Primary and secondary structure of novel ACE-inhibitory peptides from egg white protein

Peptidomics and molecular dynamics on bioactive peptides produced and characterized from the fermented whey of "Panchali" sheep of West India

The study assessed the peptide production by using potent Lactiplantibacillus plantarum KGL3A (MG722814) culture to ferment the sheep milk for evaluation of α-glucosidase inhibition, ACE inhibition, α-amylase inhibition, & inhibiting lipase activities. The maximal ACE inhibitory, α-amylase, α-glucosidase, & lipase inhibiting actions were 71.69 %, 71.32 %, 67.14 %, and 64.15 %, respectively, at 37 °C after 48 h. Proteolytic activity was tested at various incubation times & inoculation rates to maximise the conditions for growth and the greatest action (9.38 mg/mL) was reported at 2.5 % rate of inoculation after incubation of 48 h. The anti-diabetic as well as ACE inhibitory properties of less than 3 kDa were maximum in contrast to >3 kDa, <10 kDa, and > 10 kDa cut-off fractions. Further, when LPS stimulation is applied to RAW 267.4 macrophage cells, the overabundance generation of IL-6, IL-1β, NO, and TNF-α is greatly reduced by using KGL3A to ferment sheep milk. 2D gel electrophoresis & SDS-PAGE were utilized in relation to protein purifications. Maximum numbers of sheep milk's fermented protein bands were present, about 10 to 124 kDa by SDS-PAGE, and 38 spots of protein were discovered using 2D gel chromatography. Ultra-filtered fractions water soluble extracts (WSEs) were employed in RP-HPLC to differentiate between various peptide fractions. The peptide sequences produced were matched using the databases of AHTPDB and BIOPEP to match hypertensive peptides & antidiabetic peptides, respectively. Furthermore, the discovered peptide sequences from the fermenting sheep milk was studied due to their penchant for binding against the active locations of human bile salt activated lipase (hBAL); human maltase-glucoamylase (hMGA); human pancreatic alpha-amylase (hPAM); & human angiotensin-converting enzyme (hACE) through molecular docking.

In vitro protein digestive properties and peptidomic characterization of five whole component plant protein beverages using a pepsin-pancreatin model

Plant protein has received great attention for its potential nutrition and health benefits. In this study, the digestive properties and peptidomics of whole component plant protein beverages from soybean, chick pea, pea, oat, and quinoa were characterized using an in vitro pepsin-pancreatin digestion model. The study found that quinoa beverage had a higher in vitro protein digestibility (80.49 %), followed by pea, soybean, chick pea, and oat beverage (79.25-70.89 %). Additionally, quinoa and soybean beverage showed comparably higher in vitro digestible indispensable amino acid score (DIAAS) of 81-97, while chick pea and pea beverage had lower in vitro DIAAS of 58-79 due to low concentration of sulfur-containing AA (SAA). Meanwhile, peptides with molecular weight (MW) below 1 kDa occupied more than 93 % of the digested fraction in quinoa beverage, which might result in its higher DPPH scavenging activity, ABTS scavenging activity and ACE inhibitory activity with the IC50 value of 2.80, 0.20 and 0.90 mg/mL, respectively. Peptidomics characterization combined with rapid screening by PeptideRanker and BIOPEP database further suggested that cereals, especially oat and quinoa, released potentially bioactive peptides with a higher percentage (30.89 % and 22.81 %, respectively) compared to legumes like soybean and chick pea (13.30-18.52 %). Additionally, the identified active peptides were more likely to be derived from globular proteins. The methods and data here provided a reference for a better understanding of the digestive properties and nutritional recommendations of whole component plant protein product.

Identification, structural characterization, and molecular dynamic simulation of ACE inhibitory peptides in whey hydrolysates from Chinese Rushan cheese by-product

To realize the high-value utilization of Rushan cheese by-product, Rushan cheese whey was used as a raw material to prepare angiotensin-Ⅰ-converting enzyme inhibitory peptides (ACEIPs). After enzymatic hydrolysisn and ultrafiltration, the sequences of peptides were identified by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Two novel ACE inhibitory peptides Phe-Asp-Arg-Pro-Phe-Leu (FDRPFL) and Lys-Trp-Glu-Lys-Pro-Phe (KWEKPF) were identified. Additionally, both of the peptides exhibited good water-solubility and no toxicity according to in-silico prediction. Fourier transform infrared spectroscopy results show that both FDRPFL and KWEKPF were enriched in β-turn and β-sheet structures. Lineweaver-Burk plots revealed that FDRPFL and KWEKPF exhibited non-competitive and mixed inhibition patterns, respectively. Molecular docking and MD simulation showed that hydrogen bonds and ionic bonds forces allowed FDRPFL and KWEKPF to form stable and compact complexes with ACE. In conclusion, enzymatic hydrolysis of Rushan cheese by-products yields bioactive peptides, increases the added value of whey and reduces environmental pollution.

