Comparison of critical methods developed for fatty acid analysis: A review

Comprehensive determination of fatty acids in real samples without derivatization by DMU-SPME-GC methods

The comprehensive determination of fatty acids without derivatization, including short-chain fatty acids (SCFAs), medium-chain fatty acids (MCFAs) and long-chain fatty acids (LCFAs), is a big challenge but powerful for lipidomics in biology, food, and environment. Herein, the dual mode unity solid-phase microextraction (DMU-SPME) combined with gas chromatography-flame ionization detector (GC-FID) or mass spectrometry (MS) was proposed as a powerful method for the determination of comprehensive free fatty acids in real samples. Under the optimized DMU-SPME conditions, the proposed method has good linearity (R2 ≥ 0.994) and low limits of determination (0.01-0.14 mg/L). In the stability analysis, the intra-day relative standard deviation was 1.39-12.43 %, and the inter-day relative standard deviation was 2.84-10.79 %. The recoveries of selected 10 fatty acids in real samples ranged from 90.18 % to 110.75 %, indicating that the method has good accuracy. Fatty acids ranging from C2 to C22 were detected in real samples by the untargeted determination method of DMU-SPME combined with gas chromatography-mass spectrometry (GC-MS). The DMU-SPME method proposed in this study can be used for lipid metabolism analysis and free fatty acid determination in the fields of biology, food, and environment.

Targeting Lipid Metabolism in Obese Asthma: Perspectives and Therapeutic Opportunities

BACKGROUND

Obese asthma represents a unique phenotype of asthma characterized by severe symptoms, poor medication controls, increased frequency of exacerbations, and an overall diminished quality of life. Numerous factors, including the complex interactions between environment, mechanical processes, inflammatory responses, and metabolites disturbance, contribute to the onset of obese asthma.

SUMMARY

Notably, multiple metabolomics studies in the last several years have revealed the significant abnormalities in lipid metabolism among obese asthmatic patients. Several bioactive lipid messengers participate in the development of obese asthma has also been observed. Here, we present and discuss the latest advances regarding how bioactive lipid molecules contribute to the pathogenic process and mechanisms underlying obese asthma. The key roles of potentially significant effector cells and the pathways by which they respond to diverse lipid metabolites are also described. We finally summarize current lipid-related therapeutic options for the treatment of obese asthma and discuss their application prospects.

KEY MESSAGES

This review underscores the impacts of abnormal lipid metabolism in the etiopathogenesis of obese asthma and asks for further investigation to elucidate the intricate correlations among lipids, obesity, and asthma.

Exploration of the Lipid Profile of Edible Oleaginous Microgreens by Mass Spectrometry-Based Lipidomics

The spreading awareness of the health benefits associated with the consumption of plant-based foods is fueling the market of innovative vegetable products, including microgreens, recognized as a promising source of bioactive compounds. To evaluate the potential of oleaginous plant microgreens as a source of bioactive fatty acids, gas chromatography-mass spectrometry was exploited to characterize the total fatty acid content of five microgreens, namely, chia, flax, soy, sunflower, and rapeseed (canola). Chia and flax microgreens appeared as interesting sources of α-linolenic acid (ALA), with total concentrations of 2.6 and 2.9 g/100 g of dried weight (DW), respectively. Based on these amounts, approximately 15% of the ALA daily intake recommended by the European Food Safety Authority can be provided by 100 g of the corresponding fresh products. Flow injection analysis with high-resolution Fourier transform single and tandem mass spectrometry enabled a semi-quantitative profiling of triacylglycerols (TGs) and sterol esters (SEs) in the examined microgreen crops, confirming their role as additional sources of fatty acids like ALA and linoleic acid (LA), along with glycerophospholipids. The highest amounts of TGs and SEs were observed in rapeseed and sunflower microgreens (ca. 50 and 4-5 μmol/g of DW, respectively), followed by flax (ca. 20 and 3 μmol/g DW). TG 54:9, 54:8, and 54:7 prevailed in the case of flax and chia, whereas TG 54:3, 54:4, and 54:5 were the most abundant TGs in the case of rapeseed. β-Sitosteryl linoleate and linolenate were generally prevailing in the SE profiles, although campesteryl oleate, linoleate, and linolenate exhibited a comparable amount in the case of rapeseed microgreens.

