Tryptic phosphopeptides from whole casein. I. Preparation and analysis by fast protein liquid chromatography

Identification of Novel Phosphopeptides After Simulated Digestion of αs2-casein by Tandem Mass Spectrometry

Casein phosphopeptides (CPPs) are encrypted in αs1-, αs2-and β-casein (CN) and can be released by in vitro, in vivohydrolysis or food processing of dairy foods. Bovine αs2-CN contains two cluster sequences of anionic phosphoseryl and glutamyl residues SpSpSpEE in its structure (residues 8–12 and 56–63), which can modulate mineral bioavailability. In this study αs2-casein (αs2-CN) was subjected to simulated gastrointestinal digestion. CPPs released were sequenced by on-line reversed-phase high performance liquid chromatography coupled to electrospray ionisation tandem mass spectrometry (RP-HPLC-ESIMS/MS). Six novel αs2-CN derived CPPs, Three of them (αs2-CN(54–87)4P,αs2-CN(24–70)4P and αs2-CN(14–73)5P) with the mineral binding cluster sequence SpSpSpEE were identified and characterised. CPPs from αs2-CN identified in this study resist simulated gastrointestinal digestion. As the molecular weights of these CPPs are approx. 2,165–7,112Da, they could be absorbed by intestinal cells. Consequently, these αs2-CN derived CPPs could be promising candidates for incorporation to mineral fortified foods as functional ingredients.

Determination of molecular weight of a purified fraction of colloidal calcium phosphate derived from the casein micelles of bovine milk

Colloidal calcium phosphate (CCP) plays a key role in the formation and integrity of casein (CN) micelles. However, limited information is available on the molecular weight (M(w)) of CCP. Recently, we theoretically derived the M(w) of CCP and the objectives of this study were to experimentally determine the M(w) of CCP. We used 2 methods to prepare CCP fractions: skim milk was enzymatically digested with either trypsin or a combination of papain and proteinase enzymes to remove most CN. The CN phosphopeptides are resistant to trypsin hydrolysis. Digestion was carried out in a membrane tube that was dialyzed against the same bulk milk used in sample preparation to remove small peptides and to minimize perturbation of CCP. After digestion, the protein contents of the enzyme-treated milks were 0.92 and 0.36% for the trypsin and papain-proteinase treatments, respectively. Size-exclusion chromatography, coupled with multi-angle laser light scattering, was used to separate the CCP-phosphopeptide fraction from the digested mixture. Simulated milk ultrafiltrate was used as a mobile phase during size-exclusion chromatography separation to try to preserve the integrity of CCP. Size-exclusion chromatography peaks, which had higher Ca and P contents than the baseline, were identified as the likely fractions containing the phosphopeptide-stabilized CCP; this peak eluted with retention times of 100 to approximately 110 min for trypsinated samples. The papain-proteinase treatment caused excessive loss of CN that were needed to stabilize CCP, which resulted in no obvious peak that had elevated Ca and P contents. Debye plots at these retention times indicated that the weight-average M(w) for the fraction prepared by trypsin was 17,450 g/mol. Attempts to estimate the M(w) of the phosphopeptides associated with CCP using sodium dodecyl sulfate-PAGE were not successful, as we did not observe any peptide bands in these gels, presumably because of their low concentration in the isolated, unconcentrated fraction. Assuming that 4 CN phosphopeptides stabilized each CCP and if the M(w) of each of these phosphopeptides was about 2,500 g/mol, then the M(w) of CCP would be around 7,450 g/mol. This experimental value was close to the theoretically-derived M(w) of 4,897 and 9,757 g/mol for tetrahedron and bi-pyramid shaped objects, respectively, when using the brushite form of calcium phosphate.

Nanocarrier possibilities for functional targeting of bioactive peptides and proteins: state-of-the-art

This review attempts to provide an updated compilation of studies reported in the literature pertaining to production of nanocarriers encasing peptides and/or proteins, in a way that helps the reader direct a bibliographic search and develop an integrated perspective of the subject. Highlights are given to bioactive proteins and peptides, with a special focus on those from dairy sources (including physicochemical characteristics and properties, and biopharmaceutical application possibilities of e.g. lactoferrin and glycomacropeptide), as well as to nanocarrier functional targeting. Features associated with micro- and (multiple) nanoemulsions, micellar systems, liposomes and solid lipid nanoparticles, together with biopharmaceutical considerations, are presented in the text in a systematic fashion.

