Angiotensin I-Converting Enzyme Inhibitory Peptides from Snakehead Fish Sarcoplasmic Protein Hydrolysate

Peptide derived C. striata albumin as a natural angiotensin-converting enzyme inhibitor

As one of the most popular sources for fish albumin, Channa striata has been considered as a promising substitute for human albumin. However, scientific information regarding its genomic and proteomic is very limited, making its identification rather complicated. In this study, we aimed to isolate, characterize, and examine the bioactivity of protein and peptide derivatives of C. striata albumin. Fractionation of albumin from C. striata extract was conducted using Cohn Process and the yield was evaluated. The peptides were further produced by enzymatic hydrolysis. All these proteins were studied using tricine-SDS PAGE and tested for in vitro ACE inhibition. Dry weights of the Fraction-5, where the albumin was more abundant and purer, was 3.8 ± 2.1%. Based on tricine-SDS PAGE analysis, two bands of protein, e.g., approximately 10 and 13 kDa, were detected with highest intensity found in Fraction-5, which might be albumin of C. striata. An increasing trend of ACE inhibition by the fractions was observed, ranging from 7.09 to 22.99%. The highest ACEI activity was found in peptides from alcalase hydrolysis with molecular size <3 kDa (56.65 ± 2.32%, IC₅₀ 36.93 μg/mL). This value was also statistically significant compared with the non-hydrolyzed Fraction-5 and Parental Fraction, which were 23.48 ± 3.11% (P < 0.05) and 13.02 ± 0.68% (P < 0.01), respectively. Taken together, these findings suggest a promising potential of peptide-derived C. striata albumin for natural antihypertensive agents.

Novel Peptide Sequences with ACE-Inhibitory and Antioxidant Activities Derived from the Heads and Bones of Hybrid Groupers (Epinephelus lanceolatus × Epinephelus fuscoguttatus)

The heads and bones of hybrid groupers are potential precursors for angiotensin-converting enzyme (ACE)-inhibitory and antioxidant peptides. The aim of this study was to isolate the dual-action peptides from the Alcalase-treated head and bone hydrolysate of hybrid groupers followed by identification of the novel peptides. The stability of these peptides against stimulated in vitro gastrointestinal digestion (SGID) was also determined. Fraction HB-IV (less than 1 kDa) obtained from ultrafiltration showed the strongest ACE-inhibition ability (IC50: 0.28 mg/mL), which was comparable to the potency of the commercial supplement, PeptACE (IC50: 0.22 mg/mL). This fraction also demonstrated the highest hydroxyl radical scavenging and metal-chelating activities. However, further fractionation of HB-IV by a series of chromatography resulted in peptide fractions of reduced ACE-inhibitory and antioxidant activities. The hydroxyl radical scavenging and reduction potential of HB-IV were enhanced, whereas ACE-inhibitory and metal-chelating activities were reduced following SGID. A total of 145 peptide sequences were identified from HB-IV, of which 137 peptides were novel to the BIOPEP database. The results suggested that the bioactive peptides isolated from the heads and bones of hybrid groupers could be used as functional foods/ingredients with potential ACE-inhibitory and antioxidant effects.

Nutritional Evaluation of Sea Buckthorn “Hippophae rhamnoides” Berries and the Pharmaceutical Potential of the Fermented Juice