Evaluation of Lipids for the Study of Photosynthetic Membranes

The biological role of lipids goes far beyond the formation of a structural membrane bilayer platform for membrane proteins and controlling fluxes across the membranes. For example, in photosynthetic thylakoid membranes, lipids occupy well-defined binding niches within protein complexes and determine the structural organization of membrane proteins and their function by controlling generic physicochemical membrane properties. In this chapter, two-dimensional thin-layer chromatography (2D TLC) and gas chromatography (GC) techniques are presented for quantitative analysis of lipid classes and fatty acids in thylakoid membranes. In addition, lipid extraction methods from isolated thylakoid membranes and leaves are described together with a procedure for the derivatization of fatty acids to fatty acid methyl esters (FAME) that is required for GC analysis.

Component analysis of fat, oil and grease in wastewater: challenges and opportunities

The presence of fat, oil and grease can lead to blockages in sewer lines, pumps, and treatment plant operations, thereby creating health risks and environmental hazards. These deposits primarily consist of fatty acids, triglycerides and soap, among other components. These three main components are hydrophobic and insoluble in water. The composition of FOG can vary significantly depending on the source, such as food service establishments, households, or industrial processes. Several analytical methods, such as chromatographic, gravimetric, chemical and spectroscopic analysis, are used to measure different FOG components. AOAC, Gerber and APHA are the most commonly utilized standardized analytical methods for measuring FOG components. The AOAC and Gerber methods, which use gas chromatography, tend to provide more accurate results compared to other methods. This can be attributed to GC's ability to measure individual fatty acids in FOG samples by separating and quantifying each compound based on its unique chemical properties, such as volatility, polarity and molecular weight. Similarly, high-performance liquid chromatography is capable of measuring glycerides by separating and quantifying them based on their polarity and molecular weight. This article delves into the challenge of accurately measuring FOG concentrations and evaluates various FOG measurement technologies. The study also discusses the need for standardized methods for FOG measurement, highlighting the importance of understanding FOG deposits and the performance of grease interceptors.

Development of UPLC-UV-ELSD Method for Fatty Acid Profiling in Polysorbate 80 and Confirmation of the Presence of Conjugated Fatty Acids by Mass Spectrometry, UV Absorbance and Proton Nuclear Magnetic Resonance Spectroscopy

Polysorbate 80 (PS80), a chemical substance composed of sorbitol, ethylene glycol, and fatty acids, is commonly used in pharmaceutical drug products to stabilize formulations. However, recent studies have demonstrated that PS80 may hydrolyze over time and the released free fatty acids (FFAs) may lead to particle formation. Naming conventions of fatty acids in current pharmacopeia and in products' certificates of analysis (CoA) of PS80 do not typically distinguish between isomeric species of fatty acids in PS80. Thus, methods to fully characterize the fatty acid species present in PS80 raw materials are needed to enhance quality control strategies of pharmaceuticals using PS80. Here, extended effort is taken to characterize fatty acids in hydrolyzed PS80 raw materials and elucidate the identities of isomeric fatty acid species. In this work, a method was developed and optimized for separation and detection of fatty acids in alkaline hydrolyzed PS80 raw materials using ultra performance liquid chromatography (UPLC) with ultra-violet (UV) detection and evaporative light scattering detection (ELSD). Fatty acids not specified in the current pharmacopeias were detected in PS80 raw material by the developed LC-UV-ELSD method including conjugated forms of linoleic and linolenic fatty acid species. Their identities were orthogonally confirmed by retention time agreement with analytical standards, accurate mass by high resolution mass spectrometry, UV absorbance, and proton nuclear magnetic resonance spectroscopy. The detected conjugated fatty acids are theoretically more hydrophobic and less soluble than their unconjugated counterparts and may increase the propensity of PS80 to form particles upon hydrolysis. This work highlights the need for better quality control of PS80 raw material, as it may eventually play a critical role in product quality of therapeutic proteins.

