Ultra-high-performance liquid chromatography–ion trap mass spectrometry characterisation of milk polar lipids from dairy cows fed different diets

Pseudo-targeted lipidomics insights into lipid discrepancies between yak colostrum and mature milk based on UHPLC-Qtrap-MS

Yak milk is essential to maintain the normal physiological functions of herders in Tibetan areas of China. However, the lipid components of yak colostrum (YC) and mature milk (YM) have not been systematically studied. We employed a quantitative lipidomics to comprehensively describe the alterations in the milk lipid profile of lactating yaks. Herein, totally 851 lipids from 28 lipid subclasses in YC and YM were identified and screened for 43 significantly different lipids (SDLs; variable importance in projection > 1, fold change < 0.5 or > 2 with P < 0.05), with cholesterol ester (CE, 16:0) and triacylglycerol (TAG, 54:6 (20:5), 50:1 (16:0), 56:6 (20:5)) were the potential lipid biomarkers. Fourteen SDLs were modulated downwards, and 29 SDLs were modulated upwards in YM. Moreover, by analyzing lipid metabolic pathways in these SDLs, glycerophospholipid metabolism was the most critical. Our results furnish integral lipid details for evaluating yak milk's nutritional quality.

Effects of dietary forage-to-concentrate ratio and forage type on milk phospholipids and fatty acid composition of polar lipids

The effects of grass silage and red clover silage on milk fatty acid (FA) composition are extensively studied, but little is known of their effects on minor lipid constituents of milk fat globule membrane. We investigated the effects of forage:concentrate (FC) ratio in grass silage-based diets and forage type (grass silage vs. red clover silage) on selected molecular species of milk phospholipids (PL) and the FA composition of PL. Ten multiparous Nordic Red cows were offered following dietary treatments: grass silage-based diets containing 70:30 (HG) or 30:70 (LG) FC ratio or a red clover silage-based diet (RC) comprising 50:50 FC ratio on a dry matter basis. The most abundant molecular species within the phosphatidylcholines was 16:0-18:1 phosphatidylcholine that was increased by 18% in HG compared with LG milk. Dietary treatments did not affect the relative proportion of 18:1-18:1+18:0-18:2 phosphatidylethanolamine that was the most prevalent species (ca. 44%-45%) in that class. We identified the d18:1-22:0 sphingomyelin as the most abundant sphingomyelin species that tended to increase in HG milk compared with LG. The FC ratio did not affect the relative proportions of saturated FA nor monounsaturated FA in PL, but the proportion of cis-9 18:1 was elevated in HG versus LG milk, whereas the proportion of 18:2n-6 was 50% higher in LG versus HG milk. The RC diet increased monounsaturated FA and 18:3n-3 levels in PL compared with grass silage-based diets and decreased the relative proportion of saturated FA. However, the RC diet did not affect the relative proportion of polyunsaturated FA in PL, although red clover silage typically increases the proportion of polyunsaturated FA in milk fat. This study provides valuable knowledge of the minor lipid components in milk on species level in relation to common feeding strategies in high-forage systems.

Analysis of milk with liquid chromatography–mass spectrometry: a review

As a widely consumed foodstuff, milk and dairy products are increasingly studied over the years. At the present time, milk profiling is used as a benchmark to assess the properties of milk. Modern biomolecular mass spectrometers have become invaluable to fully characterize the milk composition. This review reports the analysis of milk and its components using liquid chromatography coupled with mass spectrometry (LC–MS). LC–MS analysis as a whole will be discussed subdivided into the major constituents of milk, namely, lipids, proteins, sugars and the mineral fraction.

Comparison of Workflows for Milk Lipid Analysis: Phospholipids

Milk is a rich source of lipids, with the major components being triglycerides (TAG) and phospholipids (mainly phosphatidylcholine (PC), sphingomyelin (SM), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI)). Liquid chromatography-mass spectrometry (LC-MS) is the predominant technique for lipid identification and quantification across all biological samples. While fatty acid (FA) composition of the major lipid classes of milk can be readily determined using tandem MS, elucidating the regio-distribution and double bond position of the FA remains difficult. Various workflows have been reported on the quantification of lipid species in biological samples in the past 20 years, but no standard or consensus methods are currently available for the quantification of milk phospholipids. This study will examine the influence of several common factors in lipid analysis workflow (including lipid extraction protocols, LC stationary phases, mobile phase buffers, gradient elution programmes, mass analyser resolution and isotope correction) on the quantification outcome of bovine milk phospholipids. The pros and cons of the current LC-MS methods as well as the critical problems to be solved will also be discussed.

