Mapping the regioisomeric distribution of fatty acids in triacylglycerols by hybrid mass spectrometry

Crystallization Behavior of Plant-Based Fat Blends Formulated as an Alternative for Anhydrous Milk Fat in Milk Chocolate

Due to the increasing global demand for chocolate products and changes in consumer preferences, chocolate manufacturers have recently started to explore novel solutions to reformulate chocolate. Milk fat alternatives (MFA) are blends of triglycerides from different plant-based sources that resemble anhydrous milk fat in physical properties, particularly thermal behavior and solid fat content. However, in order to use MFA as potential ingredients for vegan milk chocolate formulations, it is necessary to understand their crystallization behavior, particularly in light of their chemical composition. Here, we applied synchrotron X-ray scattering, polarized light microscopy, and differential scanning calorimetry to investigate the crystallization behavior of four selected commercial MFAs (MF1, 2, 3, and 4), on their own and mixed with cocoa butter (CB). Chemical characterization revealed significant differences among samples and with both anhydrous milk fat (MF) and CB. POP-rich MF1 presented a specific polymorphic and thermal behavior, with the unstable β' form persisting for longer times than all other samples. Sample MF2 exhibited a polymorphic behavior more similar to CB in terms of number, type, and melting behavior due to the compositional similarities (e.g., prevalence of both SOS and POP). SOS-rich MF3 was characterized by metastable forms γ and β'(3L), whereas MF4 at ambient conditions showed only β(2L) forms due to its specific composition. Mixtures of CB and all MFAs behaved similarly to CB and MF mixtures, with good miscibility at ambient temperature and a lower melting point. Despite significant differences in chemical composition, MF4 presented similar solid fat content compared to MF; this is due to the high amount of relatively long chain, unsaturated fatty acids and the broad distribution of different TAGs, which all lower the melting point of this sample.

A synchrotron X-ray scattering study of the crystallization behavior of mixtures of confectionary triacylglycerides: Effect of chemical composition and shear on polymorphism and kinetics

Cocoa butter equivalents (CBE) are mixtures of triglycerides from multiple sources (e.g., sunflower oil, mango kernel and sal), which resemble cocoa butter (CB) in both physical and chemical properties. Despite being widely used to replace CB in chocolate products, the crystallization behavior of many CBEs is still poorly understood. The aim of this work was to develop a fundamental understanding, at the molecular level, of the crystallization behavior of selected CBEs, and compare it with that of CB. Chromatography was used to determine the composition of CBEs, in terms of fatty acids and triacylglycerides (TAGs), while their thermodynamic behavior and crystallization kinetics were studied using polarized microscopy, differential calorimetry and three different synchrotron X-ray scattering setups. CBEs of different origin and chemical composition (e.g., different ratios of the main CB TAGs, namely POP, SOS and POS) crystallized in different polymorphs and with different kinetics of nucleation, growth and polymorphic transformation. SOS rich CBEs presented showed more polymorphs than CB and POP rich samples; whereas, CBEs with high concentration of POP showed slow kinetic of polymorphic transformation towards the stable β(3L) form. Additionally, it was observed that the presence of small amounts (<1% w/w) of specific TAGs, such as OOO, PPP or SSS, could significantly affect the crystallization behavior of CBEs and CBs in terms of kinetics of polymorphic transformation and number of phases detected (multiple high melting β(2L) polymorphs were identified in all samples studied). Finally, it was found that, regardless of the CBE composition, the presence of shear could promote the formation of stable β polymorphs over metastable β' and γ forms, and reduced the size of the crystal agglomerates formed due to increased secondary nucleation.

