The Formation, Structural Characteristics, Absorption Pathways and Bioavailability of Calcium–Peptide Chelates

Development and characterization of gelatin peptides and peptide‑calcium chelates from tuna processing by-products of skins and bones

This study used hydrothermal extraction to obtain gelatin from tuna processing by-products. After treatment, the yield (w/w dry weight) of gelatin from skins and bones were 70.22 ± 2.07 % and 28 ± 3.03 %, respectively. Enzymatic hydrolysis using alkaline protease and pancreatin converted the gelatins into peptides, with the content of oligopeptide up to 87.67 ± 1.44 %. The tuna bone gelatin peptides exhibiting higher scavenging abilities against hydroxyl radicals (·OH-), 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH·), and hydrogen peroxide (H2O2) compared to tuna skin gelatin peptides. Gelatin peptides were chelated with CaCl2 at 50 °C for 60 min, pH 8.0, and a 1:2 peptide-to‑calcium ratio, achieving a maximum calcium binding capacity of 56.70 ± 1.67 %. Fourier-transform infrared spectroscopy indicated the participation of amino and carboxyl groups in the reaction. These findings provide technical and theoretical support for the development of calcium-chelated gelatin peptides.

A dual absorption pathway of novel oyster-derived peptide-zinc complex enhances zinc bioavailability and restores mitochondrial function

Zinc deficiency is a global health issue that impairs immune function, growth, and energy metabolism. Although conventional zinc supplements have been developed, their effectiveness is limited by poor bioavailability and susceptibility to dietary inhibitors. In this study, a peptide-zinc complex (IE-Zn) derived from oysters was developed to enhance zinc uptake and address metabolic disruptions caused by deficiency. It was determined that Zn2+ binds with high affinity to the IE peptide, promoting structural flexibility that facilitates zinc transport through both zinc ion transporters and oligopeptide transporters. In Caco-2 and IEC-6 cell models, IE-Zn was shown to significantly improve zinc absorption and retention compared to ZnSO4, driven by the upregulation of ZIP4 and PEPT1 transporters. In vivo studies in a zinc-deficient mouse model confirmed enhanced zinc absorption and distribution across serum, intestine, and liver. Moreover, IE-Zn restored energy homeostasis by activating the AMPK/PGC1-α/NRF-1/TFAM signaling pathway, promoting mitochondrial biogenesis and reducing oxidative stress. These findings suggest that IE-Zn is a superior zinc supplement with higher bioavailability and serves as a potent regulator of cellular energy metabolism, offering therapeutic potential for managing conditions related to zinc deficiency and mitochondrial dysfunction. This study lays the foundation for further exploration of peptide-mineral complexes as advanced nutritional supplements with broad applications. Subsequent studies will further investigate the absorption pathway and targeting of peptide-zinc complex. The hope is to provide potential preventive applications for people in need, including zinc deficiency and a range of diseases caused by zinc deficiency.

The negative electrostatic potential of the coordination between calcium and carboxyl/oxygen group in calcium-peptide complexes contributes to calcium utilization

The coordination electrostatic potential has significantly influenced the binding energy of calcium-peptide coordination complexes. However, its impact on calcium bioavailability is unclear. A calcium-binding peptide (CBP) DEDEQIPSHPPR, purified from soybean yogurt was selected. The study selected tetrapeptide residues of acidic amino acids that play an important role in CBP and designed sixteen tetrapeptides rich in carboxyl oxygen atoms to investigate the influence of electrostatic potential on calcium-peptide binding. The results indicated that DEDE exhibited the strongest binding energy (-375.27 kcal/mol) and binding capacity (464.11 ± 2.14 mg/g) with calcium ions compared to other peptides. Moreover, DEDE also increased intracellular calcium concentration the most, being 2.04 times higher than CaCl2. Calcium ions coordinated with carboxyl oxygen atoms possessing negative electrostatic potential, which correlated positively with the bioavailability of calcium ions. This electrostatic potential analysis provides a theoretical basis for developing and screening bioactive peptides with high calcium bioavailability.

