Selective extraction of phospholipids from dairy products by micro-solid phase extraction based on titanium dioxide microcolumns followed by MALDI-TOF-MS analysis

MALDI-TOF Mass Spectrometry Applications for Food Fraud Detection

Chemical analysis of food products relating to the detection of the most common frauds is a complex task due to the complexity of the matrices and the unknown nature of most processes. Moreover, frauds are becoming more and more sophisticated, making the development of reliable, rapid, cost-effective new analytical methods for food control even more pressing. Over the years, MALDI-TOF MS has demonstrated the potential to meet this need, also due to a series of undeniable intrinsic advantages including ease of use, fast data collection, and capability to obtain valuable information even from complex samples subjected to simple pre-treatment procedures. These features have been conveniently exploited in the field of food frauds in several matrices, including milk and dairy products, oils, fish and seafood, meat, fruit, vegetables, and a few other categories. The present review provides a comprehensive overview of the existing MALDI-based applications for food quality assessment and detection of adulterations.

Rapid Liquid AP-MALDI MS Profiling of Lipids and Proteins from Goat and Sheep Milk for Speciation and Colostrum Analysis

Rapid profiling of the biomolecular components of milk can be useful for food quality assessment and for food fraud detection. Differences in commercial value and availability of milk from specific species are often the reasons for the illicit and fraudulent sale of milk whose species origin is wrongly declared. In this study, a fast, MS-based speciation method is presented to distinguish sheep from goat milk and sheep colostrum at different phases. Using liquid atmospheric pressure (AP)-matrix-assisted laser desorption/ionisation (MALDI) MS, it was possible to classify samples of goat and sheep milk with 100% accuracy in one minute of data acquisition per sample. Moreover, an accuracy of 98% was achieved in classifying pure sheep milk samples and sheep milk samples containing 10% goat milk. Evaluating colostrum quality and postnatal stages represents another possible application of this technology. Classification of sheep colostrum samples that were collected within 6 hours after parturition and 48 hours later was achieved with an accuracy of 84.4%. Our data show that substantial changes in the lipid profile can account for the accurate classification of colostrum collected at the early and late time points. This method applied to the analysis of protein orthologs of different species can, as in this case, allow unequivocal speciation analysis.

A comprehensive perspective of food nanomaterials

Nanotechnology is a rapidly developing toolbox that provides solutions to numerous challenges in the food industry and meet public demands for healthier and safer food products. The diversity of nanostructures and their vast, tunable functionality drives their inclusion in food products and packaging materials to improve their nutritional quality through bioactive fortification and probiotics encapsulation, enhance their safety due to their antimicrobial and sensing capabilities and confer novel sensorial properties. In this food nanotechnology state-of-the-art communication, matrix materials with particular focus on food-grade components, existing and novel production techniques, and current and potential applications in the fields of food quality, safety and preservation, nutrient bioaccessibility and digestibility will be detailed. Additionally, a thorough analysis of potential strategies to assess the safety of these novel nanostructures is presented.

Bioanalysis of farnesyl pyrophosphate in human plasma by high-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry and hybrid quadrupole Orbitrap high-resolution mass spectrometry

The isoprenoids farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) are pivotal intermediates for cholesterol homeostasis and cell signaling in the mevalonate pathway. We developed a sensitive and selective high-performance liquid chromatography tandem triple quadrupole mass spectrometry (LC-QQQ-MS) method for FPP in human plasma without the need for a derivatization process. We optimized the sample preparation procedure to extract FPP and ¹³C₅-FPP (as internal standard) from sample fluids using methanol. Phosphate-buffered saline was used as the surrogate matrix for the preparation of calibration curves and quality control samples. Using an XBridge C18 column (3.5 μm, 2.1 × 100-mm ID) with gradient elution composed of 10 mmol/L ammonium carbonate/ammonium hydroxide (1000:5, v/v) and acetonitrile/ammonium hydroxide (1000:5, v/v) provided the sharp peaks of FPP and ¹³C₅-FPP in human plasma. The calibration curve ranged from 0.2 to 20 ng/mL in human plasma with acceptable intra-day and inter-day precision and accuracy. The sensitivity of this bioanalytical method was sufficient for clinical analysis. The endogenous FPP plasma concentrations in 40 human healthy volunteers ascertained by LC-QQQ-MS and high-performance liquid chromatography tandem hybrid quadrupole Orbitrap high-resolution mass spectrometry (LC-Q-Orbi-MS) were comparable. Furthermore, the endogenous GGPP in human plasma was selectively detected for the first time by LC-Q-Orbi-MS. In conclusion, a sensitive bioanalytical method for FPP in human plasma by means of LC-QQQ-MS and LC-Q-Orbi-MS was developed in this study. Taking into account the versatility of LC-Q-Orbi-MS, the simultaneous detection of FPP and GGPP may be feasible in clinical practice.

