A novel calcium-binding peptide from Antarctic krill protein hydrolysates and identification of binding sites of calcium-peptide complex

Purification, Identification, Activity Evaluation, and Stability of Antioxidant Peptides from Alcalase Hydrolysate of Antarctic Krill (Euphausia superba) Proteins

For utilizing the largest source of marine proteins, Antarctic krill (Euphausia superba) proteins were defatted and hydrolyzed separately using pepsin, alcalase, papain, trypsin, and netrase, and alcalase hydrolysate (EPAH) showed the highest DPPH radical (DPPH·) and hydroxyl radical (HO·) scavenging activity among five hydrolysates. Using ultrafiltration and chromatography methods, fifteen antioxidant peptides were purified from EPAH and identified as Asn-Gln-Met (NQM), Trp-Phe-Pro-Met (WFPM), Gln-Asn-Pro-Thr (QNPT), Tyr-Met-Asn-Phe (YMNF), Ser-Gly-Pro-Ala (SGPA), Ser-Leu-Pro-Tyr (SLPY), Gln-Tyr-Pro-Pro-Met-Gln-Tyr (QYPPMQY), Glu-Tyr-Glu-Ala (EYEA), Asn-Trp-Asp-Asp-Met-Arg-Ile-Val-Ala-Val (NWDDMRIVAV), Trp-Asp-Asp-Met-Glu-Arg-Leu-Val-Met-Ile (WDDMERLVMI), Asn-Trp-Asp-Asp-Met-Glu-Pro-Ser-Phe (NWD-DMEPSF), Asn-Gly-Pro-Asp-Pro-Arg-Pro-Ser-Gln-Gln (NGPDPRPSQQ), Ala-Phe-Leu-Trp-Asn (AFLWA), Asn-Val-Pro-Asp-Met (NVPDM), and Thr-Phe-Pro-Ile-Tyr-Asp-Tyr-Pro-Gln (TFPIYDPQ), respectively, using a protein sequencer and ESI/MS. Among fifteen antioxidant peptides, SLPY, QYPPMQY and EYEA showed the highest scavenging activities on DPPH· (EC₅₀ values of 1.18 ± 0.036, 1.547 ± 0.150, and 1.372 ± 0.274 mg/mL, respectively), HO· (EC₅₀ values of 0.826 ± 0.027, 1.022 ± 0.058, and 0.946 ± 0.011 mg/mL, respectively), and superoxide anion radical (EC₅₀ values of 0.789 ± 0.079, 0.913 ± 0.007, and 0.793 ± 0.056 mg/mL, respectively). Moreover, SLPY, QYPPMQY and EYEA showed strong reducing power, protective capability against H₂O₂-damaged plasmid DNA, and lipid peroxidation inhibition ability. Furthermore, SLPY, QYPPMQY, and EYEA had high stability under temperatures lower than 80 °C, pH values ranged from 6-8, and simulated GI digestion for 180 min. The results showed that fifteen antioxidant peptides from alcalase hydrolysate of Antarctic krill proteins, especially SLPY, QYPPMQY and EYEA, might serve as effective antioxidant agents applied in food and health products.

Identification, Characterization and Antihypertensive Effect In Vivo of a Novel ACE-Inhibitory Heptapeptide from Defatted Areca Nut Kernel Globulin Hydrolysates

The areca (Areca catechu L.) nut kernel (ANK) is a good potential protein source for its high protein content of 9.89-14.62 g/100 g and a high yield of around 300,000 tons per year in China. However, utilization of the areca nut kernel is limited. To expand the usage of ANK in pharmaceutical or foods industries, areca nut kernel globulin was extracted and angiotensin-I converting enzyme (ACE) inhibition peptides were prepared and identified using gel chromatography, reversed phase HPLC separation, UPLC-ESI-MS/MS analysis and in silico screening. Finally, a novel ACE-inhibitory heptapeptide (Ala-Pro-Lys-Ile-Glu-Glu-Val) was identified and chemically synthesized. The combination pattern between APKIEEV and ACE, and the inhibition kinetics, antihypertensive effect and endothlein-1 inhibition activity of APKIEEV were studied. The results of the molecular docking demonstrated that APKIEEV could bind to four active sites (not the key active sites) of ACE via short hydrogen bonds and demonstrated high ACE-inhibitory activity (IC₅₀: 550.41 μmol/L). Moreover, APKIEEV exhibited a significantly lowering effect on both the systolic blood pressure and diastolic blood pressure of spontaneously hypertensive rats, and had considerable suppression ability on intracellular endothelin-1. These results highlight the potential usage of APKIEEV as ingredients of antihypertensive drugs or functional foods.