Sea buckthorn is a temperate bush plant native to Asian and European countries, explored across the world in traditional medicine to treat various diseases due to the presence of an exceptionally high content of phenolics, flavonoids and antioxidants. In addition to the evaluation of nutrients and active compounds, the focus of the present work was to assess the optimal levels for L. plantarum RM1 growth by applying response surface methodology (RSM), and to determine the impact of juice fermentation on antioxidant, anti-hypertension and anticancer activity, as well as on organoleptic properties. Sea buckthorn berries were shown to contain good fiber content (6.55%, 25 DV%), high quality of protein (3.12%, 6.24 DV%) containing: histidine, valine, threonine, leucine and lysine (with AAS 24.32, 23.66, 23.09, 23.05 and 21.71%, respectively), and 4.45% sugar that provides only 79 calories. Potassium was shown to be the abundant mineral content (793.43%, 22.66 DV), followed by copper and phosphorus (21.81 and 11.07 DV%, respectively). Sea buckthorn juice exhibited a rich phenolic, flavonoid and carotenoid content (283.58, 118.42 and 6.5 mg/g, respectively), in addition to a high content of vitamin C (322.33 mg/g). The HPLC profile indicated that benzoic acid is the dominant phenolic compound in sea buckthorn berries (3825.90 mg/kg). Antioxidant potentials (DPPH and ABTS) of sea buckthorn showed higher inhibition than ascorbic acid. Antimicrobial potentials were most pronounced against Escherichia coli BA12296 (17.46 mm). The probiotic growth was 8.5 log cfu/mL, with juice concentration, inoculum size and temperature as the main contributors to probiotic growth with a 95% confidence level. Fermentation of sea buckthorn juice with L. plantarum RM1 enhanced the functional phenolic and flavonoid content, as well as antioxidant and antimicrobial activities. The fermentation with L. plantarum RM1 enhanced the anti-hypertension and anticancer properties of the sea buckthorn juice and gained consumers’ sensorial overall acceptance.

An updated review on food-derived bioactive peptides: Focus on the regulatory requirements, safety, and bioavailability

Food-derived bioactive peptides (BAPs) are recently utilized as functional food raw materials owing to their potential health benefits. Although there is a huge amount of scientific research about BAPs' identification, purification, characterization, and physiological functions, and subsequently, many BAPs have been marketed, there is a paucity of review on the regulatory requirements, bioavailability, and safety of BAPs. Thus, this review focuses on the toxic peptides that could arise from their primary proteins throughout protein extraction, protein pretreatment, and BAPs' formulation. Also, the influences of BAPs' length and administration dosage on safety are summarized. Lastly, the challenges and possibilities in BAPs' bioavailability and regulatory requirements in different countries were also presented. Results revealed that the human studies of BAPs are essential for approvals as healthy food and to prevent the consumers from misinformation and false promises. The BAPs that escape the gastrointestinal tract epithelium and move to the stomach are considered good peptides and get circulated into the blood using different pathways. In addition, the hydrophobicity, net charge, molecular size, length, amino acids composition/sequences, and structural characteristics of BAPs are critical for bioavailability, and appropriate food-grade carriers can enhance it. The abovementioned features are also vital to optimize the solubility, water holding capacity, emulsifying ability, and foaming property of BAPs in food products. In the case of safety, the possible allergenic and toxic peptides often exhibit physiological functions and could be produced during the hydrolysis of food proteins. It was also noted that the production of iso-peptides bonds and undesirable Maillard reaction might occur during protein extraction, sample pretreatments, and peptide synthesis.

Isolation, identification and in vivo antihypertensive effect of novel angiotensin I-converting enzyme (ACE) inhibitory peptides from Spirulina protein hydrolysate

The side effects of traditional antihypertensive drugs have driven people's interest in discovery of novel angiotensin-I converting enzyme (ACE) inhibitory peptides with efficiency and safety. Spirulina possesses abundant proteins and...

Purification, characterization and molecular docking study of angiotensin-I converting enzyme (ACE) inhibitory peptide from shortfin scad (Decapterus macrosoma) protein hydrolysate

Hypertension is a threatening chronic disease, which become a global killer among the adult population. The mortality rate increasing day by day even several Angiotensin I-converting enzyme (ACE) inhibitor drugs were introduced. Bioactive peptides derived from aquatic resources exhibits potential ACE inhibitory activity. The objective of this work is to report the purification and molecular docking studies of angiotensin-I converting enzyme (ACE) inhibitory peptide isolated from shortfin scad (Decapterus macrosoma) waste protein hydrolysate (SWH), enzymatically prepared by using alcalase. The purification process included ultrafiltration, gel filtration and reverse phase high performance liquid chromatography (RP-HPLC). Results showed that ultra-filtered peptide fraction (< 3 kDa) possessed the highest ACE inhibitory activity, followed by the fraction 14 by gel filtration. Fraction P obtained by RP-HPLC, with the amino acid sequence of RGVGPVPAA (IC₅₀ = 0.20 mg/ml) was identified. In terms of ACE inhibition, the Lineweaver-Burk plot showed that the SWH peptide obtained acted as a competitive ACE inhibitor. The molecular docking studies showed that the SWH peptide exhibit hydrogen bonds and Pi-interactions with ACE by Z-dock scores. These results showed that the purified peptide isolated from shortfin scad waste hydrolysate has potential antihypertensive properties which could potentially be used as functional food ingredients.

