Preparation and characterization of β-lactoglobulin hydrolysate-iron complexes

Screening, separation and identification of metal-chelating peptides for nutritional, cosmetics and pharmaceutical applications

Metal-chelating peptides, which form metal-peptide coordination complexes with various metal ions, can be used as biofunctional ingredients notably to enhance human health and prevent diseases. This review aims to discuss recent insights into food-derived metal-chelating peptides, the strategies set up for their discovery, their study, and identification. After understanding the overall properties of metal-chelating peptides, their production from food-derived protein sources and their potential applications will be discussed, particularly in nutritional, cosmetics and pharmaceutical fields. In addition, the review provides an overview of the last decades of progress in discovering food-derived metal-chelating peptides, addressing several screening, separation and identification methodologies. Furthermore, it emphasizes the methods used to assess peptide-metal interaction, allowing for better understanding of chemical and thermodynamic parameters associated with the formation of peptide-metal coordination complexes, as well as the specific amino acid residues that play important roles in the metal ion coordination.

Active peptides from Eupolyphaga sinensis walker attenuates experimental hyperlipidemia by regulating the gut microbiota and biomarkers in rats with dyslipidemia

Eupolyphaga sinensis Walker (ESW) is a traditional Chinese medicine formulation used to treat hyperlipidemia. However, the hypolipidemic effect of the active peptides from E. sinensis Walker (APE) is incompletely understood. We studied the hypolipidemic effect of APE and explored the impact of APE on the gut microbiota (GM) in rats suffering from hyperlipidemia. APE was prepared by enzymatic digestion, and its structure was characterized using various methods. The anti-hyperlipidemic activity of APE was assessed using a high-fat diet (HFD)-induced model in zebrafish and rats. In rats, HFD administration caused abnormalities of lipid metabolism and disturbances of the GM and amino acid (AA) profile in plasma. The abundance of bacteria of the phyla Firmicutes and Bacteroides was increased significantly (p < 0.05), and the relative abundance of Lactobacillus species and Clostridium species was decreased significantly (p < 0.05). HFD therapy affected the levels of 12 AAs in vivo: 10 AAs showed increased levels and two AAs had decreased levels (p < 0.05). Similar results were demonstrated in an experiment on fecal microbiota transplantation. APE treatment dose-dependently decreased lipid factors and liver damage (p < 0.05). Sequencing of the 16 S rRNA gene indicated that APE improved the intestinal-flora structure of rats with HL markedly, and increased the relative abundance of Lactobacillus species and Clostridium species. Metabolomics analysis indicated that APE could alter the levels of 10 AAs affected by HFD consumption. Spearman correlation analysis revealed that gamma-aminobutyric acid (GABA) could be a crucial metabolite, and Lactobacillus species and Clostridium species might be important bacteria for the action of APE against hyperlipidemia. We speculate that APE exhibited an anti-hyperlipidemic effect by regulating GABA synthesis in the presence of Lactobacillus species and Clostridium species.

Characterization of Oyster Protein Hydrolysate-Iron Complexes and their In Vivo Protective Effects against Iron Deficiency-Induced Symptoms in Mice

Iron is one of the trace mineral elements, and iron deficiency is a common phenomenon that negatively influences human health. Food-derived iron supplements were considered excellent candidates for improving this syndrome. In this work, oyster-protein hydrolysates (OPH) and ferrous chloride successfully formed the OPH-Fe complex (6 mg/mL, 40 °C, 30 min), where the main binding sites involved were the carboxyl and amino groups. The OPH-Fe complex showed no obvious changes in the secondary structure, while the iron changed the morphological appearance and also showed fluorescence quenching, an ultraviolet shift, and an increase in size distribution. The OPH-Fe complex showed better dynamic absorption of iron (64.11 μmol/L) than ferrous sulfate (46.90 μmol/L), and the medium dose had better protective effects against iron-deficiency anemia in vivo. Three representative peptides (DGKGKIPEE, FAGDDAPRA, and VLDSGDGVTH) that were absorbed intact were identified. This experiment provided a theoretical foundation for further study of the digestion and absorption of the OPH-Fe complex.

Process Optimization, Structural Characterization, and Calcium Release Rate Evaluation of Mung Bean Peptides-Calcium Chelate

To reduce grievous ecological environment pollution and protein resource waste during mung bean starch production, mung bean peptides-calcium chelate (MBP-Ca) was synthesized as a novel and efficient calcium supplement. Under the optimal conditions (pH = 6, temperature = 45 °C, mass ratio of mung bean peptides (MBP)/CaCl₂ = 4:1, MBP concentration = 20 mg/mL, time = 60 min), the obtained MBP-Ca achieved a calcium chelating rate of 86.26%. MBP-Ca, different from MBP, was a new compound rich in glutamic acid (32.74%) and aspartic acid (15.10%). Calcium ions could bind to MBP mainly through carboxyl oxygen, carbonyl oxygen, and amino nitrogen atoms to form MBP-Ca. Calcium ions-induced intra- and intermolecular interactions caused the folding and aggregation of MBP. After the chelation reaction between calcium ions and MBP, the percentage of β-sheet in the secondary structure of MBP increased by 1.90%, the size of the peptides increased by 124.42 nm, and the dense and smooth surface structure of MBP was transformed into fragmented and coarse blocks. Under different temperatures, pH, and gastrointestinal simulated digestion conditions, MBP-Ca exhibited an increased calcium release rate compared with the conventional calcium supplement CaCl₂. Overall, MBP-Ca showed promise as an alternative dietary calcium supplement with good calcium absorption and bioavailability.