The reference genome and transcriptome of the limestone langur, Trachypithecus leucocephalus, reveal expansion of genes related to alkali tolerance

Background

Trachypithecus leucocephalus, the white-headed langur, is a critically endangered primate that is endemic to the karst mountains in the southern Guangxi province of China. Studying the genomic and transcriptomic mechanisms underlying its local adaptation could help explain its persistence within a highly specialized ecological niche.

Results

In this study, we used PacBio sequencing and optical assembly and Hi-C analysis to create a high-quality de novo assembly of the T. leucocephalus genome. Annotation and functional enrichment revealed many genes involved in metabolism, transport, and homeostasis, and almost all of the positively selected genes were related to mineral ion binding. The transcriptomes of 12 tissues from three T. leucocephalus individuals showed that the great majority of genes involved in mineral absorption and calcium signaling were expressed, and their gene families were significantly expanded. For example, FTH1 primarily functions in iron storage and had 20 expanded copies.

Conclusions

These results increase our understanding of the evolution of alkali tolerance and other traits necessary for the persistence of T. leucocephalus within an ecologically unique limestone karst environment.

A specific selenium-chelating peptide isolated from the protein hydrolysate of Grifola frondosa

Background: Grifola frondosa is a type of edible medicinal mushroom with abundant proteins. Selenium (Se) is an essential micronutrient for human. Many animal experiments and clinical studies had indicated that Se plays an important role in diverse physiologic actions. Most inorganic selenium compounds are toxic, and the lowest lethal dose is relatively small. Peptide-Se chelate can probably be dietary supplements in functional foods for humans with Se deficiency. Methods: In this study, a specific tripeptide Arg-Leu-Ala (RLA) with strong Se-chelating capacity was purified from Grifola frondosa through ultrafiltration, reversed-phase HPLC and gel filtration chromatography. The UV, SEM, XRD, 1H NMR spectra are shown to provide more information about characterization of RLA-Se chelates. The bioavailability of RLA-Se chelate in Caco-2 cell line was investigated by using human colon cancer Caco-2 cells as model. iTRAQ comparative proteomics approach were used to identify the differentially expressed proteins. Results: The Se binding capacity of RLA was 84.47 ± 1.21 mg g-1. The results of UV, X-ray diffraction (XRD), 1H NMR and SEM structure analysis showed that the binding of selenium in the hydrolysate of Grifola frondosa protein was successful, and the amino and carboxyl groups of RLA were involved in the coordination of Se, which was the main site of chelation. The results of absorption of RLA-Se chelate in Caco-2 cells showed that RLA-Se chelate could be used as selenium supplement source. Using iTRAQ comparative proteomics approach, 40 proteins found significant. RLA-Se treatment had been demonstrated to present a higher accumulation of Se compared with control treatment and show an effective absorption by Caco-2 with the result that E3 protein performed up regulation. RLA-Se may play roles in cell cycle and apoptosis as an essential micronutrient. To sum up, our research results show that Grifola polypeptide-Se chelate is a promising multifunctional organic selenium product, which can be used as a new functional supplement for selenium deficiency.