Milk metabolome reveals pyrimidine and its degradation products as the discriminant markers of different corn silage-based nutritional strategies

The purpose of this study was to evaluate the effect of 6 different feeding systems (based on corn silage as the main ingredient) on the chemical composition of milk and to highlight the potential of untargeted metabolomics to find discriminant marker compounds of different nutritional strategies. Interestingly, the multivariate statistical analysis discriminated milk samples mainly according to the high-moisture ear corn (HMC) included in the diet formulation. Overall, the most discriminant compounds, identified as a function of the HMC, belonged to AA (10 compounds), peptides (71 compounds), pyrimidines (38 compounds), purines (15 compounds), and pyridines (14 compounds). The discriminant milk metabolites were found to significantly explain the metabolic pathways of pyrimidines and vitamin B₆. Interestingly, pathway analyses revealed that the inclusion of HMC in the diet formulation strongly affected the pyrimidine metabolism in milk, determining a significant up-accumulation of pyrimidine degradation products, such as 3-ureidopropionic acid, 3-ureidoisobutyric acid, and 3-aminoisobutyric acid. Also, some pyrimidine intermediates (such as l-aspartic acid, N-carbamoyl-l-aspartic acid, and orotic acid) were found to possess a high discrimination degree. Additionally, our findings suggested that the inclusion of alfalfa silage in the diet formulation was potentially correlated with the vitamin B₆ metabolism in milk, being 4-pyridoxic acid (a pyridoxal phosphate degradation product) the most significant and up-accumulated compound. Taken together, the accumulation trends of different marker compounds revealed that both pyrimidine intermediates and degradation products are potential marker compounds of HMC-based diets, likely involving a complex metabolism of microbial nitrogen based on total splanchnic fluxes from the rumen to mammary gland in dairy cows. Also, our findings highlight the potential of untargeted metabolomics in both foodomics and foodomics-based studies involving dairy products.

Authenticity of Hay Milk vs. Milk from Maize or Grass Silage by Lipid Analysis

Hay milk is a traditional dairy product recently launched on the market. It is protected as “traditional specialty guaranteed” (TSG) and subjected to strict regulations. One of the most important restrictions is that the cow’s feed ration must be free from silage. There is the need for analytical methods that can discriminate milk obtained from a feeding regime including silage. This study proposes two analytical approaches to assess the authenticity of hay milk. Hay milk and milk from cows fed either with maize or grass silage were analyzed by targeted GC-MS for cyclopropane fatty acid (dihydrosterculic acid, DHSA) detection, since this fatty acid is strictly related to the bacterial strains found in silage, and by HPLC-HRMS. The presence of DHSA was correlated to the presence of maize silage in the feed, whereas it was ambiguous with grass silage. HPLC-HRMS analysis resulted in the identification of 14 triacylglycerol biomarkers in milk. With the use of these biomarkers and multivariate statistical analysis, we were able to predict the use of maize and grass silage in the cow’s diet with 100% recognition. Our findings suggest that the use of analytical approaches based on HRMS is a viable authentication method for hay milk.

Effects of the Oxygen Content and Light Intensity on Milk Photooxidation Using Untargeted Metabolomic Analysis

Photooxidation is the main cause of milk quality deterioration during processing and transportation. Oxygen and light are responsible for dairy milk photooxidation. The objective of this study was to determine the characteristic metabolites after photooxidation and how they are affected by oxygen exposure and light intensity. Ultra-performance liquid chromatography coupled with triple time-of-flight mass spectrometry and multivariate data analysis were used for the high-throughput evaluation of milk photooxidation. Four products were identified as biomarkers: uric acid, riboflavin, lumichrome, and indole-3-carboxaldehyde. Afterward, the effects of oxygen content and light intensity on the biomarkers were investigated, and a sensory evaluation was performed. Both oxygen exposure and light intensity affected the contents of photooxidation biomarkers in milk samples. The sensory score correlated well with the oxygen content but not with the light intensity. The untargeted metabolomic method was an effective tool to identify biomarkers for milk photooxidation evaluation.

