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

Preparation of a cattle bone collagen peptide-calcium chelate by the ultrasound method and its structural characterization, stability analysis, and bioactivity on MC3T3-E1 cells

This study was designed to prepare a cattle bone-derived collagen peptide-calcium chelate by the ultrasound method (CP-Ca-US), and its structure, stability, and bioactivity on MC3T3-E1 cells were characterized. Single-factor experiments optimized the preparation conditions: ultrasound power 90 W, ultrasound time 40 min, CaCl₂/peptides ratio 1/2, pH 7. Under these conditions, the calcium-chelating ability reached 39.48 μg mg^-1. The result of Fourier transform-infrared spectroscopy indicated that carboxyl oxygen and amino nitrogen atoms were chelation sites. Morphological analysis indicated that CP-Ca-US was characterized by a porous surface and large particles. Stability analysis demonstrated that CP-Ca-US was stable in the thermal environment and under intestinal digestion. CP-Ca-US showed more stability in gastric juice than the chelate prepared by the hydrothermal method. Cell experiments indicated that CP-Ca-US increased osteoblast proliferation (proliferation rate 153% at a concentration of 300 μg mL^-1) and altered the cell cycle. Significantly, CP-Ca-US enhanced calcium absorption by interacting with calcium-sensing receptors and promoted the mineralization of MC3T3-E1 cells. This study provides the scientific basis for applying the ultrasound method to prepare peptide-calcium chelates and clarifies the positive role of chelates in bone building.

Isolation and Characterization of Collagen and Collagen Peptides with Hyaluronidase Inhibition Activity Derived from the Skin of Marlin (Istiophoridae)

Type I and V collagens are the major components of fibrillogenic proteins in fish skin, and their hydrolysis products possess hyaluronidase inhibitory activity. In this study, for the first time, type I and V collagens were isolated from the skin of shortbill spearfish and striped marlin. Type I (2α1[I]α2[I]) and type V (α1[V]α3[V]α2[V]) collagens composed of distinct α-peptide chains with comparable structures were investigated using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and UV spectrophotometric chromatography. After enzymatic digestion, the collagen peptides were purified by using ultrafiltration (30 KDa) and high-performance liquid chromatography (RP-HPLC) to yield CPI-F3 and CPV-F4 fractions with strong hyaluronidase inhibition rates (42.17% and 30.09%, respectively). Based on the results of simulated gastrointestinal fluid, temperature, and pH stability assays, CPI-F3 and CPV-F4 exhibited stability in gastric fluid and showed no significant changes under the temperature range from 50 to 70 °C (p > 0.05). The results of this first research on the bioactivity of type V collagen peptides provide valuable information for the biomedical industry and show the potential for future bioactivity investigations of type V collagen and its peptides.

A novel Atlantic salmon (Salmo salar) bone collagen peptide delays osteoarthritis development by inhibiting cartilage matrix degradation and anti-inflammatory

Nowadays, the biological activity of collagen peptides has been revealed, but the effect of Atlantic salmon (Salmo salar) bone-derived collagen peptide (CPs) on osteoarthritis remains unclear. In this study, CPs was identified as a small molecular weight peptide rich in Gly-X-Y structure. Meanwhile, interleukin-1β (IL-1β)-induced hypertrophic chondrocytes and partial medial meniscectomy (pMMx) surgery model in rats were performed. In IL-1β stimulated chondrocytes, CPs significantly increased the type-II collagen content, reduced the type-X collagen abundance and chondrocytes apoptosis. Meanwhile, CPs reversed the increased expression of matrix metalloproteinase, metalloproteinase with thrombospondin motifs and RUNX family transcription factor 2 in chondrocytes induced by IL-1β. In vivo, CPs increased pain tolerance of rats and without organ toxicity at 1.6 g/kg.bw. CPs significantly decreased the levels of COMP and Helix-II in serum. Furthermore, a significant decrease of IL-1β in synovial fluid and cartilage tissue were observed by CPs intervention. From Micro-CT, CPs (0.8 g/kg.bw) significantly decreased Tb.sp and SMI value. Meanwhile, the expression of tumor necrosis factor and interleukin-6 were reduced by CPs administration both in vitro and in vivo. Together, CPs showed potential to be a novel and safe dietary supplement for helping anti-inflammatory and cartilage regeneration, ultimately hindering osteoarthritis development. However, the clear mechanism of CPs's positive effect on osteoarthritis needs to be further explored.

