Antioxidant activity of peptides derived from egg white proteins by enzymatic hydrolysis

This work reports the antioxidant activity of peptides produced by enzymatic hydrolysis of crude egg white with pepsin. Four peptides included in the protein sequence of ovalbumin possessed radical scavenging activity higher than that of Trolox. The hydrolysate of egg white with pepsin for 3 h was previously found to exhibit a strong angiotensin I-converting enzyme (ACE) inhibitory activity in vitro. The combined antioxidant and ACE inhibition properties make it a very useful multifunctional preparation for the control of cardiovascular diseases, particularly hypertension. No correlation was found between antioxidant and ACE inhibitory activities. However, the peptide Tyr-Ala-Glu-Glu-Arg-Tyr-Pro-Ile-Leu, which was a strong ACE inhibitor (50% inhibitory concentration, 4.7 microM) also exhibited a high radical scavenging activity (oxygen radical absorbance capacity-fluorescein value, 3.8 micromol of Trolox equivalent per micromol of peptide) and delayed the low-density lipoprotein lipid oxidation induced by Cu2+ at a concentration of approximately 0.16 mg/mg of low-density lipoprotein. Present results support that antioxidant peptides and amino acids not only act individually, but also cooperatively and synergistically.

Biologically active peptides and enzymatic approaches to their production

This review briefly surveys various classes of biologically active and flavor peptides that have been isolated and characterized in recent years, and analyzes emerging trends and advances in biotechnological methods for their production.

Angiotensin I-converting enzyme inhibitory activity of peptides derived from egg white proteins by enzymatic hydrolysis

The hydrolysis of crude egg white with pepsin, trypsin, and chymotrypsin produced peptides with angiotensin-converting enzyme (ACE) inhibitory properties. These peptides were mainly derived from the proteolysis of ovalbumin. The most active hydrolysates were obtained after treatment with pepsin (50% inhibitory concentration [IC50], 55.3 microg/ml), with the fraction having a molecular mass lower than 3,000 Da giving the highest ACE inhibitory activity (IC50, 34.5 microg/ml). Nine subfractions were collected from the fraction with a molecular mass lower than 3,000 Da using semipreparative reversed-phase high-performance liquid chromatography. Considerable ACE inhibitory activity (IC50 < 40 microg/ml) was found in three of them. These subfractions were analyzed by reversed-phase high-performance liquid chromatography-tandem mass spectrometry, and 14 peptides were identified. These sequences were synthesized, and their ACE inhibitory activities were measured. Among the identified peptides, two novel sequences with potent ACE inhibitory activity were found. The amino acid sequences of these inhibitors were identified as Arg-Ala-Asp-His-Pro-Phe-Leu and Tyr-Ala-Glu-Glu-Arg-Tyr-Pro-Ile-Leu and showed IC50 values of 6.2 and 4.7 microM, respectively.

Effect of the long-term intake of an egg white hydrolysate on the oxidative status and blood lipid profile of spontaneously hypertensive rats

This paper examines the effects of the long-term consumption of egg white hydrolysed with pepsin (hEW) on the antioxidant status and lipid profile of spontaneously hypertensive rats (SHR). The antioxidant capacity was measured by the oxygen radical absorbance capacity (ORAC) and the oxidative status by the malon-dialdehyde (MDA) assay. The lipid profile was analysed spectrophotometrically. The radical-scavenging capacity of the plasma was increased and the MDA concentration in the aorta was decreased in the SHR treated with 0.5g/kg/day of hEW. Our findings indicate that hEW played an important role in antioxidative defence of SHR and exerted a beneficial effect on the lipid profile, lowering triglycerides and total cholesterol without changing HDL levels. Therefore, hEW may be useful to prevent or reverse abnormalities associated with the metabolic syndrome and its complications, such as hypertension, oxidative stress and hyperlipidemia.

Short-term effect of egg-white hydrolysate products on the arterial blood pressure of hypertensive rats