Extracellular collagenase isolated from Streptomyces antibioticus UFPEDA 3421: purification and biochemical characterization

Collagenases are proteases able to degrade native and denatured collagen, with broad applications such as leather, food, and pharmaceutical industries. The aim of this research was to purify and characterize a collagenase from Streptomyces antibioticus. In the present work, the coffee ground substrate provided conditions to obtaining high collagenase activity (377.5 U/mL) using anion-exchange DEAE-Sephadex G50 chromatographic protocol. SDS-PAGE revealed the metallo-collagenase with a single band of 41.28 kDa and was able to hydrolyzed type I and type V collagen producing bioactive peptides that delayed the coagulation time. The enzyme activity showed stability across a range of pH (6.0-11) and temperature (30-55 °C) with optima at pH 7.0 and 60 °C, respectively. Activators include Mg+2, Ca+2, Na+, K+, while full inhibition was given by other tested metalloproteinase inhibitors. Kinetic parameters (Km of 27.14 mg/mol, Vmax of 714.29 mg/mol/min, Kcat of 79.9 s-1 and Kcat/Km of 2.95 mL/mg/s) and thermodynamic parameters (Ea of 65.224 kJ/mol, ΔH of 62.75 kJ/mol, ΔS of 1.96 J/mol, ΔG of 62.16 kJ/mol, ΔGE-S of 8.18 kJ/mol and ΔGE-T of -2.64 kJ/mol) were also defined. Coffee grounds showed to be an interesting source to obtaining a collagenase able to produce bioactive peptides with anticoagulant activity.

Insight into the molecular mechanism underlying the enhancement of antioxidant activity in ovalbumin by high-energy electron beam irradiation

The effects of high-energy electron beam irradiation (HE-EBI) at various doses (0, 25, 50, 75, and 100 kGy) on the antioxidant activity of ovalbumin (OVA) were studied, and the molecular mechanism was investigated. The results showed that the antioxidant activity of HE-EBI-treated OVA was significantly enhanced in a dose-dependent manner. The irradiated OVA structure gradually unfolded to form a "honeycomb" structure, exposing the buried hydrophobic and free sulfhydryl groups inside the molecule. Two oxidation sites (M35 and T170), adjacent to the antioxidant peptide were identified by mass spectrometry, possibly exposing the antioxidant peptide through structural deconvolution. In addition, aspartic residues generated dicarbonyl compound under high-energy electron beam stress, and its accumulation further enhanced the antioxidant activity. Conclusively, HE-EBI can enhance the antioxidant activity of OVA through ionization effects, providing valuable information for the potential application of HE-EBI in the food industry.

Identification and Molecular Mechanism of Novel Immunomodulatory Peptides from Gelatin Hydrolysates: Molecular Docking, Dynamic Simulation, and Cell Experiments

The purpose of this study was to identify donkey-hide gelatin-derived immunomodulatory peptides targeting Toll-like receptor 4-myeloid differentiation 2 (TLR4-MD2) and elucidate their binding modes using physicochemical property prediction, molecular docking, molecular dynamics simulations, and in vitro cell experiments. After hydrolyzing gelatin, 519 peptides were identified by liquid chromatography-tandem mass spectrometry. Peptides VQLSGEEK and GFSGLDGAKG bound to TLR4-MD2 with high binding affinity. In TLR4-MD2, Arg90, Ser118, Phe126, Tyr131, and Arg264 were key residues involved in the binding of these peptides. The RMSD and R_g values demonstrated that VQLSGEEK-TLR4-MD2 and GFSGLDGAKG-TLR4-MD2 complexes had stable and compact conformations. VQLSGEEK and GFSGLDGAKG were found to increase the cell viability and phagocytic activity of RAW264.7 macrophages; significantly promote the production of cytokines TNF-α, IL-1β, and IL-6 in cells; and inhibit the overproduction of nitric oxide (NO) and cytokines in lipopolysaccharide (LPS)-induced RAW264.7 cells. Our results provided preliminary evidence that VQLSGEEK and GFSGLDGAKG could function as two-way immunomodulatory peptides with immunostimulatory and anti-inflammatory activities.