Effects of Iron Supplementation on Metabolism in Calves Receiving Whole Milk

The objective of this study was to determine the effects of feeding a protein-iron complex (PIC) to calves. Specifically, the aim was to understand how it influences productive performance and indicators of iron metabolism, hematology and biochemical and parameters during feeding with whole milk before weaning. The study was carried out on 20 Polish Holstein Friesian calves. The calves were then divided into a control group (CON), fed with full milk (n = 10), and an experimental group (MFe), who received a PIC additive in milk at 16 g/day (n = 10). In order to determine the production parameters, the calves were weighed at the beginning (i.e., on the 7th day of life) and at the end of the experiment (42nd day of life) using an electronic platform scale. Production parameters such as average weight gain (AWG), feed conversion ratio (FCR), and growth rate (GR) were assessed. Blood was collected from an external jugular vein (vena jugularis externa) on the 7th, 14th, 28th, and 42nd days of life. The mean daily gains in body weight (ADG), growth rate (GR), and the feed conversion ratio were highest in the experimental group, MFe. Therefore, it can be concluded that the addition of a protein-iron complex entailed a significant impact on the iron metabolism indicators in the MFe experimental group.

A Step for the Valorization of Spent Yeast through Production of Iron–Peptide Complexes—A Process Optimization Study

Given the importance of iron in human nutrition and the significance of waste and by-product valorisation in a circular economy environment, we investigated the effects of protein and iron concentration on the production yield of iron–peptide complexes from spent Saccharomyces cerevisiae. For this purpose, different amounts of protein and iron were used in the complexation process. The results have shown that higher concentrations, although permitting a faster and larger scale process, provide a significantly lower complexation yield, which deems the process less feasible. This is corroborated by fluorescence analysis, which shows a lower degree of complexation with higher protein concentration. In addition, varying the concentration of iron does not change the quality of formed complexes, as evidenced by Fourier transform infrared spectroscopy (FT-IR) analysis. The morphology of all samples was also evaluated using scanning electron microscopy (SEM). Therefore, further studies are needed to optimize the process and to evaluate the best conditions for an economically sound valorization process for iron–peptide complexes. Nonetheless, current results in the development of a new process for the valorisation of spent yeast, in the form of iron-peptide complexes, look promising.

Discovery of calcium-binding peptides derived from defatted lemon basil seeds with enhanced calcium uptake in human intestinal epithelial cells, Caco-2

It is anticipated that calcium-chelating peptides may serve to enhance the absorption of calcium. This research examined defatted lemon basil seeds (DLBS) which had been treated with Alcalase under optimized parameters for the degree of hydrolysis for proteolysis, discovering that the activity for calcium-binding in a competitive condition with phosphate ion was 60.39 ± 1.545%. The purification of the hydrolysates was performed via ultrafiltration along with reversed-phase high performance liquid chromatography (RP-HPLC). Determination of the purified peptide amino acid sequence was confirmed for both peptides and reported as Ala-Phe-Asn-Arg-Ala-Lys-Ser-Lys-Ala-Leu-Asn-Glu-Asn (AFNRAKSKALNEN; Basil-1), and Tyr-Asp-Ser-Ser-Gly-Gly-Pro-Thr-Pro-Trp-Leu-Ser-Pro-Tyr (YDSSGGPTPWLSPY; Basil-2). The respective activities for calcium-binding were 38.62 ± 1.33%, and 42.19 ± 2.27%. Fluorescence spectroscopy, and fourier transform infrared spectroscopy were employed in order to assess the chelating mechanism between calcium and the peptides. It was found that the calcium ions took place through the activity of the amino nitrogen atoms and the oxygen atoms on the carboxyl group. Moreover, both of these peptides served to improve calcium transport and absorption in Caco-2 cell monolayers, depending on the concentration involved. It was revealed that the peptide-calcium complexes offered an increased calcium absorption percentage when compared to free calcium at similar concentrations. It might be concluded that the peptide within the peptide-calcium complex can promote calcium absorption through both active and passive transport pathways by increasing calcium concentration and promoting cell membrane interaction. Accordingly, DLBS protein can be considered a strong potential source of protein which can be used to produce calcium-binding peptides and might therefore play a role in the production of nutraceutical foods as a bioactive ingredient.

