Phosphopeptides from Grana Padano cheese: nature, origin and changes during ripening

Proteolysis and Process-Induced Modifications in Synbiotic Yogurt Investigated by Peptidomics and Phosphopeptidomics

Probiotic and synbiotic yogurt preparations were manufactured at the semi-industrial pilot scale with Lactobacillus acidophilus and Bifidobacteria strains without inulin or fortified with 1 and 3% (w/w) inulin. The pathway of casein breakdown was determined in probiotic, synbiotic, conventional yogurt, and nonstarted milk base using HPLC-ESI-MS/MS-based peptidomics and phosphopeptidomics; in the latter case, casein phosphorylated peptides (CPPs) were previously enriched by hydroxyapatite chromatography. Compared with traditional yogurt, casein proteolysis increased in probiotic and even more in synbiotic yogurt with 1% inulin. Fortification with 3% inulin greatly modified the proteolytic pattern, indicating a characteristic contribution of probiotics to proteolysis. The enhanced proteolysis in synbiotic yogurt exposed the neo-formed peptides to progressively increase enzymatic or chemical modifications, such as dephosphorylation of CPPs, methionine oxidation, and formation of N-terminal pyroglutamic acids. These modifications might constitute molecular signature descriptors of metabolic processes mediated by complex bacterial communities, with technological, nutritional, and sensorial significance.

The protein and peptide fractions of kashk, a traditional Middle East fermented dairy product

Kashk is a typical dairy product of Iran, made from sour milk. It is traditionally produced from buttermilk in a dry, round-shaped form. Today, it is also produced at industrial level in a liquid form starting from fermented milk. We aimed to characterise the kashk proteome and peptidome comparing a traditional product with the industrial using a combination of proteomic approaches including advanced chromatographic and electrophoretic separation technique coupled to tandem mass spectrometry. We identified also phosphorylated casein-derived peptides (CPP) and investigated kashk protein digestibility using a static model of food protein digestion. The molecular characterization, coupled with bioinformatic in silico analysis, allowed the identification of potential bioactive peptides.

Comprehensive analysis of proteolysis during 8 months of ripening of high-cooked Old Saare cheese

We applied capillary electrophoresis, liquid chromatography coupled with tandem mass-spectrometry (MS/MS), and ultra-performance liquid chromatography to determine the composition of water-insoluble and water-soluble proteinaceous fractions of the cheese and to study in detail the degradation of caseins during 8 mo of ripening of Estonian high-temperature cooked hard cheese Old Saare. The application of high-resolution and high-accuracy MS/MS enabled identification of more than 3,000 small peptides, representing a fairly full casein peptidome containing peptides of 4 to 25 AA in length: 1,049 from β-casein (CN), 944 from α_S1-CN, 813 from α_S2-CN, and 234 from κ-CN. The majority of β-CN- and α_S1-CN-derived peptides originated from the N-terminal parts of the molecule, f6-93 and f1-124, respectively; peptides from α_S2-CN arose predominantly from the C-terminal end f100-162. At the beginning of ripening, we found a relatively high amount of peptides originating from the glycomacropeptide part of κ-CN, whereas peptides from para-κ-CN prevailed during the later stages of ripening of the cheese. The cleavage patterns of β-CN, α_S2-CN, as well as α_S1-CN, showed that primary proteolysis was started mainly by plasmin, although a low proteolytic activity of chymosin was also evident. Based on the analysis of cleavage sites, we observed a significant participation of proteolytic enzymes, including amino- and carboxypeptidases, of both mesophilic and thermophilic starter bacteria in further hydrolysis of oligopeptides during the ripening. Several new phosphopeptides were detected in the result of MS/MS data analysis. The profiles of the estimated concentrations of phosphopeptides revealed that those originating from β-CN and α_S1-CN accumulated during cheese maturation. In contrast, we did not notice any generation of phosphopeptides from the highly phosphorylated part of α_S2-CN, f25-80, presumably due to the inaccessibility of this region to the action of plasmin and chymosin. The analysis of cleavage sites and the combination of principal component and clustering analyses provided a characterization of the complex dynamics of formation and degradation of peptides during cheese maturation. We made an attempt to obtain a comprehensive picture of proteolysis during Old Saare cheese ripening on the basis of the detailed peptidomic data, including also the less abundant peptides determined by MS/MS, and complemented by the data on intact caseins and free AA and reported the results in the paper.

