Application of a mass spectrometry sequencing technique for identifying peptides present in Cheddar cheese

Cell-Penetrating Milk-Derived Peptides with a Non-Inflammatory Profile

Milk-derived peptides are known to confer anti-inflammatory effects. We hypothesised that milk-derived cell-penetrating peptides might modulate inflammation in useful ways. Using computational techniques, we identified and synthesised peptides from the milk protein Alpha-S1-casein that were predicted to be cell-penetrating using a machine learning predictor. We modified the interpretation of the prediction results to consider the effects of histidine. Peptides were then selected for testing to determine their cell penetrability and anti-inflammatory effects using HeLa cells and J774.2 mouse macrophage cell lines. The selected peptides all showed cell penetrating behaviour, as judged using confocal microscopy of fluorescently labelled peptides. None of the peptides had an effect on either the NF-κB transcription factor or TNFα and IL-1β secretion. Thus, the identified milk-derived sequences have the ability to be internalised into the cell without affecting cell homeostatic mechanisms such as NF-κB activation. These peptides are worthy of further investigation for other potential bioactivities or as a naturally derived carrier to promote the cellular internalisation of other active peptides.

Can cheese mites, maggots and molds enhance bioactivity? Peptidomic investigation of functional peptides in four traditional cheeses

Aside from their amino acid content, dairy proteins are valuable for their ability to carry encrypted bioactive peptides whose activities are latent until released by digestive enzymes or endogenous enzymes within the food. Peptides can possess a wide variety of functionalities, such as antibacterial, antihypertensive, and antioxidative properties, as demonstrated by in vitro and in vivo studies. This phenomenon raises the question as to what impact various traditional cheese-making processes have on the formation of bioactive peptides in the resulting products. In this study, we have profiled the naturally-occurring peptides in two hard and two soft traditional cheeses and have identified their known bioactive sequences. While past studies have typically identified fewer than 100 peptide sequences in a single cheese, we have used modern instrumentation to identify between 2900 and 4700 sequences per cheese, an increase by a factor of about 50. We demonstrated substantial variations in proteolysis and peptide formation between the interior and rind of each cheese, which we ascribed to the differences in microbial composition between these regions. We identified a total of 111 bioactive sequences among the four cheeses, with the greatest number of sequences, 89, originating from Mimolette. The most common bioactivities identified were antimicrobial and inhibition of the angiotensin-converting enzyme. This work revealed that cheese proteolysis and the resulting peptidomes are more complex than originally thought in terms of the number of peptides released, variation in peptidome across sites within a single cheese, and variation in bioactive peptides among cheese-making techniques.

Peptide profile and angiotensin-converting enzyme inhibitory activity of Prato cheese with salt reduction and Lactobacillus helveticus as an adjunct culture

Among strategies to improve the health-related aspects of dairy products, great prominence has been given to salt reduction and the use of adjunct cultures that can favor the release of bioactive peptides during cheese ripening. This study aimed to evaluate the effect of the salt reduction, the addition of Lactobacillus helveticus LH-B02 and the ripening time of Prato cheese on the casein hydrolysis profile by capillary electrophoresis, peptide profile by mass spectrometry, and antihypertensive potential evaluated in vitro through the inhibitory activity of the angiotensin-converting enzyme (ACE). Both the salt reduction and the addition of adjunct culture favored the accumulation of the bioactive peptide β-CN (f193-209) (m/z 1881). The adjunct culture led to a higher ACE inhibitory activity during the ripening of Prato cheese, thus proving to be an effective strategy for the development of potentially bioactive cheese.

Peptide profile of Camembert-type cheese: Effect of heat treatment and adjunct culture Lactobacillus rhamnosus GG

Several factors might impact the proteolysis during cheese manufacture and ripening and, therefore, the release of bioactive peptides. These factors include the heat treatment of the milk, the type of starter and secondary culture used and the ripening time. Thus, the objective of this study was to evaluate the effect of the milk heat treatment and the use of adjunct culture in the development of the peptide profile of Camembert-type cheese during ripening. The cheeses were made from raw and heat-treated milk, with and without the addition of Lactobacillus rhamnosus GG. The results obtained by mass spectrometry (MALDI ToF/MS) and analyzed by chemometrics (PLS-DA) revealed a complex hydrolysis profile of the caseins with 103 peaks found, of which 70 peptides were identified and 15 presented bioactive potential. The potential bioactive peptides important for the separation of cheeses were all derived from β-casein. The heat treatment of the milk, the addition of the adjunct culture and the ripening time affected the peptide profile of the cheeses. At the beginning of ripening the cheeses presented a very similar peptide profile, which differed over time, and this differentiation is clearer for cheeses obtained from raw milk.

