Regiospecific determination of short-chain triacylglycerols in butterfat by normal-phase HPLC with on-line electrospray-tandem mass spectrometry

Chiral analysis of glycerol phosphates - can bacteria biosynthesize heterochiral phospholipid membranes?

Phosphatidylglycerol (1,2-diacyl-sn-glycero-3-phospho-glycerol) (PG) is one of the most abundant lipids in bacteria. However, the chirality of the carbon atom on glycerol phosphate is different between the three kingdoms, Archaea, Bacteria, and Eukarya. Archaea membranes consist of phospholipids with glycerol-1-phosphate (G1P) in the S configuration, whereas phospholipids of the other two kingdoms contain glycerol-3-phosphate (G3P) having R stereochemistry. In the present study, GC/MS and LC/MS methods sensitively detected G3P and G1P from four bacterial strains (Bacillus amyloliquefaciens, B. subtilis, Clavibacter michiganensis, and Geobacillus stearothermophilus). Strain selection was carried out based on a GenBank search that revealed bacterial sequences associated with both enzymes involved in glycerol-phosphate synthesis, i.e., glycerol-3-phosphate dehydrogenase and glycerol-1-phosphate dehydrogenase. The detection of G1P and G3P was made by comparing the retention times of synthetic standards with those of analyzed samples. The structures of both glycerol phosphates were confirmed by selected ion monitoring (SIM) at m/z 171.006. The total concentration of G3P and G1P was around 30 µM, with a ratio of G3P to G1P of 4:1. We showed that PG was the most abundant phospholipid in all four bacteria by using the following analytical techniques and chromatographic modes: hydrophilic interaction liquid chromatography (HILIC), reversed-phase high-performance liquid chromatography high-resolution electrospray ionization tandem mass spectrometry (RP-HPLC/HR-ESI tandem MS) in negative and positive ionization modes, and an enzymatic cleavage by phospholipase C. By using chiral chromatography, the presence of both enantiomers in the glycerol backbone of some molecular species of PG was revealed. These results allow us to conclude that the bacteria examined here produce both enantiomer glycerol phosphates.

Structural Characterization of Mono- and Dimethylphosphatidylethanolamines from Various Organisms Using a Complex Analytical Strategy Including Chiral Chromatography

Two minor phospholipids, i.e., mono- and/or dimethylphosphatidylethanolamines, are widespread in many organisms, from bacteria to higher plants and animals. A molecular mixture of methyl-PE and dimethyl-PE was obtained from total lipids by liquid chromatography and further identified by mass spectrometry. Total methyl-PE and dimethyl-PE were cleaved by phospholipase C, and the resulting diacylglycerols, in the form of acetyl derivatives, were separated into alkyl-acyl, alkenyl-acyl, and diacylglycerols. Reversed-phase LC/MS allowed dozens of molecular species to be identified and further analyzed. This was performed on a chiral column, and identification by tandem positive ESI revealed that diacyl derivatives from all four bacteria were mixtures of both R and S enantiomers. The same applied to alkenyl-acyl derivatives of anaerobic bacteria. Analysis thus confirmed that some bacteria biosynthesize phospholipids having both sn-glycerol-3-phosphate and sn-glycerol-1-phosphate as precursors. These findings were further supported by data already published in GenBank. The use of chiral chromatography made it possible to prove that both enantiomers of glycerol phosphate of some molecular species of mono- and dimethylphosphatidylethanolamines are present. The result of the analysis can be interpreted that the cultured bacteria do not have homochiral membranes but, on the contrary, have an asymmetric, i.e., heterochiral membranes.