Identification of casein phosphopeptides released after simulated digestion of milk-based infant formulas

Adapted, follow-up, probiotic follow-up, toddler, and probiotic toddler infant formulas were subjected to an in vitro enzymatic procedure simulating physiological digestion. The formation and identification of casein phosphopeptides (CPPs) in the milk-based infant formulas were studied using reversed phase high-performance liquid chromatography coupled on line to an ion trap mass spectrometer. Most CPPs formed contained the cluster sequence SpSpSpEE, a mineral binding site. Phosphopeptide alpha(s2)-CN(1-19)4P was present in all formulas analyzed. Probiotic formulas released CPPs not detected in nonprobiotic formulas and probably formed by bifidobacteria action. These observations suggest that physiological digestion of these products promotes the formation of bioactive peptides with mineral carrier properties in the gastrointestinal tract, which resist further proteolysis.

Speciation analysis of calcium, iron, and zinc in casein phosphopeptide fractions from toddler milk-based formula by anion exchange and reversed-phase high-performance liquid chromatography?mass spectrometry/flame atomic-absorption spectroscopy

Casein phosphopeptides (CPP) are phosphorylated casein-derived peptides that can be released by in-vitro or in-vivo enzymatic hydrolysis of alpha(s1)-casein, alpha(s2)-casein, and beta-casein (CN). Many of these peptides contain a highly polar acidic sequence of three phosphoseryl groups followed by two glutamic acid residues. These domains are binding sites for minerals such as calcium, iron, and zinc and play an important role in mineral bioavailability. The aim of this study was speciation analysis of calcium, iron, and zinc in CPP fractions from the soluble fraction of a toddler milk-based formula. Methods for CPP separation by anion-exchange high-performance liquid chromatography (AE-HPLC) were combined with CPP identification by reversed-phase high performance liquid chromatography-electrospray ionization mass spectrometry and determination of the calcium, iron, zinc, and phosphorus content of the fractions obtained by AE-HPLC. Calcium and phosphorus were detected in all the analyzed AE-HPLC fractions. Calcium and zinc could be bound to CPP derived from alpha(s1)-CN and alpha(s2)-CN in fraction 3. Iron could be bound to CPP in fraction 4 in which beta-CN(15-34)4P was present with the cluster sequence S(P)S(P)S(P)EE. The results obtained prove the different distribution of calcium, iron, and zinc in heterogeneous CPP fractions.

Mineral-binding milk proteins and peptides; occurrence, biochemical and technological characteristics

Minerals and trace elements in cow's milk occur as inorganic ions and salts or form complexes with proteins and peptides, carbohydrates, fats and small molecules. The main mineral binder or chelators of calcium are the caseins, alphas1-casein, alphas2-casein, beta-casein and kappa-casein, but also whey proteins and lactoferrin bind specific minerals like calcium, magnesium, zinc, iron, sodium and potassium. Less documented is the binding of trace elements. Peptides obtained by in vitro or in vivo hydrolysis act as mineral trappers through specific and non-specific binding sites. They may then function as carriers, chelators, of various minerals and thus enhance or inhibit bioavailability. Peptides from milk proteins have found interesting new applications in the food industry as products with improved functionality or as ingredients of dietary products, or used in pharmaceutical industry. Fortification of foods with minerals in a low concentration has for a long time been used in some countries to overcome mineral deficiency, which is an increasing problem in humans. These types of foods are being used to create a new generation of super foods in the industry today.

Preparation of novel functional oligophosphopeptides from hen egg yolk phosvitin

Novel hen egg phosvitin phosphopeptides (PPP) with molecular masses of 1-3 kDa were prepared from tryptic hydrolysis following partial alkaline dephosphorylation. The phosvitin treated with various NaOH concentrations (0.05-0.4 N) resulted in different dephosphorylated proteins ranging from 17.5 to 96.3% of phosphate retention. The protein was digested into 10-20 amino acid peptides with trypsin. Calcium-binding properties of PPP were compared with those of commercial casein phosphopeptides in vitro. The PPP with 35% phosphate retention is shown to be effective for enhancing calcium binding capacity and inhibiting the formation of insoluble calcium phosphate. The results provide potential novel functional oilgophosphopeptides as nutraceuticals.