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.

Assessment of the biological activity of fish muscle protein hydrolysates using in vitro model systems

The generation of biologically active fish protein hydrolysates (FPH) is a useful technique to produce value-added products with potential application in the functional food and nutraceutical industries. Fish muscle is an attractive substrate for the production of protein hydrolysates due to its rich protein content, containing 15-25% of total fish protein. This paper reviews the production of protein hydrolysates from fish muscle, most commonly via enzymatic hydrolysis, and their subsequent bioactivities including anti-obesity, immunomodulatory, antioxidant, angiotensin I-converting enzyme (ACE)-inhibitory, anti-microbial, and anti-cancer activities as measured by in vitro testing methods. Disease prevention with FPH potentially offers a safe and natural alternative to synthetic drugs. Small molecular weight (MW) FPHs generally exhibit favourable bioactivity than large MW fractions via enhanced absorption through the gastrointestinal tract. This review also discusses the relationship between amino acid (AA) composition and AA sequence of FPH and peptides and their exhibited in vitro bioactivity.

Dual-enzyme hydrolysis for preparation of ACE-inhibitory peptides from sesame seed protein: Optimization, separation, and identification

To prepare and identify ACE-inhibitory peptides originated from sesame seed protein, peptides with strong ACE-inhibitory activities were obtained via the optimization of protease and hydrolysis conditions, and these peptides were purified and identified by membrane separation, gel filtration, and liquid chromatography-mass spectrometry. Results showed that the dual-enzyme comprised alcalase and trypsin with the enzyme activity ratio of 3:7 was suitable to produce ACE-inhibitory peptides. The highest ACE-inhibitory activity of 98.10 ± 0.26% was obtained at the following parameters, pH 8.35, E/S ratio of 6,145 U/g, and hydrolysis time of 4.4 hr. ISGAQPSLR and VVISAPSK ranked the first and second ACE-inhibitory activity among 15 identified ACE-inhibitory peptides. Both peptides influenced ACE via binding with the S1 pocket, S2 pocket, and Zn²⁺ ion. ISGAQPSLR even impacted the S1' pocket. ISGAQPSLR and VVISAPSK acted as a competitive and noncompetitive inhibitor, respectively. ACE-inhibitory peptides derivated from sesame seed protein have potential applications in functional food. PRACTICAL APPLICATIONS: Although sesame seed protein is proven as the precursor of ACE-inhibitory peptide, preparing ACE-inhibitory peptide from sesame seed protein is still suffering from insufficient information on hydrolysis condition and the peptide sequence. Therefore, the performance of the typical protease on preparing ACE-inhibitory peptide from sesame seed protein has been evaluated, the effect of the amino acid composition of sesame seed protein and cleavage specificity of protease on the generation of ACE-inhibitory peptide has been investigated, hydrolysis conditions have been optimized, the peptide sequence has been identified to illuminate the effect of sesame seed protein fraction on the formation of ACE-inhibitory peptide and discuss the structural characteristics. ACE-inhibitory peptides originating from sesame seed protein could apply in functional food. It is promising for dual-enzyme hydrolysis to utilize in preparation of high-value bioactive peptides.