Sensoproteomics: A New Approach for the Identification of Taste-Active Peptides in Fermented Foods

Aiming at the identification of the key bitter peptides in fermented foods, a new approach, coined "sensoproteomics", was developed and applied to fresh cheese samples differing in bitter taste intensity. By means of MPLC fractionation of the water-soluble cheese extracts in combination with taste dilution analysis, complex fractions with intense bitter taste were located and then screened by UPLC-MS/MS for the entire repertoire of ∼1600 candidate peptides, extracted from a literature meta-analysis on dairy products, by using a total of 120 selected reaction monitoring methods computed in silico. A total of 340 out of the 1600 peptides were found in the cheese samples, among which 17 peptides were identified as candidate bitter peptides by considering only peptides that were located in the bitter-tasting MPLC fractions (signal-to-noise ratio: ≥10) with a fold-change of ≥3 when comparing the less bitter to the more bitter cheese sample and that were validated by comparison with the synthetic reference peptides. While EIVPNS[phos]VEQK (α_s1-CN_70-78) and INTIASGEPT (κ-CN_122-131) did not exhibit any bitter taste up to 2000 μmol/L, 15 of the 17 target peptides showed bitter taste thresholds ranging from 30 (ARHPHPHLSFM, κ-CN_96-106) to 690 μmol/L (IQKEDVPS, α_s1-CN_81-88). Finally, quantitative peptide analysis followed by calculation of dose-overthreshold factors revealed a primary contribution of MAPKHKEMPFPKYPVEPF (β-CN_102-119) and ARHPHPHLSFM (κ-CN_96-106) to the perceived bitter taste of the fresh cheese samples. Finally, the evolution of the bitter peptides throughout two different fresh cheese manufacturing processes was quantitatively recorded.

A Survey of the Peptide Profile in Prato Cheese as Measured by MALDI-MS and Capillary Electrophoresis

In this study, we describe the characterization of the peptide profile in commercial Prato cheese by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and capillary electrophoresis (CE). Ten commercial Prato cheese brands were characterized via their physicochemical composition and subjected to fractionation according to solubility at pH 4.6. The pH 4.6 insoluble fraction was evaluated by CE, whereas MALDI-MS was applied to the fraction soluble at pH 4.6 and in 70% ethanol. CE revealed a characteristic pattern of hydrolysis, with formation of para-κ-casein, hydrolysis of α_s1 -casein at the Phe₂₃ - Phe₂₄ bond, and hydrolysis of β-casein. For the MALDI-MS data, a complex peptide profile was observed, with the identification of 44 peptides previously reported (24 peptides from α_s1 -casein, 14 from β-casein, 3 from κ-casein, and 3 from α_s2 -casein). It was also observed that cheeses with salt-in-moisture content greater than 5% showed an accumulation of a bitter-tasting peptide (m/z 1536, α_s1 -CN f1-13), suggesting a relationship between the higher salt concentration and the abundance of this peptide. In conclusion, the results showed that even commercial cheeses produced with different raw material and processing conditions showed very similar peptide profiles when assessed at the molecular level, and only 9 peptides were responsible for discrimination of cheeses.

Proteomic and peptidomic profiling of Brazilian artisanal 'Coalho' cheese

BACKGROUND

Artisanal 'Coalho' cheese is a product typically popular in the Brazilian north-eastern region. Production of this cheese represents about 9.2% of the internal crude product of Pernambuco State. Several peptides are generated from hydrolysis of αS1 -, αS2 -, β-, and κ-caseins during manufacture of this cheese. The commercial importance of Brazilian artisanal 'Coalho' cheese justifies the examination of both the protein and peptide profiles of cheeses from six cities of the semi-arid region of Pernambuco State, Brazil.