Preparation, characterization and in vitro stability of iron-chelating peptides from mung beans

Mung bean protein was enzymatically hydrolyzed with either alcalase, neutral protease, or papain. The mung bean protein hydrolysates (MPH) showed good ability to chelate ferrous ions, and the chelates had high stability in vitro. The hydrolysates prepared by alcalase showed the highest degree of hydrolysis and the highest ferrous chelating rate. Single factor tests showed that the pH and the material ratio had significant effects on ferrous chelating rates. The optimal MPH to FeCl₂·4H₂O material ratio was 8:1 (w/w) and the optimal pH of the reaction was 7.0, which yielded a chelating rate of 96.19 ± 0.94%. The fraction 3 with the highest ferrous chelating activity up to 61.25 ± 1.02 μg/mg was obtained from MPH by affinity chromatography. Meanwhile, the MPH-Fe complex had higher digestive stability than just MPH in both in vitro and acid-alkali tolerance assays. The characterization results showed that ferrous ions mainly combined with the amino, carboxyl, imidazole and other chelating active groups in mung bean peptides to form peptide-iron chelates. Scanning electron microscopy (SEM) analysis showed that mung bean peptide chelated ferrous ions to form polymer particles. These results provided insight into ways to develop functional foods such as iron-fortified cereals.

Chicken foot broth byproduct: A new source for highly effective peptide-calcium chelate

As a means of adding value, chicken foot broth byproduct can be processed to obtain calcium and bioactive peptides from the separated bones and meat residues. In this study, cleaned, dried, and powdered bones yielded 31.4 ± 0.6% calcium content. The meat residues were hydrolyzed to obtain over a hundred distinctive peptides, which were analyzed using LC-MS/MS and the SpirPep web-based tool. The peptides were rich in Glu, Asp, Lys, Gly and Leu, and also exhibited diverse bioactivities, among them primarily inhibition of dipeptidyl peptidase IV and angiotensin-converting enzyme. Calcium chelation assay determined the peptides to bind calcium at 235.7 ± 20.0 mg/g peptide-calcium chelate. Caco-2 cells treated with the chelate at calcium concentrations of 0-10 mM exhibited enhanced absorption relative to CaCl₂. This demonstrates that calcium and chelating peptides generated from the same byproduct can produce peptide-calcium chelate, a potential ingredient in functional foods.

Research progress on applications of calcium derived from marine organisms

Calcium is an important mineral that plays an integral role in human health, especially bone health. Marine biological calcium is an abundant resource that is generally accepted and has a complex active structure. This review evaluates research progress on marine biological calcium with regards to its sources, use of calcium supplements, calcium bioavailability, and novel applications of marine calcium. The potential for future development and the use of products incorporating marine biological calcium in biomedical research and the pharmaceutical, health care, and food industries are also reviewed. The goal of this review is to provide a comprehensive documentation on resource utilization and product development from marine organisms.

Bioactive peptides from food fermentation: A comprehensive review of their sources, bioactivities, applications, and future development

Bioactive peptides (BPs) are specific protein fragments that exert various beneficial effects on human bodies and ultimately influence health, depending on their structural properties and amino acid composition and sequences. By offering promising solutions to solve diverse health issues, the production, characterization, and applications of food-derived BPs have drawn great interest in the current literature and are of particular interest to the food and pharmaceutical industries. The microbial fermentation of protein from various sources is indubitably a novel way to produce BPs with numerous beneficial health effects. Apart from its lower cost as compared to enzymes, the BPs produced from microbial fermentation can be purified without further hydrolysis. Despite these features, current literature shows dearth of information on the BPs produced from food via microbial fermentation. Hence, there is a strong necessity to explore the BPs obtained from food fermentation for the development of commercial nutraceuticals and functional foods. As such, this review focuses on the production of BPs from different food sources, including the extensively studied milk and milk products, with emphasis on microbial fermentation. The structure-activity (antihypertensive, antioxidant, antimicrobial, opiate-like, anti-inflammatory, anticancer/antiproliferative, antithrombotic, hypolipidemic, hypocholesterolemic, and mineral binding) relationship, potential applications, future development, and challenges of BPs obtained from food fermentation are also discussed.