Post-translational phosphorylation affects the IgE binding capacity of caseins

IgE response specific to those molecular regions of casein that contain a major phosphorylation site was analyzed using native and modified caseins and derived peptides. This study included (i) the naturally occurring common variants A1 and A from beta- and alphas2-caseins, respectively, which were purified in the native form and then dephosphorylated, (ii) a purified rare variant D of alphas2-casein which lacks one major phosphorylation site, and (iii) the native and dephosphorylated tryptic fragment f(1-25) from beta-casein. Direct and indirect ELISA using sera from patients allergic to milk showed that the IgE response to caseins is affected by modifying or eliminating the major phosphorylation site.

Iron tissue storage and hemoglobin levels of deficient rats repleted with iron bound to the caseinophosphopeptide 1-25 of beta-casein

Caseinophosphopeptides (CPP) issued from enzyme digestion of caseins bind cations and keep them soluble in the digestive tract. They could be used as ligands to improve iron (Fe) bioavailability. Fe-deficient young rats were repleted with Fe (40 or 200 mg/kg of diet) bound either to the beta-CN (1-25) of beta-casein or to whole beta-casein or as FeSO(4). A control pair-fed group was given 200 mg of Fe (FeSO(4))/kg of diet for 6 weeks. After repletion, hemoglobin concentration of the control group was reached only by the ) animals fed 200 mg of Fe/kg; beta-CN (1-25) bound Fe (40 and 200 mg) produced higher Fe liver and spleen stores than FeSO(4). Binding Fe to the whole, nonhydrolyzed beta-casein gave results intermediate between the other experimental groups. Binding Fe to phosphoserine residues of low molecular weight CPP improved its ability to cure anemia and to restore iron tissue stores, as compared to Fe bound to the whole casein and to inorganic salts.

Preparation of phosphopeptides derived from alpha s-casein and beta-casein using immobilized glutamic acid-specific endopeptidase and characterization of their calcium binding

Phosphopeptides that were derived from alpha s-CN or beta-CN were prepared with immobilized glutamic acid-specific endopeptidase, and their Ca2+ binding was characterized. alpha s-Casein or beta-CN was hydrolyzed in a fluidized bed bioreactor containing 2 ml of immobilized glutamic acid-specific endopeptidase by recirculating 20 ml of alpha s-CN or beta-CN solution (10 mg/ml in 50 mM Tris.HCl and 0.02% NaN3, pH 8.0) for 3 h at 20 degrees C. The molecular masses of casein peptides were monitored by SDS-PAGE. Each hydrolysate was applied to an anion-exchange column using stepwise elution with various concentrations of KCl to separate peptides. The casein phosphopeptide content of the elution profile was monitored by analysis of protein and P concentrations. Calcium binding in phosphopeptide-enriched fractions was determined by CaCl2 titration and measurement of free Ca2+ with a Ca-selective electrode. The electrophoresis patterns showed four major peptides having molecular masses of 10.8, 9.0, 6.6, and 3.6 kDa in the alpha s-CN hydrolysate and 9.3, 8.2, and 6.2 kDa in the beta-CN hydrolysate. The highest concentrations of P were detected in the fractions that eluted with 0.4 and 0.5 M KCl for the alpha s-CN hydrolysate and with 0.4 M KCl for the beta-CN hydrolysate. The calcium-binding ability was found only in the fraction that was eluted with 0.4 M KCl; the maximum Ca2+ binding and the apparent binding constant were 0.24 mmol/mg of protein and 75 M-1, and 0.14 mmol/mg of protein and 148 M-1, respectively. alpha s-Casein phosphopeptides had different patterns for Ca2+ binding than did beta-CN phosphopeptides as the total Ca concentration was increased. Calcium binding to these casein phosphopeptides differed from that previously characterized for the tryptic peptides.

Calcium binding of phosphopeptides derived from hydrolysis of alpha s-casein or beta-casein using immobilized trypsin

