Bioactive milk peptides: a prospectus

Peptides from Lactobacillus hydrolysates of bovine milk caseins inhibit prolyl-peptidases of human colon cells

Prolyl-rich peptides derived from hydrolysates of bovine caseins have been previously shown to inhibit angiotensin converting enzyme (ACE) activity, suggesting that they may also be able to inhibit the enzymatic activities of prolyl-specific peptidases. This study shows that peptides derived from α(S1)-casein and β-casein inhibited the enzymatic activities of purified recombinant matrix metalloprotease (MMP)-2, MMP-7, and MMP-9. The inhibitory efficacy was sequence-dependent. These peptides also selectively inhibited the enzymatic activities of prolyl-amino-peptidases, prolyl-amino-dipeptidases, and prolyl-endopeptidases in extracts of HT-29 and SW480 human colon carcinoma cells, but not in intact cells. They were not cytotoxic or growth inhibitory for these cells. Thus, the prolyl-rich selected peptides were good and selective inhibitors of MMPs and post-proline-cleaving proteases, demonstrating their potential to control inadequate proteolytic activity in the human digestive tract, without inducing cytotoxic effects.

Determination of calcium-binding constants of caseins, phosphoserine, citrate and pyrophosphate: A modelling approach using free calcium measurement

Dairy products contain large amount of calcium which is bound to caseins and different chelating agents like citrate and polyphosphates. The present study aimed to determine the calcium-binding capacities of phosphoserine (SerP), caseinophosphopeptide (CPP), β-casein, caseinate, citrate and pyrophosphate in the same conditions of temperature, pH and ionic strength. The free calcium (Ca(2+)) was measured using a calcium ion-selective electrode and plotted as a function of total calcium concentration. The association constants and the number of calcium-binding sites were determined by fitting the experimental data to a theoretical model. The phosphate groups of caseins were the main binding sites with evidence for participation of carboxylate groups. The intrinsic association constants determined by the best fit of the data were in the order: pyrophosphate (557×10(3)M(-1))>citrate (20×10(3)M(-1))>β-casein (5×10(3)M(-1))>caseinate, CPP and SerP (∼10(3)M(-1)). These findings may be of interest for the development of calcium-enriched products to overcome calcium deficiency in specific populations.

Bioactive peptides derived from milk proteins and their health beneficial potentials: an update

It has been well recognized that dietary proteins provide a rich source of biologically active peptides. Today, milk proteins are considered the most important source of bioactive peptides and an increasing number of bioactive peptides have been identified in milk protein hydrolysates and fermented dairy products. Bioactive peptides derived from milk proteins offer a promising approach for the promotion of health by means of a tailored diet and provide interesting opportunities to the dairy industry for expansion of its field of operation. The potential health benefits of milk protein-derived peptides have been a subject of growing commercial interest in the context of health-promoting functional foods. Hence, these peptides are being incorporated in the form of ingredients in functional and novel foods, dietary supplements and even pharmaceuticals with the purpose of delivering specific health benefits.

The consumption of milk and dairy foods and the incidence of vascular disease and diabetes: an overview of the evidence

The health effects of milk and dairy food consumption would best be determined in randomised controlled trials. No adequately powered trial has been reported and none is likely because of the numbers required. The best evidence comes, therefore, from prospective cohort studies with disease events and death as outcomes. Medline was searched for prospective studies of dairy food consumption and incident vascular disease and Type 2 diabetes, based on representative population samples. Reports in which evaluation was in incident disease or death were selected. Meta-analyses of the adjusted estimates of relative risk for disease outcomes in these reports were conducted. Relevant case-control retrospective studies were also identified and the results are summarised in this article. Meta-analyses suggest a reduction in risk in the subjects with the highest dairy consumption relative to those with the lowest intake: 0.87 (0.77, 0.98) for all-cause deaths, 0.92 (0.80, 0.99) for ischaemic heart disease, 0.79 (0.68, 0.91) for stroke and 0.85 (0.75, 0.96) for incident diabetes. The number of cohort studies which give evidence on individual dairy food items is very small, but, again, there is no convincing evidence of harm from consumption of the separate food items. In conclusion, there appears to be an enormous mis-match between the evidence from long-term prospective studies and perceptions of harm from the consumption of dairy food items.