Formulations with microencapsulated Fe–peptides improve in vitro bioaccessibility and bioavailability

The bioaccessibility and the bioavailability of iron complexed to peptides (active) in microparticles forms contained in dry beverages formulations were evaluated. The peptide-iron complexes microparticles were obtained by spray drying and added in three dry formulations (tangerine, strawberry, and chocolate flavors). The peptides isolated by iron ion affinity (IMAC-Fe III) had their biological activity predicted by BIOPEP® database and were evaluated by molecular coupling. The bioaccessibility was evaluated by solubility and dialysability and the bioavalability was assessed by Caco-2 cellular model. The proportion 10:1 of peptide-iron complexes presented higher rates of bioaccessibility (49%) and bioavailability (56%). The microparticle with peptide-iron complex showed greater solubility after digestion (39.1%), bioaccessibility (19.8%), and bioavailability (34.8%) than the ferrous sulfate salt (control) for the three assays (10.2%; 12.9%; 9.7%, respectively). Tangerine and strawberry formulations contributed to the iron absorption according to the results of bioaccessibility (36.2%, 30.0% respectively) and bioavailability (80.5%, 84.1%, respectively). The results showed that iron peptide complexation and microencapsulation process improve the bioaccessibility and bioavailability when incorporated into formulations.

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Iron solubility is increased in iron peptide complexes.

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In silico interaction between peptides > 5 KDa and ferric iron (Fe²⁺).

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Microparticle with Fe-peptides increase iron bioavailability after digestion.

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Microparticle formulations improve iron bioaccessibility and bioavailability.

Elucidating the Calcium-Binding Site, Absorption Activities, and Thermal Stability of Egg White Peptide-Calcium Chelate

With the current study, we aimed to determine the characteristics and calcium absorption capacity of egg white peptide-calcium complex (EWP-Ca) and determine the effect of sterilization on EWP-Ca to study the possibility of EWP-Ca as a new potential calcium supplement. The results of SEM and EDS showed a high calcium chelating ability between EWP and calcium, and the structure of EWP-Ca was clustered spherical particles due its combination with calcium. The FTIR and Raman spectrum results showed that EWP could chelate with calcium by carboxyl, phosphate, and amino groups, and peptide bonds may also participate in peptide-calcium binding. Moreover, the calcium absorption of EWP-Ca measured by the intestinal everted sac model in rats was 32.38 ± 6.83 μg/mL, significantly higher than the sample with CaCl2, and the mixture of EWP and Ca (p < 0.05) revealed appropriate calcium absorption capacity. The fluorescence spectra and CD spectra showed that sterilization caused a decrease in the content of α-helix and β-sheet and a significant increase in β-turn (p < 0.05). Sterilization changed the EWP-Ca structure and decreased its stability; the calcium-binding capacity of EWP-Ca after sterilization was decreased to 41.19% (p < 0.05). Overall, these findings showed that EWP could bind with calcium, form a peptide-calcium chelate, and serve as novel carriers for calcium supplements.

Desalination of duck egg white by biocoagulation to obtain peptide-ferrous chelate as iron delivery system: Preparation, characterization, and Fe2+ release evaluation in vitro

The annual output of salted duck egg white (SDEW) is estimated to be over 1.5 million tons in China, most of which is discarded due to high salt content. This has led to serious waste and environmental impact. Therefore, we developed an eco-friendly biocoagulation separation technology by combining chitosan and sodium alginate in order to produce a novel iron-binding peptide (DPs-Fe2+) from SDEW. The structure of DPs-Fe2+ was characterized by ultraviolet-visible spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy, followed by measuring DPs-Fe2+ response in a simulated digestion/Caco-2 cell model. Results showed that chitosan and sodium alginate complex could remove 91.21% of salt from SDEW, and the protein recovery rate reached 95.50%. Characterization results indicated that DPs bonded with Fe2+ to form a soluble chelate. Moreover, Caco-2 cell monolayer model indicated that the transport rate of Fe2+ was as high as 10.02% at 0.1 mg/ml concentration of digested chelates. The results demonstrate the potential application of DPs as a novel carrier for enhancing iron absorption. This research contributes to the development of an effective industrial desalination method and highlights an opportunity for recycling an otherwise discarded processing byproduct. PRACTICAL APPLICATION: Salted duck egg whites (SDEW) are the primary byproduct of salted egg yolk production, most of which is discarded due to high salt content. Hence, efficient utilization of the high-value proteins in SDEW is an urgent problem that must be resolved. Herein, we developed an effective industrial desalination method by combining chitosan and sodium alginate, which achieved excellent SDEW desalination and protein recovery. Furthermore, we produced a novel iron-binding peptide (DPs-Fe2+), which enhanced the transportation and absorption of Fe2+ in Caco-2 cell model, suggesting its potential as an iron supplement.

Characterization of iron reducibility of soy protein amyloid fibrils and their applications in iron fortification

Iron deficiency is a common nutritional disorder worldwide. Iron fortification of food is an effective strategy to control iron deficiency anemia (IDA), however, traditional iron fortificants usually provoke undesirable organoleptic changes or have limited colloid stability. In this research, we investigated iron reducibility of soy protein amyloid fibrils made from soy protein isolates (SPI), soy β-conglycinin (7S) and soy glycinin (11S), and explored their applications in iron fortification. All three protein fibrils showed iron reducibility. The reducibility was utilized to generate fibril-iron nanoparticle composites. The iron reducibility was affected by fibril concentration, degree of fibrillation and reducing amino acid composition. We identified 11S had the most significant effect on reducing Fe (III) to more bioavailable Fe (II) state, whereas 7S showed the optimal result for generation of iron nanoparticle on fibrils in situ. The resulted fibril-iron nanoparticle hybrids showed high dispersibility in various liquid foods, without distinct color change.