Comparison of Functional Properties of Blood Plasma Collected from Black Goat and Hanwoo Cattle

Slaughterhouse blood is a by-product of animal slaughter that can be a good source of animal protein. This research purposed to examine the functional qualities of the blood plasma from Hanwoo cattle, black goat, and their hydrolysates. Part of the plasma was hydrolyzed with proteolytic enzymes (Bacillus protease, papain, thermolysin, elastase, and α-chymotrypsin) to yield bioactive peptides under optimum conditions. The levels of hydrolysates were evaluated by 15% sodium dodecyl sulfate polyacrylamide gel electrophoresis. The antioxidant, metal-chelating, and angiotensin I-converting enzyme (ACE) inhibitory properties of intact blood plasma and selected hydrolysates were investigated. Accordingly, two plasma hydrolysates by protease (pH 6.5/55°C/3 h) and thermolysin (pH 7.5/37°C/3-6 h) were selected for analysis of their functional properties. In the oil model system, only goat blood plasma had lower levels of thiobarbituric acid reactive substances than the control. The diphenyl picrylhydrazyl radical scavenging activity was higher in cattle and goat plasma than in proteolytic hydrolysates. Ironchelating activities increased after proteolytic degradation except for protease-treated cattle blood. Copper-chelating activity was excellent in all test samples except for the original bovine plasma. As for ACE inhibition, only non-hydrolyzed goat plasma and its hydrolysates by thermolysin showed ACE inhibitory activity (9.86±5.03% and 21.77±3.74%). In conclusion, goat plasma without hydrolyzation and its hydrolysates can be a good source of bioactive compounds with functional characteristics, whereas cattle plasma has a relatively low value. Further studies on the molecular structure of these compounds are needed with more suitable enzyme combinations.

A novel polypeptide-modified fluorescent gold nanoclusters for copper ion detection

Biomolecule-functionalized fluorescent gold nanocluster (AuNCs) have attracted a lot of attention due to good biocompatibility, stable physicochemical properties and considerable cost advantages. Inappropriate concentration of Cu²⁺ may cause a variety of diseases. In this study, AuNCs were synthesized in alkaline aqueous solution using bovine serum albumin (BSA) as a template. And then, the peptide CCYWDAHRDY was coupled to AuNCs. Furthermore, the fluorescence of synthesized CCYWDAHRDY-AuNCs response to Cu²⁺ was evaluated. As the results shown that the CCYWDAHRDY-AuNCs can sensitively detect Cu²⁺. After adding Cu²⁺ to the probe system, the fluorescence of the CCYWDAHRDY-AuNCs was quenched. The detection conditions were at pH 6 and 30 °C for 10 min, the linear relationship between Cu²⁺ concentration and fluorescence intensity were good in the range of 0.1 ~ 4.2 μmol/L. The regression equation was y = − 105.9x + 693.68, the linear correlation coefficient is 0.997, and the minimum detection limit was 52 nmol/L.

Identification and Effects of Skim Milk-Derived Bioactive Antihypertensive Peptides

Bioactive peptides are generated during milk fermentation or enzymatic hydrolysis. Lactobacillus (L) helveticus is commonly used to produce some types of fermented milk products. Fermented milk derived bioactive peptides are known to be beneficial in human health. Anti-hypertensive peptides play a dual role in the regulation of hypertension through the production of the vasoconstrictor angiotensin II and its inactivation of the vasodilator bradykinin. MALDI MS/MS, nano-LC/MS/MS and RP-HPLC were used to isolate peptides showing angiotensin converting enzyme inhibition (ACE-I) from 12% fermented skim milk using a combination of L. helveticus and Flavourzyme®. The fermentation procedure facilitated the identification of 133 anti-hypertensive peptides and 75% short chain amino acids, and the three with the highest ACE-I activity reduced blood pressure in a rat model of hypertension. The freeze- dried extract was supplemented in rodent chow. In this study 14-week-old male spontaneously hypertensive rats were fed for 10 weeks with the identified peptides added to chow and compared to controls supplemented with skim milk powder. Blood pressure (BP) decreased significantly (p < 0.05) from 6 to 10 weeks of FS groups (120/65 mmHg) compared with the NFS control groups, where the BP increased significantly (220/150 mmHg) (p < 0.05). The F6 fraction provided bioactive peptides with stronger antihypertensive properties than other fractions. Skim milk fermented by L. helveticus and Flavourzyme® generates several bioactive peptides which have a blood pressure lowering effect in hypertensive disease.

Advancement and prospects of production, transport, functional activity and structure-activity relationship of food-derived angiotensin converting enzyme (ACE) inhibitory peptides

Food-derived antihypertensive peptides have attracted increasing attention in functional foods for health promotion, due to their high biological activity, low toxicity and easy metabolism in the human body. Angiotensin converting enzyme (ACE) is a key enzyme that causes the increase in blood pressure in mammals. However, few reviews have summarized the current understanding of ACE inhibitory peptides and their knowledge gaps. This paper focuses on the food origins and production methods of ACE inhibitory peptides. Compared with conventional methods, the advanced technologies and emerging bioinformatics approaches have recently been applied for efficient and targeted release of ACE inhibitory peptides from food proteins. Furthermore, the transport and underlying mechanisms of ACE inhibitory peptides are emphatically described. Molecular modeling and the Michaelis-Menten equation can provide information on how ACE inhibitors function. Finally, we discuss the structure-activity relationships and other bio-functional properties of ACE inhibitory peptides. Molecular weight, hydrophobic amino acid residues, charge, amino acid composition and sequence (especially at the C-terminal and N-terminal) have a significant influence on ACE inhibitory activity. Some studies are required to increase productivity, improve bioavailability of peptides, evaluate their bio-accessibility and efficiency on reducing blood pressure to provide a reference for the development and application of health products and auxiliary treatment drugs.