Antihypertensive peptides of animal origin: A review

Many bioactive peptides trigger certain useful antihypertensive activities in the living body system and there is a mounting worldwide interest in the therapeutic potential of these bioactive peptides for exploitation in vivo against the hypertension. Studies suggest the antihypertensive properties for many bioactive peptides of animal origin with underlying mechanisms ranging from inhibition of angiotensin-converting enzyme to additional mechanisms to lower blood pressure such as opioid-like activities and mineral-binding and antithrombotic properties. Antihypertensive peptides are the most extensively studied of all the bioactivities induced by food protein hydrolysates, highlighting their importance in human health and disease prevention and treatment. There exist enormous opportunities for the production of novel peptide-based products in biopharmaceutical manufacturing industries for the treatment, prevention, and mitigation of hypertension. Numerous products have already struck on the global market and many more are in process. This article focuses on antihypertensive peptides identified in the meat, fish, blood, milk, dairy products, and egg and their probable application as novel ingredients in the development of functional food products as dietary treatment of hypertension.

Identification of protein markers for the occurrence of defrosted material in milk through a MALDI-TOF-MS profiling approach

Mozzarella di Bufala Campana is a soft, stretched curd Italian cheese made from fresh buffalo milk that obtained the Protected Designation of Origin (PDO) registration in EU legislation. Seasonality of buffalo milk production, rapid cheese decay and transport of its preserving liquid have relevant practical/economic consequences for mozzarella production; consequently, a progressive diffusion of cheese products realized with frozen curd or frozen milk has recently been observed. In order to meet the demand of the dairy producers and consumers for a reduction of starting material adulterations and for the certification of the raw milk used for cheese manufacturing, we have developed a rapid/robust MALDI-TOF-MS polypeptide profiling procedure that assays material quality through the identification of specific markers of its freshness. Massive analysis of fresh and frozen buffalo milks (stored for different times) was realized to this purpose; a tough statistical evaluation of the resulting data ultimately permitted the typing of milk samples. We identified 28 polypeptide markers of the milk freezing storage, among which 13 and 15 showed down- and over-representation, respectively. Quantitative data were confirmed by an independent analytical approach on selected markers. GLYCAM1-derived phosphopeptides (1-53), β-casein-derived phosphopeptides (1-68), β-casein-derived γ2-, γ3- and γ4-fragments, α-lactalbumin and β-lactoglobulin were components showing the highest significance. The occurrence of the first compounds in buffalo milk is here described for the first time; their formation in the frozen material was ascribed to the activity of plasmin or of unknown bacterial proteases/peptidases stable at low temperatures. In conclusion, data reported here suggest the application of this MALDI-TOF-MS polypeptide profiling platform to other high-quality dairy productions, in which milk freshness has important consequences on final product organoleptic properties.

BIOLOGICAL SIGNIFICANCE

In the last decades, several studies have provided the molecular basis underlying the relation between food quality and human wellness/health. In this context, Foodomics emerged as a novel scientific discipline studying food and nutrition domains through the application of advanced omics technologies, including genomics, transcriptomics, proteomics and/or metabolomics. Above-mentioned technologies have been used in an integrated, holistic way to study foods for: i) compound profiling, authenticity, and/or biomarker-detection related to product quality or safety; ii) contaminants and their whole toxicity; iii) bioactivity and general effects on human health; iv) their digestion and assumption in human body; v) development of new transgenic products; and vi) evaluation of their modifications within the digestive tract. In the first context, a highly reproducible MALDI-TOF-MS polypeptide profiling procedure is here presented, which provides information on buffalo milk quality through the identification of specific markers of its freshness. Among identified markers, some were indicative of the action of various proteolytic enzymes and the resulting occurrence of specific defense components in buffalo milk having the physiological role to limit bacterial/virus content in this biological fluid. Data suggest the possible application of similar MALDI-TOF-based platforms to other high-quality food productions, where storage conditions of the starting materials may have important consequences on final product characteristics.