Isolation of a novel calcium-binding peptide from phosvitin hydrolysates and the study of its calcium chelation mechanism

A new peptide with strong calcium binding capacity was isolated from phosvitin hydrolysates. Taking calcium chelating rate as an indicator, phosvitin hydrolysates were separated gradually by anion-exchange chromatography, gel filtration chromatography and reversed-phase high performance liquid chromatography. A peptide with a molecular weight of 1106.44402 Da was identified by liquid chromatography-electrospray/mass spectrometry (LC-ESI/MS), and its amino acid sequence was DEEENDQVK, the calcium binding capacity reached 151.10 ± 3.57 mg/g. Its chelating mechanism was investigated. Results showed that, the β-sheet structure of peptide increased after adding calcium ion, and the main binding sites were carboxyl oxygen atom and amino nitrogen atom. In vitro simulated digestion experiments showed that, the solubility and dialysis rate of calcium in peptide-calcium chelate were higher than those in CaCO₃ and D-calcium gluconate. This finding would promote the development of calcium supplements from food resources.

Preparation and characterization of iron-chelating peptides from whey protein: An alternative approach for chemical iron fortification

Iron fortification of staple food is a strategy utilized worldwide to address the concern of dietary iron deficiency. However, traditional salt-based fortification methods have limitations with gastrointestinal stability and bioavailability. Iron chelating peptides from easily available and scalable proteins such as whey protein have been proposed as promising candidates to circumvent the above mentioned limitations by enhancing iron absorption and bioavailability. In this study, we report methods to produce whey protein derived iron-chelating peptides and describe their physicochemical characteristics. Peptides derived from whey proteins prepared by ultrafiltration of whey followed by hydrolysation were iron chelated to produce peptide-iron complexes. These complexes had a size of 422.9 ± 3.41 nm, chelated iron content of 36.42 µg/ mg protein, and a low zeta potential (-10.80 mV) compared to whey peptides. Spectra analysis using ultraviolet-visible absorption and Fourier transform infrared spectroscopy showed structural transformation indicating iron chelation. Mass spectrometric analysis using LC-MS/MS confirmed the presence of both hydrophilic and hydrophobic peptides in the complexes with sizes ranging from 275 Da to 1916 Da. Furthermore, reduction in the antioxidant property of peptides following iron complexing indicates iron chelation. Our results suggest that whey protein derived peptide-iron complexes can be used as a potential alternative for chemical iron fortificants for food products and also as iron supplements.

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.

Iron-caseinglycomacropeptide complexes: Characterization and application in beverages

Complexing iron with organic compounds has been considered an alternative strategy to mitigate the problems associated with the level of bioavailable iron and the acceptability of products supplemented with this mineral. CMP contains specific amino acids associated with iron binding. The present study aims to optimize the conditions of Fe/CMP complex formation and understand the molecular basis of interactions between CMP and iron ions. Results showed that CMP can bind ferrous iron in a 1:1.5 M ratio, forming a stable peptide-iron complex, where CMP assembles in a tetrameric form. FTIR spectra indicated that iron binding altered the secondary structures of CMP. The iron-binding sites of CMP corresponded primarily to acid residues of Glu, Asp and sialic acid. Moreover, Fe/CMP complex remained stable in a wide pH range (2.0-6.5), suggesting the adequacy to be efficiently added in food or beverages and to keeping complexed in the digestion environment. Finally, Fe/CMP complex was added to a commercial beverage (2 mg of Fe per serving of beverage) and no changes were observed in their colour during storage. A model to explain the binding between CMP and iron is proposed. These results suggest a potential application of this peptide for iron fortification.

Investigating the calcium binding characteristics of black bean protein hydrolysate

The black bean protein has been widely utilized to prepare hydrolysates with different bioactive properties. Herein, we hydrolyzed the black bean protein to prepare hydrolysate with calcium binding activity and characterized its behavior. Our results showed that ficin was superior in obtaining hydrolysate with calcium binding capacity in comparison with trypsin, alcalase and bromelain. In particular, the optimal capacity of ficin hydrolysate reached 77.54 ± 1.61 μg mg-1, where the optimal hydrolysis conditions of ficin were a temperature of 70 °C, a pH value of 6.2, an enzyme concentration of 1.61% and a time of 3 h. This might be due to high proportions of aspartic acid and glutamic acid (35.59%). Further spectral analysis evidenced the formation of hydrolysate-calcium complexes, demonstrating that the interaction between hydrolysate and calcium ions primarily occur on carboxyl oxygen atoms and amino nitrogen atoms. These findings provide a possible utilization of black bean hydrolysate to serve as a calcium supplement nutraceutical to enhance the absorption and bioavailability.

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.