High-efficiency secretory expression and characterization of the recombinant type III human-like collagen in Pichia pastoris

Collagen, the highest content protein in the body, has irreplaceable biological functions, and it is widespread concerned in food, beauty, and medicine with great market demand. The gene encoding the recombinant type III human-like collagen α1 chain fragment was integrated into P. pastoris genome after partial amino acids were substituted. Combined with promoter engineering and high-density fermentation technology, soluble secretory expression with the highest yield of 1.05 g L-1 was achieved using two-stage feeding method, and the purity could reach 96% after affinity purification. The determination of N/C-terminal protein sequence were consistent with the theoretical expectation and showed the characteristics of Gly-X-Y repeated short peptide sequence. In amino acid analysis, glycine shared 27.02% and proline 23.92%, which were in accordance with the characteristics of collagen. Ultraviolet spectrum combined with Fourier transform infrared spectroscopy as well as mass spectrometry demonstrated that the target product conformed to the characteristics of collagen spectrums and existed as homologous dimer and trimer in the broth. This work provided a sustainable and economically viable source of the recombinant type III human-like collagen.

Casein phosphopeptide-calcium chelate: Preparation, calcium holding capacity and simulated digestion in vitro

In this work, CPP-Ca chelate was synthesized by chelating casein phosphopeptide (CPP) and calcium and characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The antioxidant activity and calcium holding capacity of CPP-Ca were evaluated and its secondary structure transition was monitored during gastrointestinal digestion by in situ Raman spectroscopy. The results demonstrated that calcium chelating rate reached 40 % and calcium ion was bound to CPP mainly through the interaction of carboxyl and amino groups. The result of calcium holding capacity confirmed the formation of calcium phosphate precipitates could be delayed by 10-15 min with increasing CPP concentration. In vitro simulated digestion revealed CPP-Ca exhibited excellent calcium solubility and its secondary structural changes occurred, especially α-helix and β-sheet content. These findings provided significant insights into enhancing bioavailability of calcium supplements and developing of calcium functional foods for human and animals.

Peptide-Calcium Chelate from Antler (Cervus elaphus) Bone Enhances Calcium Absorption in Intestinal Caco-2 Cells and D-gal-Induced Aging Mouse Model

Antler bone calcium (AB−Ca) and bioactive peptides (ABPs) were extracted from antler bones (Cervus elaphus) to maximize their value. In this study, 0.14 g calcium was obtained from 1 g antler bone. The peptide−calcium chelate rate was 53.68 ± 1.80%, and the Gly, Pro, and Glu in ABPs were identified to donate most to the increased calcium affinity through the mass spectrometry. Fourier transform infrared spectroscopy showed that calcium predominantly interacted with amino nitrogen atoms and carboxyl oxygen atoms, thereby generating a peptide–calcium chelate. The peptide−calcium chelates were characterized using scanning electron microscopy. A Caco-2 cell monolayer model showed that ABPs significantly increased calcium transport. Furthermore, the D-gal-induced aging mouse model indicated that the ABPs + AB−Ca group showed higher Ca and PINP levels, lower P, ALP, and CTX-1content in serum, and considerably higher tibia index and tibia calcium content. Results showed that ABPs + AB-Ca increased bone formation and inhibited bone resorption, thereby providing calcium supplements for ameliorating senile osteoporosis (SOP).