Lysozyme affects the microbial catabolism of free arginine in raw-milk hard cheeses

Lysozyme (LZ) is used in several cheese varieties to prevent late blowing which results from fermentation of lactate by Clostridium tyrobutyricum. Side effects of LZ on lactic acid bacteria population and free amino acid pattern were studied in 16 raw-milk hard cheeses produced in eight parallel cheese makings conducted at four different dairies using the same milk with (LZ+) or without (LZ-) addition of LZ. The LZ-cheeses were characterized by higher numbers of cultivable microbial population and lower amount of DNA arising from lysed bacterial cells with respect to LZ + cheeses. At both 9 and 16 months of ripening, Lactobacillus delbrueckii and Lactobacillus fermentum proved to be the species mostly affected by LZ. The total content of free amino acids indicated the proteolysis extent to be characteristic of the dairy, regardless to the presence of LZ. In contrast, the relative patterns showed the microbial degradation of arginine to be promoted in LZ + cheeses. The data demonstrated that the arginine-deiminase pathway was only partially adopted since citrulline represented the main product and only trace levels of ornithine were found. Differences in arginine degradation were considered for starter and non-starter lactic acid bacteria, at different cheese ripening stages.

A simple competitive enzyme-linked immunosorbent assay for the specific detection of the multiphosphorylated 1–25 β-casein fragment

A specific and simple competitive enzyme-linked immunosorbent assay (ELISA) was developed to determine bovine β-casein phosphopeptides (β-CPP) in casein phosphopeptides (CPP) or CPP complexes such as casein phosphopeptide amorphous calcium phosphate complexes added into dairy products. The method combines sample pretreatment designed for CPP enrichment and anti-β-CPP(f(1–25)) monoclonal antibody 1A5 (mAb 1A5). The mAb 1A5 bound specifically to the tryptic phosphopeptides from β-casein but not from αs1- or αs2-casein. Reactivity was also influenced by the extent of the phosphorylated form of serine residues. Based on the sequence-specific recognition and contribution of phosphorylated serine residues, the epitope of mAb 1A5 was found to reside within the cluster motif Ser(P)-Ser(P)-Ser(P)-Glu-Glu and the surrounding residues in β-CPP. The competitive ELISA developed here can be used as an alternative to specialised and expensive techniques such as mass spectrometry. In particular, it is suitable for the measurement of CPP or CPP complexes in dairy products, which contain closely related endogenous molecular species.

Cheese peptidomics: a detailed study on the evolution of the oligopeptide fraction in Parmigiano-Reggiano cheese from curd to 24 months of aging

In this work, we performed a detailed evaluation of the evolution of the oligopeptide fractions in samples of Parmigiano-Reggiano cheese from the curd up to 24 mo of aging. The samples were taken from wheels produced the same day, in the same factory, from the same milk, during the same caseification process, thus simplifying the natural variability of a whey-based starter fermentation. This unique and homogeneous sampling plan, never reported before in the literature, provided a detailed study of the peptides produced by enzymatic events during Parmigiano-Reggiano aging. Given the large dimensions of the 35-kg wheels of Parmigiano-Reggiano, samples were taken from both the internal and external parts of the cheese, to evidence eventual differences in the oligopeptide composition of the different parts. Fifty-seven peptides were considered, being among the most abundant during at least one of the periods of ripening considered, and their semiquantification indicated that the peptide fraction of Parmigiano-Reggiano cheese constantly evolves during the aging period. Five trends in its evolution were outlined, which could be clearly correlated to the enzymatic activities present in the cheese, making it possible to discriminate cheeses according to their aging time. Several known bioactive peptides were also found to be present in Parmigiano-Reggiano cheese samples, and for the first time, the age at which they are most abundant has been identified. Aged cheeses have been shown to be dominated by nonproteolytic aminoacyl derivatives, a new class of peptide-like molecules recently reported. Finally, the changing peptide pattern may be related to the changing enzymatic activities occurring inside the cheeses during the aging period, which, in turn, are also related to the microbiological composition.

