Effect of high hydrostatic pressure on the conformation of β-lactoglobulin A as assessed by proteolytic peptide profiling

Peptidomic analysis of the angiotensin-converting-enzyme inhibitory peptides in milk fermented with Lactobacillus delbrueckii QS306 after ultrahigh pressure treatment

In this study, we assessed the effect of ultrahigh pressure (UHP) treatment on the concentration of peptides and angiotensin-converting enzyme (ACE) inhibitory activity in milk fermented with Lactobacillus delbrueckii QS306. The peptides were identified using peptidomic analysis, and 313 unique peptides were identified. These peptides were derived from 53 precursor proteins. Before and after UHP treatment, 361 (22.2%) peptide sequences exhibited difference, and 53 peptide segments were significantly different. Among them, small peptides (amino acid residues ≤6) isoelectric were point at pH 5-6, and the net charge was mainly positive or neutral. With hydrophobicity and ACE inhibitory activity as screening indicators, 214 small peptides with potential ACE inhibitory activity were identified, and 130 new peptides had potential ACE inhibitory activity. A novel ACE inhibitory peptide VAPFP was synthesized, whose in vitro inhibition rate was 10.56 μmol\/L. Therefore, using peptidomics, the changes in peptide sequences and enhancement in ACE inhibitory activity before and after UHP treatment could be effectively identified in milk fermented with Lactobacillus delbrueckii QS306. This study provided a convenient method for the discovery and identification of new ACE inhibitory peptides.

Conventional and Novel Technologies in the Production of Dairy Bioactive Peptides

Background

In recent years, researchers have focused on functional ingredients, functional foods, and nutraceuticals due to the rapidly increasing interest in bioactive components, especially in bioactive peptides. Dairy proteins are a rich and balanced source of amino acids and their derived bioactive peptides, which possess biological and physiological properties. In the dairy industry, microbial fermentation and enzymatic hydrolysis are promising methods for producing bioactive peptides because of their rapid efficiency, and mild reaction conditions. However, these methods utilize less raw material, take long reaction time, result in low yields, and low activity products when used alone, which pose industry to seek for novel methods as pretreatments to increase the yield of bioactive peptides.

Scope and Approach

This review emphasizes the production of peptides from the dairy proteins and discusses the potential use of novel technologies as pretreatments to conventional methods of bioactive peptides production from dairy proteins, including the mechanisms of novel technologies along with respective examples of use, advantages, limitations, and challenges to each technology.

Key Findings and Conclusion

Noteworthily, hydrolysis of dairy proteins liberate wide-range of peptides that possess remarkable biological functions to maintain human health. Novel technologies in the dairy industry such as ultrasound-assisted processing (UAP), microwave-assisted processing (MAP), and high pressure processing (HPP) are innovative and environmentally friendly. Generally, novel technologies are less effectual compared to conventional methods, therefore used in combination with fermentation and enzymatic hydrolysis, and are promising pretreatments to modify peptides’ profile, improve the yields, and high liberation of bioactive peptides as compared to conventional technologies. UAP is an innovative and most efficient technology as its mechanical effects and cavitation change the protein conformation, increase the biological activities of enzymes, and enhance enzymatic hydrolysis reaction rate.

Effects of High Hydrostatic Pressure Pretreatment on the Functional and Structural Properties of Rice Bran Protein Hydrolysates

Rice bran protein (RBP) hydrolysis was conducted after high hydrostatic pressure (HHP) pretreatment. The structural and functional properties of HHP-pretreated rice bran protein hydrolysates (RBPH) were investigated. HHP pretreatments were conducted at 100, 200, and 300 MPa; then, enzymatic hydrolysis at atmospheric pressure was performed using trypsin. An RBPH sample that had not been pretreated by HHP was used as a control. Free sulfhydryl (SH) content, SDS-PAGE profiles, high-performance size exclusion chromatography (HPSEC), Fourier transform infrared (FTIR) spectrum, scanning electron microscopy (SEM), intrinsic fluorescence spectrum, solubility, and emulsifying and foaming properties were evaluated. Changes in particle size and ζ-potential were monitored. Compared with the control, the results of solubility, the emulsifying activity index (EAI) and the emulsifying stability index (ESI) increased significantly (p < 0.05) at 200 MPa. The content of free SH increased significantly (p < 0.05) at 100 MPa. FTIR spectrum and fluorescence analysis confirmed the changes in the secondary and tertiary structures. The experimental results indicated that the structural and functional properties of HHP-pretreated RBPH improved.

