Zwitterionic hydrophilic interaction solid-phase extraction and multi-dimensional mass spectrometry for shotgun lipidomic study of Hypophthalmichthys nobilis

Charge inversion under plasma-nanodroplet reaction conditions excludes Fischer esterification for unsaturated fatty acids: a chemical approach for type II isobaric overlap

Direct infusion ionization methods provide the highest throughput strategy for mass spectrometry (MS) analysis of low-volume samples. But the trade-off includes matrix effects, which can significantly reduce analytical performance. Herein, we present a novel chemical approach to tackle a special type of matrix effect, namely type II isobaric overlap. We focus on detailed investigation of a nanodroplet-based esterification chemistry for differentiating isotopologue [M + 2] signal due to unsaturated fatty acid (FA) from the monoisotopic signal from a saturated FA. The method developed involves the online fusion of nonthermal plasma with charged nanodroplets, enabling selective esterification of saturated FAs. We discovered that unsaturated FAs undergo spontaneous intramolecular reaction via a novel mechanism based on a carbocation intermediate to afford a protonated lactone moiety (resonance stabilized cyclic carbonium ion), whose mass is the same as the original protonated unsaturated FA. Therefore, the monoisotopic signal from any saturated FA can be selectively shifted away from the mass-to-charge position where the isobaric interference occurs to enable effective characterization by MS. The mechanism governing the spontaneous intramolecular reactions for unsaturated FAs was validated with DFT calculations, experimentation with standards, and isotope labeling. This novel insight achieved via the ultrafast plasma-nanodroplet reaction environment provides a potentially useful synthetic pathway to achieve catalyst-free lactone preparation. Analytically, we believe the performance of direct infusion MS can be greatly enhanced by combining our approach with prior sample enrichment steps for applications in biomedicine and food safety. Also, combination with portable mass spectrometers can improve the efficiency of field studies since front-end separation is not possible under such conditions.

Development and application of lipidomics for food research

Lipidomics is an emerging and promising omics derived from metabolomics to comprehensively analyze all of lipid molecules in biological matrices. The purpose of this chapter is to introduce the development and application of lipidomics for food research. First, three aspects of sample preparation are introduced: food sampling, lipid extraction, and transportation and storage. Second, five types of instruments for data acquisition are summarized: direct infusion-mass spectrometry (MS), chromatographic separation-MS, ion mobility-MS, MS imaging, and nuclear magnetic resonance spectroscopy. Third, data acquisition and analysis software are described for the lipidomics software development. Fourth, the application of lipidomics for food research is discussed such as food origin and adulteration analysis, food processing research, food preservation research, and food nutrition and health research. All the contents suggest that lipidomics is a powerful tool for food research based on its ability of lipid component profile analysis.

Hydrophilic interaction chromatography-type sorbent prepared by the modification of methacrylate-base resin with polyethyleneimine for solid-phase extraction of polar compounds

Hydrophilic interaction chromatography (HILIC)-type sorbents were newly developed for the solid-phase extraction (SPE) of polar compounds. Two methacrylate-base resins with different cross-linking monomers and pore properties were synthesized, and three polyethyleneimines (PEIs) with different molecular weights were modified onto each base resin. In both cases, PEIs with a molecular weight of 10,000 (PEI-10,000) exhibited the highest adsorption properties for polar compounds (uracil, uridine, adenosine, cytidine, and guanosine). To control the water-enriched layer at the surface of the PEI-10,000-modified sorbents, the additive amount of PEI-10,000 in the modified reaction was also optimized. When 10 times the amount of PEI-10,000 to each base resin was added, an improvement in adsorption property was observed. Moreover, the use of a nonaqueous sample solution (100% acetonitrile) during the sample loading process drastically improved adsorption, especially for uracil (about 80%) and adenosine (100%). These results indicate that the formation of a strong water-enriched layer at the surface of sorbents with an effective expression of hydrophilic interaction was an important factor in the adsorption properties of polar compounds in HILIC mode-SPE.

