Characterization of size and composition of milk fat globules from Sarda and Saanen dairy goats

Comprehensive review of milk fat globule membrane proteins across mammals and lactation periods in health and disease

Milk fat globule membrane (MFGM) is a three-layer membrane-like structure encasing natural milk fat globules (MFGs). MFGM holds promise as a nutritional supplement because of the numerous physiological functions of its constituent protein. This review summarizes and compares the differences in MFGM protein composition across various species, including bovines, goats, camels, mares, and donkeys, and different lactation periods, such as colostrum and mature milk, as assessed by techniques such as proteomics and mass spectrometry. We also discuss the health benefits of MFGM proteins throughout life. MFGM proteins promote intestinal development, neurodevelopment, and glucose and lipid metabolism by upregulating tight junction protein expression, brain function-related genes, and glucose and fatty acid biosynthesis processes. We focus on the mechanisms underlying these beneficial effects of MFGM proteins. MFGM proteins activate key substances in in signaling pathways, such as the phosphatidylinositol 3-kinase/protein kinase B, mitogen-activated protein kinase, and myosin light chain kinase signaling pathways. Overall, the consumption of MFGM proteins plays an essential role in conferring health benefits, some of which are important throughout the mammalian life cycle.

Seasonal Variations of Milk Composition of Sarda and Saanen Dairy Goats

Traditionally, in Mediterranean areas the goat population was composed of autochthonous breeds with strong milk production seasonality. In the last decades, high productive alpine breeds were introduced together with more widespread out-of-season milk production practices. This study is a large-scale survey on the seasonal variations of the main compositional characteristics of goat milk obtained from Sarda and Saanen breeds reared on the Mediterranean island of Sardinia (Italy). Analysis of data indicated that milk from the Sarda breed was significantly richer, at p < 0.001, in protein, fat, and lactose, and had a lower urea mean content than Saanen. Throughout the year, fluctuations of mean contents of the milk parameters were similar for the two groups of goats, indicating that, besides genetic intrinsic differences, climate and herbage growth influenced the Sarda as well as the Saanen goats. During the summer, milk from Saanen showed a marked drop in fat and protein contents, with 21% of samples showing a fat-to-protein ratio <1. No significant differences were found for the somatic cell count; however, the Sarda breed showed a higher bacterial count, suggesting improper milk handling and/or storage equipment more frequently encountered in extensive and semi-extensive farm systems.

A Comparative Study of Milk Fat Extracted from the Milk of Different Goat Breeds in China: Fatty Acids, Triacylglycerols and Thermal and Spectroscopic Characterization

Goat milk (GM) is an excellent alternative to cow milk and has recently been used in commercial infant formula preparation due to its superior fat composition. Here, the fatty acid (FA) composition, triacylglycerol (TAG) molecular species, thermal behavior and infrared spectra of extracted milk fat from the milk of the two main breeds of dairy goat bred in China (Guanzhong GM (GZG) and Xinong Saanen GM (XSG)) are investigated. Gas chromatography, Fourier-transform infrared spectroscopy, differential scanning calorimetry and ultra-performance convergence chromatography with quadrupole time-of-flight mass spectrometry are applied. The obtained results evidence significant fat compositional differences based on the breed that produced the considered GM. The major FAs in both GM fats were capric (C10:0), myristic (C14:0), palmitic (C16:0), stearic (C18:0) and oleic (C18:1 n-9c). GZG presented a higher content of medium-chain saturated FAs, while XSG had higher unsaturated FAs with higher ratios of L/Ln and n-6/n-3. A total of 339 and 359 TAGs were detected and quantified in GZG and XSG, and the major TAGs were those of m/z 740.6712 (14.10 ± 0.27%) and m/z 684.6094 (10.94 ± 0.02%), respectively. Milk TAGs of GZG and XSG showed 24–54 and 26–54 total acyl carbon numbers with a 0–4 and 0–5 double bond number at 68 and 72 various retention times, respectively. Thermal analysis showed that all GM fat samples melted below normal body temperature. Infrared spectra revealed higher absorption values of GZG milk fat. This study provides valuable information to the dairy industry sector about GM fat produced in China, assessing the appropriateness of Chinese GM fat to be applied in Chinese infant formula.