Bovine Milk Triacylglycerol Regioisomer Ratio Shows Remarkable Inter-Breed and Inter-Cow Variation

Regioisomers (or positional isomers) of triacylglycerols (TAGs) of milk are known to show differential outcome in relation to human absorption. Quantitation of TAG regioisomers remains a big challenge due to the lack of facile chromatographic separation technique. The feasibility of using fragment ion intensity ratio to determine the ratio of co-eluting AAB/ABA-type regioisomer pairs was confirmed in this study. The ability of C30 stationary phase in resolving interfering TAG isomers was demonstrated for the first time. This allowed us to reveal the complexity of using fragment ion intensity to quantify 1,2-olein-3-palmitin (OOP), 1,3-olein-2-palmitin (OPO), 1,2-olein-3-stearin (OOS), and 1,3-olein-2-stearin (OSO) regioisomers in milk samples. A novel algorithm was proposed to consider the contribution of OPO/OOP and OSO/OOS double bond (DB)-isomers and to eliminate the interference of isobaric ions from other isomers, an aspect overlooked in previous studies. This liquid chromatography-mass spectrometry method that requires no pre-fractioning and a moderate chromatographic separation time of 36 min is simple and, thus, suitable for screening a large number of samples for genetic analysis of this trait. Preliminary results using a small cohort of animals showed that OPO/OOP ratio differs significantly between Jersey and Holstein cows, and a large variation was also observed across individual Holstein cows.

Separation and identification of diacylglycerols containing branched chain fatty acids by liquid chromatography-mass spectrometry

A combination of two chromatographic and two enzymatic methods was used for the analysis of molecular species of lipids from Gram-positive bacteria of the genus Kocuria. Gram-positive bacteria contain a majority of branched fatty acids (FAs), especially iso- and/or anteiso-FAs. Two strains K. rhizophila were cultivated at three different temperatures (20, 28, and 37°C) and the majority phospholipid, i.e., the mixture of molecular species of phosphatidylglycerols (PGs) was separated by means of hydrophilic interaction liquid chromatography (HILIC). After enzymatic hydrolysis of PGs by phospholipase C and derivatization of the free OH group, the sn-1,2-diacyl-3-acetyl triacylglycerols (AcTAGs) were separated by reversed phase HPLC. Molecular species such as i-15:0/i-15:0/2:0, ai-15:0/ai-15:0/2:0, and 15:0/15:0/2:0 (straight chains) were identified by liquid chromatography-positive electrospray ionization mass spectrometry. The tandem mass spectra of both standards and natural compounds containing iso, anteiso and straight chain FAs with the same carbons were identical. Therefore, for identification of the ratio of two regioisomers, i.e. i-15:0/ai-15:0/2:0 vs. ai-15:0/i-15:0/2:0, they were cleavage by pancreatic lipase. The mixture of free fatty acids (FFAs) and 2-monoacylglycerols (2-MAGs) was obtained. After their separation by TLC and esterification and/or transesterification, the fatty acid methyl esters were quantified by GC-MS and thus the ratio of regioisomers was determined. It has been shown that the ratio of PG (containing as majority i-15: 0 / i-15: 0, i-15: 0 / ai-15: 0 and / or ai-15: 0 / i-15: 0 and ai-15: 0 / ai-15: 0 molecular species) significantly affected the membrane flow of bacterial cells cultured at different temperatures.

Simulated in vitro infant gastrointestinal digestion of yak milk fat globules: A comparison with cow milk fat globules

Lipolysis products released during digestion exert positive metabolic impacts on the nutrition of newborns. However, the lipolysis behavior of yak milk lipids during digestion remains unknown. In this study, the simulated in vitro infant gastrointestinal digestion of cow, yak and standardized yak milk fat globules the same size as those from cow milk (Cow MF, Yak MF and Yak SMF) were compared. Although Cow MF showed a higher lipolysis rate at the beginning of gastric digestion, Yak MF and Yak SMF exhibited a higher lipolysis level during later gastrointestinal digestion. Higher hydrolysis efficiency of yak milk lipids was due to their lipid properties, including their composition and structure. Furthermore, yak milk lipids released more unsaturated fatty acids than Cow MF throughout digestion. This study highlights the crucial role of lipid characteristics in the efficient digestion of milk lipids and provides new insight for the design of yak milk infant diets.