Calcium binding to casein phosphopeptides that were derived from alpha s-CN or beta-CN was studied. Purified alpha s-CN or beta-CN was prepared from fresh skim milk using an anion-exchange column. Peptides were prepared by casein hydrolysis using a fluidized bed bioreactor containing 2 ml of immobilized trypsin (activity: 49.4 U/g of beads). The disappearance of intact protein and the appearance of products of low molecular mass were monitored by SDS-PAGE. alpha s-Casein and beta-CN hydrolysates were loaded on an anion-exchange column, followed by stepwise elution with 0, 0.1, 0.2, 0.4, and 0.5 M KCl in equilibration buffer to separate the phosphopeptides from the other casein peptides. Protein and P were measured in the elution peaks. Calcium binding to each fraction was determined with a Ca-selective electrode. Electrophoresis showed that intact proteins were hydrolyzed rapidly, and peptides appeared on the gel in greater concentrations as the incubation time increased. The major products were a main band with a molecular mass of 6.2 kDa from beta-CN hydrolysates and a series of bands from 4.0 to 12.8 kDa from alpha s-CN hydrolysate. The greatest yield and concentration of phosphate from beta-CN hydrolysate were found in the peak that eluted with 0.4 M KCl in equilibration buffer and for alpha s-CN in the peak that eluted with 0.1 M KCl. The alpha s-CN phosphopeptides showed greater Ca2+ binding than the phosphopeptides from beta-CN. Separation of casein phosphopeptides using anion exchange was not specific. However, results showed that each peak containing high concentrations of phosphate had Ca(2+)-binding ability. Further characterization of these casein phosphopeptides might result in a Ca-complexing food ingredient.

Casein phosphopeptides from casein micelles by successive digestion with pepsin and trypsin

When milk is ingested, casein micelles will be successively digested by pepsin in the stomach and trypsin in the intestine. Therefore, we digested casein micelles successively with pepsin at pH 4.0 and trypsin at pH 7.0, and recovered casein phosphopeptides (CPP) as CPP-calcium phosphate (CP) complexes. The CPP-CP complexes contained 248 mg of calcium/g peptides and 175 mg of inorganic phosphorus/g peptides, which were higher than those of CPP-CP complexes driven from acid-precipitated casein and casein micelles by tryptic digestion only. It contained more alpha S1-CN-5P(f59-79) than the other CPP preparations did.

Effect of casein phosphopeptides on zinc and calcium absorption from bread meals

Animal studies suggest that casein phosphopeptides (CPP), formed by proteolytic digestion of casein, have a positive effect on Ca availability. The aim of this study was to investigate the ability of CPP to improve Zn and Ca absorption from phytate-containing bread meals. Secondly, it was tested whether the Ca content of the meal influenced the effect of CPP on Zn absorption from a high-phytate meal. Zn and Ca absorption from single model meals was determined by extrinsic labeling with 65Zn and 47Ca and measurement of whole-body retention. Thirty-one healthy adults (19-30 y) divided into three groups received one of three meal types based on white-wheat rolls with different phytate and Ca content: A: low-phytate/high-Ca (n = 10), B: high-phytate/high-Ca (n = 10) and C: high-phytate/low-Ca (n = 11). Each individual received the same meal type at three different occasions with 0, 250 and 1000 mg CPP added. CPP had no effect on Zn absorption: A: 14.3 +/- 4.4% (mean +/- SD) (0 mg CPP), 16.7 +/- 6.6% (250 mg CPP) and 16.0 +/- 8.8% (1000 mg CPP); B: 7.0 +/- 1.6%, 7.7 +/- 3.0% and 8.0 +/- 2.6%; C: 7.7 +/- 2.5%, 7.0 +/- 2.3% and 6.5 +/- 1.6%, respectively. Addition of 1000 mg CPP reduced fractional Ca absorption from meal A: 33.8 +/- 7.1%, 30.5 +/- 6.3% and 25.9 +/- 8.7% (p < 0.05), whereas CPP had no effect in meal B: 29.3 +/- 8.3%, 27.0 +/- 7.4% and 27.6 +/- 11.0%. However, the absolute quantity of Ca absorbed was unaffected. In conclusion, Zn and Ca absorption from these meals were not significantly influenced by the addition of CPP, Ca addition could not explain the failure of CPP to improve Zn absorption.

Isolation, purification, and alteration of some functional groups of major milk proteins: a review

This review covers selected methods of isolation and purification of mainly alpha s-casein, beta-casein, kappa-casein, beta-lactoglobulin, and alpha-lactalbumin. Selected methods of alteration of some functional groups of these proteins also were reviewed. Isolation and purification of milk proteins per se are methods of modifying the individual milk proteins. Gram quantities of these proteins can now be purified in a relatively short time using ion-exchange resins. Due to the prominent use of non-food-grade reagents in the procedures for preparation of these milk proteins, individual proteins are not maximally utilized for the manufacture of food/feed and pharmaceutical products. Therefore, intensive research efforts are needed to obviate the problems associated with underutilization of milk proteins.