Extending the Lipidome Coverage by Combining Different Mass Spectrometric Platforms: An Innovative Strategy to Answer Chemical Food Safety Issues

From a general public health perspective, a strategy combining non-targeted and targeted lipidomics MS-based approaches is proposed to identify disrupted patterns in serum lipidome upon growth promoter treatment in pigs. Evaluating the relative contributions of the platforms involved, the study aims at investigating the potential of innovative analytical approaches to highlight potential chemical food safety threats. Serum samples collected during an animal experiment involving control and treated pigs, whose food had been supplemented with ractopamine, were extracted and characterised using three MS strategies: Non-targeted RP LC-HRMS; the targeted Lipidyzer™ platform (differential ion mobility associated with shotgun lipidomics) and a homemade LC-HRMS triglyceride platform. The strategy enabled highlighting specific lipid profile patterns involving various lipid classes, mainly in relation to cholesterol esters, sphingomyelins, lactosylceramide, phosphatidylcholines and triglycerides. Thanks to the combination of non-targeted and targeted MS approaches, various compartments of the pig serum lipidome could be explored, including commonly characterised lipids (Lipidyzer™), triglyceride isomers (Triglyceride platform) and unique lipid features (non-targeted LC-HRMS). Thanks to their respective characteristics, the complementarity of the three tools could be demonstrated for public health purposes, with enhanced coverage, level of characterization and applicability.

Structural elucidation of triacylglycerol using online acetone Paternò-Büchi reaction coupled with reversed-phase liquid chromatography mass spectrometry

Triacylglycerol (TG) is a class of lipids that is responsible for energy storage and cell metabolism in biological systems; it is found in relatively high abundances in biological fluids such as human plasma. Due to structural complexity, analyzing TGs using shotgun lipidomic approaches is challenging because of the presence of multiple fatty acyl compositional isomers. In this work, reversed-phase liquid chromatography (RPLC) was used for separation of TG species due to the capability of separating lipids based on fatty acyl chain lengths and degrees of unsaturation. RPLC alone does not provide structurally informative information for the location of carbon-carbon double-bonds (C[double bond, length as m-dash]Cs) without using synthesized standards that correspond to each species analyzed. The Paternò-Büchi (PB) reaction was employed online to confidently characterize the location of C[double bond, length as m-dash]Cs within lipid species via photo-initiated modification of the alkene group with acetone, which was later subjected to electrospray ionization (ESI) and tandem mass spectrometry (MS/MS) to form signature fragmentation peaks. This online RPLC-PB-MS/MS system was able to distinguish fatty acyl level and C[double bond, length as m-dash]C level isomeric species. The systems allowed for the identification of 46 TG molecular species in human plasma with confident C[double bond, length as m-dash]C location assignment in fatty acyls at a limit of identification of 50 nM.

Quantification of 1,3-olein-2-palmitin (OPO) and Palmitic Acid in sn-2 Position of Triacylglycerols in Human Milk by Liquid Chromatography Coupled with Mass Spectrometry

This study describes the identification and quantification of fatty acids in the sn-2 position of triacylglycerols (TAG) and of the most abundant TAG regioisomers in human milk by liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS). Over 300 individual TAG species were observed and 1,3-olein-2-palmitin (OPO) was identified as the most abundant TAG regioisomer. Validation of the HPLC-HRMS method showed repeatability and intermediate reproducibility values ranging from 3.1 to 16.6% and 4.0 to 20.7%, respectively, and accuracy ranging from 75 to 97%. Results obtained by the HPLC-HRMS method were comparable to results from the ISO 6800 method for the quantification of palmitic acid in the sn-2 position of TAG (81.4 and 81.8 g 100 g⁻¹ total palmitic acid, respectively). Processing the data obtained with the HPLC-HRMS method is extremely time consuming and, therefore, a targeted method suitable for the quantification of OPO in human milk samples by ultra-performance (UP) LC coupled with triple quadrupole (QQQ) MS was developed and validated. OPO identification and quantification by UPLC-QQQ were based on nominal mass and a fragmentation pattern obtained by multiple reaction monitoring experiments. The method was validated in terms of accuracy and precision by analyzing different aliquots of the same human milk sample over time and comparing the results with values obtained by HPLC-HRMS. Intermediate reproducibility was <15% and trueness comparable to HPLC-HRMS. Quantification of OPO in human milk samples collected at 30, 60 and 120 days postpartum showed that OPO content varies between 333 ± 11.8 and 383 ± 18.0 mg 100mL⁻¹.