Variation in milk fat globule size and composition: A source of bioactives for human health

Milk fat globules (MFGs) are secreted from the mammalian gland and are composed of a triacylglycerol core surrounded by a triple membrane structure, the milk fat globule membrane (MFGM). The MFGM contains complex lipids and proteins reported to have nutritional, immunological, neurological and digestive functions. Human and ruminant milk are shown to share a similar MFG structure but with different size, profile and abundance of protein and polar lipids. This review summarizes the reported data on human, bovine, caprine and ovine MFG composition and concentration of bioactive components in different MFG-size fractions. A comprehensive understanding of compositional variations between milk from different species and MFG size fractions may help promote various milk sources as targeted supplements to improve human development and health. MFG size and MFGM composition are species-specific and affected by lactation, diet and breed (or maternal origin). Purification and enrichment methods for some bioactive proteins and lipids present in the MFGM have yet to be established or are not scaled sufficiently to be used to supplement human diets. To overcome this problem, MFG size selection through fractionation or herd selection may provide a convenient way to pre-enrich the MFG fraction with specific protein and lipid components to fulfill human dietary and health requirements.

Proteomic changes in the milk of water buffaloes (Bubalus bubalis) with subclinical mastitis due to intramammary infection by Staphylococcus aureus and by non-aureus staphylococci

Subclinical mastitis by Staphylococcus aureus (SAU) and by non-aureus staphylococci (NAS) is a major issue in the water buffalo. To understand its impact on milk, 6 quarter samples with >3,000,000 cells/mL (3 SAU-positive and 3 NAS-positive) and 6 culture-negative quarter samples with <50,000 cells/mL were investigated by shotgun proteomics and label-free quantitation. A total of 1530 proteins were identified, of which 152 were significantly changed. SAU was more impacting, with 162 vs 127 differential proteins and higher abundance changes (P < 0.0005). The 119 increased proteins had mostly structural (n = 43, 28.29%) or innate immune defence functions (n = 39, 25.66%) and included vimentin, cathelicidins, histones, S100 and neutrophil granule proteins, haptoglobin, and lysozyme. The 33 decreased proteins were mainly involved in lipid metabolism (n = 13, 59.10%) and included butyrophilin, xanthine dehydrogenase/oxidase, and lipid biosynthetic enzymes. The same biological processes were significantly affected also upon STRING analysis. Cathelicidins were the most increased family, as confirmed by western immunoblotting, with a stronger reactivity in SAU mastitis. S100A8 and haptoglobin were also validated by western immunoblotting. In conclusion, we generated a detailed buffalo milk protein dataset and defined the changes occurring in SAU and NAS mastitis, with potential for improving detection (ProteomeXchange identifier PXD012355).

The goat β‑casein/CMV chimeric promoter drives the expression of hLF in transgenic goats produced by cell transgene microinjection

There is growing interest in the application of lactoferrin (LF) as a drug or food additive for animals and humans. The objective of this study was to produce transgenic cloned goats that would serve as living bioreactors, expressing high levels of recombinant human LF (rhLF) in their milk. We designed a pCL25 expression vector containing goat β-casein/CMV chimeric promoter in order to facilitate rhLF expression. This pCL25-rhLF-Neo vector was microinjected into goat fetal fibroblasts. G418 selection and PCR analysis were used to identify transgenic donor cells suitable for somatic cell nuclear transfer (SCNT). After SCNT and embryo transplantation, goats harboring the hLF gene were produced, as confirmed via PCR and southern blotting. The average rhLF concentration in milk from this transgenic goat was 3.89 mg/ml as determined via ELISA. We also used an optimized buffer in order to effectively elute high-purity (95.8%) rhLF from a cation-exchange column, with the recovered rhLF exhibiting high biological activity. Findings from this study demonstrated that it is possible to generate a transgenic goat harboring the hLF transgene driven by the goat β-casein/CMV chimeric promoter. It represents an initial step towards the production of rhLF, potentially allowing for industrialized purification in the future.

Human Milk Fat Globule Membrane Contains Hundreds of Abundantly Expressed and Nutritionally Beneficial Proteins That Are Generally Lacking in Caprine Milk

BACKGROUND

Bioactive proteins from milk fat globule membrane (MFGM) play extensive roles in cellular processes and defense mechanisms in infants. The aims of this study were to identify differences in protein compositions in human and caprine MFGM using proteomics and evaluate possible nutritional benefits of caprine milk toward an infant's growth, as an alternative when breastfeeding or human milk administration is not possible or inadequate.