Peptide-Mineral Complexes: Understanding Their Chemical Interactions, Bioavailability, and Potential Application in Mitigating Micronutrient Deficiency

Iron, zinc, and calcium are essential micronutrients that play vital biological roles to maintain human health. Thus, their deficiencies are a public health concern worldwide. Mitigation of these deficiencies involves micronutrient fortification of staple foods, a strategy that can alter the physical and sensory properties of foods. Peptide-mineral complexes have been identified as promising alternatives for mineral-fortified functional foods or mineral supplements. This review outlines some of the methods used in the determination of the mineral chelating activities of food protein-derived peptides and the approaches for the preparation, purification and identification of mineral-binding peptides. The structure-activity relationship of mineral-binding peptides and the potential use of peptide-mineral complexes as functional food ingredients to mitigate micronutrient deficiency are discussed in relation to their chemical interactions, solubility, gastrointestinal digestion, absorption, and bioavailability. Finally, insights on the current challenges and future research directions in this area are provided.

Recent advances on protein separation and purification methods

Protein, as the material basis of vita, is the crucial undertaker of life activities, which constitutes the framework and main substance of human tissues and organs, and takes part in various forms of life activities in organisms. Separating proteins from biomaterials and studying their structures and functions are of great significance for understanding the law of life activities and clarifying the essence of life phenomena. Therefore, scientists have proposed the new concept of proteomics, in which protein separation technology plays a momentous role. It has been diffusely used in the food industry, agricultural biological research, drug development, disease mechanism, plant stress mechanism, and marine environment research. In this paper, combined with the recent research situation, the progress of protein separation technology was reviewed from the aspects of extraction, precipitation, membrane separation, chromatography, electrophoresis, molecular imprinting, microfluidic chip and so on.

Preparation process optimization, structural characterization and in vitro digestion stability analysis of Antarctic krill (Euphausia superba) peptides-zinc chelate

In the study, a novel kind of peptides-zinc (AKP-Zn) chelate was obtained using the Antarctic krill (Euphausia superba) peptides (AKP) as raw material, the reaction was carried out with the mass ratio of the AKP to ZnSO₄·7H₂O of 1:2 at pH 6.0 and 60 °C for 10 min. The structure and composition of the AKP, including particle size, Zeta potential, molecular weight distribution, amino acid composition, microstructure and surface elemental composition, changed significantly after chelating with zinc. The result of Fourier transform infrared spectroscopy indicated that zinc could be chelated by carboxyl oxygen and amino nitrogen atoms of the AKP. Furthermore, compared with zinc sulfate and zinc gluconate, the AKP-Zn chelate was more stable at various pH conditions and the simulated gastrointestinal digestion experiment. These findings would provide a scientific basis for developing new zinc supplements and the high-value utilization of Antarctic krill protein resource.

Use of a combination of the MD simulations and NMR spectroscopy to determine the regulatory mechanism of pulsed electric field (PEF) targeting at C-terminal histidine of VNAVLH

In this study, the targeted regulatory mechanism of pulsed electric field (PEF) was explored for antioxidant activity improvement in four peptides, RGAVIH, RGAVLH, VNAVIH, and VNAVLH, of the pine nut (Pinus koraiensis Sieb. et Zucc). The VNAVLH peptide exhibited the best antioxidant activity and the β-sheet content decreased to a minimum value at 40 kV/cm. Moreover, the chemical shifts of hydrogen atoms of 2-H Asn and 6-H His shifted to a higher magnetic field. The connectivity between N_αH (3.62 ppm) and C_αH (8.10 ppm) of 6-His residue disappeared in PEF-treated peptide. Molecule dynamics (MD) simulation verified that the distances of N_α(H₇₈)-C_α(H₈₀) and H₈₂-O₉₄ increased, whereas -OH and -C_β(H₈₃) got closer in histidine residue after applying the electric field force. Therefore, the antioxidant activity enhancement of VNAVLH might due to the targeted regulation of PEF treatment on N_αH-C_αH and imidazole group in histidine.