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.

Principal component analysis of proteolytic profiles as markers of authenticity of PDO cheeses

The casein fraction of 13 Portuguese PDO cheeses were analysed using Urea-PAGE and reverse phase-high performance liquid chromatography (RP-HPLC) and then subjected to chemometric evaluation. The chemometric techniques of cluster analysis (CA) and principal component analysis (PCA) were used for the classification studies. Peptide mapping using Urea-PAGE followed by CA revealed two major clusters according to the similarity of the proteolytic profile of the cheeses. PCA results were in accordance with the grouping performed using CA. CA of RP-HPLC results of the matured cheeses revealed the presence of one major cluster comprising samples manufactured with only ovine milk or milk admixtures. When the results of CA technique were compared with the two PCA approaches performed, it was found that the grouping of the samples was similar. Both approaches, revealed the potential of proteolytic profiles (which is an essential aspect of cheese maturation) as markers of authenticity of PDO cheeses in terms of ripening time and milk admixtures not mentioned on the label.

Uncommonly thorough hydrolysis of peptides during ripening of Ragusano cheese revealed by tandem mass spectrometry

Ragusano is a pasta filata cheese produced from raw milk in Sicily. The proteolysis was extensively analyzed after stretching (day 0), at 4 and 7 months of ripening through soluble nitrogen, urea-PAGE, and peptide identification by tandem mass spectrometry. After stretching, 123 peptides were identified: 72 arising from β-casein, 34 from α(s1)-casein, and 17 from α(s2)-casein. The main protein splitting corresponded to the action of plasmin, chymosin, cathepsin D, cell envelope proteinase, and peptidase activities of lactic acid bacteria. Unlike other types of cheeses, <10% residual β- and α(s)-caseins remained intact at 7 months, indicating original network organization based on large casein fragments. The number of identified soluble peptides also dramatically decreased after 4 and 7 months of ripening, to 47 and 25, respectively. Among them, bioactive peptides were found, that is, mineral carrier, antihypertensive, and immunomodulating peptides and phosphopeptides.

Hydroxyapatite as a concentrating probe for phosphoproteomic analyses

A novel method for the selective enrichment of casein phosphoproteins/phosphopeptides (CPP) from complex mixtures is reported herein. This method employs ceramic hydroxyapatite (HA) as a solid-phase adsorbent to efficiently capture phosphoproteins and CPP from complex media. Casein was chosen as the model phosphoprotein to test the protocol. CPP immobilized on HA microgranules formed a complex that was included in the matrix-assisted laser desorption/ionization mass spectrometry (MALDI) matrix before desorbing directly from the well plate. Casein fractions with different levels of phosphorylation were desorbed based upon the specific concentration of trifluoroacetic acid (TFA) included in the MALDI matrix. The HA-bound casein enzymolysis was performed in situ with trypsin to remove non-phosphorylated peptides and isolate the immobilized CPP. The latter were recovered by centrifugation, dried, and co-crystallized with a 1% phosphoric acid (PA) solution in the matrix that was appropriate for detecting CPP in MALDI-MS spectra. This approach for the selection of casein/CPP resulted in the identification of 32 CPP by MALDI-time of flight (TOF). The analytical process involved two steps requiring ∼2h, excluding the time required for the enzymatic reaction. The alkaline phosphatase (AP)-assisted de-phosphorylation of tryptic CPP allowed the phosphorylation level of peptides to be calculated concurrently with MALDI-TOF MS and liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS/MS). The effectiveness of the extraction procedure assayed on eggshell phosphoproteins resulted in the identification of 5 phosphoproteins and 14 derived phosphopeptides with a phosphoprotein global recovery of ∼70% at least.