Determination of fatty acid and sphingoid base composition of eleven ceramide subclasses in stratum corneum by UHPLC/scheduled-MRM

INTRODUCTION

Ceramides play a key role in skin barrier function in homeostatic and pathological conditions and can be sampled non-invasively through stratum corneum collection.

OBJECTIVES

To develop a novel UHPLC/Scheduled MRM method for the identification and relative distribution of eleven classes of ceramides, which are separated by UHPLC and determined by their specific retention times. The precise composition of the fatty acid and sphingoid base parts of each individual ceramide is determined via mass fragmentation.

METHODS

More than 1000 human and pig ceramides were identified. Three human and minipig ceramide classes, CER[AS], CER[NS] and CER[EOS] have been investigated in depth.

RESULTS

Sphingoid bases were characterized by a prevalence of chain lengths with sizes from C16 to C22, whereas fatty acids were mainly observed in the range of C22-C26. Overall, the ceramide profiles between human and minipig stratum corneum were similar. Differences in the CER[AS] and CER[NS] classes included a more homogeneous distribution of fatty acids (16-30 carbon atoms) in minipig, whereas in human longer fatty acid chains (> 24 carbon atoms) predominated.

CONCLUSION

The method will be useful for the analysis of healthy and pathological skin in various specie, and the measurement of the relative distribution of ceramides as biomarkers for pharmacodynamic studies.

LC-MS/MS Analysis of Triglycerides in Blood-Derived Samples

The increasing interest in the analysis of triglyceride (TG) species and the individual fatty acid (FA) composition requires expeditious and reliable quantification strategies. The utilization of flow injection analysis (FIA) coupled to quadrupole tandem mass spectrometry (MS/MS) for the simultaneous quantitation of TG and identification of FA composition facilitates the multiplexed verification of various biomarkers from small sample quantities. Enzymatic methods based on saponification and glycerol analysis are not suited for the determination of the FA distribution in TGs. This protocol proposes a procedure for the establishment of a relative quantitation method for middle- to high-abundance plasma TGs and the corresponding FA composition. Essential topics as FIA-MS/MS method development as well as sample preparation and validation strategies are described in detail.

Lipidomic profile in three species of dinoflagellates (Amphidinium carterae, Cystodinium sp., and Peridinium aciculiferum) containing very long chain polyunsaturated fatty acids

This study describes the identification of very long chain polyunsaturated fatty acids (VLCPUFAs) in three strains of dinoflagellates (Amphidinium carterae, Cystodinium sp., and Peridinium aciculiferum). The strains were cultivated and their lipidomic profiles were obtained by high resolution mass spectrometry with the aid of positive and negative electrospray ionization (ESI) mode by Orbitrap apparatus. Hydrophilic interaction liquid chromatography (HILIC/ESI) was used to separate major lipid classes of the three genera of dinoflagellates by neutral loss scan showing the ion [M + H-28:8]⁺, where 28:8 was octacosaoctaenoic acid, and by precursor ion scanning of ions at m/z 407, which was an ion corresponding to the structure of acyl of 28:8 acid (C₂₇H₃₉COO^-). Based on these analyzes, it was found that out of more than a dozen lipid classes present in the total lipids, only two classes of neutral lipids, i.e. major triacylglycerols and minor diacylglycerols contain VLCPUFAs. In polar lipids, VLCPUFAs were identified only in phosphatidic acid (PA) and phosphatidyl choline (PC) or in their lyso-forms (LPA and LPC). Further analysis of individual lipid classes by reversed-phase high-performance liquid chromatography (RP-HPLC) showed the presence of triacylglycerols (TAGs) containing VLCPUFAs, i.e. molecular species of the sn-28:7/28:8/28:8, sn-26:7/28:7/28:8, or sn-26:7/28:8/28:8 types. These TAGs are the longest and most unsaturated TAGs isolated from a natural source that have yet been synthesized. In the case of PA and PC, tandem MS identified sn-28:8/16:0-PA and sn-28:8/16:0-PC and the corresponding lyso-forms (28:8-LPC and 28:8-LPA). All these results indicate that TAGs containing VLCPUFAs are biosynthesized in dinoflagellates in the same manner as in higher eukaryotic organisms, which means that the PA, after conversion to DAG, serves as a precursor in the biosynthesis of other phospholipids, e.g. PC, and, after further acylation, also of TAG.