Improved Sensitivity of Allergen Detection by Immunoaffinity LC-MS/MS Using Ovalbumin as a Case Study

Food allergies are caused by severe hypersensitivity to specific food allergens such as the egg protein ovalbumin. It is therefore important to test food products for the presence of allergens to protect allergic people from accidental ingestion. For egg detection, ELISA is the only reasonable commercially available test format, although the recognition of target allergens can be affected by food processing, which may lead to false negative results. Current mass spectrometry-based detection methods may overcome this issue, but these approaches are often less sensitive. Here we combined the advantages of antibody-based and MS-based methods by developing an immunoaffinity LC-MS/MS technique to detect the common egg allergen Gal d 2. We investigated the principal functionality of this method with incurred cookie material containing whole egg powder. We found that the new method matched easily the sensitivity of egg specific ELISA tests. Further western blot experiments indicated that this strategy may be unaffected by food processing, providing an important alternative strategy for the detection and quantification of allergens in food.

Effect of processing on in vitro digestibility (IVPD) of food proteins

Proteins are important macronutrients for the human body to grow and function throughout life. Although proteins are found in most foods, their very dissimilar digestibility must be taking into consideration when addressing the nutritional composition of a diet. This review presents a comprehensive summary of the in vitro digestibility of proteins from plants, milk, muscle, and egg. It is evident from this work that protein digestibility greatly varies among foods, this variability being dependent not only upon the protein source, but also the food matrix and the molecular interactions between proteins and other food components (food formulation), as well as the conditions during food processing and storage. Different approaches have been applied to assess in vitro protein digestibility (IVPD), varying in both the enzyme assay and quantification method used. In general, animal proteins tend to show higher IVPD. Harsh technological treatments tend to reduce IVPD, except for plant proteins, in which thermal degradation of anti-nutritional compounds results in improved IVPD. However, in order to improve the current knowledge about protein digestibility there is a vital need for understanding dependency on a protein source, molecular interaction, processing and formulation and relationships between. Such knowledge can be used to develop new food products with enhanced protein bioaccessibility.

Structure and adsorption behavior of high hydrostatic pressure-treated β-lactoglobulin

HYPOTHESIS

High hydrostatic pressure treatment causes structural changes in interfacial-active β-lactoglobulin (β-lg). We hypothesized that the pressure-induced structural changes affect the intra- and intermolecular interactions which determine the interfacial activity of β-lg. The conducted experimental and numerical investigations could contribute to the mechanistic understanding of the adsorption behavior of proteins in food-related emulsions.

EXPERIMENTS

We treated β-lg in water at pH 7 with high hydrostatic pressures up to 600 MPa for 10 min at 20 °C. The secondary structure was characterized with Fourier-transform infrared spectroscopy (FTIR) and circular dichroism (CD), the surface hydrophobicity and charge with fluorescence-spectroscopy and ζ-potential, and the quaternary structure with membrane-osmometry, analytical ultracentrifugation (AUC) and mass spectrometry (MS). Experimental analyses were supported through molecular dynamic (MD) simulations. The adsorption behavior was investigated with pendant drop analysis.

FINDINGS

MD simulation revealed a pressure-induced molten globule state of β-lg, confirmed by an unfolding of β-sheets with FTIR, a stabilization of α-helices with CD and loss in tertiary structure induced by an increase in surface hydrophobicity. Membrane-osmometry, AUC and MS indicated the formation of non-covalently linked dimers that migrated slower through the water phase, adsorbed more quickly due to hydrophobic interactions with the oil, and lowered the interfacial tension more strongly than reference β-lg.