Optimization of Encapsulation Using Milk Polar Lipid Liposomes with S-Layer Protein and Transport Study of the ACE-Inhibitory Peptide RLSFNP

The purpose of this study is to develop a new type of nanodrug delivery material by modifying milk polar lipid (MPL) liposomes with the S-layer protein. LIP-RLSFNP (MPL liposomes encapsulating RLSFNP (Arg-Leu-Ser-Phe-Asn-Pro)) and SLP-LIP-RLSFNP (S-layer protein-modified LIP-RLSFNP) were prepared and characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, confocal laser scanning microscopy, surface plasmon resonance, and mastersizer dynamic light scattering measurements. The results showed that the S-layer protein could modify the surface of MPL liposomes, stabilize the shape of the vesicles, and improve the resistance to external interference. Furthermore, SLP-LIP-RLSFNP showed better performance in in vitro and in vivo experiments compared with LIP-RLSFNP in terms of promoting absorption and delayed release. The findings suggested that MPL liposomes modified with the S-layer protein have potential for use as an effective delivery system for therapeutic proteins and peptides.

Prevention of Necrotizing Enterocolitis through Milk Polar Lipids Reducing Intestinal Epithelial Apoptosis

Neonatal necrotizing enterocolitis (NEC) is a common and devastating disease. The objective of this research was to investigate the protective mechanisms of milk polar lipids (MPLs) on the attenuation of lipopolysaccharides (LPS)-induced intestinal inflammation and apoptosis. MPLs were extracted from buttermilk and analyzed using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). A neonatal NEC rat model was used to investigate the effects of MPLs on NEC and its underlying mechanisms. Hematoxylin-eosin (H&E) staining and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) assay were used to observe intestinal morphological changes and intestinal epithelial cell apoptosis, which showed that MPLs could reduce NEC symptoms and intestinal apoptosis. The expressions of IL-6, IL-8, and TNF-α in the MPL group was significantly downregulated (P < 0.05), and the expression levels of IL-10 were significantly upregulated (P < 0.05). At the same time, MPLs also significantly reduced (P < 0.05) activation of the LPS-induced TLR4/NF-κB signaling pathway. Furthermore, MPLs inhibit apoptosis by reducing the expressions of Bax, caspase-9, and caspase-3 and by increasing the expression of Bcl-2. In conclusion, MPLs could reduce NEC symptoms in mice by inhibiting cell inflammation and protecting against intestinal apoptosis.

Comprehensive Characterization of Bovine Milk Lipids: Phospholipids, Sphingolipids, Glycolipids, and Ceramides

A comprehensive survey on phospholipids (PLs), sphingolipids, glycolipids, and ceramides (Cer) of bovine milk was conducted by liquid chromatography tandem-mass spectrometry. A total of 514 species belonging to 15 classes were identified by an automated search tool (LipidSearch) and a manual analysis of MS2 spectra. Over 60 species were detected for the classes of phosphatidylcholine (PC), phosphatidylinositol, phosphatidylserine, and sphingomyelin (SM), between 20 and 45 species for phosphatidylethanolamine (PE), phosphatidic acid (PA), and lactosylceramide (LacCer), and between 7 and 20 species for phosphatidylglycerol (PG), lyso-phosphatidylcholine, lyso-phosphatidylethanolamine, glucosylceramide (GluCer), PC-plasmalogen (PC-P), PE-plasmalogen, ganglioside, and Cer. The structural assignment for PL classes is straightforward based on class-specific product ion/neutral losses and fatty acid-related product ions. By contrast, structural determination of lipid classes containing a backbone of sphingoid bases (SM, GluCer, LacCer, ganglioside, and Cer) is much more challenging, and combining MS2/MS3 information acquired in both positive and negative modes is sometimes needed. The quantification of all 15 classes of lipids was performed at the species level. A large variation in abundance was observed across the lipid classes; PC, PE, and SM are the most abundant polar lipid classes, with concentrations reaching 120, 150, and 90 μmol/L, respectively, whereas PA, PG, and PC-P are present at very low levels (<1.5 μmol/L) and the remaining classes at an intermediate level (2-45 μmol/L). This is the first comprehensive characterization of minor lipid classes from bovine milk and the information provided can be used as a reference for studying milk lipids.

Arsenosugar Phospholipids (As-PL) in Edible Marine Algae: An Interplay between Liquid Chromatography with Electrospray Ionization Multistage Mass Spectrometry and Phospholipases A1 and A2 for Regiochemical Assignment

