Hydrophobic peptides from oyster protein hydrolysates show better zinc-chelating ability

Zn2+ chelating peptide GFLGSP: Characterization of structure/Zn2+ chelating mode and the potential mechanisms for promoting Zn2+ transport in Caco-2 cells

This study focused on exploring the Zn2+ chelating peptide GFLGSP: the characterization of structure/Zn2+ chelating mode and the potential mechanisms for promoting Zn2+ transport in Caco-2 cells. The findings revealed the bidentate chelating between Zn2+ and carboxyl oxygen atom in Pro6 residue. Thereafter, the secondary structure of GFLGSP remained unchanged, but there was an increase in zeta potential and particle size. Notably, the GFLGSP-Zn2+ complex enhanced the Zn2+ transport rate and modulated ZIP4 and ZNT1 expression in a Caco-2 cells monolayer model. As revealed by molecular docking analysis, GFLGSP interacted with ZIP4 through intermolecular hydrogen bonds as well as Van der Waals forces. The Zn2+ transport mechanisms of the GFLGSP-Zn2+ complex encompassed ZIP4 (vital channel), endocytosis (primary pathway) and paracellular transport (supplementary pathway). Based on these results, the tilapia skin collagen-derived GFLGSP hold promise as the potential dietary Zn2+ supplement.

Effect of baking on the structure and bioavailability of protein-binding zinc from oyster (Crassoetrea hongkongensis)

To compare the bioavailability of protein-binding zinc, we investigated the impact of baking on the structure of zinc-binding proteins. The results showed that zinc-binding proteins enriched in zinc with relative molecular weights distributed at 6 kDa and 3 kDa. Protein-binding zinc is predisposed to separate from proteins' interiors and converge on proteins' surface after being baked, and its structure tends to be crystalline. Especially -COO, -C-O, and -C-N played vital roles in the sites of zinc-binding proteins. However, baking did not affect protein-binding zinc's bioavailability which was superior to that of ZnSO4 and C12H22O14Zn. They were digested in the intestine, zinc-binding complexes that were easily transported and uptaken by Caco-2 cells, with transport and uptake rates as high as 62.15% and 15.85%. Consequently, baking can alter the conformation of zinc-binding proteins without any impact on protein-binding zinc's bioavailability which is superior to that of ZnSO4 and C12H22O14Zn.

Dietary zinc supplements: beneficial health effects and application in food, medicine and animals

Zinc, a crucial trace element is vital for the growth and development of humans. It is frequently described as 'the flower of life' and 'the source of intelligence'. Zinc supplements play a pivotal role in addressing zinc deficiency by serving as a vital source of this essential micronutrients, effectively replenishing depleted zinc levels in the body. In this paper, we first described the biological behavior of zinc in the human body and briefly described the physiological phenomena associated with zinc levels. The benefits and drawbacks of various zinc supplement forms are then discussed, with emphasis on the most recent zinc supplement formulations. Finally, the application of zinc supplements in food, medicine, and animal husbandry is further summarized. © 2024 Society of Chemical Industry.

Preparation, characterization and microencapsulation of walnut (Juglans regia L.) peptides-zinc chelate

In this research, a novel kind of walnut (Juglans regia L.) peptides-zinc (Zn-WPs) chelate was obtained using the mass ratio of the walnut peptides (WPs) to ZnSO4.7H2O of 3.5:1 at pH 8.5 and 50°C for 84 min, with the chelation rate of 84.5%. In comparison to walnut peptides (WPs), the contents of aspartic acid and glutamic acid in Zn-WPs chelate are approximately 27%, indicating that hydrophilic amino acids predominantly bind with walnut peptides. Following chelation with zinc ions, the ultraviolet-visible (UV) characteristic absorption peak shifted from 213 nm to 210 nm, while the average particle size of the chelate increased to 8.0 ± 0.14 µm, presenting a loose spherical structure under scanning electron microscopy. These findings suggest the formation of new substances. Fourier-transform infrared spectroscopy (FTIR) revealed carboxyl, amino, and peptide bonds as the chelation sites of WPs and zinc. The IC50 of walnut peptides-zinc (Zn-WPs) chelate is 2.91 mg/mL, indicative of a favorable DPPH radical scavenging rate. Furthermore, Zn-WPs chelate microcapsules were produced via the spray drying method, achieving an encapsulation rate of 75.67 ± 0.83% under optimal conditions. These microcapsules demonstrate robust stability across diverse environmental conditions. This study underscores the potential of Zn-WPs and its chelate microcapsules to enhance stability and bioactivity under varying circumstances. PRACTICAL APPLICATION: In this study, a new walnut peptide-zinc (Zn-WPs) chelate was prepared. The presence of zinc ions changes the structure and properties of walnut peptides and improves its stability. The production of Zn-WPs chelate microcapsules enables Zn-WPs to have strong in vitro stability under different pH and simulated gastrointestinal digestion conditions. These results provide novel insights for developing the walnut peptides as bioactive ingredients in functional foods.