In the present study we evaluate the blood pressure-lowering effect of the following products: the hydrolysate obtained from egg white (EW) by enzymatic treatment with pepsin (HEW), the peptide fraction of HEW with molecular mass lower than 3000 Da (HEW<3000 Da), and three peptide sequences isolated from HEW<3000 Da (Tyr-Ala-Glu-Glu-Arg-Tyr-Pro-Ile-Leu: YAEERYPIL); (Arg-Ala-Asp-His-Pro-Phe-Leu: RADHPFL); and (Ile-Val-Phe (IVF)). These peptides, and also HEW and HEW<3000 Da, had been characterized previously in vitro as potent inhibitors of angiotensin-converting enzyme (ACE). EW and the products mentioned earlier were orally administered by gastric intubation, to 17–20-week-old male spontaneously hypertensive rats (SHR) and normotensive Wistar–Kyoto (WKY) rats. We measured the systolic blood pressure (SBP) and the diastolic blood pressure (DBP) of the rats by the tail cuff method before administration and also 2, 4, 6, 8 and 24h post-administration. Distilled water served as negative control, and we used captopril (50mg/kg) as positive control to carry out similar experiments with a known ACE inhibitor. HEW, HEW<3000 Da and the three peptide sequences decreased SBP and DBP in SHR but they did not modify these variables in WKY rats. The peptide sequences YAEERYPIL, RADHPFL and IVF showed a potency to decrease blood pressure greater than HEW or HEW<3000 Da. The results obtained suggest that the studied products could be used as a functional food with potential therapeutic benefit in the prevention and treatment of hypertension.

Egg white ovalbumin digestion mimicking physiological conditions

Gastrointestinal digestion of ovalbumin (OVA) was simulated using an in vitro system in two steps, which mimicked digestion in the stomach and duodenum, to assess the effect of different gastric pHs, different concentrations of proteases, and the presence of surfactants, such as phosphatidylcholine (PC) and bile salts (BS). OVA was very resistant to pepsin action at an enzyme/substrate ratio that would resemble a physiological situation (1:20 w/w, 172 units/mg) at pH values equal or above 2. The presence of PC did not change the susceptibility of OVA to proteolysis with pepsin. Fluorescence experiments showed that OVA interacted with PC vesicles, particularly at acidic pH, but it is likely that the protein maintained a high degree of conformational stability, resisting pepsin action. The presence of BS at physiological concentrations considerably increased the proteolysis of OVA by a mixture of pancreatic enzymes. The addition of PC made OVA even more sensitive to proteolytic degradation, suggesting that OVA could associate with the surfactants under duodenal conditions, increasing its exposure to pancreatic proteinases. Immunoreactivity against IgE from sera of allergic patients was retained after in vitro gastric digestion, depending on the reactivity of the sera, but it decreased considerably after in vitro duodenal digestion.

Human immunoglobulin E (IgE) binding to heated and glycated ovalbumin and ovomucoid before and after in vitro digestion

This study focuses on the effect of heating and Maillard reaction (MR) on the in vitro digestibility and rabbit IgG- and human IgE-binding properties of ovalbumin (OVA) and ovomucoid (OM) to estimate the impact of processing on their allergenicity. With the human sera studied, heat treatment significantly reduced IgE binding to both OVA and OM, whereas MR reduced the IgE binding to OVA but increased IgE binding to OM. In contrast, heat treatment significantly favored OVA digestibility but glycation impaired it, and these treatments did not affect the digestibility of OM. The changes observed in the digestibility affected the immunogenicity of the digests accordingly, so that the higher the digestibility, the lower the antibody binding. Heat treatment and glycation by MR showed an influence on the potential allergenicity of the main egg white proteins that could be related to their resistance to denaturation and digestive enzymes.

Vascular effects, angiotensin I-converting enzyme (ACE)-inhibitory activity, and antihypertensive properties of peptides derived from egg white

In this study, we have identified novel antihypertensive peptides derived from egg-white proteins. The sequences YRGGLEPINF and ESIINF produced an acute blood-pressure-lowering effect in spontaneously hypertensive rats upon a single oral administration. Our results suggest that the antihypertensive action could be attributed to a vascular-relaxing mechanism that would occur in vivo independently of angiotensin I-converting enzyme (ACE) inhibition, because neither these peptides nor their main digestion fragments, except for the dipeptide YR, acted as ACE inhibitors in vitro. The vasodilator and antihypertensive activity of the sequences ESI and NF would explain the blood-pressure-lowering effect of ESIINF. With regard to YRGGLEPINF, in addition to NF, YR appeared as the main fragment responsible for its activity. The dipeptide YR, named kyotorphin and previously identified as an endogenous analgesic neuropeptide in the central nervous system, showed strong vasodilator and antihypertensive properties. The structure-activity features of the vasodilator peptides are discussed.