In-Depth Lipidomic Analysis of Molecular Species of Triacylglycerides, Diacylglycerides, Glycerophospholipids, and Sphingolipids of Buttermilk by GC-MS/FID, HPLC-ELSD, and UPLC-QToF-MS

Buttermilk, a byproduct of butter manufacturing, has gained considerable attention due to its high concentration of polar lipids as phospho- and sphingolipids from the milk fat globule membrane (MFGM). These polar lipids (PLs) are essential components of all cellular membranes and exert a variety of indispensable metabolic, neurological, and intracellular signaling processes. Despite its importance, there are few research studies that report a comprehensive characterization of the lipid molecular species of MFGM that could contribute to a better understanding of their putative healthful activities. In this study, procedures such as pressurized liquid extraction of polar and nonpolar lipids and their fractionation by flash chromatography have been carried out. The obtained fractions were submitted to an exhaustive characterization from a lipidomic point of view. The characterization includes new data about the identification and quantification of triacylglycerides (TAG), diacylglycerides (DAG), and phospho- and sphingolipids using different chromatographic techniques. The fatty acid profile was comparable to that of the milk fat but with a highly diverse composition of fatty acids. Molecular species have also been determined by using ultra-high performance liquid chromatography/quadruple-time-of-flight mass spectrometry (UPLC/QToF-MS). The TAG (16:0/16:0/6:0) and TAG (16:0/16:0/8:0) were the predominant saturated TAG species and TAG (14:0/18:1/16:0) and TAG (16:0/16:0/18:1) presented the highest content of monounsaturated TAG species. Furthermore; over 30 molecular species of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylinositol (PI) could be identified within PL, with PC (16:0/18:1) being the most abundant species. Whereas C16:0 was found to be the preferred FA in TAGs, it was C18:1 in PLs. Several ganglioside species have also been characterized with d18:1 ceramide moiety and secondary acyl chains ranging from C20:0 to C26:1. This approach could broaden the applications of high-resolution mass spectrometry for a better understanding of the role of MFGM and its functionality.

Isolation and Analysis of Phospholipids in Dairy Foods

The lipid fraction of milk is one of the most complex matrixes in foodstuffs due to the presence of a high number of moieties with different physical and chemical properties. Glycerolipids include glycerol and two fatty acids esterified in positions sn-1 and sn-2 with higher concentration of unsaturated fatty acids than in the triglyceride fraction of milk. Sphingolipids consist of a sphingoid base linked to a fatty acid across an amide bond. Their amphiphilic nature makes them suitable to be added into a variety of foods and recent investigations show that phospholipids, mainly phosphatidylserine and sphingomyelin, can exert antimicrobial, antiviral, and anticancer activities as well as positive effects in Alzheimer's disease, stress, and memory decline. Polar lipids can be found as natural constituents in the membranes of all living organisms with soybean and eggs as the principal industrial sources, yet they have low contents in phosphatidylserine and sphingomyelin. Animal products are rich sources of these compounds but since there are legal restrictions to avoid transmission of prions, milk and dairy products are gaining interest as alternative sources. This review summarizes the analysis of polar lipids in dairy products including sample preparation (extraction and fractionation/isolation) and analysis by GC or HPLC and the latest research works using ELSD, CAD, and MS detectors.