Characterization and in vitro calcium release of the novel calcium-loaded complexes using Antarctic krill protein and pectin: Effect of different blending sequences

Food-grade biopolymer-based complexes are of particular interest in the field of biologic ingredient delivery owing to unique controlled-release properties. Herein, three calcium-loaded complexes using Antarctic krill protein (P) and pectin (HMP) with different blending sequences were designed, named P + Ca + HMP, P + HMP + Ca and HMP + Ca + P, respectively. The calcium-loaded capacity, structural properties, and in vitro gastrointestinal calcium release of the complexes were investigated. The results demonstrated that the calcium binding rate and content of the P + Ca + HMP complex were the highest, reaching to 90.3 % and 39.0 mg/g, respectively. Particularly, the P + Ca + HMP complex exhibited a more stable fruit tree-like structure. Furthermore, the structural analysis confirmed that the primary interaction forces involved hydrogen bond, electrostatic, hydrophobic and ionic bond interaction. Ultimately, the P + Ca + HMP complex demonstrated superior calcium delivery. In conclusion, a novel calcium delivery system was successfully developed based on optimized the self-assembly sequence, which held significant importance in promoting the high-value utilization of Antarctic krill protein and enhancing the in vitro bioaccessibility of calcium.

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.

A novel antioxidant iron-chelating peptide from yak skin: analysis of the chelating mechanism and digestion stability in vitro

BACKGROUND

The global prevalence of iron deficiency has posed significant public health risks. Animal-derived collagen peptides have been recognized for their potent metal ion-chelating capabilities, which can greatly enhance the bioavailability of iron. Yak skins, typically discarded during production and processing, serve as a valuable resource. Based on yak skin collagen peptide (YSP), we have developed a novel iron-chelating peptide: yak skin collagen iron-chelating peptide (YSP-Fe).

RESULTS

The maximum level of iron chelation of YSP-Fe achieved was 42.72 ± 0.65 mg g-1. Structural analysis indicated that YSP-Fe was primarily formed from amino, carboxyl and carbonyl groups combined with ferrous ions. Through examination of the amino acid composition, molecular docking and peptide sequence identification, it was determined that Gly, Asp and Arg played crucial roles in the chelation of ferrous ions by YSP. Furthermore, YSP-Fe was more stable in simulated gastrointestinal digestion compared to FeSO4.

CONCLUSION

YSP-Fe demonstrated dual benefits of iron supplementation and antioxidant effects. These significant findings provide a foundation for the development of novel iron supplements and the effective utilization of yak skin as a valuable resource. © 2024 Society of Chemical Industry.

Plastein reaction augments the metal chelating capabilities of silver carp (Hypophthalmichthys molitrix) hydrolysates: Unlocking the chemical modification mechanism

Plastein reaction mechanisms and the alteration of its product properties have been studied for decades. This study investigated the plastein-mediated modifications in silver carp protein hydrolysate (SCPH) from both mechanistic and functional perspectives. Unlike prior research, this investigation uncovered that hydrogen bonding supplemented the dominant hydrophobic interactions in plastein's mechanism for the first time, as supported by peptide concentrations, molecular weight, amino acids, chemical forces, and peptide sequence by LC-MS/MS. This innovative reaction mechanism cascaded into the enhancement of SCPH functional attributes. Plastein induced increased COOH in SCPH's side-chain groups significantly enhanced Fe2+ (from 4.49 to 14.12 %) and Zn2+ (from 53.53 to 64.47 %) chelation. Moreover, the elevated DPPH (17.56 %-23.97 %) and hydroxyl radical (68.49 %-79.32 %) scavenging power indicated a broader improvement in SCPH with plastein. In SCPH, plastein elucidated reaction intricacies and enhanced its utility, propelling SCPH into a realm of extended potential.