Comparative high-density microarray analysis of gene expression during growth of Lactobacillus helveticus in milk versus rich culture medium

Lactobacillus helveticus CNRZ32 is used by the dairy industry to modulate cheese flavor. The compilation of a draft genome sequence for this strain allowed us to identify and completely sequence 168 genes potentially important for the growth of this organism in milk or for cheese flavor development. The primary aim of this study was to investigate the expression of these genes during growth in milk and MRS medium by using microarrays. Oligonucleotide probes against each of the completely sequenced genes were compiled on maskless photolithography-based DNA microarrays. Additionally, the entire draft genome sequence was used to produce tiled microarrays in which noninterrupted sequence contigs were covered by consecutive 24-mer probes and associated mismatch probe sets. Total RNA isolated from cells grown in skim milk or in MRS to mid-log phase was used as a template to synthesize cDNA, followed by Cy3 labeling and hybridization. An analysis of data from annotated gene probes identified 42 genes that were upregulated during the growth of CNRZ32 in milk (P < 0.05), and 25 of these genes showed upregulation after applying Bonferroni's adjustment. The tiled microarrays identified numerous additional genes that were upregulated in milk versus MRS. Collectively, array data showed the growth of CNRZ32 in milk-induced genes encoding cell-envelope proteinases, oligopeptide transporters, and endopeptidases as well as enzymes for lactose and cysteine pathways, de novo synthesis, and/or salvage pathways for purines and pyrimidines and other functions. Genes for a hypothetical phosphoserine utilization pathway were also differentially expressed. Preliminary experiments indicate that cheese-derived, phosphoserine-containing peptides increase growth rates of CNRZ32 in a chemically defined medium. These results suggest that phosphoserine is used as an energy source during the growth of L. helveticus CNRZ32.

Purification and identification of water-soluble phosphopeptides from cheese using Fe(III) affinity chromatography and mass spectrometry

Water-soluble phosphopeptides from cheese were isolated using immobilized metal affinity chromatography (IMAC). Phosphopeptides from aqueous cheese extracts were completely retained on iminodiacetic acid (IDA) Sepharose equilibrated with FeCl3 and subsequently eluted with ammonium dihydrogen phosphate. Peptides in the eluate from the IMAC-Fe(III) column were identified using reversed phase liquid chromatography-electronic spray identification-tandem mass spectrometry. Phosphopeptides from two different cheeses were analyzed using the described method: a 10-month-old semihard Herrgard cheese made with mesophilic starter and a 24-month-old Parmigiano Reggiano cheese made with thermophilic starter. Elution of the IMAC-Fe(III) column with a gradient of ammonium dihydrogen phosphate resulted in three distinct peaks for Herrgard cheese corresponding to peptides carrying one, two, and four phosphorylated serine residues, respectively. Sixty-five different phosphopeptides were identified from the Herrgard, whereas only 9 from the Parmigiano Reggiano.

Study of the oligopeptide fraction in Grana Padano and Parmigiano-Reggiano cheeses by liquid chromatography electrospray ionization mass spectrometry

The oligopeptide fractions of Grana Padano and Parmigiano Reggiano cheese samples, at various stages of ageing (6, 12, 18 and 24 months), were analysed by means of high-performance liquid chromatography coupled to electrospray ionisation mass spectrometry (ESI-MS). The main oligopeptides (< 5000 Da) present in the samples were extracted by using an originally developed method which allowed good enrichment of the oligopeptide fractions and identified according to their molecular weights. The casein sequences compatible with the found molecular weights were determined and the exact oligopeptide sequences were identified by using the fragmentation peaks originated by in-source collisionally-induced dissociation (CID). The ESI-MS method reported here allowed the sequence identification of oligopeptides very quickly with a single liquid chromatography-mass spectrometry run. Oligopeptides were also semi-quantified by comparison with a suitable internal standard (the dipeptide phenylalanyl-phenylalanine, Phe-Phe). This methodology demonstrated that, as far as the main oligopeptides are concerned, Grana Padano and Parmigiano Reggiano presented very similar composition. Anyway, the evolution of the fractions during ageing time was characteristically distinct among the two cheeses: in Grana Padano cheeses most of the oligopeptides reached a maximum at 12 months of ageing and then decreased, whereas in Parmigiano Reggiano cheeses the oligopeptide amounts were usually lower and had a less regular trend. The reason for this different behaviour may be ascribed to the different production techniques.