Purification and characterization of a novel angiotensin I-converting enzyme-inhibitory peptide derived from Alaska pollack skins

Hydrolysates containing angiotensin I-converting enzyme (ACE)-inhibitory peptide were prepared from protein of Alaska pollack skins using alcalase and trypsin. The protein hydrolysate was separated by ultrafiltration, Sephadex G-25 gel filtration chromatography and reversed phase high-performance liquid chromatography (HPLC), from which a novel purified peptide was obtained. Both random coil structure and β-sheet in the purified peptide were revealed in Fourier transform infrared spectrum. The amino sequence of the purified peptide was identified as GPLGVP, VLYPVK, VFLENVLR, and FEEF by HPLC-Q-TOF-MS (HPLC-quadrupole time-of-flight mass spectrometry). The peptide GPLGVP whose molecular weight was 538.31 Da showed the highest ACE inhibitory activity (IC₅₀  = 105.8 µM). The purified peptide featured a noncompetitive inhibition kinetic mechanism was shown in the Lineweaver-Burk plots and was susceptible to enzymes as indicated in the studies on stability of gastrointestinal proteases. Moreover, the peptide GPLGVP can combine ACE catalytic pocket through hydrogen bonds and other forces with high binding power as disclosed in molecular docking simulation, which provides the inhibitory effect of GPLGVP on ACE.

Activity and bioavailability of food protein-derived angiotensin-I-converting enzyme-inhibitory peptides

Angiotensin-I-converting enzyme (ACE) inhibitory peptides are able to inhibit the activity of ACE, which is the key enzymatic factor mediating systemic hypertension. ACE-inhibitory peptides can be obtained from edible proteins and have the function of antihypertension. The amino acid sequences and the secondary structures of ACE-inhibitory peptides determine the inhibitory activities and stability. The resistance of ACE-inhibitory peptides to digestive enzymes and peptidase affect their antihypertensive bioactivity in vivo. In this paper, the mechanism of ACE-inhibition, sources of the inhibitory peptides, structure-activity relationships, stability during digestion, absorption and transportation of ACE-inhibitory peptides, and consumption of ACE-inhibitory peptides are reviewed, which provide guidance to the development of new functional foods and production of antihypertensive nutraceuticals and pharmaceuticals.

Bioactive Peptides and Hydrolysates from Egg Proteins as a New Tool for Protection Against Cardiovascular Problems

The aim of the present work is to review the potential beneficial effects of dietary supplementation with bioactive egg protein hydrolysates or peptides on cardiometabolic changes associated with oxidative stress. The development of nutritionally improved food products designed to address specific health concerns is of particular interest because many bioactive food compounds can be potentially useful in various physiological functions such as for reducing oxidative stress. The results presented suggest that egg hydrolysates or derived peptides could be included in the diet to prevent and/or reduce some cardiometabolic complications associated with oxidative stress-related diseases.

Chicken Egg Proteins and Derived Peptides with Antioxidant Properties

In addition to their high nutritional value, some chicken egg proteins and derivatives such as protein hydrolysates, peptides and amino acids show antioxidant properties which make them prominent candidates for the development of functional foods, drawing attention to both the food and biopharmaceutical industries. This review summarizes current knowledge on antioxidant activity of chicken egg proteins and their derived peptides. Some egg proteins such as ovalbumin, ovotransferrin and lysozyme from egg white or phosvitin from yolk have shown antioxidant properties, although derived peptides have higher bioactive potential. The main process for obtaining egg bioactive peptides is enzymatic hydrolysis of its proteins using enzymes and/or processing technologies such as heating, sonication or high-intensity-pulsed electric field. Different in vitro assays such as determination of reducing power, DPPH and ABTS radical-scavenging activity tests or oxygen radical absorbance capacity assay have been used to evaluate the diverse antioxidant mechanisms of proteins and peptides. Similarly, different cell lines and animal models including zebrafish, mice and rats have also been used. In summary, this review collects all the knowledge described so far regarding egg proteins and derived peptides with antioxidant functions.

Identification of ovalbumin-derived peptides as multi-target inhibitors of AChE, BChE, and BACE1

BACKGROUND

Alzheimer's disease (AD) is a kind of progressive neurodegenerative disease that affects the elderly. There is no ideal treatment for AD. Thus, the purpose of this study is to identify anti-AD peptides from ovalbumin.

