-2 carbon. Nearly 50% of yolk TAGs contained 52 carbon atoms with two or three double bonds. Linoleic, oleic, and palmitic acids were in the sn-2 location in decreasing quantities in palm oil and its fractions. Triacylglycerols of equal molecular weight behaved similarly in the fractionation process. Randomization of the parent oil TAGs was seen in the transesterified oil. The tandem mass spectrometric analysis applied provided detailed information of the distribution of fatty acids in individual combinations in TAGs.

Software (MSPECTRA) for automatic interpretation of triacylglycerol molecular mass distribution spectra and collision induced dissociation product ion spectra obtained by ammonia negative ion chemical ionization mass spectrometry

Rapid analysis of molecular mass distributions of triacylglycerol (TAG) mixtures and regioisomeric structures of selected molecular mass species is possible using ammonia negative ion chemical ionization mass spectrometry utilizing sample introduction by direct exposure probe. However, interpretation of spectra and calculation of results is time consuming, thus lengthening the total analysis time. To facilitate result calculation a software package (MSPECTRA 1.3) was developed and applied to automatic processing of triacylglycerol molecular mass distribution spectra and collision induced dissociation (CID) product ion spectra. The program is capable of identifying triacylglycerol molecular mass species possessing different ACN:DB (acyl carbon number:number of double bonds) ratios on the basis of m/z values of [M - H](-) ions. In addition to such identification the program also corrects spectra for abundances of naturally occurring (13)C isotopes and calculates relative proportions of triacylglycerol molecular species in the analyzed samples. If several replicate spectra are processed simultaneously the program automatically calculates an average and standard deviation of relative proportions of molecular species. In the case of CID spectra the program identifies fatty acid fragment ions [RCO(2)](-) and the corresponding [M - H - RCO(2)H - 100](-) ions, and calculates the relative proportions of ions in both groups. These proportions are then used automatically to calculate the fatty acid combinations comprising the parent triacylglycerol molecule and the regiospecific positions of fatty acids. Processing of several replicate product ion spectra simultaneously produces averaged proportions of regioisomers comprising the parent triacylglycerol molecular species and the standard deviation of the analysis. The performance of the program was tested by analyzing triacylglycerol samples of human milk, human milk substitutes, human chylomicron and cocoa butter, and by comparing results obtained by automated processing of the data with manually calculated results.

Development of rancidity in wheat germ analyzed by headspace gas chromatography and sensory analysis

Wheat germ is susceptible to oxidation due to its high content of unsaturated oil. Volatile compounds in stored wheat germ were evaluated using dynamic headspace gas chromatography (HS-GC) and sensory analysis. Preliminary comparisons were also made between freshly prepared wheat germ and wheat germ subjected to microwave heating at 45 and 55 degrees C prior to storage at room temperature. The progress of oxidation was followed in untreated wheat germ for 4 weeks and in heat-treated wheat germ for 7 weeks by HS-GC and sensory evaluation. Significant (p < 0.05) changes in rancid odor and flavor were observed in the untreated wheat germ after 3 weeks, whereas no corresponding difference was observed in the microwave-heated wheat germ after 7 weeks of storage. Identification of a total of 36 volatile compounds was performed according to their mass spectra and Kovats indices. The major volatiles were hexanal, alpha-pinene, 1-hexanol, and 3-carene. In addition to analysis of a short period of storage, 30 volatile compounds were identified from the headspace of wheat germ stored for >1 year.

Rapid complexing of oxoacylglycerols with amino acids, peptides and aminophospholipids

We prepared model Schiff bases from 2-[9-oxo]nonanoyl glycerol (2-MAG-ALD) and various amino compounds. 2-MAG-ALD was obtained by pancreatic lipase hydrolysis of trioleoyl glycerol and reductive ozonolysis of the resulting 2-monooleoyl glycerol. The reaction products were purified by thin-layer chromatography. Schiff bases were synthesized in greater than 50% yield by reacting 2-MAG-ALD with twofold molar excess of valine, Nalpha-acetyl-L-lysine methyl ester and the tripeptides glycyl-glycyl-glycine, glycyl-glycyl-histidine, and glycyl-histidyl-lysine in aqueous methanol and with 1-palmitoyl-2-stearoyl glycerophosphoethanolamine (PE) in chloroform/methanol for 16 h at room temperature. Prior to analysis the bases were reduced with sodium cyanoborohydride in methanol for 30 min at 4 degrees C. Reaction products were analyzed by high-performance liquid chromatography/electrospray ionization/mass spectrometry (HPLC/ESI/MS). Reduced Schiff bases of 2-MAG-ALD with PE and amino acids were analyzed by normal-phase HPLC/ESI/MS and those with peptides by reversed-phase HPLC/ESI/MS. Single adducts were obtained in all cases and both the alpha-amino group of valine and the epsilon-amino group of Nalpha-acetyl-L-lysine methyl ester were reactive. Molecular ions of reaction products were the only detected ions in the negative ionization mode, whereas in the positive ion mode sodiated molecular ions were also detected. The present study suggests that 2-MAG-ALD may form Schiff base adducts with amino compounds in other aqueous media, such as the intestinal lumen and in the hydrophobic environment of cell membranes.

Elution factors of synthetic oxotriacylglycerols as an aid in identification of peroxidized natural triacylglycerols by reverse-phase high-performance liquid chromatography with electrospray mass spectrometry

Selected elution factors were determined for model oxotriacylglycerols as an aid in identification of the peroxidation products of natural triacylglycerols by reverse-phase high-performance liquid chromatography (HPLC) with electrospray mass spectrometry (LC/ES/MS). For this purpose synthetic triacylglycerols of known structure were converted to hydroperoxides, hydroxides, epoxides, and core aldehydes and their dinitrophenylhydrazones by published procedures. The oxotriacylglycerols were resolved by normal-phase thin-layer chromatography and reverse-phase HPLC, and the identities of the oxotriacylglycerols confirmed by LC/ES/MS. Elution factors of oxotriacylglycerols were determined in relation to a homologous series of saturated triacylglycerols, ranging from 24 to 54 acyl carbons, and analyzed by reverse-phase HPLC, using a gradient of 20-80% isopropanol in methanol as eluting solvent and an evaporative light-scattering detector. It was shown that the elution times varied with the nature of the functional group and its regiolocation in the triacylglycerol molecule. A total of 31 incremental elution factors were calculated from chromatography of 33 oxygenated and nonoxygenated triacylglycerol species, ranging in carbon number from 36 to 54 and in double-bond number from 0 to 6.

The effects of gamma-irradiation on some pure aroma compounds of spices

Chemical changes due to gamma-irradiation were investigated in 11 pure aroma compounds typically found in spices. Samples were irradiated with doses of 0, 10, and 50 kGy. The irradiation source was 60Co. Irradiated samples and unirradiated controls were analyzed by gas chromatography alone and coupled with mass spectrometry. Significant changes due to the irradiation occurred only in (+/-)-linalool and alpha-terpineol, which are typical components of, for example, coriander and bay leaf. Their total amounts decreased by about 4-13% and some minor peaks increased as a result of irradiation. However, different results may be obtained when the spices themselves are irradiated.