Characterization of the protein profile of donkey's milk whey fraction

Preventive effect of fermented whey protein mediated by Lactobacillus gasseri IM13 via the PI3K/AKT/FOXO pathway in muscle atrophy

This study investigated the preventive effects of whey protein fermented with Lactobacillus gasseri IM13 (F-WP) against dexamethasone (DEX)-induced muscle atrophy. C2C12 muscle cells were treated with F-WP followed by DEX treatment. Dexamethasone treatment inhibited myotube formation and the expression of myogenic regulatory factors; however, pretreatment with F-WP attenuated DEX-induced damage. The F-WP significantly activated the phosphorylation of the IGF-1/PI3K/AKT pathway and improved muscle homeostasis suppressed by DEX. Moreover, F-WP alleviated the phosphorylation of mTOR, S6K1, and 4E-BP1 and enhanced muscle protein synthesis. Muscle-specific ubiquitin ligases and autophagy lysosomes, which were activated by the dephosphorylation of FOXO3a by DEX treatment, were significantly attenuated by F-WP pretreatment of myotubes. For peptidomic analysis, F-WP was fractionated using preparative HPLC (prep-HPLC), and the AA sequences of 11 peptides were identified using MALDI-TOF/MS/MS. In conclusion, fermentation of whey protein by the specific probiotic strain IM13 produced bioactive peptides with high antioxidant and anti-sarcopenic-sarcopenic effects, which markedly enhanced myogenesis and muscle protein synthesis while diminishing muscle protein degradation compared with intact whey protein.

Milk proteomic analysis reveals differentially expressed proteins in high-yielding and low-yielding Guanzhong dairy goats at peak lactation

The aim of this experiment was to investigate the differential proteomic characteristics of milk from high- and low-yielding Guanzhong dairy goats during the peak lactation period under the same feeding conditions. Nine Guanzhong dairy goats with high yield (H: 3.5 ± 0.17 kg/d) and nine with low yield (L:1.2 ± 0.25 kg/d) were selected for milk proteomic analysis using tandem mass tag technology. A total of 78 differentially expressed proteins were identified. Compared with L, 50 proteins including HK3, HSPB1 and ANXA2 were significantly upregulated in H milk, while 28 proteins including LALBA and XDH were significantly downregulated. Bioinformatics analysis of the differentially expressed proteins showed that galactose metabolism, purine metabolism, glycolysis/gluconeogenesis, MAPK signaling pathway, regulation of actin cytoskeleton and other pathways were closely related to milk yield. HK3, HSPB1, ANXA2, LALBA and XDH were important candidate proteins associated with the milk production characteristics of Guanzhong dairy goats. Our data provide relevant biomarkers and a theoretical basis for improving milk production in Guanzhong dairy goats.

Biomolecular Profiling by MALDI-TOF Mass Spectrometry in Food and Beverage Analyses

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has frequently been applied to the analysis of biomolecules. Its strength resides not only in compound identification but particularly in acquiring molecular profiles providing a high discriminating power. The main advantages include its speed, simplicity, versatility, minimum sample preparation needs, and a relatively high tolerance to salts. Other benefits are represented by the possibility of automation, high throughput, sensitivity, accuracy, and good reproducibility, allowing quantitative studies. This review deals with the prominent use of MALDI-TOF MS profiling in food and beverage analysis ranging from the simple detection of sample constituents to quantifications of marker compounds, quality control, and assessment of product authenticity. This review summarizes relevant discoveries that have been obtained with milk and milk products, edible oils, wine, beer, flour, meat, honey, and other alimentary products. Marker molecules are specified: proteins and peptides for milk, cheeses, flour, meat, wine and beer; triacylglycerols and phospholipids for oils; and low-molecular-weight metabolites for wine, beer and chocolate. Special attention is paid to sample preparation techniques and the combination of spectral profiling and statistical evaluation methods, which is powerful for the differentiation of samples and the sensitive detection of frauds and adulterations.