Extraction, semi-quantification, and fast on-line identification of oligopeptides in Grana Padano cheese by HPLC-MS

Sixteen samples of Grana Padano cheese aged from 2 to 33 months were analyzed by HPLC-MS. The extraction process involved the use of diluted HCl, thus avoiding a strong deproteinizing agent (TCA), and allowing to maintain in solution also very lipophilic peptides. The molecular mass of the most abundant peptides were determined by electrospray ionization (ESI) mass spectrometry. A new method was developed based on the small fragmentation peaks arising from in-source fragmentation and from software analysis of the known casein sequences, which in many cases allowed the direct on-line identification of the oligopeptide sequences. Several new peptides never previously reported were identified, some of which containing bioactive sequences, consistently with what was described in the literature. Semiquantification of peptides at the different stages of aging was also performed by using a suitable internal standard, providing new insights into the evolution of the oligopeptide fraction during aging.

Yeasts associated with Manteca

Manteca is a traditional milk product of southern Italy produced from whey deriving from Caciocavallo Podolico cheese-making. This study was undertaken to obtain more information about the microbiological properties of this product and particularly about the presence, metabolic activities, and technological significance of the different yeast species naturally occurring in Manteca. High numbers of yeasts were counted after 7 days ripening (10(4)-10(5) cfu g(-1)) and then decreased to 10(2) at the end. A total of 179 isolates were identified and studied for their phenotypic and genotypic characteristics. The most frequently encountered species were Trichosporon asahii (45), Candida parapsilosis (33), Rhodotorula mucilaginosa (32), Candida inconspicua (29). Some of these yeasts showed lipolytic activity (32 strains) and proteolytic activity (29 strains), NaCl resistance up to 10% and growth up to 45 degrees C (42 strains). Biogenic amines were formed by proteolytic strains, in particular phenylethylamine, putrescine and spermidine. Spermidine was produced by all the yeasts tested in this work, but only Trichosporon produced a great quantity of this compound. Histamine was not detectable. Caseinolytic activity was common to almost all strains, corresponding to the ability to efficiently split off amino-terminal amino acids. The highest and most constant activity expressed by all species was X-prolyl-dipeptidyl aminopeptidase. The findings suggest that the presence of yeasts may play a significant role in justifying interactions with lactic acid bacteria, and consequently with their metabolic activity in the definition of the peculiar characteristics of Manteca cheese.

Peptides identified during Emmental cheese ripening: origin and proteolytic systems involved

To determine the proteolytic changes occurring during Emmental cheese ripening, peptides released in cheese aqueous phase were analyzed by reversed-phase HPLC and identified by tandem mass spectrometry sequencing, for which different strategies were illustrated by some examples. Among the 91 peptides identified, most of them arose from alpha(s1)- (51) and beta-caseins (28), and a few arose from alpha(s2)- (9) and kappa-caseins (1). An attempt was made to correlate the released peptides with the proteolytic systems potentially involved during Emmental cheese manufacture. Besides the well-known action of plasmin on beta- and alpha(s2)-caseins, and in the absence of residual fungal coagulant from Endothia parasitica, two other proteinases seem to be involved in the hydrolysis of alpha(s1)-casein in Emmental cheese: cathepsin D originated from milk and cell-envelope proteinase from thermophilic starters. Moreover, peptidases from starters were also active throughout ripening, presumably like those from nonstarter lactic acid bacteria, in contrast to those from propionic acid bacteria.