Regioisomeric and enantiomeric analysis of triacylglycerols

A survey of useful methods for separation and identification of regioisomers and enantiomers of triacylglycerols. Gas chromatography, gas chromatography-mass spectrometry, ¹³C NMR determination of regioisomers by enzymatic methods, and supercritical fluid chromatography are briefly surveyed, whereas a detailed description is given of the analysis of triacylglycerols by liquid chromatography, especially with silver ion (Ag⁺; argentation), and nonaqueous reversed phase liquid chromatography. Special attention is paid to chiral chromatography. Details of mass spectrometry of triacylglycerols are also described, especially the identification of important triacylglycerol ions such as [M + H-RCOOH]⁺ in atmospheric pressure chemical ionization mass spectra.

Comparison of Molecular Species Distribution of DHA-Containing Triacylglycerols in Milk and Different Infant Formulas by Liquid Chromatography-Mass Spectrometry

Long-chain polyunsaturated fatty acids (LC-PUFA) are an important nutritional lipid and have potential in being able to promote human health. Docosahexaenoic acid (DHA, C22:6ω3) is often added in infant formulas to meet the nutritional requirement of formula-fed infants. A comprehensive survey on DHA-containing triacylglycerol (DHA-TAG) molecular species has been conducted for seven infant formulas (IFs) sourced from Australia, Europe, and the USA as well as bovine milk and human milk. Using LC-triple quadrupole MS and LC-LTQ-orbitrap MS we were able to identify and quantify 56 DHA-TAG species in these samples; the fatty acid structure of these species was assigned using their MS(2) spectra. The species composition of DHA-TAG was found to be different between bovine milk, human milk, and IFs and also between different brands of IFs. Bovine milk and human milk contain DHA-TAG of smaller molecular size (728-952 Da), whereas five out of the seven IF samples contain species of broader mass range (from 728 to 1035 Da). Our study indicates that two types of DHA were used in the seven IF products surveyed and that there is very large difference in molecular species distribution in different IF products that may influence the fine nutritional profile and biological functions of IF products.

Ionic liquid based microextraction of targeted lipids from serum using UPLC-MS/MS with a chemometric approach: a pilot study

An ionic liquid based vortex assisted surfactant-enhanced emulsification microextraction method followed by using liquid chromatography-electrospray mass spectrometry have been used for the determination of fatty acids, triglycerides and phospholipids in serum samples.

A versatile ultra-high performance LC-MS method for lipid profiling

A new UPLC-based untargeted lipidomic approach using a qTOF hybrid mass spectrometer is introduced. The applied binary gradient enables separations of lipid species including constitutional isomeric compounds and low abundant lipid classes such as phosphatidic acid (PA). Addition of phosphoric acid to the solvents improves peak shapes for acidic phospholipids. MS(E) scans allow simultaneous acquisition of full scan data and collision induced fragmentation to improve identification of lipid classes and to obtain structural information. The method was used to investigate the lipidome of yeast.

Separation and identification of neutral cereal lipids by normal phase high-performance liquid chromatography, using evaporative light-scattering and electrospray mass spectrometry for detection

A novel method was developed for the analysis of molecular species in neutral lipid classes, using separation by normal phase high-performance liquid chromatography, followed by detection by evaporative light-scattering and electrospray ionization tandem mass spectrometry. Monoacid standards, i.e. sterol esters, triacylglycerols, fatty acids, diacylglycerols, free sterols and monoacylglycerols, were separated to baseline on microbore 3 microm-silica gel columns. Complete or partial separation of molecular species in each lipid class permitted identification by automatic tandem mass spectrometry of ammonium adducts, produced via positive electrospray ionization. After optimization of the method, separation and identification of molecular species of various lipid classes was comprehensively tested by analysis of neutral lipids from the free lipid extract of maize flour.