The chemical identity of arsenosugar phospholipids (As-PL) as mono- (i.e., lyso, L-As-PL) and diacyl-arsenosugar PL in four edible and common marine alga samples, such as nori (Porphyra spp.), wakame (Undaria pinnatifida), dulse (Palmaria palmata), and kombu (Saccharina japonica), was successfully investigated. Adopting negative polarity electrospray ionization (ESI), not common for As-PL, conjugated with hydrophilic interaction liquid chromatography (HILIC) and mass spectrometry (MS), performed either at low resolution using a linear ion trap (LIT) with sequential MSn (n = 2, 3) or at high resolution using a high-resolution/high-accuracy Fourier-transform MS (FTMS), based on an orbital trap instrument, more than 20 As-PL and 2 L-As-PL species were identified. The absence of As-PL standard compounds encouraged us to generate an in-house-built database of As-PL/L-As-PL for a rapid and simple classification. Despite their compositional diversity, tandem MS of deprotonated As-PL and L-As-PL ([M - H]-) demonstrated the occurrence of a highly diagnostic product ion at m/z 389.0 ([AsC10H19O9P]-). The fatty acid composition and distribution of As-PL were easily assigned on the basis of the ratio intensity between sn-1 and sn-2 product ions. Indeed, the preferential formation of [R1C3H5O4P]- ions over [R2C3H5O4P]- ions, both containing the glycerol backbone, enabled the regiochemical assignment of As-PL. These outcomes were confirmed by MSn (n = 2, 3) analyses and using sn-1- and sn-2-regioselective hydrolase enzymes (i.e., phospholipases A1 and A2). The predominant As-PL's in samples of nori (red alga), wakame, and kombu (both brown algae) were identified as containing palmitic acyl chains (i.e., As-PL958 (As-PL 16:0/16:0) with ca. 66 ± 3, 82 ± 4, and 58 ± 3% as relative abundances, respectively), while the main species in dulse (red alga) samples was As-PL982 (As-PL 18:1/16:1) at ca. 38 ± 3%.

Natural phospholipids: Occurrence, biosynthesis, separation, identification, and beneficial health aspects

During the last years, phospholipids (PLs) have attracted great attention because of their crucial roles in providing nutritional values, technological and medical applications. There are considerable proofs that PLs have unique nutritional benefits on human health, such as reducing cholesterol absorption, improving liver functions, and decreasing the risk of cardiovascular diseases. PLs are the main structural lipid components of cell and organelle membranes in all living organisms, and therefore, they occur in all organisms and the derived food products. PLs are distinguished by the presence of a hydrophilic head and a hydrophobic tail, consequently they possess amphiphilic features. Due to their unique characteristics, the extraction, separation, and identification of PLs are critical issues to be concerned. This review is focused on the content of PLs classes in several sources (including milk, vegetable oils, egg yolk, and mitochondria). As well, it highlights PLs biosynthesis, and the methodologies applied for PLs extraction and separation, such as solvent extraction and solid-phase extraction. In addition, the determination and quantification of PLs classes by using thin layer chromatography, high-performance liquid chromatography coupled with different detectors, and nuclear magnetic resonance spectroscopy techniques.

Seasonal variation of polar lipid content in bovine milk

Seasonal change of milk composition could offer opportunities for dairy manufacturers. A systematic survey on seasonal variation of six classes of polar lipids was conducted with 19 Holstein cows over the entire milking season using liquid chromatography-mass spectrometry technique. This study revealed that most polar lipid classes were positively correlated with the total fat content, but negatively correlated with fat globule size. All polar lipid classes displayed a large cow-to-cow variation as well as seasonal variation. All of the six classes showed a gradual increase over the milking season with the highest concentration observed in May (autumn). However, the proportion of different polar lipid classes remained constant during the entire milking season. This finding suggests that the production of polar lipids is highly regulated in the mammary gland. The implication of such a seasonal variation of polar lipids in the nutritional and technological aspects of milk is discussed.

Ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry MSE-based untargeted milk metabolomics in dairy cows with subclinical or clinical mastitis

In this study, a novel metabolomics technique based on ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry in the MS^E mode was used to investigate the milk metabolomics of healthy, subclinical, and clinical mastitis cows, which were classified based on somatic cell count and presentation of clinical symptoms. Meanwhile, univariate and multivariate statistical analyses were performed to identify the significant differences across the 3 groups. Compared with healthy milk samples, less glucose, d-glycerol-1-phosphate, 4-hydroxyphenyllactate, l-carnitine, sn-glycero-3-phosphocholine, citrate, and hippurate were detected in the clinical mastitic milk samples, whereas less d-glycerol-1-phosphate, benzoic acid, l-carnitine, and cis-aconitate were found in the subclinical mastitic milk samples. Meanwhile, the milk concentration of arginine and Leu-Leu increased in both the clinical and subclinical mastitis groups. Besides, less 4-hydroxyphenyllactate, cis-aconitate, lactose, and oxoglutarate were detected in the clinical than the subclinical mastitic milk samples, whereas the abundance of some oligopeptides (Leu-Ala, Phe-Pro-Ile, Asn-Arg-Ala-Ile, and Val-Phe-Val-Tyr) increased by over 7.95-fold. Our results suggest that significant variations exist across healthy and mastitis cows. The current metabolomics approach will help in better understanding the pathobiology of mastitis, although clinical validation will be required before field application.