In situ generation of milk protein-derived peptides in drying-off cows

Our previous studies demonstrated prompt elevation of proteinase activity in mammary secretion of drying-off cows and goats. The current study examined the progressive changes in composition of cow mammary secretion following drying-off and, in parallel, characterized the mode of peptide neogenesis using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and liquid chromatography-electrospray-ionization (LC-ESI) MS/MS. The results show that the percentage of casein of total milk protein at time of drying-off was 76%, which dropped to 41%, 24%, and 16%, respectively, 1, 2, and 3 weeks after drying-off. Levels of β-lactoglobulin and α-lactoalbumin in mammary secretions of drying-off cows decreased prominently while levels of lactoferrin, BSA, and casein derived-proteins increased concomitantly compared with regular milk. A fractionation procedure was applied to remove molecules larger than 10 kDa before MALDI-TOF MS and LC-ESI MS/MS and the results show that the MALDI-TOF MS peptide profile of mammary secretion ranging from m/z 600 to 4000 was apparently modified after drying-off for 1 week, whereas species 1590 m/z and 2460 m/z were most obviously enriched compared with regular milk. LC-ESI MS/MS results were used to map peptide sequence with Mascot search server and under no post translational modification to reduce database size and 202 novel β-casein-derived peptides were successfully identified in mammary secretion after drying-off for 1 week in contrast to regular milk. Accordingly at least 48 additional cleavage positions were assigned on β-casein for mammary secretion. Among the 202 novel peptides, 5 are homologous with confirmed opioid agonists, angiotensin 1-converting enzyme inhibitors, or immuno-modulators. In conclusion, peptides are released in situ from milk proteins within short intervals following drying-off in cows. They might play roles in the transition of mammary glands from lactating to non-lactating. With specified post-translational modifications and focused functional screening, novel peptides are yet to be discovered in dry cow mammary secretion.

Suitability of buttermilk for fermentation with Lactobacillus helveticus and production of a functional peptide-enriched powder by spray-drying

AIM

To ferment buttermilk, a low-cost by-product of the manufacture of butter, with a proteolytic strain of Lactobacillus helveticus, to enhance its value by the production of a functional peptide-enriched powder.

METHODS AND RESULTS

Buttermilk was fermented with Lact. helveticus 209, a strain chosen for its high proteolytic activity. To enhance the release of peptidic fractions, during fermentation pH was kept at 6 by using NaOH, Ca(CO)(3) or Ca(OH)(2). Cell-free supernatant was recovered by centrifugation, supplemented or not with maltodextrin and spray-dried. The profile of peptidic fractions released was studied by RP-HPLC. The lactose, Na and Ca content was also determined. The powder obtained was administered to BALB/c mice for 5 or 7 consecutive days, resulting in the proliferation of IgA-producing cells in the small intestine mucosa of the animals.

CONCLUSIONS

Buttermilk is a suitable substrate for the fermentation with Lact. helveticus 209 and the release of peptide fractions able to be spray-dried and to modulate the gut mucosa in vivo.

SIGNIFICANCE AND IMPACT OF THE STUDY

A powder enriched with peptides released from buttermilk proteins, with potential applications as a functional food additive, was obtained by spray-drying. A novel use of buttermilk as substrate for lactic fermentation is reported.

Major whey proteins in donkey's milk: effect of season and lactation stage. Implications for potential dietary interventions in human diseases

According to current literature, donkey's milk has been suggested as a hypoallergenic substitute in children affected by cow's milk protein allergy as well as a promising nutraceutical for aged people. However, the biologically active components of donkey's milk have not yet completely elucidated. In this framework this study is aimed at measuring α-lactalbumin (α-LA), β-lactoglobulin (β-LG), and lysozyme (LYS), the principal whey proteins in donkey's milk, in relation to lactation stage and production season. Analysis were performed by reversed-phase high-performance liquid chromatography. α-LA, β-LG, and LYS resulted to be affected by lactation stage (P < 0.01) and production season (P < 0.01). Overall, the protein content was higher (0.01 > P < 0.05) during the first four lactation's months and decreased until the month 8. The β-LG was the major protein (1.75 mg mL(-1) as mean; peak 2.24 ± 0.09 mg mL(-1)), while the α-LA had a mean concentration of 1.32 mg mL(-1) and peaked at month 1 (1.57 ± 0.09 mg mL(-1)) and LYS (0.66 mg mL(-1) as mean) showed the highest value equal to 0.76 ± 0.03 mg mL(-1). The highest (P < 0.01) concentration of all proteins was recorded at spring (α-LA: 1.69 mL(-1); β-LG: 2.07 mL(-1); LYS: 0.76 mL(-1)).