A Response Surface Methodology (RSM) Approach for Optimizing the Attenuation of Human IgE-Reactivity to β-Lactoglobulin (β-Lg) by Hydrostatic High Pressure Processing

The response surface methodology (RSM) and central composite design (CCD) technique were used to optimize the three key process parameters (i.e., pressure, temperature and holding time) of the high-hydrostatic-pressure (HHP) processing either standalone or combined with moderate thermal processing to modulate molecular structures of β-lactoglobulin (β-Lg) and α-lactalbumin (α-La) with reduced human IgE-reactivity. The RSM model derived for HHP-induced molecular changes of β-Lg determined immunochemically showed that temperature (temp), pressure (p²) and the interaction between temperature and time (t) had statistically significant effects (p < 0.05). The optimal condition defined as minimum (β-Lg specific) IgG-binding derived from the model was 505 MPa at 56 °C with a holding time of 102 min (R² of 0.81 and p-value of 0.01). The validation carried at the optimal condition and its surrounding region showed that the model to be underestimating the β-Lg structure modification. The molecular change of β-Lg was directly correlated with HHP-induced dimerization in this study, which followed a quadratic equation. The β-Lg dimers also resulted in the undetectable human IgE-binding.

Production and Purification of Novel Hypocholesterolemic Peptides from Lactic Fermented Spirulina platensis through High Hydrostatic Pressure-Assisted Protease Hydrolysis

This research focuses on the proteolytic capacity of Spirulina platensis and their hypocholesterolemic activity via the 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGR) inhibitory activity. To select suitable proteases for releasing peptides with high HMGR-inhibiting activity from S. platensis, eight commonly used commercial proteases were used in protease hydrolysis under high hydrostatic pressure (HHP, 100 MPa or 0.1 MPa) at 50 °C for 24 h. The Peptidase R group had the highest inhibitory capacity (67%). First, S. platensis was fermented with seven mixed lactic acid bacteria for 5 h at 42 °C. This was followed by the addition of Peptidase R under high hydrostatic pressure (100 MPa at 50 °C) for 0–6 h of enzymatic hydrolysis (HHP-FH-PR6) to determine the hydrolytic capacity of S. platensis protein. As the hydrolysis time extended to 6 h, the peptide content increased from 96.8 mg/mL to 339.8 mg/mL, and the free amino acid content increased from 24 mg/mL to 115.2 mg/mL, while inhibition of HMGR increased from 67.0% to 78.4%. In an experimental simulation of in vitro gastrointestinal digestion, the IC50 of HHP-FH-PR6G on HMGR was 3.5 μg peptide/mL. Peptides with inhibitory activity on HMGR were purified, and their sequences were identified as Arg-Cys-Asp and Ser-Asn-Val (IC50: 6.9 and 20.1 μM, respectively).

Purification and Identification of Cholesterol Micelle Formation Inhibitory Peptides of Hydrolysate from High Hydrostatic Pressure-Assisted Protease Hydrolysis of Fermented Seabass Byproduct

This research focuses on the proteolytic capacity of sea bass byproduct (SB) and their hypocholesterolemic activity via the cholesterol micelle formation (CMF) inhibition. SB was fermented with seven mixed lactic acid bacteria for 5 h at 42 °C. The lactic fermented SB was hydrolyzed with Protease N for 6 h under HHP to obtain the SB hydrolysates (HHP-assisted Protease N hydrolysis after fermentation, F-HHP-PN6). The supernatant was separated from the SB hydrolysate and freeze-dried. As the hydrolysis time extended to 6 h, soluble protein content increased from 187.1 to 565.8 mg/g, and peptide content increased from 112.8 to 421.9 mg/g, while inhibition of CMF increased from 75.0% to 88.4%. Decreasing the CMF inhibitory activity from 88.4% to 42.1% by simulated gastrointestinal digestion (FHHP-PN6 was further hydrolyzed by gastrointestinal enzymes, F-HHP-PN6-PP) reduced the CMF inhibitory activity of F-HHP-PN6. Using gel filtration chromatography, the F-HHP-PN6-PP was fractioned into six fractions. The molecular weight of the fifth fraction from F-HHP-PN6-PP was between 340 and 290 Da, and the highest inhibitory efficiency ratio (IER) on CMF was 238.9%/mg/mL. Further purification and identification of new peptides with CMF inhibitory activity presented the peptide sequences in Ser-Ala-Gln, Pro-Trp, and Val-Gly-Gly-Thr; the IERs were 361.7, 3230.0, and 302.9%/mg/mL, respectively.