RESULTS

SDS-PAGE of the aqueous extracts of 'Coalho' cheeses (WSP) showed bands of lactoferrin, β-lactoglobulin, β-lactoglobulin (dimer), α-lactoalbumin, bovine serum albumin, α-casein, β-casein, κ-casein and para-κ-casein. A total of 57 to 72 peptides were confirmed by mass spectra in the different samples of 'Coalho' cheese which 32 known peptides (11 from αS1 -casein, three from αS2 -casein, 15 from β-casein and three from κ-casein), comprising seven caseinphosphopeptides. Among the unidentified peptides, three showed high intensity peaks in all 'Coalho' cheeses studied (with molecular weights of 1597, 1725/1726, 2778/2779 Da).

CONCLUSION

The proteomic studies revealed peptides that may represent molecular markers or fingerprints for investigating the quality control and regional characterisation of these 'Coalho' cheeses. © 2016 Society of Chemical Industry.

Angiotensin-I-converting enzyme-inhibitory peptides in commercial Wisconsin Cheddar cheeses of different ages

Bioactive peptides, including angiotensin-I-converting enzyme-inhibitory (ACEI) peptides, were investigated in commercially produced Wisconsin Cheddar cheeses that ranged in age from ≤ 6d to more than 2 yr. The ACEI activity of cheese was determined in water-soluble extracts (WSE) that were fractionated for components with molecular weight (MW) ≤ 3,000 Da, and peptides identified using HPLC and tandem mass spectrometry. The number of types of bioactive peptides increased with an increase in ripening time. Six of the identified ACEI peptides, Ile-Pro-Pro (IPP), Val-Pro-Pro (VPP), Glu-Lys-Asp-Glu-Arg-Phe (EKDERF), Val-Arg-Tyr-Leu (VRYL), Tyr-Pro-Phe-Pro-Gly-Pro-Ile-Pro-Asn (YPFPGPIPN), and Phe-Phe-Val-Ala-Pro (FFVAP), with known high ACEI activity (low IC50 values, the concentration needed to inhibit ACE to 50% of its original activity) were synthesized and used to quantify the amounts of these peptides in various cheese extracts. The concentrations of these 6 ACEI peptides increased up to a certain stage of ripening. The maximum contents of IPP, VPP, and EKDERF were 2.8, 7.4, and 5.3mg/100 g of cheese, respectively, and these levels were found in a 1-yr-old Cheddar cheese sample. The maximum content of VRYL (7.5mg/100 g of cheese) was found in a 2-yr-old Cheddar cheese sample, whereas the maximum content of YPFPGPIPN (6.8 mg/100 g of cheese) was found in a 6-mo-old Cheddar cheese sample. Trace amounts of FFVAP were found in these cheeses. Aged Cheddar cheese was found to be a rich source of ACEI peptides even though large differences exist between cheeses from different manufacturers.

Bioactivity of probiotic whey cheese: characterization of the content of peptides and organic acids

BACKGROUND

Probiotic whey cheeses have been produced for several years. It is recognized that several bacterium-mediated metabolic activities contribute differently to the final sensory and nutritional profiles of dairy products. Hence the metabolic activity of probiotic strains in a whey cheese and their contribution to the bioactivity of such matrices were investigated here, including in particular Bifidobacterium animalis, Lactobacillus acidophilus and Lactobacillus casei.

RESULTS

Both L. casei and B. animalis produce lactic and acetic acids, whereas L. acidophilus produce mainly lactic acid; these metabolites may be considered bioprotection factors. Water-soluble extracts (WSE) obtained from these cheese matrices were subjected to ultrafiltration through a 3 kDa cut-off membrane, and the eluted peptides were resolved by high-performance liquid chromatography. Different qualitative and quantitative profiles were obtained, depending on the strain. WSE were further assayed for their ability to inhibit angiotensin-converting enzyme; the <3 kDa fraction exhibited higher activities in the case of L. casei and B. animalis than the control and L. acidophilus.

CONCLUSION

Whey cheeses with higher nutritional value were those inoculated with L. casei.