Arachin derived peptides as selective angiotensin I-converting enzyme (ACE) inhibitors: structure-activity relationship

Current attention focuses on mechanisms of controlling blood pressure through the inhibition of angiotensin I-converting enzyme (ACE). Bioactive antihypertensive peptides of food origin are increasingly gaining importance as alternates to synthetic drugs in hypertension therapy. The ACE inhibitory property of an enzymatic digest of arachin, the major storage globulin of peanut (Arachis hypogaea) has been demonstrated. The ACE inhibitory activity of a tripeptide (IEY) isolated from these digests has been characterized. Five synthetic structural analogs of this peptide (IEW, IKY, IKW, IEP and IKP) were assembled and their ACE inhibitory activity evaluated. Among these, the tripeptide IKP was a potent competitive inhibitor with an IC(50) of 7+/-1 x 10(-6)M similar to that of the potent whey peptides IPP and VPP. The inhibition data of these peptide analogs have been rationalized through docking simulations using the tACE-lisinopril complex at 2A resolution (PDB: 1086). The best docking poses were located at the tACE catalytic site resembling the mode of inhibition exerted by lisinopril, the synthetic drug. The degree of inhibition by the peptides correlated with the coordination distance between the catalytic Zn(II) and the carbonyl oxygen of the peptide bond between the amino-terminal and middle residue. These studies illustrate that these peptides, like lisinopril, behave as transition state analog inhibitors and are useful in therapeutic intervention for blood pressure management.

Improvement of the antimicrobial and antioxidant activities of camel and bovine whey proteins by limited proteolysis

The compositions and structures of bovine and camel milk proteins are different, which define their functional and biological properties. The aim of this study was to investigate the effects of enzymatic hydrolysis of camel and bovine whey proteins (WPs) on their antioxidant and antimicrobial properties. After enzymatic treatment, both the antioxidant and the antimicrobial activities of bovine and camel WPs were improved. The significantly higher antioxidant activity of camel WPs and their hydrolysates as compared with that of bovine WPs and their hydrolysates may result from the differences in amounts and/or in accessibilities of antioxidant amino acid residues present in their primary structures and from the prevalence of alpha-lactalbumin and beta-lactoglobulin as proteolytic substrates in camel and bovine whey, respectively. The results of this study reveal differences in antimicrobial and antioxidant activities between WP hydrolysates of bovine and camel milk and the effects of limited proteolysis on these activities.

Comparison of milk fat globule membrane (MFGM) proteins of Chianina and Holstein cattle breed milk samples through proteomics methods

Identification of proteins involved in milk production is important to understand the biology of lactation. Many studies have advanced the understanding of mammary function and milk secretion, but the critical molecular mechanisms implicated in milk fat secretion is still incomplete. Milk fat globules are secreted from the apical surface of the mammary cells, surrounded by a thin membrane bilayer, the milk fat globule membrane (MFGM), formed by proteins which have been suggested to be cholesterolemia-lowering factors, inhibitors of cancer cell growth, vitamin binders, bactericidal, suppressors of multiple sclerosis. Using a proteomic approach, we compared MFGM from milk samples of individuals belonging to two different cattle breeds, Chianina and Holstein, representative of selection for milk and meat traits, respectively. We were able to isolate some of the major MFGM proteins in the examined samples and to identify differences between the protein fractions of the two breeds. We detected differences in the amount of proteins linked to mammary gland development and lipid droplets formation, as well as host defence mechanisms. We have shown that proteomics is a suitable, unbiased method for the study of milk fractions proteins and a powerful tool in nutritional genomics.

Studies on the molecular recognition between bioactive peptides and angiotensin-converting enzyme

High blood pressure or hypertension is a condition affecting many individuals and represents a controllable risk factor for cardiovascular diseases such as coronary heart disease and stroke. A non-pharmacological approach to manage these includes the application of food components with antihypertensive activity. Milk protein-derived peptides have been exploited as natural hypotensive agents, namely the peptides Val-Pro-Pro (VPP) and Ile-Pro-Pro (IPP), already commercialized in functional foods as a potential alternative to synthetic drugs. These bioactive peptides inhibit in vitro and in vivo the Angiotensin I-converting enzyme (ACE), a protein with an important role in blood pressure regulation. In this work, we attempted to elucidate the possible mode of interaction between the peptides and ACE, including mechanisms of binding to the cofactor Zn2+, and further contrast this with the known mode of inhibition exerted by synthetic drugs (Captopril, Enalaprilat and Lisinopril). The bioactive peptide Ala-Leu-Pro-Met-His-Ile-Arg (ALPMHIR), also known to inhibit the enzyme ACE but with a lower efficiency than VPP and IPP, was utilized in the docking studies for comparison. It was observed that the best docking poses obtained for VPP and IPP were located at the ACE catalytic site with very high resemblance to the drugs mode of interaction, including the coordination with Zn2+. As for ALPMHIR, the best docking poses were located in the narrow ACE channel outside the catalytic site, representing higher affinity energies and fewer resemblances with the interaction established by drugs.