Effect of Ligands on HP-Induced Unfolding and Oligomerization of β-Lactoglobulin

To probe intermediate states during unfolding and oligomerization of proteins remains a major challenge. High pressure (HP) is a powerful tool for studying these problems, revealing subtle structural changes in proteins not accessible by other means of denaturation. Bovine β-lactoglobulin (BLG), the main whey protein, has a strong propensity to bind various bioactive molecules such as retinol and resveratrol, two ligands with different affinity and binding sites. By combining in situ HP-small-angle neutron scattering (SANS) and HP-ultraviolet/visible absorption spectroscopy, we report the specific effects of these ligands on three-dimensional conformational and local changes in BLG induced by HP. Depending on BLG concentration, two different unfolding mechanisms are observed in situ under pressures up to ∼300 MPa: either a complete protein unfolding, from native dimers to Gaussian chains, or a partial unfolding with oligomerization in tetramers mediated by disulfide bridges. Retinol, which has a high affinity for the BLG hydrophobic cavity, significantly stabilizes BLG both in three-dimensional and local environments by shifting the onset of protein unfolding by ∼100 MPa. Increasing temperature from 30 to 37°C enhances the hydrophobic stabilization effects of retinol. In contrast, resveratrol, which has a low binding affinity for site(s) on the surface of the BLG, does not induce any significant effect on the structural changes of BLG due to pressure. HP treatment back and forth up to ∼300 MPa causes irreversible covalent oligomerization of BLG. Ab initio modeling of SANS shows that the oligomers formed from the BLG-retinol complex are smaller and more elongated compared to BLG without ligand or in the presence of resveratrol. By combining HP-SANS and HP-ultraviolet/visible absorption spectroscopy, our strategy highlights the crucial role of BLG hydrophobic cavity and opens up new possibilities for the structural determination of HP-induced protein folding intermediates and irreversible oligomerization.

Functionality of Cricket and Mealworm Hydrolysates Generated after Pretreatment of Meals with High Hydrostatic Pressures

The low consumer acceptance to entomophagy in Western society remains the strongest barrier of this practice, despite these numerous advantages. More positively, it was demonstrated that the attractiveness of edible insects can be enhanced by the use of insect ingredients. Currently, insect ingredients are mainly used as filler agents due to their poor functional properties. Nevertheless, new research on insect ingredient functionalities is emerging to overcome these issues. Recently, high hydrostatic pressure processing has been used to improve the functional properties of proteins. The study described here evaluates the functional properties of two commercial insect meals (Gryllodes sigillatus and Tenebrio molitor) and their respective hydrolysates generated by Alcalase®, conventionally and after pressurization pretreatment of the insect meals. Regardless of the insect species and treatments, water binding capacity, foaming and gelation properties did not improve after enzymatic hydrolysis. The low emulsion properties after enzymatic hydrolysis were due to rapid instability of emulsion. The pretreatment of mealworm meal with pressurization probably induced protein denaturation and aggregation phenomena which lowered the degree of hydrolysis. As expected, enzymatic digestion (with and without pressurization) increased the solubility, reaching values close to 100%. The pretreatment of mealworm meal with pressure further improved its solubility compared to control hydrolysate, while pressurization pretreatment decreased the solubility of cricket meal. These results may be related to the impact of pressurization on protein structure and therefore to the generation of different peptide compositions and profiles. The oil binding capacity also improved after enzymatic hydrolysis, but further for pressure-treated mealworm hydrolysate. Despite the moderate effect of pretreatment by high hydrostatic pressures, insect protein hydrolysates demonstrated interesting functional properties which could potentially facilitate their use in the food industry.