Comparison of quality and nutritional attributes of pond-cultured and container-cultured snakehead (Channa argus argus) fillets after being boiled, fried, and baked

The objective of this study was to compare the quality and nutritional attributes of snakehead (Channa argus argus) fillets (cultured in ponds and containers) after being heated (boiling, frying, and baking). The results revealed that there were few differences in quality (flavor, color, and texture) and nutritional attributes (content of amino acid, dipeptidyl peptidase IV (DPP-IV) and angiotensin I-converting enzyme (ACE) inhibition activity, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity) of snakehead fillets obtained from two cultured modes. Container-cultured samples exhibited more beneficial effects on flavor (more esters) and bioactivity (ACE inhibition and DPPH scavenging activity) than pond-cultured. Frying increased flavor attributes but decreased nutritional value of fish. Boiling was an effective heating method for increasing quality and nutritional attributes of container-cultured snakehead fish. Generally, the container-cultured mode was applicable for culturing snakehead without decreasing quality and nutritional attributes, which deserved more attention. PRACTICAL APPLICATION: The study provided information about the differences of quality properties (flavor and texture) and nutritional attributes (bioactive functions of simulate-digested products) of pond-cultured and container-cultured snakehead fish after being heated. The results will provide some potential values for the application of container-cultured technology.

Use of Alcalase in the production of bioactive peptides: A review

This review aims to cover the uses of the commercially available protease Alcalase in the production of biologically active peptides since 2010. Immobilization of Alcalase has also been reviewed, as immobilization of the enzyme may improve the final reaction design enabling the use of more drastic conditions and the reuse of the biocatalyst. That way, this review presents the production, via Alcalase hydrolysis of different proteins, of peptides with antioxidant, angiotensin I-converting enzyme inhibitory, metal binding, antidiabetic, anti-inflammatory and antimicrobial activities (among other bioactivities) and peptides that improve the functional, sensory and nutritional properties of foods. Alcalase has proved to be among the most efficient proteases for this goal, using different protein sources, being especially interesting the use of the protein residues from food industry as feedstock, as this also solves nature pollution problems. Very interestingly, the bioactivities of the protein hydrolysates further improved when Alcalase is used in a combined way with other proteases both in a sequential way or in a simultaneous hydrolysis (something that could be related to the concept of combi-enzymes), as the combination of proteases with different selectivities and specificities enable the production of a larger amount of peptides and of a smaller size.

The intake assessment of diverse dietary patterns on childhood hypertension: alleviating the blood pressure and lipidemic factors with low-sodium seafood rich in omega-3 fatty acids

BACKGROUND

Childhood hypertension (CH) is related to the dietary intake and diversity of children. The study aimed to assess the critical role of dietary diversity, and seafood long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs) in reducing CH among the Iranian community.

METHODS

A cross-sectional two-phase study with 7-12-year-old Iranian students was designed. In the initial phase, the socio-demographic characteristics, and blood pressure status (normal, pre-hypertension, and hypertension) based on systolic (SBP) and diastolic (DBP) blood pressure data were assessed. The 24-h dietary recall questionnaire was used to generate the dietary diversity score (DDS, count of consumed food groups) and dietary variety score (DVS, the cumulative number of daily consumed food items). In the second phase, the association between CH reduction and changes in serum 25-hydroxyvitamin D (25OHD), total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein (LDL), and triglycerides (TG) levels of schoolchildren intervened by a seafood diet rich in omega-3 fatty acids were assessed using the regression analyses.

RESULTS

The pre-hypertension and hypertension prevalence rates were 7.8 and 9.15%, respectively. CH was significantly associated with age, gender, and DDS. A significant inverse association was found between the high intake of seafood and CH (P = 0.032). The gas-chromatography analysis showed the high presence of α-linolenic (ALA, 6.72%), eicosapentaenoic (EPA, 7.62%), docosapentaenoic (DPA, 5.88%), and docosahexaenoic (DHA, 18.52%) acids in the seafood-based diet (p <  0.05). The low blood pressure levels with regular consumption of this healthy-functional diet were significantly associated with a reduction in BMI, LDL, TC, and TG, and a remarkable increase in 25OHD and HDL levels. The multiple linear regression showed that the SBP was highly associated with the TC (p <  0.001; β = 0.464).