Investigation of the changes in lipid profiles induced by hydroxyl radicals in whiteleg shrimp (Litopenaeus vannamei) muscle using LC/MS-based lipidomics analysis

The oxidative effects of hydroxyl radical on the alterations of lipid profiles were investigated in shrimp muscle. Chemical results indicate peroxide value (PV) and thiobarbituric acid index (TBA-i) value in oxidation-treated shrimp significantly increased with oxidation time, and hydroxyl radical concentration increased, compared with those of in fresh samples. It was assumed that radical attack might induce lipid decomposition, backbone cleavage, and/or side-chain modifications. LC/MS-based lipidomics analysis revealed 835 lipids in shrimp assigned to 27 lipid classes, including 219 PCs and 98 CLs. In total, 86 and 34 differentially abundant lipids (DALs) accumulated at lower and higher levels, respectively, were identified in OS, compared with that in FS. This indicates hydroxyl radical attack altered the lipidomics profiles of shrimp muscle to a large extent. Furthermore, DALs, including CL 62:2, PC 38:3, and PE 34:9, could be considered as promising biomarkers to distinguish fresh and oxidation-treated shrimp products.

Advances in Lipid Extraction Methods-A Review

Extraction of lipids from biological tissues is a crucial step in lipid analysis. The selection of appropriate solvent is the most critical factor in the efficient extraction of lipids. A mixture of polar (to disrupt the protein-lipid complexes) and nonpolar (to dissolve the neutral lipids) solvents are precisely selected to extract lipids efficiently. In addition, the disintegration of complex and rigid cell-wall of plants, fungi, and microalgal cells by various mechanical, chemical, and enzymatic treatments facilitate the solvent penetration and extraction of lipids. This review discusses the chloroform/methanol-based classical lipid extraction methods and modern modifications of these methods in terms of using healthy and environmentally safe solvents and rapid single-step extraction. At the same time, some adaptations were made to recover the specific lipids. In addition, the high throughput lipid extraction methodologies used for liquid chromatography-mass spectrometry (LC-MS)-based plant and animal lipidomics were discussed. The advantages and disadvantages of various pretreatments and extraction methods were also illustrated. Moreover, the emerging green solvents-based lipid extraction method, including supercritical CO2 extraction (SCE), is also discussed.

Influence of mixture of spices on phospholipid molecules during water-boiled salted duck processing based on shotgun lipidomics

This study aimed to evaluate the influence of spices on individual phospholipid molecules of water-boiled salted duck (WSD) processing. Shotgun lipidomics was used to determine the structure of individual phospholipid molecules in raw duck meat and changes of phospholipids in processed-WSD with or without spices. A total of 118 phospholipid molecules were determined during the whole processing. Spices had a significant effect on the changes of most individual phospholipid molecules during the processing, but the overall effect on the phospholipid profile was not obvious. Nine phospholipid molecule markers were screened by partial least squares discriminant analysis, which can be used to distinguish with or without spice treatment. The effect of spices on most phospholipid molecules began on the first day of dry-ripening, and gradually became more obvious in the subsequent processing. Spice's main function was to delay the degradation of individual phospholipid molecules.

Untargeted Screening of EPA/DHA Structured Phospholipids in Krill Oil by Chain-Lock-Driven Hydrophilic Interaction Liquid Chromatography Tandem Mass Spectrometry

Eicosapentaenoic and docosahexaenoic acids structured phospholipids (PL_EPA/DHA) have multiple biochemical and pharmacological effects on human health. In this study, EPA and DHA chains were locked under precursor ion scan (PreIS) mode for untargeted screening PL_EPA/DHA in krill oil using hydrophilic interaction liquid chromatography tandem mass spectrometry (HILIC-MS/MS). The effect of collision energy and declustering potential on the fragmentation of EPA (m/z 301.2) and DHA (m/z 327.2) chains was studied. A total of 33 PL_EPA/DHA were characterized (sn-1/sn-2) and quantified using regression models, including 16 PC_EPA/DHA, 11 PE_EPA/DHA, and 6 PI_EPA/DHA. Afterward, this method was validated in terms of linearity (≥0.9978), sensitivity (LOD ≤ 4.02 μg·L^-1), precision (RSD_intraday ≤ 4.71%), and recovery (≥78.9%). Finally, the performance of HILIC-PreIS-MS/MS was compared with those of conventional methods, and the results indicated its superiority in selective screening PL_EPA/DHA in krill oil.