Comparative Whey Proteome Profiling of Donkey Milk With Human and Cow Milk

Donkey milk (DM), similar to human milk (HM) in chemical composition, has been suggested as the best potential hypoallergenic replacement diet for babies suffering from Cow milk (CM) protein allergy. In order to better understand DM protein, many studies based on proteomic have been performed. In this study, the label-free quantitative proteomic approach was conducted to quantitatively identify the differentially expressed whey proteins (DEPs) in DM vs. HM group and DM vs. CM group. In total, 241 and 365 DEPs were found in these two groups, respectively. Bioinformatics analysis of DEPs showed that the majority of DEPs participated in the lipoprotein metabolic process, regulation of cytokine production, chemical homeostasis, and catabolic process. The Kyoto Encyclopedia of Gene and Genomes (KEGG) pathways analysis found that these DEPs mainly participated in an antigen processing, complement, and coagulation cascades. These results may provide valuable information in the composition of milk whey proteins in DM, HM, and CM, especially for low abundant components, and expand our knowledge of different biological functions between DM and HM or CM.

Insights on Health and Food Applications of Equus asinus (Donkey) Milk Bioactive Proteins and Peptides-An Overview

Due to its similarity with human milk and its low allergenic properties, donkey milk has long been used as an alternative for infants and patients with cow's milk protein allergy (CMPA). In addition, this milk is attracting growing interest in human nutrition because of presumed health benefits. It has antioxidant, antimicrobial, antitumoral, antiproliferative and antidiabetic activity. In addition, it stimulates the immune system, regulates the gastrointestinal flora, and prevents inflammatory diseases. Although all donkey milk components can contribute to functional and nutritional effects, it is generally accepted that the whey protein fraction plays a significant role. This review aims to highlight the active proteins and peptides of donkey milk in comparison with other types of milk, emphasizing their properties and their roles in different fields of health and food applications.

Functional milk proteome analysis of genetically diverse goats from different agro climatic regions

Goat milk, a choice of substitution to mother's milk for its composition, fulfils nutritional requirement of infants, pregnant mothers and older people. The present study was carried out to unravel the milk proteome profiles from geographically and genetically diverse goat breeds by gel based 2DE and nLC-MS/MS. A total of 1307 functional proteins comprising casein and other low abundance proteins were identified. Gene annotations revealed that the majority of the proteins were involved in binding function, catalytic activity and structural molecules and localised in nucleus and membrane. The distinguished proteins were involved in 144 KEGG pathways in information processing, metabolism, cellular process, organismal systems and diseases. The large number of proteins and peptides including bioactive peptides were reported from goat milk from diverse agro-climatic regions of India indicating their significant potential for human health applications. SIGNIFICANCE: Goat milk in India is used in various Ayurvedic formulations to treat a number of ailments and allergies as well as for nutraceutical formulations. The study identifies milk protein variants both at protein and DNA level and subsequent identification of proteins by 2DE and nLC-MS/MS resulting in a proteome comprising of 1307 proteins. The specific proteins and peptides having significant role in immune regulation, disease pathways, cellular growth and metabolism have been identified. The results contribute to goat milk protein and peptide database which is very limited. We identified proteins for specific functional categories and associated them with different pathways for studying functional diversity of goat milk proteins. The proteins and peptides identified can be used for multiple human health application.

Favorable effect of creams with skimmed donkey milk encapsulated in nanoliposomes on skin physiology

The use of donkey milk has a long history in external dermal application for cosmetic and medical purposes. The encapsulation of different drugs into nanoliposomes and nutrients may have many benefits for the delivery of the targeted substance. The aim of the present study is to test creams with nanoliposomes encapsulated with skimmed donkey milk, reported in our registered patent, compared with effect of the placebo cream and the untreated skin. To investigate the effect of formulated cream, we have measured the electrical capacitance, transepidermal water loss and the skin pH value. The study included 15 healthy volunteers (11 women and 4 men). The patented creams exhibited satisfactory moisturizing properties very soon after application, while hydration was reached earlier in the spots treated with night cream. Transepidermal water loss slightly decreased only after 4 weeks of treatment in each of the spots assessed. The pH value was similar after each of the treatments. Tested creams may enhance the moisture of skin very soon after application, in this way potentially enable deeper permeation of phospholipids and essential proteins, without changing the pH. It may also contribute to additional anti-aging effects.