Preparation, structural characterisation, absorption and calcium transport studies of walnut peptide calcium chelate

In this study, a walnut peptide (WP) with calcium-binding capacity was prepared using a combination of alkalase and neutrase. The conditions for the preparation of walnut peptide calcium chelate (WP-Ca) were optimised (a peptide/calcium chloride ratio of 1 : 4 for 70 min at 50 °C and pH 9.5). Fractionation via ultrafiltration showed that peptides with a size <1 kDa demonstrated the highest calcium binding capacity at 106.4 mg g-1. Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, zeta potential and other analyses were performed to characterize WP-Ca. The combined results indicate that calcium binds by interacting with the carboxyl oxygen, hydroxyl oxygen and amino nitrogen of walnut peptides to form WP-Ca. The chelate showed good gastrointestinal stability. Furthermore, using the Caco-2 cell monolayer model, WP-Ca was shown to significantly increase calcium bioavailability and effectively reverse the inhibitory effects of dietary factors (phytates and phosphates) on calcium absorption. The results provide a scientific basis for developing novel calcium supplements and high-value walnut utilisation.

Novel Insights Into Peptide-Calcium Chelates From Lentinula edodes: Preparation and Its Structure, Stability, and Calcium Transport Analysis

Peptide-Ca chelates are innovative calcium supplements. Lentinula edodes possesses nutritional advantages for preparing calcium-binding peptides (CBPs), although there are limited studies on this subject. Therefore, this paper investigated the optimal condition for preparing Lentinula edodes CBPs and Lentinula edodes peptide-calcium chelates (LP-Ca), along with analyzing their microstructure, calcium-binding mechanisms, stability, and calcium transporting efficacy. The optimal protease and hydrolysis time for preparing CBPs were neutral protease and 3 h, respectively. The optimized parameters for LP-Ca preparation were as follows: pH9, time 50 min, mass ratio of peptide/CaCl2 5:1, and temperature 65°C. The chelates contain 4.23% ± 0.01% Ca. After chelation, Glu, Asp, Lys, Ser, His, and Cys were enriched. LP-Ca possessed a rough and porous structure, exhibiting a pronounced calcium signal. -COO-, C=O, and N-H groups were contributed to the chelation, with calcium primarily existing in an amorphous form. LP-Ca exhibited enhanced thermal stability and retained most of the calcium (62.33% ± 4.51%) after digestion, and calcium transportation was enhanced in the LP-Ca group (9.57 ± 0.60 μg). Collectively, LP-Ca are studied for the first time and the study is of great significance for developing novel calcium supplements.

Investigating the Role of Food-Derived Peptides in Hyperuricemia: From Mechanisms of Action to Structural Effects

Hyperuricemia, a disorder of purine metabolism associated with cardiovascular disease, gout, and kidney disease, can be alleviated by food-derived peptides. However, the precise mechanisms remain unclear, hindering their development. This study reviews uric acid-lowering peptides from various sources, focusing on two pathways: inhibiting uric acid production and promoting excretion. Low-molecular-weight peptides (<1000 Da) exhibited superior uric acid-lowering effects. We further explored the relationships between amino acid composition and their target interactions. Peptides rich in cyclic amino acids (tryptophan, phenylalanine, and histidine) and containing small amounts of linear amino acids (leucine, cysteine, and glycine) demonstrated significant potential for lowering uric acid. These findings provide theoretical support for developing novel functional foods for the management of hyperuricemia.

Non-Covalent Interaction of Folic Acid and 5-Methyltetrahydrofolate with Caseinates Improves the Folates Stability Studied by Multi-Spectroscopic Analysis and Molecular Docking

Folates, a crucial B-group vitamin, serve as a significant functional food supplement. Nevertheless, considerable obstacles persist in improving folates stability in liquid products. In this study, folic acid (FA) and 5-methyltetrahydrofolate (MTFA), two approved sources of folates, were encapsulated with sodium caseinate (NaCas) to enhance their stability. The protective effect of NaCas on folate molecules was investigated using experimental and computational methods. Meanwhile, the influence of divalent calcium ion (Ca2+) on the properties of the NaCas-MTFA complex was examined to evaluate the potential application of calcium 5-methyltetrahydrofolate (CaMTFA). Fluorescence tests showed both folates had static quenching behavior and bound to NaCas with a binding constant of 104-105 M-1. Hydrophobic interactions were crucial in NaCas-FA complex formation, while hydrogen bonding drove NaCas-MTFA binding. The encapsulation of caseinate notably slowed down the degradation of folates under both light and dark conditions. Moreover, the addition of a low concentration of Ca2+ did not adversely impact the binding mechanism of the NaCas-MTFA complex or the degradation curve of MTFA. The results of this study could serve as a valuable resource for the utilization of caseinates in incorporating folates, specifically MTFA, in the creation of natural liquid dietary supplements.