Chemical and instrumental approaches to cheese analysis

Overcoming the complexity of cheese matrix to reliably analyze cheese composition, flavor, and ripening changes has been a challenge. Several sample isolation or fractionation methods, chemical and enzymatic assays, and instrumental methods have been developed over the decades. While some of the methods are well established standard methods, some still need to be researched and improved. This chapter reviews the chemical and instrumental methods available to determine cheese composition and monitor biochemical events (e.g., glycolysis, lipolysis, and proteolysis) during cheese ripening that lead to the formation of cheese flavor. Chemical and enzymatic methods available for analysis of cheese composition (fat, protein, lactose, salt, nitrogen content, moisture, etc.) are presented. Electrophoretic, chromatographic, and spectroscopic techniques are also reviewed in the light of their application to monitor cheese ripening and flavor compounds. Novel instrumental methods based on Fourier-transform infrared spectroscopy that are currently being researched and applied to cheese analysis are introduced.

Proteolysis in miniature cheddar-type cheeses manufactured using extracts from the crustacean Munida as coagulant

Miniature (20 g) Cheddar-type cheeses were manufactured using enzymes extracted from the crustacean Munida or chymosin as coagulant. Cheeses were ripened at 8 degrees C and samples were collected for analysis after 2, 6 and 12 weeks. Proteolysis was assessed by urea-polyacrylamide gel electrophoresis, which showed that cheeses manufactured with the Munida extracts had a higher extent of degradation of beta-casein than cheeses made using chymosin as coagulant. Patterns of proteolysis were also obtained by reverse-phase high-performance liquid chromatography (RP-HPLC) and matrix assisted laser desorption ionisation-time of flight (MALDI-ToF) mass spectrometry. In general, the products of proteolysis were more complex in cheese made using the Munida extracts than in cheese made by chymosin as coagulant. Statistical analysis of results clearly discriminated the cheeses on the basis of coagulant used. Molecular mass of peptides found in cheese made using Munida extracts were similar to those of peptides commonly detected in cheeses made using chymosin as coagulant.

Nomenclature of the Proteins of Cows’ Milk—Sixth Revision

This report of the American Dairy Science Association Committee on the Nomenclature, Classification, and Methodology of Milk Proteins reviews changes in the nomenclature of milk proteins necessitated by recent advances of our knowledge of milk proteins. Identification of major caseins and whey proteins continues to be based upon their primary structures. Nomenclature of the immunoglobulins consistent with new international standards has been developed, and all bovine immunoglobulins have been characterized at the molecular level. Other significant findings related to nomenclature and protein methodology are elucidation of several new genetic variants of the major milk proteins, establishment by sequencing techniques and sequence alignment of the bovine caseins and whey proteins as the reference point for the nomenclature of all homologous milk proteins, completion of crystallographic studies for major whey proteins, and advances in the study of lactoferrin, allowing it to be added to the list of fully characterized milk proteins.

Mass mapping analysis as a tool for the identification of genetic variants of bovine beta-casein

Matrix-assisted laser desorption ionisation time-of-flight mass spectrometric analysis of the tryptic digest of beta-casein A2 and beta-casein B was performed before and after the separation of the peptides by LC. The overlapping of the chromatograms showed that all peaks were present in both samples, except for one only found in the tryptic digest of the A2 variant and two in the B variant. Experimental masses could be assigned to those peptides produced by tryptic digest of beta-casein variant. This peptide mapping strategy and current methodological improvements represent a promising tool for the identification of milk genetic variants with the difference of an amino acid substitution.

Relationship between MALDI-TOF analysis of beta-CN f193-209 concentration and sensory evaluation of bitterness intensity of aged cheddar cheese

An internal standard method was previously developed to measure the concentration of a synthetic bitter peptide, beta-CN f193-209, by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The objective of this study was to evaluate the relationship between beta-CN f193-209 concentration in an aqueous extract of aged Cheddar cheese and bitterness intensity of the cheese. Concentrations of beta-CN f193-209 in cheese extracts were determined by MALDI-TOF at 0, 120, 180, and 270 days. Trained panels evaluated the bitterness intensity of the cheeses at 180 and 270 days. Correlation coefficients between MALDI and sensory data at 180 and 270 days were 0.803 and 0.554, respectively. The decreased correlation may be due to the presence of other bitter peptides more responsible for bitterness at longer aging or the production of compounds that mask bitterness intensity.