RESULTS

The potential tripeptides IEK, LYR, and CIK were selected for molecular docking. The '-CDOCKER_Energy' values of the best docking positions of the tripeptide IEK, LYR, and CIK interacting with acetylcholinesterase (AChE) were 93.8119, 86.9556 and 73.6370 kcal mol^-1 , respectively. The '-CDOCKER_Energy' values for interaction with butyrylcholinesterase (BChE) were 96.6386, 80.8392, and 87.4341 kcal mol^-1 , respectively. Most importantly, the '-CDOCKER_Energy' values for interaction with β-site amyloid precursor protein cleavage enzyme1 (BACE1) were 85.5903, 71.3342, and 68.4290 kcal mol^-1 , respectively. Overall, in vitro assay results demonstrated that the peptide CIK exhibited impressive inhibitory activities against AChE, BChE, and BACE1, with half maximal inhibitory concentration (IC₅₀ ) values of 6.76, 7.72, and 34.48 μmol L^-1 , respectively. In particular, CIK can be joined with some peripheral anion sites (PAS) and catalytic sites on AChE, BChE, and BACE1.

CONCLUSION

Tripeptide CIK can effectively inhibit the activities of AChE, BChE, and BACE1. Tripeptide CIK therefore has the potential to treat AD effectively. © 2020 Society of Chemical Industry.

Novel ACE inhibitors derived from soybean proteins using in silico and in vitro studies

The widespread application of soybean-derived peptides is currently limited due to the challenges in the identification of peptides. In the present work, in silico and in vitro analysis were applied to identify ACE inhibitory tri-peptides from soybean protein. The soybean protein was cleaved by PeptideCutter. Then, unknown tri-peptides were selected to solubility estimation and ADME prediction. Subsequently, Discovery Studio was applied to evaluate the interaction mechanism between ACE and tri-peptides. Finally, in vitro activity of theoretical ACE inhibitory tri-peptides was verified by RP-HPLC method. As a result, DMG was selected as a potent ACE inhibitory peptide. Cell experiment showed that DMG had no cytotoxic effects on HEK-293 cells. And molecular docking results indicated that DMG contacted well with ACE's active sites (Gln281, His353, Ala354, Glu384, Lys511, His513, and Tyr520). Furthermore, DMG could exert potent activity against ACE, with IC50 value of 3.95 ± 0.11 mM. PRACTICAL APPLICATIONS: Present research showed soybean is a potential protein resource to obtain ACE inhibitory peptides. Simultaneously, virtual screening method is a feasible way to substitute for classical method in emerging nutritional fields. What's more, present study provides a theoretical basis for industrial research on foodstuff for ACE inhibitory peptides without side effects.

Marine Organisms as Potential Sources of Bioactive Peptides that Inhibit the Activity of Angiotensin I-Converting Enzyme: A Review

Angiotensin I-converting enzyme (ACE) is a paramount therapeutic target to treat hypertension. ACE inhibitory peptides derived from food protein sources are regarded as safer alternatives to synthetic antihypertensive drugs for treating hypertension. Recently, marine organisms have started being pursued as sources of potential ACE inhibitory peptides. Marine organisms such as fish, shellfish, seaweed, microalgae, molluscs, crustaceans, and cephalopods are rich sources of bioactive compounds because of their high-value metabolites with specific activities and promising health benefits. This review aims to summarize the studies on peptides from different marine organisms and focus on the potential ability of these peptides to inhibit ACE activity.

Identification and Characterization of Gastrointestinal-Resistant Angiotensin-Converting Enzyme Inhibitory Peptides from Egg White Proteins

Egg proteins are recognized as excellent sources of bioactive peptides, such as angiotensin-converting enzyme inhibitory (ACEi) peptides. Oral administration of a thermolysin-digested egg white hydrolysate (T-EWH) caused a significant blood pressure reduction in spontaneously hypertensive rats; a further ACEi assay implied that its ACEi activity was enhanced after in vitro gastrointestinal (GI) digestion. These results indicated that T-EWH contained ACEi peptides resisting GI digestion and/or being further released during GI digestion. Therefore, the objective of this study was to identify these responsible ACEi peptides from T-EWH. The conventionally activity-guided fractionation was applied, coupled with a synchronized GI digestion throughout, during which both peptide yield and ACEi activity before and after the GI digestion were measured. Finally, six ACEi peptides (LAPYK, LKISQ, LKYAT, INKVVR, LFLIKH, and LGHWVY) with good GI resistance were identified with IC₅₀ values <20 μM, especially LKYAT (0.09 μM). The structure-activity relationship of these peptides was discussed. The discovery of GI-resistant ACEi peptides could further support the application of egg white proteins as functional food ingredients.