Monodisperse microsphere-based immobilized metal affinity chromatography approach for preparing Antarctic krill phospholipids followed by HILIC-MS analysis

Phospholipids enriched krill is a functional food beneficial in cardiovascular diseases. Herein, monodisperse microsphere-based immobilized metal affinity chromatographic material (MM-IMAC) was synthesized with Ti⁴⁺ incorporated to enrich phospholipids from krill by coordination with phosphate group. The extract was profiled by hydrophilic interaction chromatography-mass spectrometry (HILIC-MS) with 154 phospholipid molecular species detected. The parameters were loading solvent n-hexane/isopropanol (2:8, v/v), flow rate 0.8 mL·min^-1, and eluting volume 1 mL. Besides, eicosapentaenoic and docosahexaenoic acids structured phospholipids were located, such as phosphatidylcholine (PC) 20:5/22:6, phosphatidylinositol (PI) 18:0/20:5, etc. Finally, this method was validated in linearity (R² ≥ 0.9953), sensitivity (LOD ≤ 0.53 μg·mL^-1 and LOQ ≤ 1.66 μg·mL^-1), precision (RSD_intraday ≤ 4.86% and RSD_interday ≤ 6.25%), and recovery (58-83%). It indicated that the MM-Ti⁴⁺-IMAC-HILIC-MS was reliable and efficient in specific study of phospholipids in food matrix.

Evaluation of the adsorption properties of nucleobase-modified sorbents for a solid-phase extraction of water-soluble compounds

We developed hydrophilic interaction chromatography (HILIC)-type sorbents modified with nucleobases for solid phase extraction (SPE). The synthesized hydrophilic base resins were modified by each nucleobase (adenine, guanine, and cytosine). The measurement of the amount of water content indicated that each nucleobase-modified sorbent had a water layer. To evaluate the adsorption properties in the HILIC mode, we chose two nucleobases (uracil and adenine) and four nucleosides (uridine, adenosine, cytidine, guanosine) as water-soluble analytes, which were loaded into an SPE cartridge packed with the nucleobase-modified sorbent. Firstly, 95% acetonitrile (ACN) solutions were used in the process of conditioning and sample loading of the above polar analytes. High recoveries of the analytes were observed in each nucleobase-modified sorbent, and the Diol-type sorbent (no modification with any of the nucleobases) did not adsorb each water-soluble analyte. On the basis of this result, a 98% ACN solution was used during the process of conditioning and sample loading to decrease the concentration of water in the sample, which potentially inhibited the formation of hydrogen bonding between each analyte and the modified nucleobase. Considerable improvements of recoveries were observed in Adenine- and Cytosine-modified sorbents. These results were possibly attributed to the effective expression of hydrogen bonding by decreasing water concentration in the sample solution. Although a non-aqueous (100% ACN) sample solution can be expected to obtain higher recoveries compared with the 98% ACN solution, a decrease in recoveries was observed in Adenine-modified sorbent. From these results, the highest adsorption property was observed in Adenine-modified sorbent using 98% ACN as a sample condition, and the combination of this sample condition and sorbent is effective for high adsorption under HILIC condition. Moreover, we also revealed that a balance between the thickness of water layer and the modification amount of nucleobase is important for retention in the HILIC-type sorbent.

Mass spectrometry-based lipidomics in food science and nutritional health: A comprehensive review

With the advance in science and technology as well as the improvement of living standards, the function of food is no longer just to meet the needs of survival. Food science and its associated nutritional health issues have been increasingly debated. Lipids, as complex metabolites, play a key role both in food and human health. Taking advantages of mass spectrometry (MS) by combining its high sensitivity and accuracy with extensive selective determination of all lipid classes, MS-based lipidomics has been employed to resolve the conundrum of addressing both qualitative and quantitative aspects of high-abundance and low-abundance lipids in complex food matrices. In this review, we systematically summarize current applications of MS-based lipidomics in food field. First, common MS-based lipidomics procedures are described. Second, the applications of MS-based lipidomics in food science, including lipid composition characterization, adulteration, traceability, and other issues, are discussed. Third, the application of MS-based lipidomics for nutritional health covering the influence of food on health and disease is introduced. Finally, future research trends and challenges are proposed. MS-based lipidomics plays an important role in the field of food science, promoting continuous development of food science and integration of food knowledge with other disciplines. New methods of MS-based lipidomics have been developed to improve accuracy and sensitivity of lipid analysis in food samples. These developments offer the possibility to fully characterize lipids in food samples, identify novel functional lipids, and better understand the role of food in promoting healt.