Deciphering calcium-binding behaviors of casein phosphopeptides by experimental approaches and molecular simulation

Casein phosphopeptides (CPPs) as premium additives in functional foods can facilitate the transport and adsorption of calcium. The atomic resolution decipherment of calcium-CPP binding behaviors is critical for understanding the calcium bioavailability enhancement potential of CPPs. In the present study, the experimental methods (UV-vis, FTIR and isothermal titration calorimetry) and molecular dynamics simulation were combined to reveal the calcium-binding behaviors of β-casein phosphopeptides (1-25) (P5) with the best capability in carrying calcium ions. We found that it could carry approximately six calcium ions, and the calcium-binding sites were primarily located at the carbonyl group of Glu-2 and the phosphate group of phosphorylated Ser-15, Ser-18, and Ser-19. An interesting finding was that calcium ions could be bound by three coordinated modes, including unidentate, bidentate and tridentate geometries, resulting in the strong binding abilities. The binding process of calcium ions to P5 was spontaneous with the binding free energies of -5.2 kcal mol-1. Hydrophobic interactions were considered to be the major driving force for the calcium ion binding. The present study provides novel molecular insights into the binding process between Ca2+ and calcium-binding peptides.

Peptide-metal complexes: obtention and role in increasing bioavailability and decreasing the pro-oxidant effect of minerals

Bioactive peptides derived from food protein sources have been widely studied in the last years, and scientific researchers have been proving their role in human health, beyond their nutritional value. Several bioactivities have been attributed to these peptides, such as immunomodulatory, antimicrobial, antioxidant, antihypertensive, and opioid. Among them, metal-binding capacity has gained prominence. Mineral chelating peptides have shown potential to be applied in food products so as to decrease mineral deficiencies since peptide-metal complexes could enhance their bioavailability. Furthermore, many studies have been investigating their potential to decrease the Fe pro-oxidant effect by forming a stable structure with the metal and avoiding its interaction with other food constituents. These complexes can be formed during gastrointestinal digestion or can be synthesized prior to intake, with the aim to protect the mineral through the gastrointestinal tract. This review addresses: (i) the amino acid residues for metal-binding peptides and their main protein sources, (ii) peptide-metal complexation prior to or during gastrointestinal digestion, (iii) the function of metal (especially Fe, Ca, and Zn)-binding peptides on the metal bioavailability and (iv) their reactivity and possible pro-oxidant and side effects.

Three Newly Isolated Calcium-Chelating Peptides from Tilapia Bone Collagen Hydrolysate Enhance Calcium Absorption Activity in Intestinal Caco-2 Cells

In this study, we used reversed-phase high performance liquid chromatography (LC) to isolate three novel peptides with calcium-chelating capacity from tilapia bone collagen hydrolysate. Using LC-tandem mass spectrometry, we determined the amino acid sequences to be GPAGPHGPVG, FDHIVY, and YQEPVIAPKL. We then synthesized the three peptides and verified their calcium-chelating activity. Results showed that the calcium-chelating activity of GPAGPHGPVG, FDHIVY, and YQEPVIAPKL reached 18.80 ± 0.49, 35.73 ± 0.74, and 28.4 ± 0.94 mg/g, respectively. We next investigated how each peptide enhanced intestinal calcium absorption using Caco-2 cell monolayers. Compared with the control group, GPAGPHGPVG, FDHIVY, and YQEPVIAPKL potently enhanced calcium transport within 30 min by 89 ± 9, 202 ± 12, and 130 ± 7%, respectively. Results suggest that these peptides isolated from tilapia bone hydrolysate can be used as dietary supplements to increase calcium absorption.

Identification and characterization of the peptides with calcium-binding capacity from tilapia (Oreochromis niloticus) skin gelatin enzymatic hydrolysates

The aim of this study was to isolate and identify the peptides with calcium-binding capacity from the different tilapia skin gelatin enzymatic hydrolysates. The complex protease was selected and its hydrolysates were further separated using gel filtration chromatography (Sephadex G-25) and reverse phase high-performance liquid chromatography. Two purified peptides with strong calcium-binding capacity were identified as Tyr-Gly-Thr-Gly-Leu (YGTGL, 509.25 Da) and Leu-Val-Phe-Leu (LVFL, 490.32 Da). The calcium-binding capacities of YGTGL and LVFL reached 76.03 and 79.50 µg/mg, respectively. The structures of the complex of purified peptides and calcium (YGTGL-Ca and LVFL-Ca) were characterized by ultraviolet-visible spectroscopy (UV-VIS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and mass spectrometry (LC-MS/MS). The results of UV-VIS, SEM, and XRD indicated that YGTGL-Ca and LVFL-Ca were formed as new compounds. The results of FTIR and LC-MS/MS indicated the nitrogen atom of the amino group and the oxygen atom of the carboxyl group in terminates of the peptides provided primary binding sites. Moreover, the hydrophobic amino acids in purified peptides could provide more chelating spaces. This study was of great significance for the development of calcium supplement foods. PRACTICAL APPLICATION: Compared with inorganic calcium and organic calcium, the bioactive gelatin peptide chelated calcium has the characteristics of high utilization rate, high solubility, and high absorption rate. The raw materials are extracted from the tilapia processed waste, which reduce the cost, make full use of resources, and improve the bioavailability. The tilapia skin gelatin peptide calcium chelate can be directly absorbed by the human body, and the absorption efficiency is high, further improving the resource utilization rate and having high economic benefits, which is a comprehensive supplement that can also be used as a functional food.