Recent Advances in Phospholipids from Colostrum, Milk and Dairy By-Products

Milk is one of the most important foods for mammals, because it is the first form of feed providing energy, nutrients and immunological factors. In the last few years, milk lipids have attracted the attention of researchers due to the presence of several bioactive components in the lipid fraction. The lipid fraction of milk and dairy products contains several components of nutritional significance, such as ω-3 and ω-6 polyunsaturated fatty acids, CLA, short chain fatty acids, gangliosides and phospholipids. Prospective cohort evidence has shown that phospholipids play an important role in the human diet and reinforce the possible relationship between their consumption and prevention of several chronic diseases. Because of these potential benefits of phospholipids in the human diet, this review is focused on the recent advances in phospholipids from colostrum, milk and dairy by-products. Phospholipid composition, its main determination methods and the health activities of these compounds will be addressed.

Identification of phospholipids classes and molecular species in different types of egg yolk by using UPLC-Q-TOF-MS

Egg phospholipids (PLs) are currently the products of greatest commercial interest with major area of importance in various fields. Therefore, in this study, duck, hen and quail egg yolk PLs were isolated by solvent extraction with chilled acetone precipitation, and subsequently separated and identified by using ultra-performance liquid chromatography with quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF-MS). Egg PLs were separated on hydrophilic interaction liquid chromatography (HILIC) with ethylene bridged hybrid (BEH) column by gradient elution using acetonitrile/ammonium formate as a mobile phase, and detected by mass spectrometry (MS) under electrospray ionization in positive and negative ion mode. Structural characterizations of 57 molecular species of egg yolk PLs were identified based on MS/MS fragment ion information and elemental composition in MassLynx 4.1 software. The obtained results showed that phosphatidylcholine (16:0-18:1), phosphatidylethanolamine (18:0-20:4), phosphatidylinositol (18:0-18:2), phosphatidylserine (18:0-18:2), sphingomyelin (d18:1/16:0) and lysophosphatidylcholine (16:0) were the predominant species among the different classes of egg yolk phospholipids.

Influence of pasture-based feeding systems on fatty acids, organic acids and volatile organic flavour compounds in yoghurt

The influence of different pasture-based feeding systems on fatty acids, organic acids and volatile organic flavour compounds in yoghurt was studied. Pasture is the main source of nutrients for dairy cows in many parts of the world, including southeast Australia. Milk and milk products produced in these systems are known to contain a number of compounds with positive effects on human health. In the current study, 260 cows were fed supplementary grain and forage according to one of 3 different systems; Control (a traditional pasture based diet offered to the cows during milking and in paddock), PMR1 (a partial mixed ration which contained the same supplement as Control but was offered to the cows as a partial mixed ration on a feedpad), PMR 2 (a differently formulated partial mixed ration compared to Control and PMR1 which was offered to the cows on a feedpad). Most of the yoghurt fatty acids were influenced by feeding systems; however, those effects were minor on organic acids. The differences in feeding systems did not lead to the formation of different volatile organic flavour compounds in yoghurt. Yet, it did influence the relative abundance of these components.

Comprehensive polar lipid identification and quantification in milk by liquid chromatography-mass spectrometry

Polar lipids (PLs) are a significant functional component of milk that are difficult to quantitate. A simple method for comprehensive identification and quantitative analysis of all essential PL species using bovine milk is described. The lipid fraction was extracted by a mix of chloroform and methanol and the extract was directly used for PL identification and quantification. PLs were separated by hydrophilic interaction liquid chromatography (HILIC) and detected by an Orbitrap mass analyser in positive mode. The structure of PLs was established or confirmed by tandem MS in both positive and negative modes. The method is sensitive (with a LOD for all PL classes ≤0.1 ng) and reproducible, enabling simultaneous quantification of 70 PL species within a run of 45 min. Application of this method to the quantification of PLs in 32 bovine milk samples revealed the relative abundance of different PL classes, significant variation of PL content between individual samples and the correlation between the major PL classes. The method provides a tool for investigating the variation and metabolism of important PL components in bovine and human milk and in diverse mammalian species.