Antarctic Krill Derived Nonapeptide as an Effective Iron-Binding Ligand for Facilitating Iron Absorption via the Small Intestine

A novel nonapeptide DTDSEEEIR identified from Antarctic krill (Euphausia superba) iron-binding peptides was used in this study to analyze its iron-binding sites and structural changes after iron coordination. The enzymatic resistance and transport of DTDSEEEIR-iron during gastrointestinal digestion and absorption as well as the relationship between the DTDSEEEIR stability and the enhancement of iron absorption were further explored. Results revealed that iron ions spontaneously bound to the carboxyl, hydroxyl, and amino groups of the DTDSEEEIR peptide, which induced the folding of DTDSEEEIR to form a more orderly structure. The DTDSEEEIR peptide remained stable to a certain extent (79.60 ± 0.19%) after gastrointestinal digestion and the coordination of iron improved the digestive stability of the DTDSEEEIR peptide (93.89 ± 1.37%). Moreover, the stability of DTDSEEEIR across intestinal epithelium had a positive effect on iron absorption, which implied that DTDSEEEIR might carry iron ions through intestinal epithelial cells.

Iron encapsulated microstructured gel beads using an emulsification-gelation technique for an alginate-caseinate matrix

Iron-deficiency anemia is an important health problem in global public issues, and development of iron fortifiers in diets is essential for the decrease of iron deficiency. However, there are problems for iron fortification in food because the common bioavailable iron compounds would contribute to iron-promoted lipid oxidation and unpleasant iron odor, presenting an adverse food quality. Ferrous fumarate loaded microstructured gel beads were prepared by an emulsification-gelation method using an alginate-caseinate matrix, and the gel network was formed by crosslinking of Ca²⁺ or Fe²⁺. Internal gelated beads showed relatively symmetrical and homogeneous spheres with no adhesion due to the simultaneous release of Fe²⁺ to initiate gelation in situ. External gelated beads displayed an irregular and adhesive structure, probably because the random contact between Na-ALG and Ca²⁺ occurred on the droplet surface, and the immediately gelated hardening layer provided a delay for further Ca²⁺ diffusion. The gel beads exhibited a lag phase in the promotion of lipid oxidation of the emulsion and restrained the iron odor release from ferrous fumarate. Ferrous ion release from microstructured gel beads in the simulated gastric juice was obviously delayed before a more progressive high release in the simulated intestinal juice, beneficial for iron absorption in the duodenum. The iron encapsulated microstructured gel beads might be developed as a promising safe iron fortifier by relieving lipid oxidation and iron odor.

Effect of Chlorella Pyrenoidosa Protein Hydrolysate-Calcium Chelate on Calcium Absorption Metabolism and Gut Microbiota Composition in Low-Calcium Diet-Fed Rats

In our current investigation, we evaluated the effect of Chlorella pyrenoidosa protein hydrolysate (CPPH) and Chlorella pyrenoidosa protein hydrolysate-calcium chelate (CPPH-Ca) on calcium absorption and gut microbiota composition, as well as their in vivo regulatory mechanism in SD rats fed low-calcium diets. Potent major compounds in CPPH were characterized by HPLC-MS/MS, and the calcium-binding mechanism was investigated through ultraviolet and infrared spectroscopy. Using high-throughput next-generation 16S rRNA gene sequencing, we analyzed the composition of gut microbiota in rats. Our study showed that HCPPH-Ca increased the levels of body weight gain, serum Ca, bone activity, bone mineral density (BMD) and bone mineral content (BMC), while decreased serum alkaline phosphatase (ALP) and inhibited the morphological changes of bone. HCPPH-Ca up-regulated the gene expressions of transient receptor potential cation V5 (TRPV5), TRPV6, calcium-binding protein-D9k (CaBP-D9k) and a calcium pump (plasma membrane Ca-ATPase, PMCA1b). It also improved the abundances of Firmicutes and Lactobacillus. Bifidobacterium and Sutterella were both positively correlated with calcium absorption. Collectively, these findings illustrate the potential of HCPPH-Ca as an effective calcium supplement.

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.

Preparation and stability of nano-scaled gel beads of λ-carrageenan bound with ferric ions

Iron-deficiency anemia (IDA) is a major global public health problem, and the iron fortifiers in diet are clearly needed in the prevention and improvement of IDA for humans. A novel nano-scaled gel beads of λ-carrageenan (λ-car) specifically binding with ferric ions was developed to be a promising iron fortifier with no adverse organoleptic changes on food. Turbidity measurement, thermogravimetric analysis and Fourier transform infrared spectroscopy confirmed the successful chelating. The gel beads of λ-car-Fe³⁺ complex showed good dispersibility and solvent stability. The in vitro cell viability of HepG2 cells treated with λ-car-Fe³⁺ was over 75% at 5 mg/mL of ferric ions, indicating a significant cytotoxicity reduction of ferric ions. The stability of λ-car-Fe³⁺ complex powder was obviously increased against browning during 60 d storage with zein coating, which was attributed to the prevention of moisture permeation. Zein coated gel beads also performed a slow release of ferric ions in simulated gastrointestinal juices, resulting from the compact and hydrophobic zein surface delaying the dissociation of λ-car-Fe³⁺ in acidic environment. This λ-car-Fe³⁺ complex would have a great potential as a safe iron fortifier and facilitate iron supplementary with the advantage to relieve the side effects of iron ions.