Systemic lupus erythematosus: Possible localization of trypsin-like and metalloprotease active centers in the protein sequence of the monoclonal light chain (NGTA2-Me-pro-Tr)

It was previously shown that several monoclonal light chains corresponding to the phagemid library of recombinant peripheral blood lymphocyte immunoglobulin light chains of patients with systemic lupus erythematosus specifically hydrolyze only myelin basic protein (MBP). Canonical enzymes usually have only one active site catalyzing some kind of chemical reaction. It was shown previously that in contrast to classical enzymes, preparations of one of the light chains (NGTA2-Me-pro-Tr) showed two optimal pH values, two optimal concentrations of metal ions, and two K_m values for MBP. One protease active site of NGTA2-Me-pro-Tr was trypsin like, whereas second one was metal dependent. In this article, a search for protein sequences of NGTA2-Me-pro-Tr responsible for catalytic functions was carried out. We performed, for the first time, analysis of the homology of the protein sequence of NGTA2-Me-pro-Tr with those of several classical Zn²⁺ - and Ca²⁺ -dependent, as well as human serine, proteases. The analysis allowed us to identify the protein sequences of NGTA2-Me-pro-Tr responsible for serine-like activity, the binding of MBP, and chelation of metal ions and catalysis directly. The data obtained are summarized using hypothetical models of the structure of the two active centers of a very unusual light chain of antibodies (Abs). The findings obtained may be very important for understanding possible structure of active centers of very unusual light chain of Abs possessing several enzymatic activities.

Calcium Delivery System Assembled by a Nanostructured Peptide Derived from the Sea Cucumber Ovum

In this study, the binding mechanism, morphological, and conformational analysis of the complex of a sea cucumber ovum derived octapeptide (EDLAALEK) with Ca²⁺ as well as its calcium delivery behavior via the gastrointestinal (GI) tract were investigated. The Ca²⁺ specifically bound to two carboxyl oxygen atoms of C-terminal Glu and Asp on the EDLAALEK peptide at a stoichiometric ratio of 1:1. Calcium coordination induced the self-assembly of the EDLAALEK peptide, resulting in the formation of a nanocomposite with a crystal structure. Furthermore, the formed nanocomposite went through dissociation and self-assembly during in vitro GI digestion, accompanied by the release and rechelation of Ca²⁺, which was related to changes in their secondary structure. Nevertheless, the GI digests of the EDLAALEK-calcium complex could significantly enhance Ca²⁺ absorption across Caco-2 cell monolayers. The findings suggest that the sea cucumber ovum derived peptide has the potential as an efficient nanocarrier to transport calcium through the GI system.

High Fischer ratio oligopeptides determination from Antartic krill: Preparation, peptides profiles, and in vitro antioxidant activity