Fractioning and Compared 1H NMR and GC-MS Analyses of Lanolin Acid Components

The management of food and food-related wastes represents a growing global issue, as they are hard to recycle and dispose of. Foremost, waste can serve as an important source of biomasses. Particularly, fat-enriched biomasses are receiving more and more attention for their role in the manufacturing of biofuels. Nonetheless, many biomasses have been set aside over the years. Wool wax, also known as lanolin, has a huge potential for becoming a source of typical and atypical fatty acids. The main aim of this work was to evaluate and assess a protocol for the fractioning of fatty acids from lanolin, a natural by-product of the shearing of sheep, alongside the design of a new and rapid quantitative GC-MS method for the derivatization of free fatty acids in fat mixtures, using MethElute™. As the acid portion of lanolin is characterized by the presence of both aliphatic and hydroxylated fatty acids, we also evaluated a procedure for the parting of these two species, by using NMR spectroscopy, benefitting of the different solubilities of the components in organic solvents. At last, we evaluated and quantified the fatty acids and the α-hydroxy fatty acids present in each attained portion, employing both analytical and synthetic standards. The performed analyses, both qualitative and quantitative, showed a good performance in the parting of the different acid components, and GC-MS allowed to speculate that the majority of α-hydroxylated fatty acids is formed of linear saturated carbon chains, while the totality of properly said fatty acids has a much more complex profile.

A validated and optimized method for separation and quantification of total fatty acids by gas chromatography-ion trap mass spectrometry in human plasma

Fatty acids (FAs) are associated with many physiological functions of tissues, and their alteration has been linked with tissue-specific or systemic diseases. The current situation warrants us to have a sensitive and specific method for analysis of total FAs simultaneously from the biological fluid so that the risk prediction, diagnosis or prognosis of the disease can be made effectively. Because of greater sensitivity and resolution, a method of gas chromatography-ion trap mass spectrometry (GC-IT/MS) has been optimized and validated to quantify simultaneously 19 total FAs levels in plasma and compared with GC-triple quadrupole mass spectrometry. FAs have been transesterified by methanolic acetyl chloride to fatty acid methyl esters (FAMEs). A 65 min GC method separated all 19 FAMEs. The calibration curve had good linearity up to 313-922 μM with a correlation coefficient between 0.9882 and 0.9998. The LODs and LOQs of FAMEs were in the range of 0.63 to 9.55 and 2.12 to 31.8 μM, respectively. The method has recovery up to 144 %, stability at 4 °C for 48 h and one freeze-thaw cycle, and good intra-day and inter-day precision. The optimized method has been used to quantify plasma total FAs in type 2 diabetes mellitus patients with and without acute coronary syndrome. Though a significant difference has been found between IT/MS and triple quadrupole mass spectrometry, the GC-IT/MS can help to quantify total FAs in the clinical setting.

Identification and direct determination of fatty acids profile in oleic acid by HPLC-CAD and MS-IT-TOF

Oleic acid is a pharmaceutical excipient and has been widely used in many dosage forms. It remains unclear in terms of the fatty acids (FAs) profile. In this study, a sensitive and direct method based on high-performance liquid chromatography coupled with charged aerosol detector (HPLC-CAD) was developed to study the compositions of oleic acid. The chromatographic conditions were optimized to achieve good separation and high sensitivity. The components of oleic acid were identified by ion trap/time of flight mass spectrometry (MS-IT-TOF). Twenty-seven FAs were identified based on the exact mass-to-charge ratio and fragments, among which 13 FAs were confirmed with the reference standards. Nine FAs in the oleic acid samples including oleic acid, linolenic acid, myristic acid, palmitoleic acid, linoleic acid, palmitic acid, stearic acid, arachidic acid and behenic acid were simultaneously determined by the developed HPLC-CAD, which showed good linearity with r²>0.999. The limit of detection (LOD) and limit of quantification (LOQ) of 9 FAs were 0.006-0.1 μg mL^-1 and 0.032-0.22 μg mL^-1, respectively. The components with concentration level not less than 0.03 % (referring to the sample concentration of 1.0 mg mL^-1) can be quantified. The mean recovery values of 9 FAs ranged from 96.5%-103.6% at three concentration levels of 80 %, 100 % and 120 %. The repeatability and intermediate precision were less than 5.0 % for oleic acid and components with concentration levels more than 0.05 %. In contrast to the conventional pre-column derivatization gas chromatography (GC), HPLC-CAD could unbiasedly and directly detect more components, especially the FAs with long carbon chains. Overall, the developed novel HPLC-CAD method can ameliorate the deficiency of the indirect GC method recorded in current pharmacopeias, thus having great potential for the comprehensive understanding and quality control of oleic acid.