Influence of Salt Content Used for Dry-Curing on Lipidomic Profiles during the Processing of Water-Boiled Salted Duck

This paper focuses on the effect of dry-cured salt content on lipidomic profiles during the processing of water-boiled salted duck (WSD). The composition of the molecular species of individual phospholipids (PLs) in raw duck meat was identified by shotgun lipidomics, and the changes in the PLs during processing were analyzed with different contents of dry-cured salt (a 4% low-salt group, a 6% medium-salt group, and an 8% high-salt group). In total, 100 molecular species of phospholipids were determined in raw meat, while 122 species were identified during manufacturing processing. We further found that the amount of dry-cured salt had a great influence on 12 phospholipid molecular species, which could be used as markers to distinguish the treatment groups with different amounts of dry-cured salt. A lower dry-cured salt content (less than 6%) not only had a significant effect on the total PL content but also promoted the degradation of individual PLs (especially those containing unsaturated fatty acids).

In situ and real-time authentication of Thunnus species by iKnife rapid evaporative ionization mass spectrometry based lipidomics without sample pretreatment

Tuna adulteration and mislabeling are serious problem worldwide and have caused economic loss and consumer rights violation. In this study, an electrometric knife (iKnife) coupling rapid evaporative ionization mass spectrometry (REIMS) and a multivariate recognition model were developed and employed for in situ and real-time authentication of four tuna species without sample preparation. The results showed that the lipidomic profiles were successfully acquired and the differences in fatty acids and phospholipids were statistically analyzed to be significant (p < 0.05). The model displayed the superb classification accuracy (>93%) and validation (R²(Y) = 0.992, Q² = 0.986), and the main contributors of m/z 817.64, m/z 809.68, etc. were screened out to be used as potential biomarkers. Based on this technique, the identity of blind tuna samples could be unambiguously authenticated with the results displayed on a monitor screen directly. This study provided a front-line rapid detection method to prove the authenticity of tuna species.

Electric Soldering Iron Ionization Mass Spectrometry Based Lipidomics for in Situ Monitoring Fish Oil Oxidation Characteristics during Storage

An electric soldering iron ion source (ESII) coupling with rapid evaporative ionization mass spectrometry (REIMS) was developed and used for in situ monitoring the dynamic variation trend in oxidation characteristics of fish oil during storage. The lipidomics profiles of fish oil stored at various days were acquired by ESII-REIMS. The fatty acid and triacylglycerol species were structurally identified, and their abundances were analyzed according to multivariate statistical models mainly including principle component analysis as well as orthogonal partial least-squares analysis. On the shared and unique structure plot, the ions of m/z 255.23, 281.24, 877.72, and 901.72 displayed the most significant variation among the oxidized fish oil samples. Based on receiver operating characteristic curve analysis with an optimal Youden index of 0.91, these markers were further verified. The variation of viscosity and volatiles were also evaluated to further verify the oxidation characteristics of fish oil. The study demonstrated that ESII-REIMS technology used as an advanced detection method could ensure fish oil quality during storage.

Real-Time Monitoring of the Oxidation Characteristics of Antarctic Krill Oil (Euphausia superba) during Storage by Electric Soldering Iron Ionization Mass Spectrometry-Based Lipidomics

Antarctic krill oil (AKO) is susceptible to oxidation due to the high unsaturation degree of bioactive substances. Herein, a lipidomics method for in situ monitoring of the dynamic oxidation characteristics in AKO was explored based on electric soldering iron ion source (ESII) coupling with rapid evaporative ionization mass spectrometry (REIMS). The lipidomics profiles of AKO at different storage periods were successfully acquired. On the basis of principal component analysis and orthogonal partial least-squares analysis, the obtained REIMS data were employed to build a multivariate recognition model. The ions of m/z 707.50, 721.50, 833.49, and 837.54 contributed the most significant effect on the multivariate data model for the authentication of different AKO samples. Besides, the variation of viscosity, astaxanthin, and volatile compounds were also evaluated to corroborate the oxidation characteristics. The results indicated that the ESII-REIMS technology could be applied as an advanced rapid detection method to secure oil and fat quality during storage.