Mineral-element-chelating activity of food-derived peptides: influencing factors and enhancement strategies

Mineral elements including calcium, iron, and zinc play crucial roles in human health. Their deficiency causes public health risk globally. Commercial mineral supplements have limitations; therefore, alternatives with better solubility, bioavailability, and safety are needed. Chelates of food-derived peptides and mineral elements exhibit advantages in terms of stability, absorption rate, and safety. However, low binding efficiency limits their application. Extensive studies have focused on understanding and enhancing the chelating activity of food-derived peptides with mineral elements. This includes obtaining peptides with high chelating activity, elucidating interaction mechanisms, optimizing chelation conditions, and developing techniques to enhance the chelating activity. This review provides a comprehensive theoretical basis for the development and utilization of food-derived peptide-mineral element chelates in the food industry. Efforts to address the challenge of low binding rates between peptides and mineral elements have yielded promising results. Optimization of peptide sources, enzymatic hydrolysis processes, and purification schemes have helped in obtaining peptides with high chelating activity. The understanding of interaction mechanisms has been enhanced through advanced separation techniques and molecular simulation calculations. Optimizing chelation process conditions, including pH and temperature, can help in achieving high binding rates. Methods including phosphorylation modification and ultrasonic treatment can enhance the chelating activity.

Evaluating the capability of soybean peptides as calcium ion carriers: a study through sequence analysis and molecular dynamics simulations

Calcium homeostasis imbalance in the body can lead to a variety of chronic diseases. Supplement efficiency is essential. Peptide calcium chelate, a fourth-generation calcium supplement, offers easy absorption and minimal side effects. Its effectiveness relies on peptide's calcium binding capacity. However, research on amino acid sequences in peptides with high calcium binding capacity (HCBC) is limited, affecting the efficient identification of such peptides. This study used soybean peptides (SP), separated and purified by gel chromatography, to obtain HCBC peptide (137.45 μg mg-1) and normal peptide (≤95.78 μg mg-1). Mass spectrometry identified the sequences of these peptides, and an analysis of the positional distribution of characteristic amino acids followed. Two HCBC peptides with sequences GGDLVS (271.55 μg mg-1) and YEGVIL (272.54 μg mg-1) were discovered. Molecular dynamics showed that when either aspartic acid is located near the N-terminal's middle, or glutamic acid is near the end, or in cases of continuous Asp or Glu, the binding speed, probability, and strength between the peptide and calcium ions are superior compared to those at other locations. The study's goal was to clarify how the positions of characteristic amino acids in peptides affect calcium binding, aiding in developing peptide calcium chelates as a novel calcium supplement.

Characterization and Mechanism of a Novel Rice Protein Peptide (AHVGMSGEEPE) Calcium Chelate in Enhancing Calcium Absorption in Caco-2 Cells

Rice protein peptides (RPP) are a potentially valuable source of high-quality calcium chelating properties. However, there is a lack of information regarding the calcium-absorption-promoting effect of RPP and its underlying mechanism. The present study adopted molecular docking methodologies to analyze the 10 most potent peptide segments from RPP. Results revealed that the peptide AHVGMSGEEPE (AHV) displayed optimal calcium binding properties (calcium-chelating capacity 55.69 ± 0.66 mg/g). Quantum chemistry analysis revealed that the AHV peptide effectively binds and forms stable complexes with calcium via the carbonyl oxygen atoms in valine at position 3 and the carbonyl of the C-terminal carboxyl group of glutamate at position 11. The spectral analysis results indicated that AHV may bind to calcium through carboxyl oxygen atoms, resulting in a transition from a smooth surface block-like structure to a dense granular structure. Furthermore, this study demonstrated that the 4 mmol/L AHV-Ca chelate (61.75 ± 13.23 μg/well) significantly increases calcium absorption compared to 1 mM CaCl2 (28.57 ± 8.59 μg/well) in the Caco-2 cell monolayer. In terms of mechanisms, the novel peptide-calcium chelate AHV-Ca derived from RPP exerts a cell-level effect by upregulating the expression of TRPV6 calcium-ion-channel-related genes and proteins (TRPV6 and Calbindin-D9k). This study provides a theoretical basis for developing functional foods with the AHV peptide as ingredients to improve calcium absorption.