Peptide Extract from Red Kidney Beans, Phaseolus vulgaris (Fabaceae), Shows Promising Antimicrobial, Antibiofilm, and Quorum Sensing Inhibitory Effects

The rapid spread of multidrug-resistant bacteria has led to an increased risk of infectious diseases. Pseudomonas aeruginosa, in particular, poses a significant obstacle due to its propensity to rapidly acquire resistance to conventional antibiotics. This has resulted in an urgent need for the development of new classes of antibiotics that do not induce resistance. Antimicrobial peptides (AMPs) have been studied as potential small-molecule antibiotics due to their unique mode of action. In this study, peptides were extracted from the seeds of Phaseolus vulgaris (Fabaceae), and the antimicrobial activities of the extract were evaluated using microbroth dilution against five different microorganisms. The extract showed antimicrobial activity against all tested organisms with minimum inhibitory concentrations (MIC) of 2.5 mg/mL, except for Candida albicans and Pseudomonas aeruginosa, which had MICs of 1.25 mg/mL. The extract was also bacteriostatic for all tested organisms. The crude peptide extract from Phaseolus vulgaris was further studied for its antibiofilm activity against Pseudomonas aeruginosa, a common nosocomial pathogen associated with biofilm formation. The extract showed good antibiofilm activity at 1/2 MIC. The extract also inhibited the expression of pyocyanin and pyoverdine (virulence factors of P. aeruginosa whose expression is mediated by quorum sensing) by 82% and 66%, respectively. These results suggest that the peptide mix from Phaseolus vulgaris may inhibit biofilm formation and virulence factor expression by interfering with cell-to-cell communication in Pseudomonas aeruginosa. The ability of the extract to inhibit the growth and biofilm formation of all tested organisms indicates its potential as an antimicrobial agent that could be further studied for drug discovery.

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.

Preparation, characterization, and bioavailability evaluation of antioxidant phosvitin peptide-ferrous complex

BACKGROUND

Iron deficiency anemia (IDA) is one of the commonest global nutritional deficiency diseases, and the low bioavailability of iron is a key contributing factor. The peptide-iron complex could be used as a novel iron supplement to improve iron bioavailability.

RESULTS

In this study, antioxidant low molecular weight (<3 kDa) phosvitin peptide (named PP-4) was separated to prepare a phosvitin peptide-ferrous complex (named PP-4-Fe); then the structural conformation of PP-4-Fe was characterized and its bioavailability by in vitro digestion was evaluated. The results showed that PP-4 had good ferrous-binding activity with 96.14 ± 2.86 μg Fe2+ mg-1 , and had a strong antioxidant effect with 995.61 ± 79.75 μmol TE mg-1 in 2,2'-azinobis'3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 62.3 ± 3.95 μmol FeSO4 mg-1 in ferric ion reducing antioxidant power (FRAP). After ferrous binding, the FRAP activity of PP-4-Fe, enhanced by 1.8 times, formed a more ordered structure with an increase in α-helix and decrease in γ-random coil. The ferrous binding sites of PP-4 involved were the amino, carboxyl, imidazole, and phosphate groups. The PP-4-Fe complex displayed excellent gastrointestinal stability and antioxidant effects during digestion. The iron dialysis percentage of PP-4-Fe was 74.59% ± 0.68%, and increased to 81.10% ± 0.89% with the addition of 0.25 times vitamin C (VC). This indicated that PP-4-Fe displayed excellent bioavailability and VC in sufficient quantities had a synergistic effect on improving bioavailability.

CONCLUSIONS

This study demonstrated that antioxidant phosvitin peptide was an efficient delivery system to protect ferrous ions and suggested that the phosvitin peptide-ferrous complex has strong potential as a ferrous supplement. © 2023 Society of Chemical Industry.