CONCLUSIONS

The age and DDS were efficient predictors for the different CH status. A regular seafood-rich dietary pattern due to the high LC n-3 PUFAs contents could significantly reduce the obesity-related cardiovascular risk factors.

Antihypertensive and Angiotensin-I-Converting Enzyme (ACE)-Inhibitory Peptides from Fish as Potential Cardioprotective Compounds

The term metabolic/cardiometabolic/insulin resistance syndrome could generally be defined as the co-occurrence of several risk factors inclusive of systemic arterial hypertension. Not only that organizations, such as the world health organization (WHO) have identified high blood pressure as one of the main risk factors of the cardiometabolic syndrome, but there is also a link between the occurrence of insulin resistance/impaired glucose tolerance and hypertension that would consequently lead to type-2 diabetes (T2D). Hypertension is medicated by various classes of synthetic drugs; however, severe or mild adverse effects have been repeatedly reported. To avoid and reduce these adverse effects, natural alternatives, such as bioactive peptides derived from different sources have drawn the attention of researchers. Among all types of biologically active peptides inclusive of marine-derived ones, this paper's focus would solely be on fish and fishery by-processes' extracted peptides and products. Isolation and fractionation processes of these products alongside their structural, compositional and digestion stability characteristics have likewise been briefly discussed to better address the structure-activity relationship, expanding the reader's knowledge on research and discovery trend of fish antihypertensive biopeptides. Furthermore, drug-likeness of selected biopeptides was predicted by Lipinski's rules to differentiate a drug-like biopeptide from nondrug-like one.

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.

Identification and synthesis of multifunctional peptides from wheat germ hydrolysate fractions obtained by proteinase K digestion

Wheat germ protein hydrolysate (WGPH) was obtained by proteinase K digestion, in order to produce bioactive antioxidant and antihypertensive peptides. Response surface methodology (RSM) was used to optimize hydrolysis conditions (enzyme-to-substrate ratio, time, and temperature) for antioxidant activity of hydrolysates. The crude WGPH produced in this way significantly inhibited angiotensin-I converting enzyme (ACE) in a concentration-dependent manner. It was next fractionated by reversed-phase semi-preparative High Performance Liquid Chromatography (HPLC) into 12 fractions that were examined for antioxidant and antihypertensive activities. Fractions with antioxidant and ACE-inhibitory activities were then submitted to further analysis by nano-LC-ESI-MS-MS. Among the various peptides identified, MDATALHYENQK (IC₅₀ : 293.3 ± 6.5 µg/ml) and SGGSYADELVSTAK (IC₅₀ : 265.5 ± 8.3 µg/ml) displayed antioxidant activity and VALTGDNGHSDHVVHF (IC₅₀ : 189.3 ± 4.05 µg/ml), VDSLLTAAK (IC₅₀ : 159.7 ± 0.33 µg/ml), MDATALHYENQK (IC₅₀ : 303.6 ± 2.47 µg/ml), IGGIGTVPVGR (IC₅₀ : 125.7 ± 2.3 µg/ml) and SGGSYADELVSTAK (IC₅₀ : 128.2 ± 1.17 µg/ml) showed good ACE-inhibitory activity. PRACTICAL APPLICATIONS: Wheat milling industries produce massive amounts of wheat germ as by-product that can be converted into valuable compounds. The present research indicates that proteinase K is useful to hydrolyze wheat germ proteins in a search for bioactive peptides with antioxidant and ACE-inhibitory properties. The identified peptides can be regarded as functional food additives, or nutraceuticals to improve human health.