Isolation, Purification and Structure Identification of a Calcium-Binding Peptide from Sheep Bone Protein Hydrolysate

To isolate a novel peptide with calcium-binding capacity, sheep bone protein was hydrolyzed sequentially using a dual-enzyme system (alcalase treatment following neutrase treatment) and investigated for its characteristics, separation, purification, and structure. The sheep bone protein hydrolysate (SBPH) was enriched in key amino acids such as Gly, Arg, Pro, Leu, Lys, Glu, Val, and Asp. The fluorescence spectra, circular dichroism spectra, and Fourier-transform infrared spectroscopy results showed that adding calcium ions decreased the α-helix and β-sheet content but significantly increased the random and β-turn content (p < 0.05). Carboxyl oxygen and amino nitrogen atoms of SBPH may participate in peptide−calcium binding. Scanning electron microscopy and energy dispersive spectrometry results showed that SBPH had strong calcium-chelating ability and that the peptide−calcium complex (SBPH−Ca) combined with calcium to form a spherical cluster structure. SBPH was separated and purified gradually by ultrafiltration, gel filtration chromatography, and reversed-phase high-performance liquid chromatography. Liquid chromatography-electrospray ionization/mass spectrometry identified the amino acid sequences as GPSGLPGERG (925.46 Da) and GAPGKDGVRG (912.48 Da), with calcium-binding capacities of 89.76 ± 0.19% and 88.26 ± 0.25%, respectively. The results of this study provide a scientific basis for the preparation of a new type of calcium supplement and high-value utilization of sheep bone.

Preparation, characterization, and osteogenic activity mechanism of casein phosphopeptide-calcium chelate

Casein phosphopeptides (CPPs) are good at calcium-binding and intestinal calcium absorption, but there are few studies on the osteogenic activity of CPPs. In this study, the preparation of casein phosphopeptide calcium chelate (CPP-Ca) was optimized on the basis of previous studies, and its peptide-calcium chelating activity was characterized. Subsequently, the effects of CPP-Ca on the proliferation, differentiation, and mineralization of MC3T3-E1 cells were studied, and the differentiation mechanism of CPP-Ca on MC3T3-E1 cells was further elucidated by RNA sequencing (RNA-seq). The results showed that the calcium chelation rate of CPPs was 23.37%, and the calcium content of CPP-Ca reached 2.64 × 10⁵ mg/kg. The test results of Ultraviolet–Visible absorption spectroscopy (UV) and Fourier transform infrared spectroscopy (FTIR) indicated that carboxyl oxygen and amino nitrogen atoms of CPPs might be chelated with calcium during the chelation. Compared with the control group, the proliferation of MC3T3-E1 cells treated with 250 μg/mL of CPP-Ca increased by 21.65%, 26.43%, and 28.43% at 24, 48, and 72 h, respectively, and the alkaline phosphatase (ALP) activity and mineralized calcium nodules of MC3T3-E1 cells were notably increased by 55% and 72%. RNA-seq results showed that 321 differentially expressed genes (DEGs) were found in MC3T3-E1 cells treated with CPP-Ca, including 121 upregulated and 200 downregulated genes. Gene ontology (GO) revealed that the DEGs mainly played important roles in the regulation of cellular components. The enrichment of the Kyoto Encyclopedia of Genes and Genomes Database (KEGG) pathway indicated that the AMPK, PI3K-Akt, MAPK, and Wnt signaling pathways were involved in the differentiation of MC3T3-E1 cells. The results of a quantitative real-time PCR (qRT-PCR) showed that compared with the blank control group, the mRNA expressions of Apolipoprotein D (APOD), Osteoglycin (OGN), and Insulin-like growth factor (IGF1) were significantly increased by 2.6, 2.0 and 3.0 times, respectively, while the mRNA levels of NOTUM, WIF1, and LRP4 notably decreased to 2.3, 2.1, and 4.2 times, respectively, which were consistent both in GO functional and KEGG enrichment pathway analysis. This study provided a theoretical basis for CPP-Ca as a nutritional additive in the treatment and prevention of osteoporosis.

Modulatory activity of a bovine hydrolyzed collagen-hydroxyapatite food complex on human primary osteoblasts after simulating its gastrointestinal digestion and absorption

INTRODUCTION

osteoporosis is the most prevalent bone disease and one of the main causes of chronic disability in middle and advanced ages. Conventional pharmacological treatments are still limited, and their prolonged use can cause adverse effects that motivate poor adherence to treatment. Nutritional strategies are traditionally based on supplementing the diet with calcium and vitamin D. Recent studies confirm that the results of this supplementation are significantly improved if it is accompanied by the intake of oral hydrolyzed collagen.

OBJECTIVE

to evaluate the possible in vitro osteogenic activity of a peptide-mineral complex formed by bovine hydrolyzed collagen and bovine hydroxyapatite (Phoscollagen®, PHC®).