Advances in MS Based Strategies for Probing Ligand-Target Interactions: Focus on Soft Ionization Mass Spectrometric Techniques

The non-covalent interactions between small drug molecules and disease-related proteins (ligand-target interactions) mediate various pharmacological processes in the treatment of different diseases. The development of the analytical methods to assess those interactions, including binding sites, binding energies, stoichiometry and association-dissociation constants, could assist in clarifying the mechanisms of action, precise treatment of targeted diseases as well as the targeted drug discovery. For the last decades, mass spectrometry (MS) has been recognized as a powerful tool to study the non-covalent interactions of the ligand-target complexes with the characteristics of high sensitivity, high-resolution, and high-throughput. Soft ionization mass spectrometry, especially the electrospray mass spectrometry (ESI-MS) and matrix assisted laser desorption ionization mass spectrometry (MALDI-MS), could achieve the complete transformation of the target analytes into the gas phase, and subsequent detection of the small drug molecules and disease-related protein complexes, and has exerted great advantages for studying the drug ligands-protein targets interactions, even in case of identifying active components as drug ligands from crude extracts of medicinal plants. Despite of other analytical techniques for this purpose, such as the NMR and X-ray crystallography, this review highlights the principles, research hotspots and recent applications of the soft ionization mass spectrometry and its hyphenated techniques, including hydrogen-deuterium exchange mass spectrometry (HDX-MS), chemical cross-linking mass spectrometry (CX-MS), and ion mobility spectrometry mass spectrometry (IMS-MS), in the study of the non-covalent interactions between small drug molecules and disease-related proteins.

In Situ Method for Real-Time Discriminating Salmon and Rainbow Trout without Sample Preparation Using iKnife and Rapid Evaporative Ionization Mass Spectrometry-Based Lipidomics

The domestic rainbow trout producers issued a standard with an aquatic association that classified rainbow trout as salmon, which raised the concern of consumers on the fish parasites infection. Herein, an in situ method was developed using "iKnife" and rapid evaporative ionization mass spectrometry based lipidomics for real-time discrimination of salmon and rainbow trout without sample preparation. A total of 12 fatty acids and 37 phospholipid species was identified and imported into statistical analysis for building an in situ and real-time recognition model. The ions with | p(corr)| > 0.5 and | p| > 0.03 were shown to be responsible for allocating samples, and the ions with high correlation values, such as of m/ z 747.50, 771.49, and 863.55, indicated large weights in identification of the salmon and rainbow trout. The results indicated that this technology could be employed as a front-line test method to ensure the authenticity of salmon products.

PRiME pass-through purification of lignans in Silybum marianum and UPLC-MS/MS analysis

A PRiME (process, robustness, improvements, matrix effects, ease of use) pass-through cleanup procedure was developed for the extraction and purification of silychristins A and B, silybins A and B, isosilybins A and B, and silydianin in Silybum marianum. After optimizing the extracting solvent types and the sample loading volume, the crude extract was diluted to 3 mL with 95% acetonitrile and then loaded on the PRiME cartridge. The eluate was analyzed by ultra-performance liquid chromatography and tandem mass spectrometry (UPLC-MS/MS). All the target analytes were deprotonated as [M-H]- at m/z 481 by conducting collision-induced dissociation (CID), and the major fragment ions were m/z 463 ([M-H2O-H]-), 453 ([M-CO-H]-), 355 ([M-C6H6O3-H]-), 301 ([M355-CO2-H]-), and 179 ([C10H11O3]-). Afterwards, this method was validated in terms of linearity (R2 > 0.9990), intra-day precision (1.02%-3.79%), inter-day precision (1.59%-4.87%), sensitivity (LOD ≤ 0.45 μg·kg-1 and LOQ ≤ 1.50 μg·kg-1), and recovery (76.9-103.4%, RSD < 8.90%). Finally, the proposed protocol was successfully applied to eight batches of S. marianum samples. The total content of the seven active compounds varied amongst the batches from different places of origin.

Rapid Evaporative Ionization Mass Spectrometry-Based Lipidomics Tracking of Grass Carp ( Ctenopharyngodon idellus) during In Vitro Multiple-Stage Digestion

A rapid evaporative ionization mass spectrometry (REIMS) method was developed for lipidomics tracking of Ctenopharyngodon idellus during in vitro multiple-stage digestion. The REIMS conditions were optimized such that the temperature of the heating probe was 500 °C, sample amount was 30 mg, and the flow rate of auxiliary solvent was 100 μL min^-1. The results showed that the phospholipids were detected with variety and quantity in the crude and multiple-stage digested samples. The enzymatic effect on the phospholipids is varied depending on the phospholipid classes, and the hydrolysis rate of phospholipids increased as the degree of unsaturation of the acyl chain increased. The principal component analysis (PCA) indicated that the ions at m/ z 809.61, 811.63, and 857.52 were the most noticeable species digested during the process. This method exhibited great potential in fast lipidomics profiling for inspecting the characteristics of nutritional lipid absorption digestion in human gastrointestin.