Immunochemical evaluation of bovine beta-casein and its 1-28 phosphopeptide in cheese during ripening

Polyclonal antibodies raised against the plasmin-released 1-28 phosphopeptide from bovine beta-casein [i.e., beta-CN(f1-28)4P] specifically recognized the tryptic beta-casein 1-25 and 2-25 peptides, whatever the degree of phosphorylation, but were unresponsive to the shortened beta-casein 16-22 phosphopeptide. These antibodies were able to recognize the parent bovine beta-casein as well as the homologous water buffalo protein, but they could not detect the homologous counterparts from ovine and caprine milks. Such antibodies were used in competitive enzyme-linked immunosorbent assays to monitor the plasmin-mediated release of the 1-28 phosphopeptide from beta-casein and to evaluate the residual native beta-casein in bovine cheese sampled during ripening. Applications of these polyclonal antibodies are suggested mainly for estimating the age of hard cheeses and, possibly, for tracing the presence of bovine casein in fresh ovine and caprine cheeses.

Applications of mass spectrometry to food proteins and peptides

The application of mass spectrometry (MS) to large biomolecules has been revolutionized in the past decade with the development of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) techniques. ESI and MALDI permit solvent evaporation and sublimation of large biomolecules into the gaseous phase, respectively. The coupling of ESI or MALDI to an appropriate mass spectrometer has allowed the determination of accurate molecular mass and the detection of chemical modification at high sensitivity (picomole to femtomole). The interface of mass spectrometry hardware with computers and new extended mass spectrometric methods has resulted in the use of MS for protein sequencing, post-translational modifications, protein conformations (native, denatured, folding intermediates), protein folding/unfolding, and protein-protein or protein-ligand interactions. In this review, applications of MS, particularly ESI-MS and MALDI time-of-flight MS, to food proteins and peptides are described.

Application of chromatography and mass spectrometry to the characterization of food proteins and derived peptides

The following review describes the development of mass spectrometry off-line and on-line coupled with liquid chromatography to the analysis of food proteins. It includes the significant results recently obtained in the field of milk, egg and cereal proteins. This paper also outlines the research carried out in the area of food protein hydrolysates, which are important components in foodstuffs due to their functional properties. Liquid chromatography and mass spectrometry have been particularly used for the characterization of food peptides and especially in dairy products.

Alternative nonallelic deletion is constitutive of ruminant alpha(s1)-casein

Multiple forms of alpha(s1)-casein were identified in the four major ruminant species by structural characterization of the protein fraction. While alpha(s1)-casein phenotypes were constituted by a mixture of at least seven molecular forms in ovine and caprine species, there were only two forms in bovine and water buffalo species. In ovine and caprine forms the main component corresponded to the 199-residue-long form, and the deleted proteins differed from the complete one by the absence of peptides 141-148, 110-117, or Gln78, or a combination of such deletions. The deleted segments corresponded to the sequence regions encoded by exons 13 and 16, and by the first triplet of exon 11 (CAG), suggesting that the occurrence of the short protein forms is due to alternative skipping, as previously demonstrated for some caprine and ovine phenotypes. The alternative deletion of Gln78 in alpha(s1)-casein, the only form common to the milk of all the species examined and located in a sequence region joining the polar phosphorylation cluster and the hydrophobic C-terminal domain of the protein, may play a functional role in the stabilization of the milk micelle structure.

The primary structure of water buffalo alpha(s1)- and beta-casein identification of phosphorylation sites and characterization of a novel beta-casein variant

The primary structure of water buffalo alpha(s1)-casein and of beta-casein A and B variants has been determined using a combination of mass spectrometry and Edman degradation procedures. The phosphorylated residues were localized on the tryptic phosphopeptides after performing a beta-elimination/thiol derivatization. Water buffalo alpha(s1)-casein, resolved in three discrete bands by isoelectric focusing, was found to consist of a single protein containing eight, seven, or six phosphate groups. Compared to bovine alpha(s1)-casein C variant, the water buffalo alpha(s1)-casein presented ten amino acid substitutions, seven of which involved charged amino acid residues. With respect to bovine betaA2-casein variant, the two water buffalo beta-casein variants A and B presented four and five amino acid substitutions, respectively. In addition to the phosphoserines, a phosphothreonine residue was identified in variant A. From the phylogenetic point of view, both water buffalo beta-casein variants seem to be homologous to bovine betaA2-casein.