In this work, alcalase and flavorzyme were chosen as the hydrolase for preparing high Fischer ratio oligopeptides from Antarctic krill (Euphausia superba) (HFP) using sequential enzyme hydrolysis process, and their hydrolysis conditions were optimized using single factor experiment. According to the Fischer ratio, granular activated carbon of XHJ-200 (200 mesh) showed the best way to remove aromatic amino acids and its optimal parameters were pH value of 6.0, adsorption time of 2.5 hr, temperature of 25°C, and solid-liquid ratio of 1:20. The Fischer ratio and average molecular weight of HFP were 21.12 (>20) and 779.9 Da, respectively. In addition, the peptide profile of HFP was established using RP-HPLC and 23 oligopeptides isolated from HFP including 6 dipeptides, 9 tripeptides, 3 tetrapeptides, and 5 pentapeptides were identified using protein amino acid sequence analyzer and mass spectrum. Furthermore, HFP exhibited high radical scavenging activity, reducing power, and lipid peroxidation inhibition capability. PRACTICAL APPLICATIONS: High Fischer ratio oligopeptides (HFO) is a kind of small peptide mixture with the mole ratio of branched-chain amino acids (BCAA) to aromatic amino acids (AAA) higher than 20, which has drawn a great attention due to its great potential in clinical nutrition approaches for the treatment of liver disease when amino acid composition is out of proportion characterized by low levels of BCAA and high levels of AAA in the systemic blood. Antarctic krill is regarded as the largest animal protein resource for various food and pharmaceutical products. However, there is no report on the preparation of HFO of Antarctic krill (HFP). Therefore, the aim of the present study was to investigate the preparation process, peptide profiles and in vitro antioxidant activity of HFP. This study will potentially enhance the value-added utilization of Antarctic krill by making it an important raw material in the health-promoting functional products.

Preparation process optimization of pig bone collagen peptide-calcium chelate using response surface methodology and its structural characterization and stability analysis

In this study, alcalase and neutrase were used in combination to prepare collagen peptides with high calcium binding ability. The optimal conditions for the preparation of peptide-calcium chelate (mass ratio of peptide/calcium of 4.5:1 for 40 min at 50 °C and pH 9) were determined by response surface methodology (RSM), under which a calcium chelating rate of 78.38% was obtained. The results of Ultraviolet-Visible (UV-Vis), fluorescence and Fourier transform infrared (FT-IR) spectra synthetically indicated that calcium could be chelated by carboxyl oxygen and amino nitrogen atoms of collagen peptides, thus forming peptide-calcium chelate. The chelate was stable at various temperatures and pH values, and exhibited excellent stability in the gastrointestinal environment, which could promote calcium absorption in human gastrointestinal tract. Moreover, Caco-2 cell monolayer model was used to investigate the effect of peptide-calcium chelate on promoting calcium absorption. Results showed that peptide-calcium chelate could significantly improve calcium transport in Caco-2 cell monolayer and reverse the inhibition of calcium absorption by phosphate and phytate. The findings provide a scientific basis for developing new calcium supplements and the high-value utilization of pig bone.

The formation mechanism of a sea cucumber ovum derived heptapeptide–calcium nanocomposite and its digestion/absorption behavior

Calcium coordination induced the self-assembly of the sea cucumber ovum derived heptapeptide (NDEELNK), resulting in the formation of the nanocomposite with potential function to transport calcium through the gastrointestinal system.

The purification, identification and bioactivity study of a novel calcium-binding peptide from casein hydrolysate

In this study, a novel calcium-binding peptide from casein hydrolysate was purified using reversed-phase high performance liquid chromatography and sequenced by high-performance liquid chromatography-mass spectrometry (MS)/MS.

Protective role of hazelnut peptides on oxidative stress injury in human umbilical vein endothelial cells