Microalgae as Sustainable Bio-Factories of Healthy Lipids: Evaluating Fatty Acid Content and Antioxidant Activity

The demand for sustainable and environmentally friendly food sources and food ingredients is increasing, and microalgae are promoted as a sustainable source of essential and bioactive lipids, with high levels of omega-3 fatty acids (ω-3 FA), comparable to those of fish. However, most FA screening studies on algae are scattered or use different methodologies, preventing a true comparison of its content between microalgae. In this work, we used gas-chromatography mass-spectrometry (GC-MS) to characterize the FA profile of seven different commercial microalgae with biotechnological applications (Chlorella vulgaris, Chlorococcum amblystomatis, Scenedesmus obliquus, Tetraselmis chui, Phaeodactylum tricornutum, Spirulina sp., and Nannochloropsis oceanica). Screening for antioxidant activity was also performed to understand the relationship between FA profile and bioactivity. Microalgae exhibited specific FA profiles with a different composition, namely in the ω-3 FA profile, but with species of the same phylum showing similar tendencies. The different lipid extracts showed similar antioxidant activities, but with a low activity of the extracts of Nannochloropsis oceanica. Overall, this study provides a direct comparison of FA profiles between microalgae species, supporting the role of these species as alternative, sustainable, and healthy sources of essential lipids.

Potential Mechanisms of Improved Activity of Natural Killer Cells Induced by the Consumption of F-MRP for 8 weeks

SCOPE

The authors used metabolomics to investigate the nutritional modulatory effect of fermented Maillard-reactive whey protein (F-MRP) on the activity of natural killer (NK) cells.

METHODS AND RESULTS

Fifty subjects who had participated in our previous intervention study were included in the present study in the test (n = 20) and placebo groups (n = 30). Additional analyses using ultra performance liquid chromatography-mass spectrometry (UPLC-MS) and gas chromatography (GC)-MS were conducted to identify relevant metabolic features. After 8 weeks, the activity of lipoprotein-associated phospholipase A₂ (Lp-PLA₂) (p = 0.021), levels of interleukin (IL)-1β (p = 0.001), and activity of NK cells were considerably increased in the test group compared with those in the placebo group. Based on the metabolites discovered by UPLC-MS, ten altered metabolic pathways were observed in the test group after 8 weeks of F-MRP consumption. Specific pathways with most pronounced associations with immune-enhancing effect of F-MRP included aminoacyl-tRNA biosynthesis, glycine/serine/threonine metabolism, arginine/proline metabolism, and sphingolipid metabolism.

CONCLUSIONS

The present study demonstrated the effects of 8 weeks of F-MRP supplementation on the metabolic status manifested as changes in the Lp-PLA₂ activity, IL-1β level, and activity of NK cells. Intermediate metabolites of the identified metabolic pathways can be used to confirm the immune-enhancing efficacy of short-term supplementation.

Rapid monitoring approaches for concentration process of lanqin oral solution by near-infrared spectroscopy and chemometric models

Qualitative and quantitative detection methods based on near-infrared spectroscopy (NIRs) have been proposed in the process analysis of traditional Chinese medicine in recent years. In this study, rapid monitoring methods were developed for quality control of concentration process of lanqin oral solution (LOS). Partial least squares regression (PLSR) method was adopted to construct quantitative models for epigoitrin, geniposide, baicalin, berberine hydrochloride and density. Simultaneously, the genetic algorithm joint extreme learning machine (GA-ELM) was first applied in qualitative analysis of NIRs to distinguish end point of concentration process. Results of PLSR models were satisfactory with the relative standard error of calibration valued at 3.80%, 3.75%, 3.79%, 11.5% and 1.22% for epigoitrin, geniposide, baicalin, berberine hydrochloride and density respectively, and the residual predictive deviation values were higher than 3. For qualitative analysis, the GA-ELM model obtained 100% prediction accuracy. The PLSR quantitative models and the end point discrimination model constructed by GA-ELM correspond with the requirements of practical applications. The results indicate that NIRs in combination with chemometrics has great potential in improving the efficiency in production.