METHODS

the digestion and absorption of PHC® were simulated using the dynamic gastrointestinal digester of AINIA and Caco-2 cell model, respectively. Primary cultures of human osteoblasts were treated with the resulting fraction of PHC® and changes were evaluated in the proliferation of preosteoblasts and in the mRNA expression of osteogenic biomarkers at different stages of osteoblast maturation: Runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), osteocalcin (OC) and type I collagen (ColA1).

RESULTS

an increase in preosteoblastic proliferation was observed (p ≤ 0,05). No changes were detected in the biomarkers of osteoblasts with 5 days of differentiation, but were with 14 days, registering an increase in Runx2 (p = 0.0008), ColA1 (p = 0.035), OC (p = 0.027) and ALP (without significance).

CONCLUSION

these results show that the PHC® peptide-mineral complex stimulates the activity of mature osteoblasts, being capable of promoting bone formation.

Purification and Characterization of a Novel Calcium-Binding Heptapeptide from the Hydrolysate of Tilapia Bone with Its Osteogenic Activity

In this study, a calcium-binding peptide was obtained by hydrolyzing tilapia bone and its osteogenic activity was evaluated. Animal protease was selected from nine enzymes, and its hydrolysate was purified through preparative and semi-preparative reverse phase high-performance liquid chromatography. The purified peptide was identified as DGPSGPK (656.32 Da) and its calcium-binding capacity reached 111.98 µg/mg. The peptide calcium chelate (DGPSGPK-Ca) was obtained, and its structure was characterized through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and mass spectrometry (MS). The results of XRD and SEM showed that DGPSGPK-Ca was formed as a new compound. The carboxyl and amino groups of Lys and Asp residues may be the chelating sites of DGPSGPK according to the FTIR and MS results. The molecular simulation showed the carbonyl groups of Asp, Pro, Ser, and Lys residues involved in the binding of calcium. The interaction of DGPSGPK and different integrins was evaluated by molecular docking simulation, and the main forces involved were electrostatic interaction forces, hydrogen bonding and hydrophobic interactions. Furthermore, DGPSGPK could inhibit the differentiation of osteoclast and promote the proliferation, differentiation and mineralization of osteoblasts.

Preparation of corn ACE inhibitory peptide-ferrous chelate by dual-frequency ultrasound and its structure and stability analyses

In order to improve iron chelating ability and retain the activity of functional peptide, corn peptide was chelated with iron to form corn ACE inhibitory peptide-ferrous chelate (CP-Fe) treated by dual-frequency ultrasound. Furthermore, the chelating mechanism was revealed by analyzing various structural changes, and the stability was further evaluated. Under this study condition, the iron-binding capacity of corn ACE inhibitory peptide (CP) and chelate yield reached 66.39% and 82.87%, respectively. Ultrasound-treated CP exhibited a high iron chelating ability, meanwhile, chelation reaction had no significant effect on the ACE inhibition activity (82.21%) of the peptide. CP-Fe was formed by binding the peptides amino, carbonyl and carboxyl groups with Fe2+ demonstrated by Ultra-violet spectroscopy, Fourier transform infrared characterization, X-ray diffraction, energy dispersion spectrum, zeta potential, amino acid composition and other multi-angle analyses. Moreover, ultrasound-treated CP-Fe chelate exhibited porous surface and uniform nanoparticle shape. Furthermore, ultrasound-treated CP-Fe chelate exhibited an excellent stability towards various pH (retention rate ≥ 95.47% at pH 6-10), temperatures (retention rate ≥ 85.10% at 25-70 °C), and gastrointestinal digestion (retention rate 79.18%). Overall, ultrasound-treated CP-Fe chelate possessed high iron-chelating ability, ACE inhibition activity and stability. This study provides a novel synthesis method of the iron-chelating corn ACE inhibitory peptide, which is promising to be applied as iron supplements with high efficiency, bioactivity, and stability.