Food-derived bioactive peptides and their role in ameliorating hypertension and associated cardiovascular diseases

Non-communicable diseases including cardiovascular diseases (CVDs) and associated metabolic disorders are responsible for nearly 40 million deaths globally per year. Hypertension or high blood pressure (BP) is one of the primary reasons for the development of CVDs. A healthy nutritional strategy complementing with physical activity can substantially reduce high BP and prevent the occurrence of CVD-associated morbidity and mortality. Bioactive peptides currently are the next wave of the promising bench to clinic options for potential targeting chronic and acute health issues including hypertension. Peptides demonstrating anti-inflammatory, anti-oxidant, and angiotensin-converting enzyme-I inhibitory activity are widely studied for the amelioration of hypertension and associated CVDs. Isolating these potent bioactive peptides from different food sources is a promising endeavor toward nutraceutical based dietary management and prevention of hypertension. Understanding the pathophysiology of hypertension and the action mechanisms of the bioactive peptides would complement in designing and characterizing more potent peptides and suitable comprehensive dietary plans for the prevention of hypertension and associated CVDs.

In vitro Angiotesin-1-converting enzyme, α-amylase and α-glucosidase inhibitory and antioxidant activities of Luffa cylindrical (L.) M. Roem seed protein hydrolysate

In recent times, researchers have explored food derived peptides to circumvent the side effects of synthetic drugs. This study therefore examined the amino acid constituents, in vitro antioxidant activities, angiotensin-1-converting enzyme (ACE), α-glucosidase and α-amylase inhibition kinetics of protein hydrolysate obtained from the seed of Luffa cylindrica. The peptide yield by pepsin (16.93 ± 0.28%) and trypsin (13.20 ± 1.02%) were significantly lower than that of Alcalase (34.04 ± 1.96%). Alcalase hydrolysate however displayed the highest ferric reducing antioxidant capacity (FRAC), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and H₂O₂ scavenging activities (0.63%, 85.88% and 41.69% respectively), while the highest superoxide scavenging activity was shown by peptic hydrolysate (57.89%). The ACE inhibition by the hydrolysates with IC₅₀ of 0.32-0.93 mg/mL, increased as the concentration of the peptic hydrolysate increased with the highest ACE-inhibitory activity (74.99 ± 0.43%) at 1.2 mg/mL of peptic hydrolysate. Tryptic and Alcalase hydrloysates exhibited a strong α-amylase inhibition having 27.96 ± 0.06% and 36.36 ± 0.71% inhibitory capacity respectively with IC₅₀ of 1.02-3.31 mg/mL. Alcalase hydrolysates demonstrated the strongest inhibition (65.81 ± 1.95%), followed by tryptic hydrolysates (54.53 ± 0.52%) in a concentration-dependent inhibition of α-glucosidase (IC_{50 ,} 0.48-0.80 mg/mL). Kinetic analysis showed that ACE-inhibition by different concentrations of Alcalase, pepsin and trypsin hydrolysates is uncompetitive, mixed-type and non-competitive respectively. α-Amylase was non-competitively inhibited while α-glucosidase was un-competitively inhibited by all the hydrolysates. The total amino acid concentration for Alcalase, trypsin and pepsin hydrolysates was 53.51g/100g, 75.40g/100g and 85.42g/100g of Luffa cylindrica seed protein hydrolysate respectively, with glutamate being the most concentrated essential amino acid in all the three hydrolysates. From these results, it can be deduced that Luffa cylindrica seed Alcalase and tryptic protein hydrolysates may play critical and indispensible role as bio-tools in diabetes and hypertension treatment.

Egg proteins: fractionation, bioactive peptides and allergenicity

Eggs are an important source of macro and micronutrients within the diet, comprised of proteins, lipids, vitamins, and minerals. They are constituted by a shell, the white (containing 110 g kg^-1 proteins: ovalbumin, ovotransferrin, ovomucoid, lysozyme and ovomucin), and the yolk (containing 150-170 g kg^-1 proteins: lipovitellins, phosvitin, livetins, and low-density lipoproteins). Owing to their nutritional value and biological characteristics, both the egg white and yolk proteins are extensively fractionated using different techniques (e.g., liquid chromatography, ultrafiltration, electrophoresis, and chemical precipitation), in which liquid chromatography is the most commonly used technique to obtain individual proteins with high protein recovery and purity to develop novel food products. However, concerns over allergenic responses induced by certain egg proteins (e.g., ovomucoid, ovalbumin, ovotransferrin, lysozyme, α-livetin, and lipoprotein YGP42) limit their widespread use. As such, processing technologies (e.g., thermal processing, enzymatic hydrolysis, and high-pressure treatment) are investigated to reduce the allergenicity by conformational changes. In addition, biological activities (e.g., antioxidant, antimicrobial, antihypertensive, and anticancer activities) associated with egg peptides have received more attention, in which enzyme hydrolysis is demonstrated as a promising way to break polypeptides sequences and produce bioactive peptides to provide nutritional and therapeutic benefits for human health. © 2018 Society of Chemical Industry.