Regioisomer compositions of vaccenic and oleic acid containing triacylglycerols in sea buckthorn (Hippophae rhamnoides) pulp oils: influence of origin and weather conditions

Triacylglycerols (TAGs) 16:1(n-7)/16:1(n-7)/18:1(n-7) (Po/Po/V) and 16:1(n-7)/16:1(n-7)/18:1(n-9) (Po/Po/O) in pulp/peel oils of various sea buckthorn (Hippophae rhamnoides) subspecies and varieties were separated by reversed-phase high-performance liquid chromatography. The regioisomerism of the TAGs was determined by tandem mass spectrometry using ammonia supplemented in the nebulizer gas to produce ammonium adducts. The regioisomer compositions of Po/Po/V (8-24% of PoVPo) and Po/Po/O (43-61% of PoOPo) both differed from the random distribution of fatty acids (33.3% of ABA) in all 32 sea buckthorn samples investigated. The regioisomer compositions were different between cultivated ssp. rhamnoides varieties, wild ssp. rhamnoides, and wild ssp. sinensis. Differences were also found in the regioisomerism of both Po/Po/V and Po/Po/O between the two cultivated ssp. rhamnoides varieties, Tytti and Terhi. In addition, growth location and harvesting years showed clear impacts on the regioisomer compositions of Po/Po/V and Po/Po/O. Higher temperatures showed positive correlations with the proportion of PoOPo in ssp. rhamnoides and wild ssp. sinensis and with the proportion of sn-PoPoV+sn-VPoPo in wild ssp. sinensis. However, higher temperatures, higher temperature sums, and radiation sums increased the accumulation of PoVPo in wild ssp. rhamnoides.

Quantification of triacylglycerol regioisomers by ultra-high-performance liquid chromatography and ammonia negative ion atmospheric pressure chemical ionization tandem mass spectrometry

The regioisomer composition of triacylglycerols (TAGs) in various vegetable oils was determined with a new liquid chromatography/tandem mass spectrometry (LC/MS/MS method). A direct inlet ammonia negative ion chemical ionization (NICI) MS/MS method was improved by adapting it to LC negative ion (NI) atmospheric pressure chemical ionization (APCI) MS/MS system using ammonia as nebulizer gas. The method is based on the preferential formation of [M-H-RCOOH-100](-) ions during collision-induced dissociation by loss of sn-1/3 fatty acids from [M-H](-) ions. Calibration curves were created from nine reference TAGs: Ala/L/L, Gla/L/L, L/L/O, L/O/O, P/O/O, P/P/O, Po/Po/V, Po/Po/O, and C/O/O. The calibration curves were used to quantify the regioisomer compositions of selected TAGs in rapeseed oil, sunflower seed oil, palm oil, black currant seed oil, and sea buckthorn pulp oil. The method discriminates the different regioisomers and the results obtained by this method were in good agreement with previous results. This proves that this new method can be used for the determination of regiospecific distribution of fatty acids in TAGs.

Effect of latitude and weather conditions on the regioisomer compositions of alpha- and gamma-linolenoyldilinoleoylglycerol in currant seed oils

The regioisomer compositions of triacylglycerols (TAG) 18:3(n-3)/18:2(n-6)/18:2(n-6) (Ala/L/L) and 18:3(n-6)/18:2(n-6)/18:2(n-6) (Gla/L/L) in seed oils of black and green currant ( Ribes nigrum L.) and red and white currant ( Ribes rubrum L.) varieties were determined by silver-ion high-performance liquid chromatography and mass spectrometry. The aim was to investigate whether latitude and weather conditions affect the regioisomer compositions of Ala/L/L and Gla/L/L and whether the regioisomerism differs between species and varieties. In R. rubrum the proportion of the symmetric regioisomer LAlaL among Ala/L/L was higher (14.1%) than in R. nigrum (12.1%) (p < 0.001). Generally in currants, the proportion of LAlaL was lower (p < 0.001) in northern Finland (12.1%) than in southern Finland (13.5%), where temperature and radiation sums were higher. In R. rubrum varieties grown in the south, the proportion of LGlaL among Gla/L/L was significantly higher in the years 2005 and 2007 (30.7-32.0%) than in 2006 (24.2-25.4%), when temperature and radiation sums were higher and the amount of precipitation was lower.