Effect of simulated gastrointestinal digestion on the antihypertensive properties of ACE-inhibitory peptides derived from ovalbumin

Food-derived bioactive peptides with ACE-inhibitory properties are receiving special attention due to their beneficial effects in the treatment of hypertension. In this work we evaluate the impact of a simulated gastrointestinal digestion on the stability and activity of two bioactive peptides that derive from ovalbumin by enzymatic hydrolysis, YAEERYPIL and RADHPFL. These peptides possess in vitro ACE-inhibitory activity and antihypertensive activity in spontaneously hypertensive rats (SHR). The results showed that YAEERYPIL and RADHPFL were susceptible to proteolytic degradation after incubation with pepsin and a pancreatic extract. In addition, their ACE-inhibitory activity in vitro decreased after the simulated digestion. The antihypertensive activity on SHR of the end products of the gastrointestinal hydrolysis, YAEER, YPI, and RADHP, was evaluated. The fragments YPI and RADHP significantly decreased blood pressure, 2 h after administration, at doses of 2 mg/kg, but they probably did not exert their antihypertensive effect through an ACE-inhibitory mechanism. It is likely that RADHP is also the active end product of the gastrointestinal digestion of the antihypertensive peptides FRADHPFL (ovokinin) and RADHPF (ovokinin 2-7).

Assessment of the quality of dairy products by capillary electrophoresis of milk proteins

This paper presents an overview of existing capillary electrophoretic methods for the study of milk proteins. The main methods of analysis of caseins, whey proteins and peptides are examined with particular attention to their application to the evaluation of the quality of dairy products. Aspects such as the study of protein polymorphism, evaluation of heat treatments, detection of adulteration and assessment of proteolysis are considered in detail.

Micellar changes induced by high pressure. influence in the proteolytic activity and organoleptic properties of milk

We investigated the effects of high-pressure treat-of 25 to 60 degrees C, on micelle structure, proteolytic activity, and sensory properties of milk. Pressure treatments at 25 degrees C considerably reduced micelle size, while pressurization at higher temperatures progressively increased micelle dimensions. Pressure-induced denaturation of beta-lactoglobulin (beta-LG) amounted 76% at 25 degrees C and was almost 100% in milks treated at 40 to 60 degrees C. alpha -Lactalbumin (alpha-LA) was resistant to pressure at temperatures up to 40 degrees C, but its denaturation reached 56% at 60 degrees C. Plasmin resisted pressurization at room temperature; however, pressure treatments at higher temperatures increased plasmin inactivation, which reached 86.5% at 60 degrees C. Pressurization at temperatures from 40 to 60 degrees C reduced the proteolytic activity and improved the organoleptical properties of milk, compared with the same treatments at 25 degrees C, which suggested that these combined treatments could be used to produce milk of good sensory properties with an increased shelf life. These results are discussed in the light of the changes found in micellar structure.

High-pressure effects on Maillard reaction between glucose and lysine

Glucose-lysine model systems prepared over a range of pH values (5-10) in unbuffered and buffered media were incubated at 60 degrees C either under atmospheric pressure or at 400 MPa. The results obtained showed that high pressure affected in different ways the different stages of the Maillard reaction and that such effects were strongly influenced by pressure-induced changes in the pH of the systems. In unbuffered media, at an initial pH < or =8.0, the formation of Amadori rearrangement products (ARP) was not considerably affected by pressure, whereas the intermediate and advanced stages of the Maillard reaction were suppressed, suggesting a retardation of the degradation of the ARP. In buffered media, at pH values < or =8.0, pressure slowed the Maillard reaction from the initial stages. These effects are attributed to the pH drop caused by the pressure-induced dissociation of the acid groups. In unbuffered and buffered media at initial pH = 10.2, high pressure accelerated the formation and subsequent degradation of ARP, leading to increased levels of intermediate and advanced reaction products.

Egg proteins as allergens and the effects of the food matrix and processing

Hen eggs are an important and inexpensive source of high-quality proteins in the human diet. Egg, either as a whole or its constituents (egg yolk and white), is a key ingredient in many food products by virtue of its nutritional value and unique functional properties, such as emulsifying, foaming, and gelling. Nevertheless, egg is also known because of its allergenic potential and, in fact, it is the second most frequent source of allergic reactions, particularly in children. This review deals with the structural or functional properties of egg proteins that make them strong allergens. Their ability to sensitize and/or elicit allergic reactions is linked to their resistance to gastroduodenal digestion, which ultimately allows them to interact with the intestinal mucosa where absorption occurs. The factors that affect protein digestibility, whether increasing it, decreasing it, or inducing a different proteolysis pattern, and their influence on their capacity to induce or trigger an allergic reaction are discussed. Special attention is paid to the effect of the food matrix and the processing practices on the capacity of egg proteins to modulate the immune response.