Anti-Alzheimers activity and molecular mechanism of albumin-derived peptides against AChE and BChE

Alzheimer's disease (AD) is a global health issue affecting millions of elderly people worldwide. The aim of the present study was to identify novel anti-AD peptides isolated from albumin. Anti-AD activities of the peptides were evaluated via inhibitory activities on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Furthermore, the potential molecular mechanisms of the KLPGF/AChE were investigated by CDOCKER of Discovery studio 2017. The results revealed that peptide KLPGF could effectively inhibit AChE with an inhibition rate of 61.23% at a concentration of 50 μg mL^-1. In addition, the peptide KLPGF came in contact with acylation sites and peripheral anion sites of AChE. The present study demonstrates that the peptide KLPGF could become a potential functional food intervention in AD.

Preparation of liposome encapsulating angiotensin-I-converting enzyme inhibitory peptides from sunflower protein hydrolysates

Liposomal angiotensin-I-converting enzyme inhibitory (ACEI) peptides were prepared from sunflower protein hydrolysates by the thin‑film ultrasonic method. Response surface methodology (RSM), in combination with fractional factorial designs and central composite design methods were utilized to optimize entrapment efficiency and balance the drug release. We found that the ratio of phospholipids to cholesterol, ultrasound time and the ratio of phospholipids to ACEI peptides were significant factors affecting entrapment efficiency (P<0.001). Optimal preparation conditions of liposomal‑ACEI peptides were the ratio of soybean phospholipids to cholesterol (w/w) of 4.1:1, PEG‑2000 dosage (%) of 4, NaCl concentration in PBS (mM) of 50, hydration temperature of 45˚C, ultrasound time of 8.05 min and the ratio of soybean phospholipids to ACEI peptides of 15:1 (w/w). The experimental entrapment efficiency of liposomal‑ACEI peptides was (91.25±0.182%). Moreover, the balanced release rate of liposome encapsulated ACEI in phosphate buffer was 77.83% after 12 h.

Egg Protein-Derived Bioactive Peptides: Preparation, Efficacy, and Absorption

The hen's egg is an important protein source of human diet. On average one large egg contains ~6g protein, which contributes to ~11% of daily protein intake. As a high-quality protein, egg proteins are well recognized as excellent sources of bioactive peptides. The objectives of this chapter are to introduce generation, bioactivities, and absorption of egg protein-derived bioactive peptides. Research on egg protein-derived bioactive peptides has been progressed during the past decades. Enzymatic hydrolysis is the major technique to prepare bioactive peptides from egg protein. Quantitative structure-activity relationships-aided in silico prediction is increasingly applied as a promising tool for efficient prediction of novel bioactive peptides. A number of bioactive peptides from egg proteins have been characterized for antioxidant, immunomodulatory, antihypertensive, antidiabetic, anticancer, and antimicrobial activities. Egg protein-derived peptides that can improve bone health have been reported as well. However, molecular mechanisms of many peptides are not fully understood. The stability and absorption routes, bioavailability, safety, and production of bioactive peptides await further investigation.

Structural Basis of Bioactivity of Food Peptides in Promoting Metabolic Health

Bioactive peptides have many structural features that enable them to become functional in controlling several biological processes in the body, especially those related to metabolic health. This chapter provides an overview of the multiple targets of food-derived peptides against metabolic health problems (e.g., hypertension, dyslipidemia, hyperglycemia, oxidative stress) and discusses the importance of structural chemistry in determining the bioactivities of peptides and protein hydrolysates.

Analysis of α-helix unfolding in the pine nut peptide Lys-Cys-His-Lys-Pro induced by pulsed electric field

BACKGROUND

A variety of analytical techniques were applied to explore the effects of pulsed electric field (PEF) on α-helix structural changes in the novel antioxidant peptide Lys-Cys-His-Lys-Pro (KCHKP, 611.76 Da).

RESULTS

The relative α-helix content of the KCHKP peptide was significantly altered from 100% to 89.91 ± 0.97% when the electric pulse frequency was 1800 Hz and the field intensity was 10 kV cm^-1 . Moreover, the 1,1-diphenyl-2-pycryl-hydrazyl (DPPH) and 2,2-azinobis diammonium salt (ABTS) radical-scavenging activities of PEF-treated KCHKP were increased from 56.31% ± 0.74% to 84.33% ± 1.23% and from 40.56% ± 0.78% to 51.33% ± 0.27%, respectively.

CONCLUSION

PEF treatment increased peptide linkage stretch vibration and altered hydrogen bonding of KCHKP. The stability of the α-helix structure was influenced by hydrogen bonds within the peptide linkage of KCHKP induced by PEF and was related to changes in antioxidant activity. © 2017 Society of Chemical Industry.