Effects of combined high pressure and enzymatic treatments on physicochemical and antioxidant properties of peanut proteins

Isolated peanut protein (PPI) dispersions were pretreated by high pressure at 100, 300, and 500 MPa prior to enzymatic hydrolysis with alkaline protease (Alcalase). The degree of hydrolysis (DH) was determined by the pH-stat method, the hydrolysates profiles were analyzed by high-performance liquid chromatography (HPLC), the molecular weight distribution (MWD) was analyzed by gel filtration chromatogram (GFC), and content of SH/S-S and antioxidant activity of hydrolysates were evaluated. Results showed that HP pretreatment improved effectively the enzymatic hydrolysis of PPI, with an effective sequence of 300 > 100 > 500 MPa. However, no significant differences were observed in the peak pattern of HPLC profiles, but the peak times were earlier in HPLC profiles of the HP-treated protein. GFC analysis showed that more peptide fractions with low molecular weight appeared in the hydrolysates of the HP-treated PPI with increasing pressure. Moreover, the level of free SH of hydrolysates of the HP-treated PPI was relatively higher than non-HP-treated PPI. The hydrolysates of the HP-treated PPI exerted higher antioxidant activity (reducing power and DPPH radical scavenging) than the hydrolysates of non-HP-treated PPI. The results indicated that high pressure treatment affected the enzymatic hydrolysis of peanut protein and some protein structure properties and improved antioxidant activity of PPI hydrolysates.

High hydrostatic pressure-assisted enzymatic hydrolysis improved protein digestion of flaxseed protein isolate and generation of peptides with antioxidant activity

Exploration of innovative high hydrostatic pressure (HHP)-assisted enzymatic hydrolysis of plant based food proteins may help improve peptide yield and bioactivity of hydrolysates. In this study, we performed enzymatic hydrolysis of flaxseed proteins using trypsin under HHP (100 and 300 MPa for 5 and 10 min) to evaluate the effect of presurization on protein denaturation, degree of hydrolysis (DH), and peptide profile and bioactivity of hydrolysate. Spectrofluorimetric analyses showed that 300 MPa induced the maximum destablization of flaxseed protein structures. The same pressure level drastically improved the DH by 1.7 times as compared to that of control. Applying HHP did not modify the peptide profiles of flaxseed protein hydrolysates but their concentrations increased with severity of treatment. Similarly, peptide molecular weight distributions were affected by pressurization parameters, increasing mainly the relative abundance of 500-1500 Da peptides. Finally, pressurization at 300 MPa for 5 and 10 min improved the antioxidant activity of flaxseed protein hydrolysates by 39 and 55%, respectively, compared to the control.

Combined effect of high hydrostatic pressure and ultraviolet radiation on quality parameters of refrigerated vacuum-packed tilapia (Oreochromis niloticus) fillets

This study investigated the effects of high hydrostatic pressure (HHP) and ultraviolet radiation (UV-C), individually and combined, on the physical, chemical and bacterial parameters of Nile tilapia (Oreochromis niloticus) fillets stored at 4 °C for 14 days. Tilapia fillets were divided into four groups: control (untreated samples), UV-C, HHP, and UV-C combined with HHP (UV-C+HHP); UV-C was applied at dose of 0.103 ± 0.002 J/cm², and HHP at a pressure of 220 MPa for 10 min at 25 °C. All samples were analyzed for total aerobic mesophilic count (TAMC), total aerobic psychrotrophic count (TAPC), Enterobacteriaceae count, pH, lipid oxidation, total volatile basic nitrogen (TVB-N), ammonia (NH₃), and biogenic amines. Although UV-C accelerated (P ≤ 0.05) the formation of cadaverine, both UV-C and HHP, alone or together, retarded bacterial growth and delayed the increase (P ≤ 0.05) in pH, TVB-N, NH₃ and biogenic amines during refrigerated storage, extending the shelf life of refrigerated tilapia fillets at least 2.5 times considering the TAMC counts. Lipid oxidation was unaffected (P > 0.05) by UV-C radiation, and decreased (P ≤ 0.05) by HHP and UV-C+HHP. HHP alone or combined with UV-C showed higher potential benefits for tilapia fillets preservation considering the positive influence on cadaverine levels and lipid oxidation.