Antihypertensive activity of fish protein hydrolysates and its peptides

The rising interest to utilize nutritionally exorbitant fish proteins has instigated research activities in fish waste utilization. The development of newer technologies to utilize fish waste has fostered use of bioactive value-added products for specific health benefits. Enzymatically obtained Fish Protein Hydrolysate (FPH) is a rich source of biologically active peptides possessing anti-oxidant, anticancer, antimicrobial and anti-hypertensive activity. Isolating natural remedies to combat alarming negative consequences of synthetic drugs has been the new trend in current research promoting identification of antihypertensive peptides from FPH. In this review, we aim to culminate data available to produce antihypertensive peptides from FPH, its composition and potential to be used as a therapeutic agent. These purified peptides are known to be rich in arginine, valine and leucine. Reports reveal peptides with low molecular weight (<1 kDa) and shorter chain length (<20 amino acids) exhibited higher antihypertensive activity. As these peptides have proven Angiotensin Converting Enzyme - I inhibitory activity in vitro and in vivo, their potential to be used as antihypertensive drugs is outrageous. However, current focus on research in the field of molecular docking is necessary to have improved understanding of interaction of the peptides with the enzyme.

Identification of two novel antioxidant peptides from edible bird's nest (Aerodramus fuciphagus) protein hydrolysates

Two novel antioxidant pentapeptides were isolated from EBN hydrolysates with a protective effect against H₂O₂-induced oxidative damage in cancer cell lines.

Angiotensin I Converting Enzyme Inhibitory Peptides Derived from Phycobiliproteins of Dulse Palmaria palmata

We examined the inhibitory activity of angiotensin I converting enzyme (ACE) in protein hydrolysates from dulse, Palmaria palmata. The proteins extracted from dulse were mainly composed of phycoerythrin (PE) followed by phycocyanin (PC) and allophycocyanin (APC). The dulse proteins showed slight ACE inhibitory activity, whereas the inhibitory activity was extremely enhanced by thermolysin hydrolysis. The ACE inhibitory activity of hydrolysates was hardly affected by additional pepsin, trypsin and chymotrypsin treatments. Nine ACE inhibitory peptides (YRD, AGGEY, VYRT, VDHY, IKGHY, LKNPG, LDY, LRY, FEQDWAS) were isolated from the hydrolysates by reversed-phase high-performance liquid chromatography (HPLC), and it was demonstrated that the synthetic peptide LRY (IC₅₀: 0.044 μmol) has remarkably high ACE inhibitory activity. Then, we investigated the structural properties of dulse phycobiliproteins to discuss the origin of dulse ACE inhibitory peptides. Each dulse phycobiliprotein possesses α-subunit (Mw: 17,477–17,638) and β-subunit (Mw: 17,455–18,407). The sequences of YRD, AGGEY, VYRT, VDHY, LKNPG and LDY were detected in the primary structure of PE α-subunit, and the LDY also exists in the APC α- and β-subunits. In addition, the LRY sequence was found in the β-subunits of PE, PC and APC. From these results, it was suggested that the dulse ACE inhibitory peptides were derived from phycobiliproteins, especially PE. To make sure the deduction, we carried out additional experiment by using recombinant PE. We expressed the recombinant α- and β-subunits of PE (rPEα and rPEβ, respectively), and then prepared their peptides by thermolysin hydrolysis. As a result, these peptides showed high ACE inhibitory activities (rPEα: 94.4%; rPEβ: 87.0%). Therefore, we concluded that the original proteins of dulse ACE inhibitory peptides were phycobiliproteins.

Cardioprotective cryptides derived from fish and other food sources: generation, application, and future markets

The primary function of dietary protein is to provide amino acids for protein synthesis. However, protein is also a source of latent bioactive peptides or cryptides with potential health benefits including the control and regulation of blood pressure. Hypertension or high blood pressure is one of the major, controllable risk factors in the development of cardiovascular disease (CVD), and it is also implicated in the development of myocardial infarction, heart failure, and end-stage diabetes. Cryptides can act on various systems of the body including the circulatory, gastrointestinal (GI), nervous, skeletal, and respiratory systems. A number of studies carried out to date have examined the health benefits of food protein isolates and hydrolysates. This review provides an overview of existing blood pressure regulating peptides and products derived from fish and other protein sources and hydrolysates. It discusses the methods used currently to generate and identify cryptides from these sources and their application in food and pharmaceutical products. It also looks at the current market for protein-derived peptides and peptide-containing products, legislation governing their use, and the future development of research in this area.