Sequential Elution from IMAC (SIMAC): An Efficient Method for Enrichment and Separation of Mono- and Multi-phosphorylated Peptides

Phosphoproteomics relies on methods for efficient purification and sequencing of phosphopeptides from highly complex biological systems, especially when using low amounts of starting material. Current methods for phosphopeptide enrichment, e.g., Immobilized Metal ion Affinity Chromatography and titanium dioxide chromatography provide varying degrees of selectivity and specificity for phosphopeptide enrichment. The number of multi-phosphorylated peptides identified in most published studies is rather low. Here we describe a protocol for a strategy that separates mono-phosphorylated peptides from multiply phosphorylated peptides using Sequential elution from Immobilized Metal ion Affinity Chromatography. The method relies on the initial enrichment and separation of mono- and multi-phosphorylated peptides using Immobilized Metal ion Affinity Chromatography and a subsequent enrichment of the mono-phosphorylated peptides using titanium dioxide chromatography. The two separate phosphopeptide fractions are then subsequently analyzed by mass spectrometric methods optimized for mono-phosphorylated and multi-phosphorylated peptides, respectively, resulting in improved identification of especially multi-phosphorylated peptides from a minimum amount of starting material.

The Use of Titanium Dioxide for Selective Enrichment of Phosphorylated Peptides

Titanium dioxide (TiO2) has very high affinity for phosphopeptides and in recent years it has become one of the most popular methods for phosphopeptide enrichment from complex biological samples. Peptide loading onto TiO2 resin in a highly acidic environment in the presence of 2,5-dihydroxybenzoic acid (DHB), phthalic acid, lactic acid, or glycolic acid has been shown to improve selectivity significantly by reducing unspecific binding of non-phosphorylated peptides. The phosphopeptides bound to the TiO2 are subsequently eluted from the chromatographic material using an alkaline buffer. TiO2 chromatography is extremely tolerant towards most buffers used in biological experiments, highly robust and as such it has become the method of choice in large-scale phosphoproteomics. Here we describe a batch mode protocol for phosphopeptide enrichment using TiO2 chromatographic material followed by desalting and concentration of the sample by reversed phase micro-columns prior to downstream MS and LC-MS/MS analysis.

TiO₂/SiO₂ core-shell composite-based sample preparation method for selective extraction of phospholipids from shrimp waste followed by hydrophilic interaction chromatography coupled with quadrupole time-of-flight/mass spectrometry analysis

A solid-phase extraction (SPE) procedure, using titania-coated silica (TiO2/SiO2) core-shell composites as the sorbent, combined with a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for extraction, visualization, and quantification of phospholipids in shrimp waste (Litopenaeus vannamei). The SPE protocol was optimized, and the best conditions were pH 5 of the loading solvent, 10% aqueous methanol as the washing solvent, and 1.0 mL of chloroform/methanol (1:2, v/v) as eluting solvents. Afterward, the eluate was separated on a diol hydrophilic interaction chromatography (HILIC) column. A total of 69 phospholipid species were identified and determined. The results indicated that, in comparison to previously published methods, this strategy was cost-effective and efficient in extraction, characterization, and determination of phospholipids. Meanwhile, phospholipids were abundant in shrimp waste, most of which contained unsaturated fatty acyl chains, such as 18:3 [α-linolenic acid (ALA)], 20:5 [eicosapentaenoic acid (EPA)], and 22:6 [docosahexaenoic acid (DHA)]. The successful application of this strategy paves the way for full use of traditionally discarded shrimp wastes.

Proteomic analysis of complex protein samples by MALDI-TOF mass spectrometry

MALDI MS has become a technique of considerable impact on many fields, from proteomics to lipidomics, including polymer analysis and, more recently, even low molecular weight analytes due to the introduction of matrix-less ionization techniques (e.g., DIOS) or new matrices such as ionic liquids, proton sponges, and metal nanoparticles. However, protein identification by peptide mass fingerprint (PMF) still remains the main routine application. In the last few years, MALDI MS has played an emerging role in food chemistry especially in detection of food adulterations, characterization of food allergens, and investigation of protein structural modifications, induced by various industrial processes that could be detrimental for food quality and safety. Sample handling and pretreatment can be very different depending on the physical state, liquid or solid, of the analyzed matrices. Here, we describe simple protocols for protein extraction and MALDI MS analysis of liquid (milk) and solid (hazelnuts) samples taken as model. A classic approach based on a preliminary SDS gel electrophoresis separation followed by in-gel digestion and a faster approach based on in-solution digestion of whole samples are described and compared.