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.

Purification, Characterization, cDNA Cloning, and Bioinformatic Analysis of Zinc-Binding Protein from Magallana hongkongensis

Oysters contain significant amounts of the zinc element, which may also be found in their proteins. In this study, a novel zinc-binding protein was purified from the mantle of the oyster Magallana hongkongensis using two kinds of gel filtration chromatograms. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that its molecular weight was approximately 36 kDa. The protein identified by the Q-Exactive mass spectrometer shared the highest sequence identity with carbonic anhydrase derived from Crassostrea gigas concerning amino acid sequence similarity. Based on homologous cloning and RACE PCR, the full-length cDNA of carbonic anhydrase from Magallana hongkongensis (designated as MhCA) was cloned and sequenced. The cDNA of MhCA encodes a 315-amino-acid protein with 89.74% homology to carbonic anhydrase derived from Crassostrea gigas. Molecular docking revealed that the two zinc ions primarily form coordination bonds with histidine residues in the MhCA protein. These results strongly suggest that MhCA is a novel zinc-binding protein in Magallana hongkongensis.

Peptide composition analysis, structural characterization, and prediction of iron binding modes of small molecular weight peptides from mung bean

Iron supplementation is a proactive approach to limit instances of iron deficiency anemia. This study is based on the enzymatic hydrolysis and fractionation of mung bean proteins (MBPs) followed by the determination of the Fe2+ chelating activities of these peptide-containing fractions. MBP-Fe complex was generated using a chemical chelation method and subsequently characterized. Following Sephadex G15 separation of MBPs, one of the fractions containing 10 different peptides, demonstrated maximum Fe2+ chelating activity of 39.97 ± 0.07 μg/mg. The sequences of these peptides were determined using liquid chromatography-tandem mass spectrometry. The Fe2+ ion content of the MBP-Fe complex was determined using X-ray photoelectron spectroscopy and 80% of the iron was found to be in Fe2+ oxidation state. After iron chelation, there was an increase in the peptide's particle size, with an average value of 550.67 ± 0.70 nm. This increase in size was attributed to the contributions of the amino proline and glycine, which extended the peptides to form the MBP-Fe complex. Finally, molecular docking studies revealed that Fe2+ mainly bound to carboxy-oxygen of glutamate and aspartate residues of mung bean peptides to form MBP-Fe complex. This research could serve as a scientific foundation for the development of dietary iron supplements using plant-derived peptides.

A critical review of a typical research system for food-derived metal-chelating peptides: Production, characterization, identification, digestion, and absorption

In the past decade, food-derived metal-chelating peptides (MCPs) have attracted significant attention from researchers working towards the prevention of metal (viz., iron, zinc, and calcium) deficiency phenomenon by primarily inhibiting the precipitation of metals caused by the gastrointestinal environment and exogenous substances (including phytic and oxalic acids). However, for the improvement of limits of current knowledge foundations and future investigation directions of MCP or their derivatives, several review categories should be improved and emphasized. The species' uniqueness and differences in MCP productions highly contribute to the different values of chelating ability with particular metal ions, whereas comprehensive reviews of chelation characterization determined by various kinds of technique support different horizons for explaining the chelation and offer options for the selection of characterization methods. The reviews of chelation mechanism clearly demonstrate the involvement of potential groups and atoms in chelating metal ions. The discussions of digestive stability and absorption in various kinds of absorption model in vitro and in vivo as well as the theory of involved cellular absorption channels and pathways are systematically reviewed and highlighted compared with previous reports as well. Meanwhile, the chelation mechanism on the molecular docking level, the binding mechanism in amino acid identification level, the utilizations of everted rat gut sac model for absorption, and the involvement of cellular absorption channels and pathway are strongly recommended as novelty in this review. This review makes a novel contribution to the literature by the comprehensive prospects for the research and development of food-derived mineral supplements.