Whey Peptide-Iron Complexes Increase the Oxidative Stability of Oil-in-Water Emulsions in Comparison to Iron Salts

Food fortification with iron may favor lipid oxidation in both food matrices and the human body. This study aimed at evaluating the effect of peptide-iron complexation on lipid oxidation catalyzed by iron, using oil-in-water (O/W) emulsions as a model system. The extent of lipid oxidation of emulsions containing iron salts (FeSO₄ or FeCl₂) or iron complexes (peptide-iron complexes or ferrous bisglycinate) was evaluated during 7 days, measured as primary (peroxide value) and secondary products (TBARS and volatile compounds). Both salts catalyzed lipid oxidation, leading to peroxide values 2.6- to 4.6-fold higher than the values found for the peptide-iron complexes. The addition of the peptide-iron complexes resulted in the formation of lower amounts of secondary volatiles of lipid oxidation (up to 78-fold) than those of iron salts, possibly due to the antioxidant activity of the peptides and their capacity to keep iron apart from the lipid phase, since the iron atom is coordinated and takes part in a stable structure. The peptide-iron complexes showed potential to reduce the undesirable sensory changes in food products and to decrease the side effects related to free iron and the lipid damage of cell membranes in the organism, due to the lower reactivity of iron in the complexed form.

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.

Characterization of sea cucumber (stichopus japonicus) ovum hydrolysates: calcium chelation, solubility and absorption into intestinal epithelial cells

BACKGROUND

Sea cucumber (Stichopus japonicus) ovum hydrolysates (SCOHs) chelated with calcium were produced to investigate the characteristics of calcium binding and solubility, as well as to study any effects on calcium absorption by human intestinal epithelial cells.

RESULTS

The results of the present study show that the calcium-binding capacity of SCOHs depended greatly on the type of proteases. The maximum level of Ca binding (0.38 mmol L^-1 ) occurred when trypsin was used, with a peptide yield of 85.7%. Investigation of the possible chelating modes between SCOHs and calcium ions indicated that calcium ions bound to SCOHs primarily via interactions with carboxyl oxygen and amino nitrogen atoms of Glu and Asp and also that the phosphoserine residues might be also responsible for SCOH-calcium chelation. Moreover, SCOH-calcium complexes maintained the solubility of calcium under simulated gastrointestinal digestion, regardless of the presence of dietary components such as oxalate. Furthermore, SCOH-Ca led to higher peak intracellular [Ca²⁺ ]_i in both Caco-2 cells (338.3 nmol L^-1 versus 269.6 nmol L^-1 ) and HT-29 cells (373.9 nmol L^-1 versus 271.7 nmol L^-1 ) than casein phosphopeptide-Ca.

CONCLUSION

Carboxyl oxygen and amino nitrogen atoms in the SCOHs could bind calcium ions, forming SCOH-calcium complexes. These complexes improved calcium solubility under simulated gastrointestinal digestion and also promoted calcium absorption in Caco-2 and HT-29 cells. © 2017 Society of Chemical Industry.

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

Trypsin was used for preparing peptides with high calcium-binding capacity from Antarctic krill. Hydroxyapatite chromatography (HAC), size-exclusion chromatography (SEC), and reversed phase high performance liquid chromatography (RP-HPLC) were used to capture and purify calcium-binding peptides. The peptide sequence was determined to be VLGYIQIR (N- to C-terminal, MW = 960.58 Da), using LTQ Orbitrap XL. According to the results of FTIR and mass spectrometry, chelating site of calcium ions may possibly involve the carbonal or amino groups of Gln, Ile and Arg residues. Molecular dynamic simulation showed the conformation of peptide was markedly varied, and the distance between calcium ion and Gln and Ile residues was changing all the time. However, the distance between calcium ion and carboxyl oxygen of arginine residues was not changed significantly from 2 ns to 100 ns. Identified peptide can be used as a novel calcium supplement.

Synthesis of whey peptide-iron complexes: Influence of using different iron precursor compounds

Iron-binding peptides are an alternative for increasing the bioavailability of iron and to decreasing its pro-oxidant effect. This study aimed to synthesize and characterize peptide-iron complexes using FeCl₂ or FeSO₄ as the iron precursor compounds. Whey protein isolate (WPI), WPI hydrolyzed with pancreatin, and its fractions obtained via ultrafiltration (cut-off 5kDa) were used as ligands. The fluorescence intensity of the ligands significantly decreased as the iron concentration increased as a result of metal coordination with the iron-binding sites, which may have led to changes in the microenvironment of tryptophan. For both iron precursor compounds, the primary iron-binding site was carboxylate groups, and the linkage occurred via a bidentate coordination mode with two vibrational modes assigned to the COOFe linkage. However, infrared spectroscopy and thermal analysis results showed that the dynamics of the interaction is different for the iron precursor. The iron source may be of great importance because it may impact iron absorption and the pro-oxidant effect of the mineral.