Cloning and expression of an oligopeptidase, PepO, with novel specificity from Lactobacillus rhamnosus HN001 (DR20)

Oligopeptidases of starter and nonstarter lactic acid bacteria contribute to the proteolytic events important in maturation and flavor development processes in cheese. This paper describes the molecular cloning, expression, and specificity of the oligopeptidase PepO from the probiotic nonstarter strain Lactobacillus rhamnosus HN001 (DR20). The pepO gene encodes a protein of 70.9 kDa, whose primary sequence includes the HEXXH motif present in certain classes of metallo-oligopeptidases. The pepO gene was cloned in L. rhamnosus HN001 and overexpressed in pTRKH2 from its own promoter, which was mapped by primer extension. It was further cloned in both pNZ8020 and pNZ8037 and overexpressed in Lactococcus lactis subsp. cremoris NZ9000 from the nisA promoter. The purified PepO enzyme demonstrated unique cleavage specificity for alpha(s1)-casein fragment 1-23, hydrolyzing the bonds Pro-5-Ile-6, Lys-7-His-8, His-8-Gln-9, and Gln-9-Gly-10. The impact of this enzyme in cheese can now be assessed.

Isolation of oligopeptides from the water-soluble extract of goat cheese and their identification by mass spectrometry

A procedure for the separation and identification of small peptides from the water-soluble fraction of a goat cheese was developed. The water-soluble extract was ultrafiltered (1000 Da membrane cutoff), and peptides were isolated by sequential chromatography: size exclusion chromatography (HPLC-grade water), anion exchange chromatography (phosphate buffer gradient), and semipreparative reverse-phase high-performance liquid chromatography (water/acetonitrile gradient). The fractions obtained were analyzed by combined mass spectrometry methods including electrospray ionization, liquid secondary ionization, and tandem mass spectrometry to identify and to confirm the sequences of 28 tri- to octapeptides naturally appearing in goat cheese during ripening. Among these peptides, 26 are produced by degradation of caseins but do not correspond to the known specific cleavages due to chymosin. Only low correlation was found between hydrophobicity of peptides and HPLC elution time with acetonitrile gradient.

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.

Follow-up of the delta4 to delta16 trans-18:1 isomer profile and content in French processed foods containing partially hydrogenated vegetable oils during the period 1995-1999. Analytical and nutritional implications

A survey of the total content of trans-18:1 acids and their detailed profile in French food lipids was conducted in 1995-1996, and 1999. For this purpose, 37 food items were chosen from their label indicating the presence of partially hydrogenated vegetable oils (PHVO) in their ingredients. The content as well as the detailed profile of these isomers was established by a combination of argentation thin-layer chromatography and gas liquid chromatography (GLC) on long polar capillary columns. With regard to the mean trans-18:1 acid contents of extracted PHVO, a significant decrease was observed between the two periods, i.e., from 26.9 to 11.8% of total fatty acids. However, only minor differences were noted in the mean relative distribution profiles of individual trans-18:1 isomers with ethylenic bonds between positions delta4 and delta16 for the two periods. The predominant isomer was delta9-18:1 (elaidic) acid, in the wide range 15.2-46.1% (mean, 27.9+/-7.2%) of total trans-18:1 acids, with the delta10 isomer ranked second, with a mean of 21.3% (range, 11.6 to 27.4%). The content of the unresolved delta6 to delta8 isomer group was higher than the delta11 isomer (vaccenic acid), representing on average 17.5 and 13.3%, respectively. Other isomers delta4, delta5, delta12, delta13/delta14, delta15, and delta16, were less than 10% each: 1.0, 1.6, 7.4, 7.1, 1.8, and 1.0%, respectively. However, considering individual food items, it was noted that none of the extracted PHVO were identical to one another, indicating a considerable diversity of such fats available to the food industry. A comparison of data for French foods with similar data recently established for Germany indicates that no gross differences occur in PHVO used by food industries in both countries. Estimates for the absolute mean consumption of individual isomers from ruminant fats and PHVO are made for the French population and compared to similarly reconstructed hypothetical profiles for Germany and North America. Differences occur in the total intake of trans-18:1 acids, but most important, in individual trans-18:1 isomer intake, with a particular increase of the delta6-delta8 to delta10 isomers with increasing consumption of PHVO. It is inferred from the present and earlier data that direct GLC of fatty acids is a faulty procedure that results (i) in variable underestimates of total trans-18:1 acids, (ii) in a loss of information as regards the assessment of individual isomeric trans-18:1 acids, and (iii) in the impossibility of comparing data obtained from human tissues if the relative contribution of dietary PHVO and ruminant fats is not known.