Silver Carp (Hypophthalmichthys molitrix) Scales Collagen Peptides (SCPs): Preparation, Whitening Activity Screening and Characterization

This study involves the preparation of scale collagen peptides (SCPs) with whitening activity from silver carp (Hypophthalmichthys molitrix) and their characterization and peptide sequence identification. In this article, scanning electron microscopy (SEM) was used to observe structure changes of sliver carp scales; enzymatic hydrolysis was optimized through protease screening and response surface optimization. The ultrafiltration was used to separate SCPs and the whitening activity was comprehensively evaluated using radical scavenging rate and tyrosinase-inhibiting activity, among others. An optimal component was characterized and identified using various modern spectral analysis techniques. The results showed that the surface of silver carp scales after decalcification was smooth and clear. The pepsin had the highest peptide yield and tyrosinase-inhibiting activity (90.01% and 82.25%, respectively). The optimal enzymatic hydrolysis conditions were an enzyme dosage of 16.1%, a solid–liquid ratio of 1:15.6 and a time of 4.9 h. The proportions of hydrophobic and basic amino acids in the peptide composition were 32.15% and 13.12%, respectively. Compared with SCPs2, SCPs1 (6096.68–9513.70 Da) showed better ·OH scavenging ability, tyrosinase-inhibiting activity and moisture absorption. SCPs1 was a macromolecular fragment of type I collagen with a triple helix structure, containing three peptide sequences with the potential for tyrosinase activity inhibition (AGPPGADGQTGQRGE, SGPAGIAGPAGPRGPAGPNGPPGKD and KRGSTGEQGSTGPLGMRGPRGAA). These results show that SCPs1 is a collagen peptide product with whitening potential.

Identification of a Novel Walnut Iron Chelating Peptide with Potential High Antioxidant Activity and Analysis of Its Possible Binding Sites

Peptide iron chelate is widely regarded as one of the best iron supplements for relieving iron deficiency. In this study, a new type of walnut peptide iron (WP-Fe) chelate was prepared using low molecular weight walnut peptides (WP) as raw materials. Under the conditions of this study, the chelation rate and iron content of the WP-Fe chelate were 71.87 ± 1.60% and 113.11 ± 2.52 mg/g, respectively. Fourier transform infrared spectroscopy (FTIR), zeta potential, amino acid composition, and other structural analysis showed that WP-Fe is formed by the combination of carboxyl, amino and carbonyl with Fe²⁺. The WP-Fe chelate exhibits a honeycomb-like bulk structure different from that of WP. In addition, we predicted and established the binding model of ferrous ion and WP by molecular docking technology. After chelation, the free radical scavenging ability of the WP-Fe chelate was significantly higher than that of the WP. Overall, the WP-Fe chelate has high iron-binding capacity and antioxidant activity. We believe that peptides from different sources also have better iron binding capacity, and peptide iron chelates are expected to become a promising source of iron supplement and antioxidant activities.

Extraction and Identification of Three New Urechis unicinctus Visceral Peptides and Their Antioxidant Activity

The viscera of Urechis unicinctus with polypeptides, fatty acids, and amino acids are usually discarded during processing to food. In order to improve the utilization value of the viscera of Urechis unicinctus and avoid resource waste, antioxidant polypeptides were isolated from the viscera of Urechis unicinctus. First, a protein hydrolysate of Urechis unicinctus (UUPH) was prepared by ultrasonic-assisted enzymatic hydrolysis, and the degree of hydrolysis was as high as 79.32%. Subsequently, three new antioxidant peptides (P1, P2, and P3) were purified from UUPH using ultrafiltration and chromatography, and their amino acid sequences were identified as VTSALVGPR, IGLGDEGLRR, TKIRNEISDLNER, respectively. Then, the antioxidant activity of the polypeptide was predicted by the structure-activity relationship and finally verified by experiments on eukaryotic cells. The P1 peptide exhibited the strongest antioxidant activity among these three antioxidant peptides. Furthermore, P1, P2, and P3 have no toxic effect on RAW264.7 cells at the concentration of 0.01~2 mg/mL and can protect RAW264.7 cells from H2O2-induced oxidative damage in a concentration-dependent manner. These results suggested that these three new antioxidant peptides were isolated from the viscera of Urechis unicinctus, especially the P1 peptide, which might serve as potential antioxidants applied in health-derived food or beverages. This study further developed a new use of the by-product of Urechis unicinctus, which improved the comprehensive utilization of marine biological resources.