Immunogenicity of casein phosphopeptides derived from tryptic hydrolysis of beta-casein

The immunogenicity of phosphopeptides derived from tryptic hydrolysis of beta-casein (CN) was investigated in a rat model system. The titers of specific immunoglobulin (Ig)G and IgE antibodies made in response to intraperitoneal sensitization to beta-CN, casein phosphopeptides, and skim milk proteins were examined using indirect and amplified indirect ELISA, respectively. Serum IgG antibodies from rats injected with beta-CN were significantly more reactive to beta-CN, casein phosphopeptides, and skim milk proteins coated on microtiter plate wells than were the IgG antibodies generated in rats that had been subjected to other treatments. A significant difference in titers because of the time of sampling (14 or 21 d postinjection) was noted for IgE but not for IgG. Rats that were injected with casein phosphopeptides did not produce IgG antibodies that crossreacted with either skim milk proteins or beta-CN. Specific antibody levels for the IgE class rarely exceeded those of unimmunized controls. The findings suggest that immunogenicity of the phosphopeptides was reduced compared with that of native beta-CN and skim milk proteins.

Casein phosphopeptides improve zinc and calcium absorption from rice-based but not from whole-grain infant cereal

BACKGROUND

Casein phosphopeptides (CPP) are phosphorus-rich peptide fragments of casein, assumed to contribute to the high bioavailability of calcium from milk.

METHODS

The effect of casein phosphopeptides on calcium and zinc absorption from infant foods was investigated. Twenty-two men and women were given single test meals extrinsically labeled with Ca and Zn. Absorption was calculated from measurements on whole-body retention of the radioisotopes. Each subject was given either rice-based cereal (n = 11) or whole-grain cereal (n = 11) on three occasions together with 250 ml water and added 0, 1, and 2 g CPP in random order. One serving of rice-based cereal contained 481 mg Ca and 1.29 mg Zn; whole-grain cereal contained 541 mg Ca and 1.77 mg Zn. One and 2 g of CPP contributed with additional 69 and 138 mg Ca, respectively.

RESULTS

From rice-based cereal, fractional calcium absorption was not affected by CPP addition (mean +/- SD): 16.0 +/- 4.0% (no CPP), 17.6 +/- 4.5% (1 g CPP), and 15.8 +/- 4.3% (2 g CPP), while the total quantity of calcium absorbed was significantly improved: 7 +/- 19 mg, 97 +/- 25 mg, and 98 +/- 26 mg, respectively (p = 0.0004). Fractional zinc absorption as well as total quantity of zinc absorbed were increased with addition of CPP: 19.4 +/- 9.0% (0.25 +/- 0.12 mg), 25.2 +/- 7.5% (0.33 +/- 0.10 mg) and 23.9 +/- 5.4% (0.31 +/- 0.07 mg) at the three CPP levels (p = 0.04). From whole-grain cereal, CPP had no effect on the percentage or actual quantity of calcium absorbed: 17.0 +/- 3.2% (92 +/- 18 mg), 17.2 +/- 4.5% (105 +/- 27 mg), and 15.0 +/- 4.6% (102 +/- 31 mg), respectively. Zinc absorption was also not influenced by CPP: 16.0 +/- 5.1% (0.28 +/- 0.09 mg), 15.3 +/- 3.1% (0.27 +/- 0.06 mg) and 18.1 +/- 4.4% (0.32 +/- 0.08 mg), respectively.

CONCLUSIONS

CPP addition improved calcium and zinc absorption from rice-based cereal, while no effect was seen from whole-grain cereal.

Incorporation of caseinoglycomacropeptide and caseinophosphopeptide into the salivary pellicle inhibits adherence of mutans streptococci

The protective effects of milk and milk products against dental caries have been demonstrated in many animal studies. We have shown that this effect was mediated by micellar casein or caseinopeptide derivatives. A reduction in the Streptococcus sobrinus population in the oral microbiota of animals fed diets supplemented with these milk components was consistently observed. A possible explanation for these findings is that milk components are incorporated into the salivary pellicle, thereby reducing the adherence of S. sobrinus. This hypothesis was tested in vitro by the incubation of bovine enamel discs with unstimulated saliva. The resulting pellicle was washed and incubated with caseinoglycomacropeptide (CGMP) and/or caseinophosphopeptide (CPP) labeled with 17- and 12-nm gold particles. All samples were prepared for electron microscopy by high-pressure freezing followed by freeze-substitution. It was demonstrated by high-resolution scanning electron microscopy with back-scattered electron imaging, as well as by transmission electron microscopy, that both peptides were incorporated into the pellicle in exchange for albumin, confirming previous findings. This protein was identified with a mouse anti-human serum albumin followed by goat anti-mouse IgG labeled with 25-nm gold particles. Incorporation of CGMP and/or CPP into salivary pellicles reduced the adherence of both S. sobrinus and S. mutans significantly. It is suggested that the calcium and phosphate-rich micellar casein or caseinopeptides are incorporated into the pellicle. The resulting ecological shifts, together with the increased remineralization potential of this biofilm, may explain its modified cariogenic potential.