Analysis of regiospecific triacylglycerols by electrospray ionization-mass spectrometry(3) of lithiated adducts

A method of regiospecific analysis of triacylglycerols (TAGs) in vegetable oils and animal fats is reported here using the electrospray ionization-mass spectrometry (MS(3)) of TAG-lithiated adducts. The fragment ions of the MS(3) from the loss of fatty acids at the sn-2 position as alpha,beta-unsaturated fatty acids were used for regiospecific identification and quantification. The ratio of the regiospecific TAGs, ABA and AAB, in an oil sample usually fraction collected by high-performance liquid chromatography can be determined by the abundance of the fragment ions of [ABA + Li-ACOOH-B'CH=CHCOOH]+ and [AAB + Li-ACOOH-A'CH=CHCOOH]+. The method was used to analyze regiospecific TAGs in extra virgin olive oil. The results showed that the saturated fatty acids, palmitic and stearic acids, were mostly located at the sn-1,3 positions and unsaturated fatty acids, oleic and linoleic acids, were mostly located at the sn-2 position.

Quantification of triacylglycerol regioisomers in oils and fat using different mass spectrometric and liquid chromatographic methods

The regioisomers (sn-ABA/sn-AAB) of four triacylglycerols (TAGs), 18:2/18:2/18:1 (LLO), 18:2/18:1/18:1 (LOO), 16:0/18:1/18:1 (POO), and 16:0/16:0/18:1 (PPO), were quantified in lard, rapeseed oil, and sunflower seed oil by three different mass spectrometric methods using liquid chromatography (LC) and two different mass spectrometers. The ionization methods used were positive ion atmospheric pressure chemical ionization (APCI), positive ion electrospray ionization (ESI), and negative ion chemical ionization (NICI) with ammonia as the reagent gas. The LC/APCI-MS results with two different instrumentation types, LC/ESI-MS/MS and direct inlet ammonia NICI-MS/MS, were compared. The LC/APCI-MS method is based on the preferential formation of diacylglycerol (DAG) fragment ions during ionization by loss of sn-1/3 fatty acids from [M+H]+ ions. Similar formation of the DAG ions from [M+NH4]+ ions by collision-induced dissociation (CID) in the LC/ESI-MS/MS method and the [M-H--RCOOH-100]- ions from [M-H]- ions by CID in the direct inlet ammonia NICI-MS/MS method is observed. These methods were found to be useful and reliable in determining the regioisomeric structure of TAGs. No statistically significant differences were found between the results obtained with these methods. For LLO, LOO, and POO the proportions of sn-ABA isomer calculated from the results from all four methods were in rapeseed oil 7.7 +/- 6.5, 57.9 +/- 3.3, and 4.5 +/- 6.1%, respectively, and in sunflower seed oil 12.2 +/- 6.9, 34.0 +/- 5.2, and 1.4 +/- 2.8%, respectively. The proportions of ABA of POO and PPO in lard were 95.3 +/- 3.2 and 4.9 +/- 5.6%, respectively. This study also proved that the LC/APCI-MS/MS method examined is not applicable in the quantification of TAG regioisomers because the formation of DAG ions is not clearly dependent on the positional distribution of the fatty acids.

Regioselective separation of isomeric triacylglycerols by reversed-phase high-performance liquid chromatography: Stationary phase and mobile phase effects

Complete regioselective separation of five pairs of isomeric dipalmitoyl polyalkenoyl glycerols with two to six double bonds in the unsaturated acyl residues has been achieved by RP-HPLC on a single ODS column. Four ODS columns with stationary phases containing different percentages of free silanol groups have been tested. Binary mobile phases of ACN admixed with dichloromethane, tetrahydrofuran, 1-propanol, 2-propanol, ethanol, or acetone have been examined. The choice of modifier depended on the nature of the stationary phase. The more polar solvents were better suited for stationary phases with higher percentage of free silanol groups. Isomeric species were eluted according to chain length, number of double bonds, and the position of the unsaturated acyl chain in the glycerol molecule. Retention increases in the order 20:5 < 22:6 < 18:3 < 20:4 << 18:2. Within each isomeric pair, the species with unsaturated acyl chain occupying either the sn-1- or the 3-position were retained preferentially. Complete simultaneous regioselective separation of 10 isomeric triacylglycerols in a single isocratic run on a single ODS column was demonstrated.