MATERIALS AND METHODS

Human and caprine MFGM proteins were isolated and analyzed, initially by polyacrylamide gel electrophoresis, and subsequently by quadrupole time-of-flight liquid chromatography-mass spectrometry. This was then followed by database search and gene ontology analysis. In general, this method selectively analyzed the abundantly expressed proteins in milk MFGM.

RESULTS

Human MFGM contains relatively more abundant bioactive proteins compared with caprine. While a total of 128 abundant proteins were detected in the human MFGM, only 42 were found in that of the caprine. Seven of the bioactive proteins were apparently found to coexist in both human and caprine MFGM.

RESULTS/DISCUSSION

Among the commonly detected MFGM proteins, lactotransferrin, beta-casein, lipoprotein lipase, fatty acid synthase, and butyrophilin subfamily 1 member A1 were highly expressed in human MFGM. On the other hand, alpha-S1-casein and EGF factor 8 protein, which are also nutritionally beneficial, were found in abundance in caprine MFGM. The large number of human MFGM abundant proteins that were generally lacking in caprine appeared to mainly support human metabolic and developmental processes.

CONCLUSION

Our data demonstrated superiority of human MFGM by having more than one hundred nutritionally beneficial and abundantly expressed proteins, which are clearly lacking in caprine MFGM. The minor similarity in the abundantly expressed bioactive proteins in caprine MFGM, which was detected further, suggests that it is still nutritionally beneficial, and therefore should be included when caprine milk-based formula is used as an alternative.

Effect of stage of lactation and production season on fat dispersion in the milk of cows of different breeds

The aim of the study was to evaluate the effect of the stage of lactation and production season on fat dispersion in the milk of cows of different breeds. A total of 738 milk samples were analysed, including 196 from Polish Black-and-White Holstein-Friesian cows, 168 from Jersey cows, 185 from Polish Red cows, and 189 from White-Backed cows. Milk samples were collected individually from each cow in two production seasons, i.e. spring/summer (May-July) and autumn/winter (December-March). Three stages of lactation were distinguished: ≤120 days, 121 to 200 days, and >200 days. The percentage content of fat and its dispersion (expressed as the mean surface area, circumference and mean diameter of fat globules) were determined. The stage of lactation and the production season (linked to the feeding season) were found to strongly influence the content and dispersion of milk fat. As lactation progressed, the fat content of the milk and its dispersion increased. A significant (p≤0.01) decrease was noted in the mean diameter and surface area of the fat globules. The fat globules obtained in the initial stage of lactation were the largest (≤120 days – 2.90 μm). The milk produced in the autumn/winter season had higher fat content and the mean size of the fat globules was significantly (p≤0.01) greater.

Effects of freeze drying and spray drying on the microstructure and composition of milk fat globules

Freeze drying and spray drying are conventional methods for converting milk into powder in the dairy industry.

Comparative proteomics of milk fat globule membrane in different species reveals variations in lactation and nutrition

In present study, 312, 554, 175 and 143 proteins were identified and quantified by label-free quantitative proteomics in human, cow, goat and yak milk fat globule membrane (MFGM), respectively. Fifty proteins involved in vesicle mediate transport and milk fat globule secretion were conserved among species. Moreover, proteins involved in lipid synthesis and secretion (xanthine dehydrogenase/oxidase, stomatin and CD36), showed different expression pattern and the host defense proteins exhibited various profiles within species. Notably, the content and activity of lipid catabolic enzymes were significantly higher in human MFGM, which could be indicative of the superior fat utilization in breast fed infants. Our findings unraveled the significant differences in protein composition of human milk and conventionally used substitutes of it. The in-depth study of lipid metabolic enzymes in human MFGM will probably contribute to the improvement of the fat utilization through modulation of lipid catabolic enzymes in infant formula.