Characterization of casein phosphopeptides prepared using alcalase: determination of enzyme specificity

Tryptic casein phosphopeptides containing the cluster sequence-Ser(P)-Ser(P)-Ser(P)-Glu-Glu- have been shown to stablize amorphous calcium phosphate at neutral and alkaline pH and be anticariogenic in various in vitro, animal and human experiments. Furthermore, metal ion complexes of the casein phosphopeptides (CPPs) have potential as dietetic supplements to increase the bioavailability of calcium, iron, and other essential metal ions. In this study, we have used a Ca2+/ethanol selective precipitation procedure to produce a range of phosphopeptides from an alcalase digest of whole casein. The CPPs released by alcalase were truncated relative to those which are released by trypsin. The peptides could be grouped into those containing the cluster sequence as well as the group of tri-, di-, and monophosphorylated peptides. The two groups contained a number of homologous peptides of varying lengths resulting from the broad specificity of alcalase. Alcalase was observed to cleave peptide bonds on the carboxyl side of Glu, Met, Leu, Tyr, Lys, and Gln; however, of the twenty-six different cleavage sites, seventeen contained a Glu in the P1 position and of these, fifteen contained a hydrophobic residue in either the P2' or P3' positions. Furthermore, of the twenty-six cleavage sites identified, twenty-two contained a hydrophobic residue in either the P2' or P3' positions. Of the four other sites cleaved by alcalase, two contained a hydrophobic residue in the P1' position and one a hydrophobic residue in the P1 position.

Characterization of multiply phosphorylated peptides selectively precipitated from a pancreatic casein digest

Anticariogenic phosphopeptides, released during the hydrolysis of casein with trypsin, contain the cluster sequence Ser(P)-Ser(P)-Ser(P)-Glu-Glu and have commercial potential as toothpaste, mouthwash, and food additives for the prevention of dental caries. To develop a commercial-scale process for the production of these peptides, we have comprehensively characterized casein phosphopeptides that were selectively precipitated using Ca2+ and ethanol from an acid-clarified (pH 4.6) pancreatic casein hydrolysate. Casein was hydrolyzed using pancreatin at 50 degrees C for 2 h. The precipitate contained a series of casein phosphopeptides that were slightly truncated relative to tryptic casein phosphopeptides. The major casein phosphopeptides released by pancreatin were beta-CN-4P(f7-24), alpha s1-CN-5P(f61-78), and alpha s1-CN-5P(f59-78), all containing the cluster sequence. The truncation of the tryptic peptides beta-CN-4P(1-25) and alpha s1-CN-5P(f59-79) resulted from the chy-motryptic and carboxypeptidase activities of the pancreatin. The peptides containing the cluster sequence constituted 77.8 +/- 6.7 mol/100 mol of the total peptides that were selectively precipitated. This composition was not significantly different from that of casein phosphopeptides produced under identical conditions using trypsin. In conclusion, pancreatin should be a suitable enzyme preparation for the production of anticariogenic casein phosphopeptides on a commercial scale.

In vitro modulation of oral bacterial adhesion to saliva-coated hydroxyapatite beads by milk casein derivatives

Bovine caseinate, derivatives of its glycosylated moiety [caseinoglycomacropeptide (CGP)], and caseinophosphopeptides were evaluated as inhibitors of adhesion of oral bacteria to saliva-coated hydroxyapatite beads (S-HA). All milk casein-derived components behaved as potent inhibitors of Streptococcus sanguis OMZ 9 and Streptococcus sobrinus OMZ 176 adhesion to S-HA, whereas neither bovine serum albumin nor polyethyleneglycol were able to interfere with the adhesion of these strains. By contrast, none of the molecular species tested was able to inhibit the attachment of Actinomyces viscosus Ny 1 to S-HA. On the other hand, casein derivatives were shown to displace human serum albumin from S-HA beads. They were also able to bind to the bacterial cell surface of all strains examined. Collectively, these findings suggest that interactions between acidic casein-derived milk components and the biological surfaces involved in bacterial adhesion to S-HA result in an inhibitory effect that is selective for the oral streptococci examined.