Quantification of triacylglycerols in butterfat by gas chromatography-electron impact mass spectrometry using molar correction factors for [M-RCOO]+ ions

A quantitative electron impact GC-MS method using molar correction factors (MCFs) for [M-RCOO]+ ions has been developed for determination of molecular species of triacylglycerols (TAGs). MCFs were determined by linear calibration for 226 ions of 104 TAG species with good reproducibility: on the average, coefficient of determination was 0.975 +/- 0.043 and 0.963 +/- 0.115 for saturated and unsaturated TAGs, respectively. The MCFs of the sn-1(3) regioisomers of short-chain TAGs were lower than those of sn-2 isomers indicating ca. 2-3-fold higher cleavage of butyroyl and caproyl groups from the primary positions than from the secondary position. The method enabled quantification of 139 and 135 individual TAG species of butterfat (BF) and interesterified butterfat, respectively, including several regioisomers of short-chain TAGs. The most abundant molecular species of the even-numbered TAGs in BF were butyroylpalmitoyloleoylglycerol (5.05 mol%), butyroyldipalmitoylglycerol (4.75 mol%), and palmitoyldioleoylglycerol (3.32 mol%). The method provides an alternative for elucidation of nutritional and technological properties of relatively saturated TAG mixtures.

Identification of (12-ricinoleoylricinoleoyl)diricinoleoylglycerol, an acylglycerol containing four acyl chains, in castor (Ricinus communis L.) oil by LC-ESI-MS

An acylglycerol (AG) containing four acyl chains, (12-ricinoleoylricinoleoyl)diricinoleoylglycerol (RRRR), was positively identified for the first time in a natural source in castor oil using electrospray ionization tandem mass spectrometry (ESI-MS/MS). HPLC-purified RRRR from castor oil was subjected to ion trap and high-resolution ESI-MS/MS. The precursor and fragment ions of [RRRR + Na]+ showed the expected masses, and the sodiated fragment ions of both diacylglycerols and fatty acids were detected. Because fragment ions of fatty acids from [AG + NH4]+ adducts cannot be detected by ESI-MS/MS, [AG + Na]+ adducts are more informative. Radiolabeled triricinolein (RRR) was incorporated into RRRR in castor microsomes, indicating that RRRR is biosynthesized in castor bean. This newly identified and biosynthesized RRRR represents a new AG subclass of tetra-acylglycerols (or acylacyldiacylglycerol).

Analysis of triacylglycerols in fat body of bumblebees by chromatographic methods

Triacylglycerols (TAGs) from the fat body of several bumblebee species (Bombus lucorum, B. terrestris, B. lapidarius, B. hypnorum, B. hortorum, and B. confusus) were studied using chromatographic techniques. Semi-preparative thin-layer chromatography was used to isolate the TAGs from the tissue extract. Gas chromatography (GC) enabled us to identify the fatty acids (FAs) that form bumblebee TAGs and to quantify their relative proportions. The TAGs were subsequently analysed by high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry. Two chromatographic systems, including non-aqueous reversed-phase chromatography and silver ion chromatography on cation exchange resin in silver (I) ionic form, were optimised and their performance compared. The most abundant fatty acids in bumblebees TAGs contained 18 or 16 carbon atoms; oleic acid predominated in most samples. TAGs were found to be a complex mixture of isomers; some of them, e.g. OLnO, PLnO, PoPoO, PoPoP, POO, or OOO (where Po is palmitoleic, P is palmitic, Ln is linolenic, and O is oleic acid) were abundant in particular species. The composition of both FAs and TAGs was found to be species-specific. Only minor differences were found among specimens of the same species.