Neutrophil extracellular traps in sheep mastitis

Neutrophil extracellular traps (NETs) are structures composed of DNA, histones, and antimicrobial proteins that are released extracellularly by neutrophils and other immune cells as a means for trapping and killing invading pathogens. Here, we describe NET formation in milk and in mammary alveoli of mastitic sheep, and provide a dataset of proteins found in association to these structures. Nucleic acid staining, immunomicroscopy and fluorescent in-situ hybridization of mastitic mammary tissue from sheep infected with Streptococcus uberis demonstrated the presence of extranuclear DNA colocalizing with antimicrobial proteins, histones, and bacteria. Then, proteomic analysis by LTQ-Orbitrap Velos mass spectrometry provided detailed information on protein abundance changes occurring in milk upon infection. As a result, 1095 unique proteins were identified, of which 287 being significantly more abundant in mastitic milk. Upon protein ontology classification, the most represented localization classes for upregulated proteins were the cytoplasmic granule, the nucleus, and the mitochondrion, while function classes were mostly related to immune defence and inflammation pathways. All known NET markers were massively increased, including histones, granule proteases, and antimicrobial proteins. Of note was the detection of protein arginine deiminases (PAD3 and PAD4). These enzymes are responsible for citrullination, the post-translational modification that is known to trigger NET formation by inducing chromatin decondensation and extracellular release of NETs. As a further observation, citrullinated residues were detected by tandem mass spectrometry in histones of samples from mastitic animals. In conclusion, this work provides novel microscopic and proteomic information on NETs formed in vivo in the mammary gland, and reports the most complete database of proteins increased in milk upon bacterial mastitis.

Phosphoproteomics of the goat milk fat globule membrane: New insights into lipid droplet secretion from the mammary epithelial cell

Mechanisms of milk lipid secretion are highly controversial. Analyzing the fine protein composition of the "milk fat globule membrane" (MFGM), the triple-layered membrane surrounding milk lipid droplets (LDs) can provide mechanistic clues to better understand LD biosynthesis and secretion pathways in mammary epithelial cells (MECs). We therefore combined a high-sensitive Q-Exactive LC-MS/MS analysis of MFGM-derived peptides to the use of an in-house database intended to improve protein identification in the goat species. Using this approach, we performed the identification of 442 functional groups of proteins in the MFGM from goat milk. To get a more dynamic view of intracellular mechanisms driving LD dynamics in the MECs, we decided to investigate for the first time whether MFGM proteins were phosphorylated. MFGM proteins were sequentially digested by lysine-C and trypsin proteases and the resulting peptides were fractionated by a strong cation exchange chromatography. Titanium beads were used to enrich phosphopeptides from strong cation exchange chromatography eluted fractions. This approach lets us pinpoint 271 sites of phosphorylation on 124 unique goat MFGM proteins. Enriched GO terms associated with phosphorylated MFGM proteins were protein transport and actin cytoskeleton organization. Gained data are discussed with regard to lipid secretory mechanisms in the MECs. All MS data have been deposited in the ProteomeXchange with identifier PXD001039 (http://proteomecentral.proteomexchange.org/dataset/PXD001039).

Production and release of antimicrobial and immune defense proteins by mammary epithelial cells following Streptococcus uberis infection of sheep

Investigating the innate immune response mediators released in milk has manifold implications, spanning from elucidation of the role played by mammary epithelial cells (MECs) in fighting microbial infections to the discovery of novel diagnostic markers for monitoring udder health in dairy animals. Here, we investigated the mammary gland response following a two-step experimental infection of lactating sheep with the mastitis-associated bacterium Streptococcus uberis. The establishment of infection was confirmed both clinically and by molecular methods, including PCR and fluorescent in situ hybridization of mammary tissues. Proteomic investigation of the milk fat globule (MFG), a complex vesicle released by lactating MECs, enabled detection of enrichment of several proteins involved in inflammation, chemotaxis of immune cells, and antimicrobial defense, including cathelicidins and calprotectin (S100A8/S100A9), in infected animals, suggesting the consistent involvement of MECs in the innate immune response to pathogens. The ability of MECs to produce and release antimicrobial and immune defense proteins was then demonstrated by immunohistochemistry and confocal immunomicroscopy of cathelicidin and the calprotectin subunit S100A9 on mammary tissues. The time course of their release in milk was also assessed by Western immunoblotting along the course of the experimental infection, revealing the rapid increase of these proteins in the MFG fraction in response to the presence of bacteria. Our results support an active role of MECs in the innate immune response of the mammary gland and provide new potential for the development of novel and more sensitive tools for monitoring mastitis in dairy animals.