Determination of Monounsaturated Fatty Acid Isomers in Biological Systems by Modeling MS3 Product Ion Patterns

Unsaturated free fatty acids are natively present in biological samples as isomers, where double bonds can be situated on different carbons in the acyl chain. While these isomers can have different actions and impacts on biological systems, they are inherently difficult to identify and differentiate by mass spectrometry alone. To address this challenge, several techniques for derivatization of the double bond or metal cationization at the carboxylic group have yielded diagnostic product ions for the respective isomer in tandem mass spectrometry. However, diagnostic product ions do not necessarily reflect quantitative isomeric ratios since fatty acid isomers have different ionization and fragmentation efficiencies. Here, we introduce a simple and rapid approach to predict the quantitative ratio of isomeric monounsaturated fatty acids. Specifically, empirically derived MS³ product ion patterns from fatty acid silver adducts are modeled using a stepwise linear model. This model is then applied to predict the proportion oleic and vaccenic acid in chemically complex samples at individual concentrations between 0.45 and 5.25 μM, with an average accuracy and precision below 2 and 5 mol %, respectively. We show that by simply including silver ions in the electrospray solvent, isomeric ratios are rapidly predicted in neat standards, rodent plasma, and tissue extract. Furthermore, we use the method to directly map isomeric ratios in tissue sections using nanospray desorption electrospray ionization MS³ imaging without any sample preparation or modification to the instrumental setup. Ultimately, this approach provides a simple and rapid solution to differentiate monounsaturated fatty acids using commonly available commercial mass spectrometers without any instrumental modifications.

Development of a Novel High-Performance Thin Layer Chromatography-Based Method for the Simultaneous Quantification of Clinically Relevant Lipids from Cells and Tissue Extracts

Lipids such as cholesterol, triacylglycerols, and fatty acids play important roles in the regulation of cellular metabolism and cellular signaling pathways and, as a consequence, in the development of various diseases. It is therefore important to understand how their metabolism is regulated to better define the components involved in the development of various human diseases. In the present work, we describe the development and validation of a high-performance thin layer chromatography (HPTLC) method allowing the separation and quantification of free cholesterol, cholesteryl esters, nonesterified fatty acids, and triacylglycerols. This method will be of interest as the quantification of these lipids in one single assay is difficult to perform.

Evaluation of Lipids for the Study of Photosynthetic Membranes

The biological role of lipids goes far beyond the formation of a structural membrane bilayer platform for membrane proteins and controlling fluxes across the membranes. For example, in photosynthetic thylakoid membranes, lipids occupy well-defined binding niches within protein complexes and determine the structural organization of membrane proteins and their function by controlling generic physicochemical membrane properties. In this chapter, two-dimensional thin-layer chromatography (2D TLC) and gas chromatography (GC) techniques are presented for quantitative analysis of lipid classes and fatty acids in thylakoid membranes. In addition, lipid extraction methods from isolated thylakoid membranes and leaves are described together with a procedure for derivatization of fatty acids to fatty acid methyl esters (FAME) that is required for GC analysis.

Tributyl phosphate assisted hollow-fiber liquid-phase microextraction of short-chain fatty acids in microbial degradation fluid using capillary electrophoresis-contactless coupled conductivity detection

A tributyl phosphate assisted hollow-fiber liquid-phase microextraction coupled with capillary electrophoresis-contactless coupled conductivity detection (HF-LPME/CE-C⁴D) method has been developed for trace analysis of common short-chain fatty acids (SCFAs) without derivatization. Under the optimum conditions, ten SCFAs including a pair of isomers were well separated from their homologous FAs and the main coexisting inorganic anions within 40 min. Tributyl phosphate assisted HF-LPME produced excellent purification and enrichment for the model sample with high-salt matrix, microbial degradation fluid, and the limits of detection could reach 0.072-0.67 ng/mL (S/N = 3). Owing to its high sensitivity, good linearity, and acceptable recovery, this proposed method provided a sensitive and environment-friendly alternative for trace analysis of SCFAs in complicated samples.