The crude protein hydrolysates of wild hazel have good immunoregulation and antioxidation effects. However, the components responsible for their antioxidation effect remain unknown. In this study, six antioxidative peptides (EW, DWDPK, ADGF, SGAF, ETTL, and AGGF) were tested for their protective effects on oxidative stress injury in human umbilical vein endothelial cells (HUVECs). The results demonstrated that the six peptides are nontoxic and have a protective effect on oxidative stress injury induced by Ang II. Three peptides (EW, ADGF, and DWDPK) inhibited the morphological changes, downregulated the content of lactate dehydrogenase and malondialdehyde, upregulated the activity of antioxidant enzymes catalase, total superoxide dismutase and glutathione peroxidase, and scavenged reactive oxygen species (ROS) in HUVECs. Quantitative reverse transcriptive polymerase chain reaction and western blot assays indicated that these three peptides regulated NADPH oxidase activity and ROS production by reducing NOX4 and p22phox levels. Overall, they have a significant protective effect against oxidative stress injury and have potential application in developing new functional foods. PRACTICAL APPLICATIONS: Corylus heterophylla Fisch is a good quality wild hazel distributed in Northeast China. Wild hazelnut of the species C. heterophylla Fisch was selected as experimental object and has high nutritive values and have abundant proteins (20%-30%), fats (40%-50%), carbohydrates (13%-24%), dietary fibers (8.2%-9.6%), vitamins, and micronutrients. Our results indicate that hazelnut peptides (EW, ADGF, and DWDPK) can ensure normal growth of cells by protecting important antioxidant enzyme systems, by enhancing antioxidant defense, by directly affecting nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, and by reducing intracellular reactive oxygen species (ROS) production in HUVECs, indicating that the three antioxidative peptides have a protective effect against Ang II-induced oxidative stress injury. Therefore, the antioxidative peptides from C. heterophylla Fisch may be a promising candidate for functional food ingredients and/or pharmaceuticals.

Potential of Food Hydrolyzed Proteins and Peptides to Chelate Iron or Calcium and Enhance their Absorption

Iron and calcium are two essential micronutrients that have strong effects on nutrition and human health because of their involvement in several biological and redox processes. Iron is responsible for electron and oxygen transport, cell respiration, and gene expression, whereas calcium is responsible for intracellular metabolism, muscle contraction, cardiac function, and cell proliferation. The bioavailability of these nutrients in the body is dependent on enhancers and inhibitors, some of which are found in consumed foods. Hydrolyzed proteins and peptides from food proteins can bind these essential minerals in the body and facilitate their absorption and bioavailability. The binding is also important because excess free iron will increase oxidative stress and the risks of developing chronic diseases. This paper provides an overview of the function of calcium and iron, and strategies to enhance their absorption with an emphasis on hydrolyzed proteins and peptides from foods. It also discusses the relationship between the structure of peptides and their potential to act as transition metal ligands.

Functional Calcium Binding Peptides from Pacific Cod (Gadus macrocephalus) Bone: Calcium Bioavailability Enhancing Activity and Anti-Osteoporosis Effects in the Ovariectomy-Induced Osteoporosis Rat Model

Calcium binding peptides from Pacific cod (Gadus macrocephalus) bone have attracted attention due to their potential effects on bone health. In this study, calcium binding peptides (CBP) were prepared from Pacific cod bone by trypsin and neutral protease. Ultraviolet spectra, circular dichroism (CD), and Fourier transform infrared spectroscopy (FTIR) revealed that carboxyl and amino groups in CBP could bind to Ca²⁺, and form the peptide-calcium complex (CBP-Ca). Single-pass intestinal perfusion (SPIP) experiments indicated that the intestinal calcium absorption was significantly enhanced (p < 0.01) in CBP-Ca treated Wistar rats. The anti-osteoporosis activity of CBP-Ca was investigated in the ovariectomized (OVX) Wistar rat model. The administration of CBP-Ca significantly (p < 0.01) improved the calcium bioavailability, trabecular bone structure, bone biomechanical properties, bone mineral density, and bone mineralization degree. CBP-Ca notably (p < 0.01) increased serum calcium, however, it remarkably (p < 0.01) reduced the levels of osteocalcin (OCN), bone alkaline phosphatase (BALP), tartrate-resistant acid phosphatase isoform 5b (TRAP5b), and C-telopeptide of type I collagen (CTX-1) in serum. Results suggested that the cod bone derived CBP could bind with calcium, improve the intestinal calcium absorption, calcium bioavailability, and serum calcium, then reduce the bone turnover rate, and thus ameliorate osteoporosis.

In vitrodigestion profile and calcium absorption studies of a sea cucumber ovum derived heptapeptide–calcium complex

A novel sea cucumber ovum derived heptapeptide (NDEELNK) could bind one calcium ionviaits carboxyl oxygen and amino nitrogen atoms, and the formed complex underwent disaggregation and self aggregation during simulated gastrointestinal digestion.