Lactobacillus helveticus-Derived Whey-Calcium Chelate Promotes Calcium Absorption and Bone Health of Rats Fed a Low-Calcium Diet

This study investigated the characteristics of Lactobacillus helveticus-derived whey-calcium chelate (LHWCC) and its effect on the calcium absorption and bone health of rats. Fourier-transform infrared spectroscopy showed that carboxyl oxygen atoms, amino nitrogen atoms, and phosphate ions were the major binding sites with calcium in LHWCC, which has a sustained release effect in simulated in vitro digestion. LHWCC had beneficial effects on serum biochemical parameters, bone biomechanics, and the morphological indexes of the bones of calcium-deficient rats when fed at a dose of 40 mg Ca/kg BW for 7 weeks. In contrast to the inorganic calcium supplement, LHWCC significantly upregulated the gene expression of transient receptor potential cation V5 (TRPV5), TRPV6, PepT1, calcium-binding protein-D9k (Calbindin-D9k), and a calcium pump (plasma membrane Ca-ATPase, PMCA1b), leading to promotion of the calcium absorption rate, whereas Ca3(PO4)2 only upregulated the TRPV6 channel in vivo. These findings illustrate the potential of LHWCC as an organic calcium supplement.

Structural characterisation of deer sinew peptides as calcium carriers, their promotion of MC3T3-E1 cell proliferation and their effect on bone deposition in mice

Deer sinew as a by-product has high collagen and nutritional value. This study focuses on its hydrolysate being used as a calcium carrier to develop functional foods. The chelation mechanism was analyzed by SEM, EDS, UV-vis, FTIR, and fluorescence spectroscopy and zeta potential analysis after using peptide-sequenced deer sinew peptides for chelation with calcium ions. The results showed that the chelation of deer sinew peptides with calcium ions occurs mainly at the O and N atoms of carboxyl, amino and amide bonds. In vitro and in vivo studies revealed that deer sinew peptide-calcium chelate (DSPs-Ca) promoted the proliferation of MC3T3-E1 cells without toxic side effects and increased the alkaline phosphatase activity. The DSPs-Ca group improved the bone microstructure induced by low calcium, as well as up-regulated the expression of genes responsible for calcium uptake in the kidneys, as evidenced by serum markers, bone sections, bone parameters, and gene expression analyses in low-calcium-fed mice. From the above, it can be concluded that DSPs-Ca is expected to be a calcium supplement food for promoting bone health.

Dexamethasone-Loaded Lipid Calcium Phosphate Nanoparticles Treat Experimental Colitis by Regulating Macrophage Polarization in Inflammatory Sites

Background

The M1/M2 polarization of intestinal macrophages exerts an essential function in the pathogenesis of ulcerative colitis (UC), which can be adjusted to alleviate the UC symptoms.

Purpose

A kind of pH-sensitive lipid calcium phosphate core-shell nanoparticles (NPs), co-loading with dexamethasone (Dex) and its water-soluble salts, dexamethasone sodium phosphate (Dsp), was constructed to comprehensively regulate macrophages in different states towards the M2 phenotype to promote anti-inflammatory effects.

Methods

Dex and Dsp were loaded in the outer lipid shell and inner lipid calcium phosphate (Cap) core of the LdCaPd NPs, respectively. Then, the morphology of NPs and methods for determining drug concentration were investigated, followed by in vitro protein adsorption, stability, and release tests. Cell experiments evaluated the cytotoxicity, cellular uptake, and macrophage polarization induction ability of NPs. The in vivo distribution and anti-inflammatory effect of NPs were evaluated through a 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced BALB/c mice ulcerative colitis model.