Characterization of the oligopeptides of Parmigiano-Reggiano cheese soluble in 120 g trichloroacetic acid/l

The non-protein nitrogen (NPN) of samples of Parmigiano-Reggiano cheese ripened for 6 and 15 months was fractionated by ion-exchange chromatography on a Cu(2+)-Chelex column to separate oligopeptides from free amino acids. Peptide components were isolated by reversed-phase HPLC and identified by fast atom bombardment-mass spectrometry (FAB-MS). Only the NPN fraction of 6 month old cheese samples contained enough peptides to be further characterized. On the basis of FAB-MNS spectral results, 39 oligopeptides were identified, the main components being phosphopeptides. Two sets of both intact and partly dephosphorylated peptides, accounting for a total of 19 phosphopeptides, were formed by the hydrolysis of beta-casein and belonged to regions 1-20 and 6-28 of beta-casein. The formation and potential role of these peptides in cheese is discussed.

The effect of casein phosphopeptides on calcium utilization in young ovariectomized rats

The effect of casein phosphopeptides (CPPs) on Ca utilization in ovariectomized (OVX) rats was studied. A mixture of CPPs corresponding to the amino acid sequences 1-25 and 1-28 in the beta-casein was isolated from the tryptic digest of beta-casein (beta CPP). After being fed a low Ca diet for 30 days, OVX rats were fed experimental diets of which the Ca level was 0.1%, 0.3% or 0.5% with or without 0.15% beta CPP for 28 days. During days 1-3 of the Ca refeeding period, rats fed beta CPP with 0.5% Ca showed a higher Ca absorption than control rats not supplemented with beta CPP. During days 7-9 and 26-28, there were no significant differences in Ca and P balances between the beta CPP group and the control group for each dietary Ca level. Femoral Ca and P contents from rats fed beta CPP tended to be higher than those from control rats. These results suggest that beta CPP supplementation could have an effect on Ca absorption at a certain degree of Ca deficiency.

Chromatographic and electrophoretic methods used for analysis of milk proteins

Current knowledge of milk proteins and their behavior in dairy foods is based on early applications of chromatography and electrophoresis. Electrophoretic identification of the number and genetic variety of milk proteins inaugurated a research effort in which chromatographic techniques were successfully applied to the isolation of each milk protein, thus facilitating the characterization and further study of milk and dairy products. This review focuses on recent applications of chromatography for separations and analysis and on analytical applications of electrophoresis.

Characterization of phosphopeptide derived from bovine beta-casein: an inhibitor to intra-intestinal precipitation of calcium phosphate

Casein phosphopeptide (CPP), a highly phosphorylated peptide fragment which inhibits the formation of hydroxyapatite crystal was isolated from pooled ileal contents of rats fed a semi-synthetic diet containing bovine beta-casein. The estimated amino acid sequence of the CPP was shorter than that of the trypsin-digested beta-casein but the core region consisting of consecutive bindings of phosphoserine was fully conserved. A moderate and exchangeable binding to Ca2+ of the CPP molecule well substantiates the high absorbability of calcium from milk and dairy products.

Tryptic phosphopeptides from whole casein. II. Physicochemical properties related to the solubilization of calcium

Casein phosphopeptides (CPP) were produced by tryptic hydrolysis of sodium caseinate and further purified by precipitation and chromatography on QAE-Sephadex A-25. Their physico-chemical properties were compared with the properties of an enzymically dephosphorylated equivalent preparation (DPP). Binding of Ca2+ to the peptides was measured using a Ca selective electrode and was found to increase with pH and to show 1/1 stoicheiometry Ca/Porg in CPP at pH 6.5 and 7.6. Klotz plots indicated equivalent binding sites at these two pH values, but some heterogeneity was seen at pH 3.5. In contrast, DPP did not bind significant amounts of Ca2+. CPP effectively inhibited the formation of insoluble calcium phosphates at different Ca/P ratios. The effective CPP concentration was 10 mg/l and complete stability of calcium phosphate solutions was obtained at about 100 mg/l. This stabilizing effect was dependent on the presence of organic P.