Lipidomic fingerprint of almonds (Prunus dulcis L. cv Nonpareil) using TiO₂ nanoparticle based matrix solid-phase dispersion and MALDI-TOF/MS and its potential in geographical origin verification

A matrix solid-phase dispersion (MSPD) procedure with titanium dioxide (TiO2) nanoparticles (NP) as sorbent was developed for the selective extraction of phospholipids from almond samples, and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF/MS) was employed for analysis. A remarkable increase in the signals of phospholipid accompanied by a decrease in those of triacylglycerols and diacylglycerols was observed in the relevant mass spectra. The proposed method was applied to five batches of almonds originating from four geographical areas, whereas principal component analysis (PCA) was utilized to normalize the relative amounts of the identified phospholipid species. The results indicated that the lipidomic fingerprint of almonds was successfully established by the negative ion mode spectrum, and the ratio of m/z 833.6 to 835.6 as well as m/z 821.6 could be introduced as potential markers for the differentiation of the tested almonds with different geographical origins. The whole method is of great promise for selective separation of phospholipids from nonphospholipids, especially the glycerides, and superior in fast screening and characterization of phospholipids in almond samples.

Analysis of phospholipids in infant formulas using high performance liquid chromatography-tandem mass spectrometry

Phospholipids have been used widely in the food industry as emulsifiers, but it is their biological and nutritional function that has been the focus over recent years. The recognition of the importance of phospholipids and sphingomyelin for infant development has led to an increase in the number of infant formulas claiming to contain these complex lipid components. Therefore, the ability to measure these lipids in infant formulas and dairy-derived complex lipid ingredients for fortification purposes is important. A high-performance liquid chromatography-tandem mass spectrometry method that quantifies phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and sphingomyelin found in infant formulas and dairy-derived complex lipid ingredients is described. The method uses external standards of similar fatty acid profile for calibration. The recovery of phospholipids ranged from 92% to 102% with a method repeatability coefficient of variation of 6-10%. In addition to the specificity and selectivity of the method, details of the molecular species in the individual phospholipid classes are available using this method.

Biocompatible phosphatidylcholine bilayer coated on magnetic nanoparticles and their application in the extraction of several polycyclic aromatic hydrocarbons from environmental water and milk samples

In this work, phosphatidylcholine (PC) was coated on magnetic nanoparticles to form lipid bilayer as solid-phase extraction (SPE) sorbents for the enrichment of polycyclic aromatic hydrocarbons (PAHs) from environmental water and milk samples. The lipid bilayer was coated on Fe(3)O(4) nanoparticles using a modified dry lipid film hydration method. The resulted Fe(3)O(4)/PC could be readily isolated from solution with a magnet, and exhibited excellent adsorption performance to organic pollutants. Only 0.1g of sorbents was enough to extract PAHs from 500 mL aqueous solution, and 6 mL of acetonitrile was required to desorb them. The method was fast and relied on 10 min extraction time and 5 min magnetic separation. The proposed method was successfully applied to determine PAHs in some environmental water and milk samples. The detection limit was in the range of 0.2-0.6 ng L(-1). The recoveries of the spiked water samples ranged from 89% to 115% with relative standard deviations (RSD) varying from 1% to 8%. For spiked milk samples, RSD was satisfactory (1-9%), but the recoveries were relatively low (42-62%). We show the potentials of Fe(3)O(4)/PC sorbents in environmental water and biological sample analyses.

Tools for analyzing the phosphoproteome and other phosphorylated biomolecules: a review

Enrichment, separation and mass spectrometric analysis of biomolecules carrying a phosphate group plays an important role in current analytical chemistry. Application areas range from the preparative enrichment of phospholipids for biotechnological purposes and the separation and purification of plasmid DNA or mRNA to the specific preconcentration of phosphoproteins and -peptides to facilitate their later identification and characterization by mass spectrometry. Most of the recent improvements in this field were triggered by the need for phosphopeptide enrichment technology for the analysis of cellular protein phosphorylation events with the help of liquid chromatography-mass spectrometry. The high sensitivity of mass spectrometry and the possibility to combine this technique with different separation modes in liquid chromatography have made it the method of choice for proteome analysis. However, in the case of phosphoprotein analysis, the low abundance of the resulting phosphopeptides and their low quality fragment spectra interfere with the identification of phosphorylation events. Recent developments in phosphopeptide enrichment and fragmentation technologies successfully helped to overcome these limitations. In this review, we will focus on sample preparation techniques in the field of phosphoproteomics, but also highlight recent advancements for the analysis of other phosphorylated biomolecules.