Bioactive peptides derived from egg proteins: A review

Egg proteins have various functional and biological activities which make them potential precursor proteins for bioactive peptide production. Simulated in vitro gastrointestinal digestion and enzymatic hydrolysis using non-gastrointestinal proteases have been used as tools to produce these peptides. Bioactive peptides derived from egg proteins are reported to display various biological activities, including angiotensin I-converting enzyme (ACE) inhibitory (antihypertensive), antioxidant, antimicrobial, anti-inflammatory, antidiabetic and iron-/calcium-binding activities. More importantly, simulated in vitro gastrointestinal digestion has indicated that consumption of egg proteins has physiological benefits due to the release of such multifunctional peptides. This review encompasses studies reported to date on the bioactive peptide production from egg proteins.

Effects of pulsed electric field on intracellular antioxidant activity and antioxidant enzyme regulating capacities of pine nut (Pinus koraiensis) peptide QDHCH in HepG2 cells

Effects of pulse electric field (PEF) on antioxidant activity of pine nut (Pinus koraiensis) peptide were discussed using H₂O₂-induced HepG2 cells and changes of peptide structures were measured by MIR, NMR and CD spectra. Using HPLC-MS/MS, a novel peptide was identified as QDHCH. After PEF treatment the DPPH and ABTS radical inhibition, and CAA values of QDHCH were increased to 85.13%±0.17%, 95.45%±0.12%, and 4670.10μmol of quercetin equivalents/100g. The PEF-treated QDHCH has better protective oxidative stress inhibitory of 74.22±3.70%, and the T-SOD, CAT, GSH-Px and GSH-Rx activities in cells were significantly increased by 91.92, 7.98, 18.5 and 18.79U/mg prot, while the MDA content was decreased to 8.45±0.71U/mg prot compared with H₂O₂ damaged group. In addition, the hydroxyl radical scavenging activity of QDHCH was increased by 10.53%; the basic structure was not changed by PEF, while the influenced secondary structures may induce the antioxidant activity improvement in HepG2 cells.

Bioactive Peptides in Animal Food Products

Proteins of animal origin represent physiologically active components in the human diet; they exert a direct action or constitute a substrate for enzymatic hydrolysis upon food processing and consumption. Bioactive peptides may descend from the hydrolysis by digestive enzymes, enzymes endogenous to raw food materials, and enzymes from microorganisms added during food processing. Milk proteins have different polymorphisms for each dairy species that influence the amount and the biochemical characteristics (e.g., amino acid chain, phosphorylation, and glycosylation) of the protein. Milk from other species alternative to cow has been exploited for their role in children with cow milk allergy and in some infant pathologies, such as epilepsy, by monitoring the immune status. Different mechanisms concur for bioactive peptides generation from meat and meat products, and their functionality and application as functional ingredients have proven effects on consumer health. Animal food proteins are currently the main source of a range of biologically-active peptides which have gained special interest because they may also influence numerous physiological responses in the organism. The addition of probiotics to animal food products represent a strategy for the increase of molecules with health and functional properties.

Antioxidant Activity Improvement and Evaluation of Structure Changes of SHECN Treated by Pulsed Electric Field (PEF) Technology

The purpose of the study was to evaluate the relationship between antioxidant activity improvement and structure changes of peptide (Ser-His-Glu-Cys-Asn (SHECN) isolated from soybean treated by pulsed electric field (PEF). The two-factor-at-a–time (TFAT) was performed to investigate interaction of electric field intensity (5, 10, 15 and 20 kV/cm) and pulse frequency (1,800 and 2,400 Hz) on antioxidant activity improvement and structure changes. Compared with untreated peptide, DPPH radical inhibition of SHECN was significantly increased to 95.54 ± 0.16 % at optimal conditions (electric field intensity 15 kV/cm, pulse frequency 1,800 Hz and a retention time of 2 h). Results showed that the primary structure of SHECN had not been changed based on the nuclear magnetic resonance analysis. However, the secondary structure of peptide, especially α-helix can be changed. These results suggested that mechanism of antioxidant activity improvement is related to secondary structure changes.

Identification of the core regulators of the HLA I-peptide binding process

During the display of peptide/human leukocyte antigen (HLA) -I complex for further immune recognition, the cleaved and transported antigenic peptides have to bind to HLA-I protein and the binding affinity between peptide epitopes and HLA proteins directly influences the immune recognition ability in human beings. Key factors affecting the binding affinity during the generation, selection and presentation processes of HLA-I complex have not yet been fully discovered. In this study, a new method describing the HLA class I-peptide interactions was proposed. Three hundred and forty features of HLA I proteins and peptide sequences were utilized for analysis by four candidate algorithms, screening the optimal classifier. Features derived from the optimal classifier were further selected and systematically analyzed, revealing the core regulators. The results validated the hypothesis that features of HLA I proteins and related peptides simultaneously affect the binding process, though with discrepant redundancy. Besides, the high relative ratio (16/20) of the amino acid composition features suggests the unique role of sequence signatures for the binding processes. Integrating biological, evolutionary and chemical features of both HLA I molecules and peptides, this study may provide a new perspective of the underlying mechanisms of HLA I-mediated immune reactions.