Pretreatment of flaxseed protein isolate by high hydrostatic pressure: Impacts on protein structure, enzymatic hydrolysis and final hydrolysate antioxidant capacities

The effect of high hydrostatic pressure (HHP) on flaxseed protein structure and peptide profiles, obtained after protein hydrolysis, was investigated. Isolated flaxseed protein (1%, m/v) was subjected to HHP (600MPa, 5min or 20min at 20°C) prior to hydrolysis with trypsin only and trypsin-pronase. The results demonstrated that HHP treatment induced dissociation of flaxseed proteins and generated higher molecular weight aggregates as a function of processing duration. Fluorescence spectroscopy showed that HHP treatment, as well as processing duration, had an impact on flaxseed protein structure since exposition of hydrophobic amino acid tyrosine was modified. Except for some specific peptides, the concentrations of which were modified, similar peptide profiles were obtained after hydrolysis of pressure-treated proteins using trypsin. Finally, hydrolysates obtained using trypsin-pronase had a greater antioxidant capacity (ORAC) than control samples; these results confirmed that HHP enhanced the generation of antioxidant peptides.

High Hydrostatic Pressure Pretreatment of Whey Protein Isolates Improves Their Digestibility and Antioxidant Capacity

Whey proteins have well-established antioxidant and anti-inflammatory bioactivities. High hydrostatic pressure processing of whey protein isolates increases their in vitro digestibility resulting in enhanced antioxidant and anti-inflammatory effects. This study compared the effects of different digestion protocols on the digestibility of pressurized (pWPI) and native (nWPI) whey protein isolates and the antioxidant and anti-inflammatory properties of the hydrolysates. The pepsin-pancreatin digestion protocol was modified to better simulate human digestion by adjusting temperature and pH conditions, incubation times, enzymes utilized, enzyme-to-substrate ratio and ultrafiltration membrane molecular weight cut-off. pWPI showed a significantly greater proteolysis rate and rate of peptide appearance regardless of digestion protocol. Both digestion methods generated a greater relative abundance of eluting peptides and the appearance of new peptide peaks in association with pWPI digestion in comparison to nWPI hydrolysates. Hydrolysates of pWPI from both digestion conditions showed enhanced ferric-reducing antioxidant power relative to nWPI hydrolysates. Likewise, pWPI hydrolysates from both digestion protocols showed similar enhanced antioxidant and anti-inflammatory effects in a respiratory epithelial cell line as compared to nWPI hydrolysates. These findings indicate that regardless of considerable variations of in vitro digestion protocols, pressurization of WPI leads to more efficient digestion that improves its antioxidant and anti-inflammatory properties.

Effect of pretreatment on enzymatic hydrolysis of bovine collagen and formation of ACE-inhibitory peptides

Bovine collagen was pre-treated (boiled or high pressure (HP)-treated) and then hydrolysed by 6 proteases. The degree of hydrolysis (DH) and the angiotensin-converting enzyme (ACE)-inhibitory activity of hydrolysates were measured. All enzymes used were able to partly degrade collagen and release ACE-inhibitory peptides. The highest ACE-inhibitory activity was obtained with Alcalase. Pretreatment significantly influenced the DH and ACE-inhibition. For most enzymes, boiling for 5 min resulted in a significantly higher DH and ACE-inhibitory activity. With Alcalase and collagenase, hydrolysis and release of ACE-inhibitory peptides occurred without any pretreatment, but HP-treatment significantly improved the DH and ACE-inhibitory activity. HP did not markedly affect the hydrolysis with the other enzymes. The major peptides obtained with Alcalase were identified; all were released from the triple helix structure of collagen. Many of these peptides had C-terminal sequences similar to known ACE-inhibitory peptides. The present results suggest that collagen-rich food materials are good substrates for the release of potent ACE-inhibitory peptides, when proper pre-treatment and enzymatic treatment is applied.