Multi-parameter evaluation of the effect of processing conditions on meat protein modification

Evaluating the interconnecting effects of pH, temperature and time on food proteins is of relevance to food processing, and food functionality. Here we describe a matrix-based approach in which meat proteins were exposed to combinations of these parameters, selected to cover coordinates in a realistic processing space, and analyzed using redox proteomics. Regions within the matrix showing high levels of protein modification were evaluated for oxidative and other modifications. Both pH and temperature, independently, had a significant effect on the oxidative modifications mostly detected in myofibrillar proteins such as myosin and troponin and also collagen. Heat induced pyroglutamic acid formation was exclusively observed in the myofibrillar proteins. Potential interdependencies between pH, temperature and exposure time were evaluated using a 3-way analysis of variance (ANOVA) on protein modification levels to better understand how industry relevant process parameters influence protein quality and function.

Comparative analysis of whey proteins in donkey colostrum and mature milk using quantitative proteomics

Donkey milk is attracting increasing attention as a nutritional milk source similar to human milk. In this study, we carried out qualitative and quantitative analysis of the donkey whey proteome using a label-free proteomic approach, combined with parallel reaction monitoring (PRM) as a validation method. A total of 300 whey proteins were identified in donkey colostrum (DC) and donkey mature (DM) milk, of which 18 were differentially expressed (P < 0.05) between the two types of milk. Gene ontology (GO) analysis showed that differentially and uniquely expressed proteins were mainly involved in cellular processes, response to stimulus, metabolic processes, and biological regulation. Their molecular functions included binding, catalytic activity, and molecular functional regulation, and their main annotated areas of origin were the cell, cell-part, and the extracellular region. Most differentially and uniquely expressed proteins were linked with malaria, systemic lupus erythematosus, or antigen processing and presentation. Our results provide insight into the complexity of the donkey whey proteome and molecular evidence for nutritional differences between different lactation stages.

Proteins and bioactive peptides from donkey milk: The molecular basis for its reduced allergenic properties

The legendary therapeutics properties of donkey milk have recently been supported by many clinical trials who have clearly demonstrated that, even if with adequate lipid integration, it may represent a valid natural substitute of cow milk for feeding allergic children. During the last decade many investigations by MS-based methods have been performed in order to obtain a better knowledge of donkey milk proteins. The knowledge about the primary structure of donkey milk proteins now may provide the basis for a more accurate comprehension of its potential benefits for human nutrition. In this aspect, experimental data today available clearly demonstrate that donkey milk proteins (especially casein components) are more closely related with the human homologues rather than cow counterparts. Moreover, the low allergenic properties of donkey milk with respect to cow one seem to be related to the low total protein content, the low ratio of caseins to whey fraction, and finally to the presence in almost all bovine IgE-binding linear epitopes of multiple amino acid differences with respect to the corresponding regions of donkey milk counterparts.

A major allergen in rainbow trout (Oncorhynchus mykiss): complete sequences of parvalbumin by MALDI tandem mass spectrometry

Fish parvalbumin (PRVB) is an abundant and stable protein in fish meat. The variation in cross-reactivity among individuals is well known and explained by a broad repertoire of molecular forms and differences between IgE-binding epitopes in fish species. PVRB has "sequential" epitopes, which retain their IgE-binding capacity and allergenicity also after heating and digestion using proteolytic enzymes. From the allergonomics perspective, PRVB is still a challenging target due to its multiple isoforms present at different degrees of distribution. Little information is available in the databases about PVRBs from Oncorhynchus mykiss. At present, only two validated, incomplete isoforms of this species are included in the protein databases: parvalbumin beta 1 (P86431) and parvalbumin beta 2 (P86432). A simple and rapid protocol has been developed for selective solubilization of PRVB from the muscle of farmed rainbow trout (Oncorhynchus mykiss), followed by calcium depletion, proteolytic digestion, MALDI MS, and MS/MS analysis. With this strategy thermal allergen release was assessed and PRVB1 (P86431), PRVB1.1, PRVB2 (P86432) and PRVB2.1 variants from the rainbow trout were sequenced. The correct ordering of peptide sequences was aided by mapping the overlapping enzymatic digests. The deduced peptide sequences were arranged and the theoretical molecular masses (Mr) of the resulting sequences were calculated. Experimental masses (Mr) of each PRVB variant were measured by linear MALDI-TOF.