Amyloid fibril systems reduce, stabilize and deliver bioavailable nanosized iron

Iron-deficiency anaemia (IDA) is a major global public health problem. A sustainable and cost-effective strategy to reduce IDA is iron fortification of foods, but the most bioavailable fortificants cause adverse organoleptic changes in foods. Iron nanoparticles are a promising solution in food matrices, although their tendency to oxidize and rapidly aggregate in solution severely limits their use in fortification. Amyloid fibrils are protein aggregates initially known for their association with neurodegenerative disorders, but recently described in the context of biological functions in living organisms and emerging as unique biomaterial building blocks. Here, we show an original application for these protein fibrils as efficient carriers for iron fortification. We use biodegradable amyloid fibrils from β-lactoglobulin, an inexpensive milk protein with natural reducing effects, as anti-oxidizing nanocarriers and colloidal stabilizers for iron nanoparticles. The resulting hybrid material forms a stable protein-iron colloidal dispersion that undergoes rapid dissolution and releases iron ions during acidic and enzymatic in vitro digestion. Importantly, this hybrid shows high in vivo iron bioavailability, equivalent to ferrous sulfate in haemoglobin-repletion and stable-isotope studies in rats, but with reduced organoleptic changes in foods. Feeding the rats with these hybrid materials did not result in abnormal iron accumulation in any organs, or changes in whole blood glutathione concentrations, inferring their primary safety. Therefore, these iron-amyloid fibril hybrids emerge as novel, highly effective delivery systems for iron in both solid and liquid matrices.

A Specific Peptide with Calcium-Binding Capacity from Defatted Schizochytrium sp. Protein Hydrolysates and the Molecular Properties

Marine microorganisms have been proposed as a new kind of protein source. Efforts are needed in order to transform the protein-rich biological wastes left after lipid extraction into value-added bio-products. Thus, the utilization of protein recovered from defatted Schizochytrium sp. by-products presents an opportunity. A specific peptide Tyr-Leu (YL) with calcium-binding capacity was purified from defatted Schizochytrium sp. protein hydrolysates through gel filtration chromatography and RP-HPLC. The calcium-binding activity of YL reached 126.34 ± 3.40 μg/mg. The calcium-binding mechanism was investigated through ultraviolet, fluorescence and infrared spectroscopy. The results showed that calcium ions could form dative bonds with carboxyl oxygen atoms and amino nitrogen atoms as well as the nitrogen and oxygen atoms of amide bonds. YL-Ca exhibited excellent thermal stability and solubility, which was beneficial for its absorption and transport in the basic intestinal tract of the human body. Moreover, the cellular uptake of calcium in Caco-2 cells showed that YL-Ca could enhance calcium uptake efficiency and protect calcium ions against precipitation caused by dietary inhibitors such as tannic acid, oxalate, phytate and metal ions. The findings indicate that the by-product of Schizochytrium sp. is a promising source for making peptide-calcium bio-products as algae-based functional supplements for human beings.

Preparation, properties, and uses of enzymatic milk protein hydrolysates

Enzymatic hydrolysis of milk proteins has been a subject of numerous research studies and patents. The driving force for these studies has been the increased utilization of milk proteins. The industrial uses of milk proteins are based on their unique composition, functionality, and nutritive values. The diversity of milk protein fraction, the large number of proteinases, and controlled hydrolysis conditions used resulted in the preparation of hydrolysates suitable for several purposes. Enzymatic hydrolysis of milk proteins modifies the techno-functional and biofunctional properties of hydrolysates depending on the enzyme(s) and hydrolysis conditions used. Milk protein hydrolysates (MPH) are used commonly in normal and clinical nutrition and as a functional food ingredient. In the present review, emphasis has been made to highlight methods applied for the preparation of MPH, and the functional properties and utilization of the obtained hydrolysates.

Novel Peptide with Specific Calcium-Binding Capacity from Schizochytrium sp. Protein Hydrolysates and Calcium Bioavailability in Caco-2 Cells

Peptide-calcium can probably be a suitable supplement to improve calcium absorption in the human body. In this study, a specific peptide Phe-Tyr (FY) with calcium-binding capacity was purified from Schizochytrium sp. protein hydrolysates through gel filtration chromatography and reversed phase HPLC. The calcium-binding capacity of FY reached 128.77 ± 2.57 μg/mg. Results of ultraviolet spectroscopy, fluorescence spectroscopy, and infrared spectroscopy showed that carboxyl groups, amino groups, and amido groups were the major chelating sites. FY-Ca exhibited excellent thermal stability and solubility, which were beneficial to be absorbed and transported in the basic intestinal tract of the human body. Moreover, the calcium bioavailability in Caco-2 cells showed that FY-Ca could enhance calcium uptake efficiency by more than three times when compared with CaCl₂, and protect calcium ions against dietary inhibitors, such as tannic acid, oxalate, phytate, and Zn²⁺. Our findings further the progress of algae-based peptide-calcium, suggesting that FY-Ca has the potential to be developed as functionally nutraceutical additives.