Results

The LdCaPd NPs showed a particle size of about 200 nm and achieved considerable loading amounts of Dex and Dsp. The in vitro and in vivo studies revealed that in the acidic UC microenvironment, the cationic lipid shell of LdCaPd underwent protonated dissociation to release Dex first for creating a microenvironment conducive to M2 polarization. Then, the exposed CaP core was further engulfed by M1 macrophages to release Dsp to restrict the pro-inflammatory cytokines production by inhibiting the activation and function of the nuclear factor kappa-B (NF-κB) through activating the GC receptor and the NF kappa B inhibitor α (I-κBα), respectively, ultimately reversing the M1 polarization to promote the anti-inflammatory therapy.

Conclusion

The LdCaPd NPs accomplished the sequential release of Dex and Dsp to the UC site and the inflammatory M1 macrophages at this site, promoting the regulation of macrophage polarization to accelerate the remission of UC symptoms.

Study on the Changes of Bone Calcium during the Fermentation of Bone Powders with Different Fermenters

Two fermenters, Lactobacillus acidophilus (LA) and the active dry yellow wine yeast (HY), were utilized to ferment cattle bones in order to release calcium. The influences of fermenters and the fermentation process on the calcium release capacity, particle properties, morphology, and chemical composition of bone powders were assessed, and the underlying mechanism was discussed. The results showed that LA had a better capacity of acid production than yeast, and therefore released more calcium during the fermentation of bone powders. The released calcium in the fermentation broth mainly existed in the forms of free Ca2+ ions, organic acid-bound calcium and a small amount of calcium-peptide chelate. For bone powders, the fermentation induced swollen bone particles, increased particle size, and significant changes of the internal chemical structure. Therefore, fermentation has a great potential in the processing of bone-derived products, particularly to provide new ideas for the development of calcium supplement products.

Recent Trends in Cereal- and Legume-Based Protein-Mineral Complexes: Formulation Methods, Toxicity, and Food Applications

Minerals play an important role in maintaining human health as the deficiency of these minerals can lead to serious health issues. To address these deficiencies, current research efforts are actively investigating the utilization of protein-mineral complexes as eco-friendly, non-hazardous, suitable mineral fortifiers, characterized by minimal toxicity, for incorporation into food products. Thus, we reviewed the current challenges in incorporating the cereal-legume protein-inorganic minerals complexes' structure, binding properties, and toxicity during fortification on human health. Moreover, we further reviewed the development of protein-mineral complexes, characterization, and their food applications. The use of inorganic minerals has been associated with several toxic effects, leading to tissue-level toxicity. Cereal- and legume-based protein-mineral complexes effectively reduced the toxicity, improved bone mineral density, and has antioxidant properties. The characterization techniques provided a better understanding of the binding efficiency of cereal- and legume-based protein-mineral complexes. Overall, understanding the mechanism and binding efficiency underlying protein-mineral complex formation provided a novel insight into the design of therapeutic strategies for mineral-related diseases with minimal toxicity.

Preparation, Structural Characterization, and Stability of Low-Molecular-Weight Collagen Peptides-Calcium Chelate Derived from Tuna Bones

This study was conducted to prepare calcium chelate of low-molecular-weight tuna bone collagen peptides (TBCPLMW) with a high chelation rate and to identify its structural characteristics and stability. The optimum conditions for calcium chelation of TBCPLMW (TBCPLMW-Ca) were determined through single-factor experiments and response surface methodology, and the calcium-chelating capacity reached over 90% under the optimal conditions. The amino acid compositions implied that Asp and Glu played important roles in the formation of TBCPLMW-Ca. Structural characterizations determined via spectroscopic analyses revealed that functional groups such as -COO-, N-H, C=O, and C-O were involved in forming TBCPLMW-Ca. The particle size distributions and scanning electron microscopy results revealed that folding and aggregation of peptides were found in the chelate. Stability studies showed that TBCPLMW-Ca was relatively stable under thermal processing and more pronounced changes have been observed in simulated gastric digestion, presumably the acidic environment was the main factor causing the dissociation of the TBCPLMW-Ca. The results of this study provide a scientific basis for the preparation of a novel calcium supplement and is beneficial for comprehensive utilization of tuna bones.