Isolation and structural analysis of antihypertensive peptides that exist naturally in Gouda cheese

Seven kinds of ripened cheeses (8-mo-aged and 24-mo-aged Gouda, Emmental, Blue, Camembert, Edam, and Havarti) were homogenized with distilled water, and water-soluble peptides were prepared by C-18 hydrophobic chromatography. The inhibitory activity to angiotensin I-converting enzyme and decrease in the systolic blood pressure in spontaneously hypertensive rats were measured before and after oral administration of each peptide sample. The strongest depressive effect in the systolic blood pressure (-24.7 mm Hg) and intensive inhibitory activity to angiotensin I-converting enzyme (75.7%) were detected in the peptides from 8-mo-aged Gouda cheese. Four peptides were isolated by HPLC with reverse-phase and gel filtration modes. Their chemical structures and origins, clarified by combination analyses of protein sequencing, amino acid composition, and mass spectrometry, were as follows: peptide A, Arg-Pro-Lys-His-Pro-Ile-Lys-His-Gln [alpha(s1)-casein (CN), B-8P; f 1-9]; peptide B, Arg-Pro-Lys-His-Pro-Ile-Lys-His-Gln-Gly-Leu-Pro-Gln (alpha(s1)-CN, B-8P; f 1-13); peptide F, Tyr-Pro-Phe-Pro-Gly-Pro-Ile-Pro-Asn (beta-CN, A2-5P; f 60-68); and peptide G, Met-Pro-Phe-Pro-Lys-Tyr-Pro-Val-Gln-Pro-Phe (beta-CN, A2-5P; f 109-119). Peptides A and F, which were chemically synthesized, showed potent angiotensin I-converting enzyme inhibitory activity with little antihypertensive effects.

Covalent Modification of Emulsified beta-Casein Resulting from Lipid Peroxidation

Competitive displacement of adsorbed protein from emulsion droplets by the surfactant Tween 20 has been used to determine the influence of the oil phase and aging on the behavior of beta-casein, the displaced protein being analyzed by reverse-phase high performance liquid chromatography HPLC. Unlike soluble beta-casein or the protein displaced from tetradecane droplets where aging had no effect on the appearance of the HPLC profile, the protein displaced from a soya oil emulsion interface was observed to change. As the soya oil emulsion aged, the retention time of the protein decreased. Mass spectrometry of the modified protein showed that the molecular weight increased, indicating that some form of covalent modification was occurring. Gas chromatography-mass spectrometry of steam distillates of the samples showed the presence of a variety of aldehydes in microfluidized soya oil samples that were not present in either the original oil or the tetradecane emulsions. Aldehydes, particularly alpha,beta-unsaturated aldehydes (enals), which are the major components formed in these soya oil emulsions, are known to react with nucleophilic amino acid side chains such as lysine. This is the probable cause of the observed modification of the emulsified protein. These aldehydes, whose concentration increased with storage time, are formed by peroxidation of the unsaturated fatty acyl chains present in the soya oil as a result of the microfluidization process used in the preparation of the emulsions. The tryptic peptide pattern also changed with age due to modification of the primary structure of the protein. Potential consequences of these chemical changes arising as a result of microfluidization are discussed. Copyright 1999 Academic Press.

Isolation and identification of some major water-soluble peptides in Feta cheese

Peptides were isolated from the water-soluble fraction of Feta cheese by reversed-phase HPLC in three successive steps. Peptide sequencing was performed by automatic Edman degradation. Most of the peptides originated from alpha s1-casein (CN), especially from the N-terminal half of the molecule. Two peptides originated from the C-terminal domain of beta-CN. Only one peptide, which was rich in histidine, originated from kappa-CN. beta-Lactoglobulin and alpha-lactalbumin were also identified in the water extract of Feta cheese. The origin of most of these peptides could be explained on the basis of known specificities of chymosin and lactococcal cell-wall proteinases.