The potential role of milk-derived peptides in cardiovascular disease

Bioactive peptides derived from milk proteins are of particular interest to the food industry due to the potential functional and physiological roles that they demonstrate, particularly in relation to cardiovascular disease (CVD). By 2020 it is estimated that heart disease and stroke will become the leading cause of death and disability worldwide. Acute and chronic cardiovascular events may result from alterations in the activity of the renin-angiotensin aldosterone system and activation of the coagulation cascade and of platelets. Medications that inhibit angiotensin converting enzyme (ACE) are widely prescribed in the treatment and prevention of cardiovascular disease. ACE inhibitory peptides are of particular interest due to the presence of encrypted inhibitory peptide sequences. In particular, Ile-Pro-Pro and Val-Pro-Pro are fore runners in ACE inhibition, and have been incorporated into commercial products. Additionally, studies to identify additional novel peptides with similar bio-activity and the ability to withstand digestion during transit through the gastrointestinal tract are ongoing. The potential sources of such peptides in cheese and other dairy products are discussed. Challenges to the bio-availability of such peptides in the gastro intestinal tract are also reviewed. Activation of platelets and the coagulation cascade play a central role in the progression of cardiovascular disease. Platelets from such patients show spontaneous aggregation and an increased sensitivity to agonists which results in vascular damage and endothelial dysfunction associated with CVD. Peptide sequences exhibiting anti-thrombotic activity have been identified from fermented milk products. Studies on such peptides are reviewed and their effects on platelet function are discussed. Finally the ability of food derived peptides to decrease the formation of blood clots (thrombi) is reviewed. In conclusion, due to the widespread nature of cardiovascular disease, the identification of food derived compounds that exhibit a beneficial effect in such widespread areas of CVD regulation will have strong clinical potential. Due to the perception that food derived products have an acceptable risk profile they have the potential for widespread acceptance by the public. In this review, selected biological effects relating to CVD are discussed with a view to providing essential information to researchers.

Changes in the ovalbumin proteolysis profile by high pressure and its effect on IgG and IgE binding

Egg proteins are responsible for one of the most common forms of food allergy, especially in children, and one of the major allergens is ovalbumin (OVA). With the aim to examine the potential of high pressure to enhance the enzymatic hydrolysis of OVA and modify its immunoreactivity, the protein was proteolyzed with pepsin under high-pressure conditions (400 MPa). Characterization of the hydrolysates and peptide identification was performed by reversed-phase high-performance liquid chromatography-tandem mass spectrometry (RP-HPLC-MS/MS). The antigenicity (binding to IgG) and binding to IgE, using the sera of patients with specific IgE to OVA, were also assessed. The results showed that, upon treatment with pepsin at 400 MPa, all of the intact protein was removed in minutes, leading to the production of hydrolysates with lower antigenicity than those produced in hours at atmospheric pressure. However, the exposure of new target residues only partially facilitated the removal of allergenic epitopes, because the hydrolysates retained residual IgG- and IgE-binding properties as a result of the accumulation of large and hydrophobic peptides during the initial stages of hydrolysis. These peptides disappeared at later stages of proteolysis, although reactivity toward IgG and IgE was not completely abolished. Some fragments identified in the hydrolysates (such as Leu124-Phe134, Ile178-Ala187, Leu242-Leu252, Gly251-Ile259, Lys322-Gly343, Phe358-Phe366, and Phe378-Pro385) carried previously identified IgE-binding epitopes. Because some of the peptides found, such as Phe358-Phe366, probably contain only one binding site for IgE, the possibility to use high pressure to tailor hydrolysates that contain mostly peptides with only one IgE-binding site, which may help the immune system to tolerate egg proteins, is suggested.

Hydrolysis under high hydrostatic pressure as a means to reduce the binding of beta-lactoglobulin to immunoglobulin E from human sera

Cows' milk allergy is the most frequent food allergy in children, and beta-lactoglobulin (beta-Lg) is a major allergen. Milk-based hypoallergenic ingredients are manufactured by enzymatic hydrolysis, a process that could be improved by the application of high-pressure treatments. This study showed that the treatment of beta-Lg dissolved in buffer with chymotrypsin and trypsin under high pressure for relatively short times accelerated proteolysis by leading to a rapid removal of the intact protein. The rapid proteolysis of the beta-Lg substrate under pressure led to the production, in 20 min, of hydrolysates with lower immunoglobulin (Ig) G binding than those produced in 8 h (chymotrypsin) or 48 h (trypsin) at atmospheric pressure. However, those hydrolysates retained some residual IgE-binding properties that could be traced to the preferential release, during the initial stages of proteolysis, of peptides containing IgE epitopes, such as (Val-41-Lys-60), (Leu-149-Ile-162), and (Ser-21-Arg-40). The formation of these fragments was favored when proteolysis was conducted under high pressure due to the preferential hydrolysis of Arg-40 and Arg-148 by trypsin, and Tyr-42 and Leu-149 by chymotrypsin, all located at the dimer interface of beta-Lg or very close to it. Although our results do not support that trypsin and chymotrypsin under high pressure selectively address the allergenic regions of beta-Lg, it is possible to select the conditions that quickly produce hydrolysates with reduced potential allergenicity that could be used in hypoallergenic foods.