Pepsin Egg White Hydrolysate Ameliorates Obesity-Related Oxidative Stress, Inflammation and Steatosis in Zucker Fatty Rats

The aim of this work was to evaluate the effect of the administration of egg white hydrolysates on obesity-related disorders, with a focus on lipid metabolism, inflammation and oxidative stress, in Zucker fatty rats. Obese Zucker rats received water, pepsin egg white hydrolysate (750 mg/kg/day) or Rhizopus aminopeptidase egg white hydrolysate (750 mg/kg/day) for 12 weeks. Lean Zucker rats received water. Body weight, solid and liquid intakes were weekly measured. At the end of the study, urine, faeces, different organs and blood samples were collected. The consumption of egg white hydrolysed with pepsin significantly decreased the epididymal adipose tissue, improved hepatic steatosis, and lowered plasmatic concentration of free fatty acids in the obese animals. It also decreased plasma levels of tumor necrosis factor-alpha and reduced oxidative stress. Pepsin egg white hydrolysate could be used as a tool to improve obesity-related complications.

Long-term intake of egg white hydrolysate attenuates the development of hypertension in spontaneously hypertensive rats

This paper evaluates the effect of the long-term intake of a hydrolysate of egg white with pepsin (HEW), with a potent angiotensin converting enzyme inhibitory activity, on the development of hypertension of spontaneously hypertensive rats (SHR). After being weaned, male 3-week-old SHR were randomly divided into five groups that were given until the 20th week of life the following drinking fluids: (1) tap water, (2) non-treated egg white 1 g/kg/day, (3) captopril 100 mg/kg/day, (4) HEW 0.5 g/kg/day, and (5) HEW 1 g/kg/day. From the 20th to 25th week of life, animals from all groups were given tap water. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured weekly in the rats, from the 6th to 25th week of life, by the tail cuff method. Development of hypertension was attenuated in the groups treated with captopril and HEW (P<0.001 vs. the group that drunk tap water). At the 20th week of life, the arterial blood pressure values of the different groups of rats were: tap water (SBP = 219.5 +/- 5.7, DBP = 167 +/- 3.7), non-treated egg white (SBP = 206.4 +/- 1.43, DBP = 166.4 +/- 4.9), captopril (SBP = 131.7 +/- 2.74, DBP = 91.5 +/- 1.62), HEW 0.5 g/kg/day (SBP = 182.9 +/- 4.64, DBP = 127.5 +/- 2.1) and HEW 1 g/kg/day (SBP = 177.7 +/- 4.72, DBP = 120.1 +/- 2.4). SBP and DBP increased in the treated SHR when the corresponding antihypertensive treatment was removed. In spite of this, SBP remained lower in the SHR that had received captopril and HEW than in the SHR of the control groups (P<0.05). The present results suggest that HEW could be used as a functional food with antihypertensive activity.

Vasodilator effects of peptides derived from egg white proteins

The aim of this work was to investigate the effect of several peptides, identified before and after simulated gastrointestinal digestion of an egg white hydrolysate, on the vascular function, in rat aorta. The sequences IVF, RADHPFL and YAEERYPIL (0.1 mM) induced vasodilatation in intact aortic rings, with the maximum percentage of dilation corresponding to RADHPFL (40.5+/-7.0%). Two of the end products of the gastrointestinal digestion, RADHP and YPI, also showed vasodilator activity with degrees of relaxation higher than 50%. However, all these peptides failed to induce relaxation in endothelium-denuded aortic rings. The relaxation induced by RADHP was concentration-dependent and it was partially blocked by the nitric oxide synthase inhibitor L-NAME (100 microM) and by the B(1) bradykinin receptor antagonist Des-HOE 140 (30 nM), thus showing that it was mediated by NO production through the activation of B(1) bradykinin receptors. These findings suggest that these peptides could reduce the vascular resistance and could be used as functional food ingredients in the prevention and treatment of hypertension.

Functional Improvement of Milk Whey Proteins Induced by High Hydrostatic Pressure

High pressure is emerging as a new processing technology that produces particular changes in the molecular structure of proteins and thus gives rise to new properties inaccessible via conventional methods of protein modification. This review deals with the main effects of high hydrostatic pressure on the physicochemical characteristics of milk whey proteins and how modifications in their structural properties contribute to functionality. In this paper the mechanism underlying pressure-induced changes in ss-lactoglobulin, a-lactabumin, and bovine serum albumin is explained, and related to functional properties such as gel-forming ability, emulsifying activity, or foaming capacity. The possibility of using high pressures to favor chemical reactions of proteins with other food components, such as carbohydrates, to produce novel molecules with new food uses is also considered.

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.