Acidic peptides enhanced genistein-dependent inhibition of human platelet aggregation: potential protective effect of digestible peptides plus genistein against atherosclerosis

The leading cause of death in the United States and European countries is coronary heart disease. We hypothesized that the ingestion of soy compounds may not only have beneficial effects on atherosclerotic risk by lowering lipid compounds, but also by reducing platelet aggregability. Therefore, we analyzed in vitro the influence of defined and digestible peptides, frequently found in glycinin and beta-conglycinin as important proteins of soy bean, on platelet aggregation of 180 healthy volunteers with or without the isoflavone genistein by aggregometry and flow cytometry. (i) The predominating share of amino acids and acidic, neutral, and basic di- and tripeptides of up to 2 mmol/L did not modify platelet aggregation induced by collagen, adenosine diphosphate, epinephrine, or arachidonic acid. (ii) Genistein inhibited agonist-induced platelet aggregation dose dependently. (iii) In the presence of the acidic peptides glutamate-glutamate and aspartate-aspartate-aspartate (1 mmol/L each), genistein reduced collagen- and ADP-dependent platelet activation stronger than 250 micromol/L of this isoflavone alone. Other peptides were less effective (eg, glutamate-glutamate-glutamate) or ineffective (eg, asparagine-asparagine). (iv) Glutamate-glutamate-glutamate (1 nmol/L), glutamate-glutamate (1 micromol/L), and aspartate-aspartate-aspartate (1 micromol/L) enhanced the inhibition of genistein on platelet aggregation induced by arachidonic acid. Thus, the results of the present in vitro investigation allow the assumption that nutrition with specific compounds of soy--acidic peptides together with genistein--might protect against coronary atherosclerosis by attenuating platelet activity. In vivo studies are warranted to check this assumption.

Effect of exopolysaccharides on the proteolytic and angiotensin-I converting enzyme-inhibitory activities and textural and rheological properties of low-fat yogurt during refrigerated storage

The aim of this study was to examine the influence of using exopolysaccharide (EPS) producing strain of Streptococcus thermophilus on the viability of yogurt starters, their proteolytic and angiotensin-I converting enzyme-inhibitory activities, and on the textural and rheological properties of the low-fat yogurt during storage at 4 degrees C for 28 d. The use of an EPS-producing strain of S. thermophilus did not have influence on pH, lactic acid content, or the angiotensin-I converting enzyme-inhibition activity of low-fat yogurt. However, EPS showed a protective effect on the survival of Lactobacillus delbrueckii ssp. bulgaricus. Presence of EPS reduced the firmness, spontaneous whey separation, yield stress, and hysteresis loop area but not the consistency and flow behavior index of low-fat yogurt.

Beneficial health effects of milk and fermented dairy products--review

Milk is a complex physiological liquid that simultaneously provides nutrients and bioactive components that facilitate the successful postnatal adaptation of the newborn infant by stimulating cellular growth and digestive maturation, the establishment of symbiotic microflora, and the development of gut-associated lymphoid tissues. The number, the potency, and the importance of bioactive compounds in milk and especially in fermented milk products are probably greater than previously thought. They include certain vitamins, specific proteins, bioactive peptides, oligosaccharides, organic (including fatty) acids. Some of them are normal milk components, others emerge during digestive or fermentation processes. Fermented dairy products and probiotic bacteria decrease the absorption of cholesterol. Whey proteins, medium-chain fatty acids and in particular calcium and other minerals may contribute to the beneficial effect of dairy food on body fat and body mass. There has been growing evidence of the role that dairy proteins play in the regulation of satiety, food intake and obesity-related metabolic disorders. Milk proteins, peptides, probiotic lactic acid bacteria, calcium and other minerals can significantly reduce blood pressure. Milk fat contains a number of components having functional properties. Sphingolipids and their active metabolites may exert antimicrobial effects either directly or upon digestion.