Preparation, Identification and Antioxidant Properties of Black-Bone Silky Fowl (Gallus gallus domesticus Brisson) Iron(II)-Oligopeptide Chelate

Black-bone silky fowl iron(II)-oligopeptide chelate was synthesized from iron(II) solution and the black-bone silky fowl oligopeptide, which was extracted from the muscle protein of black-bone silky fowl (Gallus gallus domesticus Brisson). Orthogonal array analysis was used to determine the optimal conditions for the iron(II)-oligopeptide chelate preparation. Ultraviolet-visible (UV-Vis) spectroscopy, electron microscopy, and Fourier transform infrared (FTIR) spectroscopy were used to identify the structure of iron(II)-oligopeptide chelate. 2-Diphenyl-1-picrylhydrazyl (DPPH) and superoxide radical scavenging assays were performed to compare the antioxidant abilities of the black-bone silky fowl oligopeptide and iron(II)-oligopeptide chelate. The optimal conditions for iron(II)-oligopeptide chelate preparation were 4% of the black-bone silky fowl oligopeptide and a ratio of the black- -bone silky fowl oligopeptide to FeCl₂·4H₂O of 5:1 at pH=4. Under these conditions, the chelation rate was (84.9±0.2) % (p<0.05), and the chelation yield was (40.3±0.1) % (p<0.05). The structures detected with UV-Vis spectroscopy, electron microscopy and FTIR spectra changed significantly after chelation, suggesting that Fe(II) ions formed coordinate bonds with carboxylate (-RCOOŻ) and amino (-NH₂) groups in the oligopeptides, confirming that this is a new oligopeptide-iron chelate. The iron(II)-oligopeptide chelate had stronger scavenging activity towards DPPH and superoxide radicals than did the black-bone silky fowl oligopeptide.

Effect of calcium-binding peptide from Pacific cod (Gadus macrocephalus) bone on calcium bioavailability in rats

Bone collagen peptide with high affinity to Ca was extracted from Pacific cod (Gadus macrocephalus) bone. FTIR spectra of calcium-binding bone collagen peptide showed that band at 3381cm^-1 shifted to 3361cm^-1, 1455cm^-1 moved to 1411cm^-1, and amide II became deeper valley, compared with that of bone collagen peptide. This peptide was sequenced by Q-TOF-MS and sequences of Gly-Pro-Glu-Gly, Gly-Glu-Lys, Gly-Pro-Leu-Gly and Gly-Leu-Pro-Gly appeared repeatedly in some peptides. From SEM, after chelated with calcium, the loose and porous structure turned into granular structure. From the animal experiment, Ca apparent absorption rate, Ca retention rate and femur Ca content of calcium-binding bone collagen peptide group were significantly higher than those of model and CaCO₃ groups (P<0.05), while serum ALP was significantly lower than model group (P<0.05) and similar to control group. The results suggested that calcium-binding bone collagen peptide could improve bioavailability of Ca and thus prevented Ca deficiency.

Short communication: Identification of iron-binding peptides from whey protein hydrolysates using iron (III)-immobilized metal ion affinity chromatography and reversed phase-HPLC-tandem mass spectrometry

Peptides with iron-binding capacity obtained by hydrolysis of whey protein with Alcalase (Novozymes, Araucaria, PR, Brazil), pancreatin, and Flavourzyme (Novozymes) were identified. Hydrolysates were subjected to iron (III)-immobilized metal ion affinity chromatography, and the bound peptides were sequenced by mass spectrometry. Regardless of the enzyme used, the domains f(42-59) and f(125-137) from β-lactoglobulin enclosed most of identified peptides. This trend was less pronounced in the case of peptides derived from α-lactalbumin, with sequences deriving from diverse regions. Iron-bound peptides exhibited common structural characteristics, such as an abundance of Asp, Glu, and Pro, as revealed by mass spectrometry and AA analysis. In conclusion, this characterization of iron-binding peptides helps clarify the relationship between peptide structure and iron-chelating activity and supports the promising role of whey protein hydrolysates as functional ingredients in iron supplementation treatments.

Purification and characterisation of a glutamic acid-containing peptide with calcium-binding capacity from whey protein hydrolysate

The bioavailability of dietary ionised calcium is affected by intestinal basic environment. Calcium-binding peptides can form complexes with calcium to improve its absorption and bioavailability. The aim of this study was focused on isolation and characterisation of a calcium-binding peptide from whey protein hydrolysates. Whey protein was hydrolysed using Flavourzyme and Protamex with substrate to enzyme ratio of 25:1 (w/w) at 49 °C for 7 h. The calcium-binding peptide was isolated by DEAE anion-exchange chromatography, Sephadex G-25 gel filtration and reversed phase high-performance liquid chromatography (RP-HPLC). A purified peptide of molecular mass 204 Da with strong calcium binding ability was identified on chromatography/electrospray ionisation (LC/ESI) tandem mass spectrum to be Glu-Gly (EG) after analysis and alignment in database. The calcium binding capacity of EG reached 67·81 μg/mg, and the amount increased by 95% compared with whey protein hydrolysate complex. The UV and infrared spectrometer analysis demonstrated that the principal sites of calcium-binding corresponded to the carboxyl groups and carbonyl groups of glutamic acid. In addition, the amino group and peptide amino are also the related groups in the interaction between EG and calcium ion. Meanwhile, the sequestered calcium percentage experiment has proved that EG-Ca is significantly more stable than CaCl2 in human gastrointestinal tract in vitro. The findings suggest that the purified dipeptide has the potential to be used as ion-binding ingredient in dietary supplements.