Peptidome characterization and bioactivity analysis of donkey milk

Donkey milk is an interesting commercial product for its nutritional values, which make it the most suitable mammalian milk for human consumption, and for the bioactivity associated with it and derivative products. To further mine the characterization of donkey milk, an extensive peptidomic study was performed. Two peptide purification strategies were compared to remove native proteins and lipids and enrich the peptide fraction. In one case the whole protein content was precipitated by organic solvent using cold acetone. In the other one the precipitation of the most abundant milk proteins, caseins, was performed under acidic conditions by acetic acid at pH4.6, instead. The procedures were compared and proved to be partially complementary. Considered together they provided 1330 peptide identifications for donkey milk, mainly coming from the most abundant proteins in milk. The bioactivity of the isolated peptides was also investigated, both by angiotensin-converting-enzyme inhibitory and antioxidant activity assays and by bioinformatics, proving that the isolated peptides did have the tested biological activities.

BIOLOGICAL SIGNIFICANCE

The rationale behind this study is that peptides in food matrices often play an important biological role and, despite the extensive study of the protein composition of different samples, they remain poorly characterized. In fact, in a typical shotgun proteomics study endogenous peptides are not properly characterized. In proteomics workflows one limiting point is the isolation process: if it is specific for the purification of proteins, it often comprises a precipitation step which aims at isolating pure protein pellets and remove unwonted interferent compounds. In this way endogenous peptides, which are not effectively precipitated as well as proteins, are removed too and not analyzed at the end of the process. Moreover, endogenous peptides do often originate from precursor proteins, but in phenomena which are independent of the shotgun digestion protocol, thus they can be obtained from cleavage specificities other than trypsin's, which is the main proteolytic enzyme employed in proteomic experiments. For this reason, in the end, database search will not be effective for identification of these peptides, thus the need to provide different workflows for peptide analysis. In the work presented in this paper this issue is considered for the first time for the analysis of the peptides isolated in donkey milk samples, which have been chosen for its nutritional interest. This study provides additional knowledge on this milk, already characterized by traditional proteomics studies and peptidomic studies after simulated digestion. This type of study is not just a description of the naturally occurring peptidome of a sample, but also represents a starting point to discover and characterize those naturally occurring peptides responsible for the observed bioactivities of biological samples, as in the case of donkey milk, which would remain uncharacterized by other approaches. In this paper an analytical protocol was described for the efficient isolation and purification of peptides in donkey milk, assessing the effect of the purification protocol on the final identifications. Purified peptide samples were also checked to empirically elucidate any ACE inhibitory or antioxidant activity. Finally, the peptidomic results were also further mined by a bioinformatic-driven approach for bioactive peptide identification in the donkey milk samples. In our opinion, the main strengths of this study are related to the improved analytical workflow (either as purification protocol comparison or analytical platform development) which provides a high number of identified peptides, for which the biological significance as potential bioactive peptides has also been investigated.

Mass spectrometry in food proteomics: a tutorial

In the last decades, the continuous and rapid evolution of proteomic approaches has provided an efficient platform for the characterization of food-derived proteins. Particularly, the impressive increasing in performance and versatility of the MS instrumentation has contributed to the development of new analytical strategies for proteins, evidencing how MS arguably represents an indispensable tool in food proteomics. Investigation of protein composition in foodstuffs is helpful for understanding the relationship between the protein content and the nutritional and technological properties of foods, the production of methods for food traceability, the assessment of food quality and safety, including the detection of allergens and microbial contaminants in foods, or even the characterization of genetically modified products. Given the high variety of the food-derived proteins and considering their differences in chemical and physical properties, a single proteomic strategy for all purposes does not exist. Rather, proteomic approaches need to be adapted to each analytical problem, and development of new strategies is necessary in order to obtain always the best results. In this tutorial, the most relevant aspects of MS-based methodologies in food proteomics will be examined, and their advantages and drawbacks will be discussed.