Unfolding and refolding of beta-lactoglobulin subjected to high hydrostatic pressure at different pH values and temperatures and its influence on proteolysis

The unfolding of beta-lactoglobulin during high-pressure treatment and its refolding after decompression were studied by 1H NMR and 2H/1H exchange at pH 6.8 and 2.5 and at 37 and 25 degrees C. The extent of unfolding increased with the pressure level. The structure of beta-lactoglobulin required higher pressures to unfold at pH 2.5 than at pH 6.8. More flexibility was achieved at 37 degrees C than at 25 degrees C. Results indicated that the structural region formed by strands F, G, and H was more resistant to unfold under acidic and neutral conditions. The exposure of Trp19 at an earlier time, as compared to other protein regions, supports the formation of a swollen structural state at pH 2.5. Refolding was achieved faster when beta-lactoglobulin was subjected to 200 MPa than to 400 MPa, to 37 degrees C than to 25 degrees C, and to acidic than to neutral pH. After treatment at 400 MPa for 20 min at neutral pH, the protein native structure was not recovered. All samples at acidic pH showed that the protein quickly regained its structure. Hydrolysis of beta-lactoglobulin by pepsin and chymotrypsin could be related to pressure-induced changes in the structure of the protein. Compared to the behavior of the protein at atmospheric pressure, no increased proteolysis was found in samples with no increased flexibility (100 MPa, 37 degrees C, pH 2.5). Slightly flexible structures were associated with significantly increased proteolysis (100 MPa, 37 degrees C, pH 6.8; 200 MPa, 37 degrees C, pH 2.5). Highly flexible structures were associated with very fast proteolysis (>or=200 MPa, 37 degrees C, pH 6.8; >or=300 MPa, 37 degrees C, pH 2.5). Proteolysis of prepressurized samples improved only when the protein was significantly changed after the pressure treatment (400 MPa, 25 degrees C, 20 min, pH 6.8).

In situ measurements of pH changes in beta-lactoglobulin solutions under high hydrostatic pressure

A novel in situ method, in which the spectral changes of aqueous solutions under pressure are measured using optical pH indicators in a high-pressure spectrophotometer, has been developed in order to provide a quantitative description of the pressure dependence of acid/base equilibria of proteins. The self-consistent method, insensitive to compressibility, was developed for measurement of changes in pH with pressure based on alpha-naphthyl red and neutral red as these indicators were found to have pressure insensitive pKa values. The method was validated for up to 500 MPa by measurement of the pressure-dependence of the weak acid buffers acetic acid/acetate and imidazolium/imidazole from which volumes of dissociation of DeltaV degrees = -11.2 and 3.7 mL/mol, respectively, were established. Succinic acid/hydrogensuccinate was surprisingly insensitive to pressure with DeltaV degrees = -0.9 mL/mol. For beta-lactoglobulin B in an unbuffered aqueous solution with ionic strength of 0.05 M and pH 4, pressure up to 300 MPa increased pH up to 1.5 units depending on concentration (up to 5 mg/mL investigated), followed by a decrease to the initial pH 4 for pressure up to 500 MPa. The surprising increase in pH at pressure up to 300 MPa is suggested to be caused by an increase in the effective pKa values of aspartic acid and glutamic acid side chain in hydrophobic compartments of the protein created by pressure denaturation, leading to a binding of water protons and an increase in free hydroxide ions. For higher pressure the carboxylic side chains in the fully denatured protein again becomes exposed to the solvent, and pH decreases to the initial pH of the aqueous system.