Importance of the regiospecific distribution of long-chain saturated fatty acids on gut comfort, fat and calcium absorption in infants

Gastrointestinal tolerance and fat and calcium (Ca) absorption are different between breast-fed (BF) and formula-fed (FF) infants. Certain components and/or structural particularities in human milk (HM), can contribute to favorable outcomes in BF infants. In HM, the long-chain saturated fatty acid (LCSFA) palmitic acid has a different stereospecific distribution (sn-2 position) compared to most infant formula (IF) (primarily sn-1, 3 positions), which may contribute to unfavorable outcomes. Evidence suggests palmitic acid is important in the formation of stool FA-mineral (or FA-Ca) soaps, associated with harder stools in FF infants. Partial replacement by structured palmitic acid-rich triacylglycerols (TAGs) promotes palmitic acid absorption. However, evidence for stool softening, improved fat absorption and reduced Ca excretion in stools is inconsistent. IFs with less palmitic acid can improve fat and Ca absorption, and stool consistency. The presence of other LCSFAs (myristic and stearic acids) in sn-1, 3 positions may also contribute to reduced absorption of fat and Ca, and stool hardness, in FF infants. Nevertheless, little attention has been given to modifying these other LCSFAs in IF. We review literature comparing the effect of HM and IF with different lipid compositions on stool patterns and/or fat and Ca absorption in healthy, term infants. Based on available data, we estimate a maximum level for sn-1, 3 LCSFAs of 13% of TAGs, under which fat and Ca absorption and stool consistency are improved. IF designed according to this threshold could efficiently improve nutrient absorption and stool patterns in healthy infants who cannot be breast-fed.

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.

Applicability of non-linear versus linear fractional abundance calibration plots for the quantitative determination of triacylglycerol regioisomers by tandem mass spectrometry

RATIONALE

Regioisomeric analysis of triacylglycerols is important in understanding lipid biochemistry and the involvement of lipids in disease and nutrition. The use of calibration plots employing fractional abundances provides a simple and rapid method for such analyses. These plots are believed to be linear, but evidence exists for non-linearity. The behavior of such plots needs to be understood to allow for proper interpretation of regioisomeric data.

METHODS

Solutions of five regioisomer pairs were prepared from pure standards and used to construct calibration plots using triple-stage tandem mass spectrometry (MS(3) ) with electrospray ionization (ESIMS(3) ) and cationization by lithium ions. The data were taken by direct infusion with an AB SCIEX QTRAP 2000 QqLIT mass spectrometer.

RESULTS

Non-linear calibration plots were observed for the four isomer pairs containing the polyunsaturated eicosapentaenoic (20:5) and docosahexaenoic (22:6) acids paired with palmitic acid (16:0) or myristic acid (14:0), while the pair including palmitic and stearic (18:0) acids provided a linear plot. A non-linear model was developed for these plots and then verified experimentally.

CONCLUSIONS

The fractional abundance calibration plots used in regioisomeric analysis of triacylglycerols are intrinsically non-linear, but may appear linear if the scatter in data points obscures the curvature, if the curvature is slight, or if the response factors for the two isomers in the regioisomer pair are similar. Therefore, linearity should not be assumed for these types of measurements until confirmed experimentally.