Proteomic comparison of equine and bovine milks on renneting

Rennet-induced coagulation of bovine milk is a complex mechanism in which chymosin specifically hydrolyzes κ-casein, the protein responsible for the stability of the casein micelle. In equine milk, this mechanism is still unclear, and the protein targets of chymosin are unknown. To reveal the proteins involved, the rennetability of equine milk by calf chymosin was examined using gel-free and gel-based proteomic analysis and compared to bovine milk. RP-HPLC analysis of bovine and equine milks showed the release of several peptides following chymosin incubation. The hydrolyses of equine and bovine casein by chymosin were different, and the major peptides produced from equine milk were identified by mass spectrometry as fragments of β-casein. Using two-dimensional electrophoresis, equine β-casein was confirmed as the main target of calf chymosin over 24 h at 30 °C and pH 6.5. The gel-based analysis of equine milk discriminated between the different individual proteins and provided information on the range of isoforms of each protein as a result of post-translational modifications, as well as positively identified for the first time several isoforms of κ-casein. In comparison to bovine milk, κ-casein isoforms in equine milk were not involved in chymosin-induced coagulation. The intensity of equine β-casein spots decreased following chymosin addition, but at a slower rate than bovine κ-casein.

MALDI-TOF mass spectrometry for the monitoring of she-donkey's milk contamination or adulteration

Donkey's milk (DM), representing a safe and alternative food in both IgE-mediated and non-IgE-mediated cow's milk protein allergy, can be categorized as precious pharma-food. Moreover, an economically relevant interest for the use of DM in cosmetology is also developing. The detection of adulterations and contaminations of DM is a matter of fundamental importance from both an economic and allergenic standpoint, and, to this aim, fast and efficient analytical approaches to assess the authenticity of this precious nutrient are desirable. Here, a rapid matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS)-based method aimed to the detection of bovine or caprine milk in raw DM is reported. The presence of the extraneous milks was revealed by monitoring the protein profiles of the most abundant whey proteins, α-lactalbumin (α-LA) and β-lactoglobulin, used as molecular markers. The possibility of obtaining a quantitative analysis of the level of cow or goat milk in DM based on the MALDI-TOF peak areas of α-LAs was also explored. The results showed that the experimental quantitative values were in good agreement with the real composition of each mixture. As pretreatment of the milk samples is not required, and owing to the speed and the high sensitivity of MALDI-MS, the protocol here reported could represent a reliable method for routine analyses aimed to assess the absence of contamination in raw fresh DM samples.

MS-based characterization of α(s2)-casein isoforms in donkey's milk

The primary structure of four α(s2)-casein (CN) isoforms, present as minor components in the dephosphorylated CN fraction of a milk sample collected in Eastern Sicily from an individual donkey belonging to the Ragusano breed at middle lactation stage, was determined, using the known donkey's α(s2)-CN (GenBank Acc. No. CAV00691; M(r) 26,028 Da) as reference. Proteins, with experimentally measured M(r) of 25,429, 21,939, 25,203 and 21,713 Da, were isolated by the combined use of reversed-phase high-performance liquid chromatography (RP-HPLC) and two-dimensional polyacrylamide gel electrophoresis. The major spot of each gel, corresponding to a single protein, was digested by trypsin, α-chymotrypsin and endoproteinase Glu-C. The resulting peptide mixtures were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and capillary RP-HPLC/nano-electrospray ionization tandem mass spectrometry, and the data obtained were used for the sequence determination. The isoforms are produced from differential splicing events involving exons 4, 5 and 6 and parts of the exon 17.

Farm animal milk proteomics

Milk is one of the most important nutrients for humans during lifetime. Farm animal milk in all its products like cheese and other fermentation and transformation products is a widespread nutrient for the entire life of humans. Proteins are key molecules of the milk functional component repertoire and their investigation represents a major challenge. Proteins in milk, such as caseins, contribute to the formation of micelles that are different from species to species in dimension and casein-type composition; they are an integral part of the MFGM (Milk Fat Globule Membrane) that has being exhaustively studied in recent years. Milk proteins can act as enzymes or have an antimicrobial activity; they could act as hormones and, last but not least, they have a latent physiological activity encoded in their primary structure that turns active when the protein is cleaved by fermentation or digestion processes. In this review we report the last progress in proteomics, peptidomics and bioinformatics. These new approaches allow us to better characterize the milk proteome of farm animal species, to highlight specific PTMs, the peptidomic profile and even to predict the potential nutraceutical properties of the analyzed proteins.

Size exclusion and reversed-phase high-performance liquid chromatography/UV for routine control of thermal processing of cows' and donkey milk major proteins

Cows' and donkey milks (raw and thermally processed) and respective whey were analysed for quantification of major proteins. Two different chromatographic approaches, size exclusion (SE-HPLC) and reversed-phase high performance liquid chromatography (RP-HPLC) both coupled to UV detection were used. Usefulness of these methods for routine control of the effect of thermal processing was evaluated. The external standard method was used to calibrate the SE-HPLC and RP-HPLC systems. Concerning quantification of β-lactoglobulin (β-lg), α-lactalbumin (α-la), lysozyme (lys), and total casein (cn), no significant differences between results obtained by SE-HPLC and by RP-HPLC (t-test, P>0·05) were observed for raw milks and whey. Heating of cows' milk promoted aggregation of denatured proteins as observed by SE-HPLC, whereas α-la and β-lg from donkey milk were stable to thermal processing at 100°C (5 min). Lys was quantified in donkey raw milk and whey however, in thermally processed donkey milk lys was denatured and could not be quantified by HPLC.

Review: applications of mass spectrometry techniques in the investigation of milk proteome

The introduction of "soft" desorption/ionization methods such as electrospray ionization and matrix-assisted laser desorption/ionization has determined a breakthrough in the application of mass spectrometry to the structural analysis of proteins. The contemporary advancement of bioinformatics, together with the possibility to combine these mass spectrometric methods with electrophoretic or chromatographic separation techniques has opened up the new field of proteome analysis and, more generally, has established these approaches as indispensable tools for protein and peptide analysis in complex mixtures, such as milk and milk- derived foods. Here, a necessarily not exhaustive series of current applications of mass spectrometry-based techniques for the characterization of milk proteins will be summarized. These include the characterization of milk protein polymorphism, determination of the structural modifications induced on milk proteins by industrial processes, investigation of milk adulterations and characterization of milk allergens.

Sequence determination of alphas1-casein isoforms from donkey by mass spectrometric methods

Four co-eluting components, with experimentally measured M(r) of 23 658, 23 786, 24 278 and 24 406 Da, were detected by reversed-phase high-performance liquid chromatography (RP-HPLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis in the dephosphorylated casein fraction of a milk sample collected at middle lactation stage from an individual donkey belonging to the Ragusano breed. By coupling RP-HPLC, two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), enzymatic digestions, MALDI-TOF MS and capillary RP-HPLC/nano-electrospray ionization tandem mass spectrometry (nESI-MS/MS) analyses, the four components were identified as donkey's alpha(s1)-CNs and their sequences completely characterized, using the known mare's alpha(s1)-CN (GenBank Acc. No. AAK83668; M(r) 23750.7 Da) as reference. The proteins with M(r) of 23 786 and 23 658 Da differ in the presence of a glutamine residue at position 83 in the full-length component and present the amino acid substitutions Q(8)-->H and H(115)-->Y with respect to the mare's alpha(s1)-CN. The other two components with M(r) 24 406 and 24 278 Da, which also differ in the presence of a glutamine residue at position 88 in the full-length component, show the insertion of the pentapeptide HTPRE between Leu(33) and the Glu(34). The two alpha(s1)-CNs bearing the pentapeptide insertion were named variants A (202 amino acids; M(r) 24 406) and A(1) (201 amino acids; M(r) 24 278), whereas the two alpha(s1)-CNs without the pentapeptide were named variants B (197 amino acids; M(r) 23 786) and B(1) (196 amino acids; M(r) 23 658).