Diluted Acetic Acid Softened Intermuscular Bones from Silver Carp (Hypophthalmichthys molitrix) by Dissolving Hydroxyapatite and Collagen

Intermuscular bones (IBs) pose physical hazards that threaten consumer health and food safety. This study aimed to investigate the mechanism of softening IBs from silver carp with diluted acetic acid. IBs (separated from muscle) and fillets (without removing IBs) were treated with diluted acetic acid. Analyses of sensory attributes and the hardness of treated IBs indicated that diluted acetic acid (<10 mmol/L) could soften IBs effectively. Additionally, 0.5 mmol/L acetic acid softened IBs within fillets without significantly affecting the texture and flavor of fillets. Analyses of microstructure, minerals (calcium and phosphorus) and collagen content, and the Fourier transform infrared (FTIR) spectra of IBs indicated that acetic acid broke connections (formed by collagen that shared hydroxyl groups) between collagen molecules, and between collagen and hydroxyapatite (HAP), thus inducing the dissolution of collagen and HAP. The dissolution of HAP contributed more to IBs softening than collagen.

Effect of Welsh Onion on Taste Components and Sensory Characteristics of Porcine Bone Soup

To investigate the effect of welsh onion on taste components and sensory characteristics in porcine bone soup, the stewing condition was as follows: the material–liquid ratio (m/V) was 1:1, the stewing time was 5.0 h, and the ratio of welsh onion was 2.5%. Then, the content of taste components was measured. The content of free amino acids in porcine bone soup with welsh onion (PWS) was higher than the sum of welsh onion soup (WS) and porcine bone soup (PS); particularly, the umami amino acids increased by 35.73% compared with PS. Significant increases in four organic acids (lactic acid, pyroglutamic acid, citric acid and ascorbic acid), two 5′-nucleotides (5′-AMP and 5′-GMP) and three mineral elements (K, Ca and Mg) were observed in PWS. Compared with PS, the equivalent umami concentration (EUC) value was increased from 79.09 to 106.47 mg MSG/100 g in PWS, which was due to the high content of umami amino acids and the synergistic effect with 5′-nucleotides. The results of the sensory analysis indicated a certain enhancement of umami taste in PWS, and the sweet and salty tastes were also increased with the addition of welsh onion. The correlation analysis was consistent with the variation of the components tested above.

Fabrication of a ferritin-casein phosphopeptide-calcium shell-core composite as a novel calcium delivery strategy

Plant ferritin has a natural cage-like nanospace for carrying bioactive ingredients. By taking advantage of the calcium binding ability of casein phosphopeptide (CPP) and the cage-like conformation of plant ferritin, a ferritin-CPP shell-core complex (FC) was fabricated with the reversible self-assembly character of ferritin induced by a pH 2.0/7.0 transition strategy. The FC-calcium composite (FCC) was further fabricated by binding of the FC with calcium ions. When the same amount of calcium was loaded, the calcium binding capacity of the FCC was 28.13 ± 1.65%, which was significantly higher than that of ferritin and CPP alone. Fluorescence and Fourier transform infrared analysis indicated that the CPP encapsulation and the calcium binding in the FCC influenced the ferritin structure. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) results showed that the spherical morphology and the 12 nm-diameter size were sustained in the FC and FCC. Moreover, the FCC as a transport carrier could increase the precipitation time of calcium phosphate, and the encapsulated calcium could be released in a more sustained manner as compared with ferritin and CPP under simulated in vitro gastrointestinal conditions. This study presents a novel calcium delivery strategy based on the ferritin cage and CPP, which will improve the applicability of ferritin and CPP and enhance the bioavailability of calcium ions.

A comprehensive review of calcium and ferrous ions chelating peptides: Preparation, structure and transport pathways

Calcium and iron play crucial roles in human health, deficiencies of which have globally generated public health risks. The poor solubility, low bioavailability and gastrointestinal irritation of existing commercial mineral supplements limit their further application. As an emerging type of mineral supplement, mineral chelating peptides have drawn plenty of attention due to their advantages in stability, absorptivity and safety. A majority of calcium and ferrous ions chelating peptides have been isolated from food processing by-products. Enzymatic hydrolysis combined with affinity chromatography, gel filtration and other efficient separation techniques is the predominant method to obtain peptides with high calcium and ferrous affinity. Peptides with small molecular weight are more likely to chelate metals, and carboxyl, amino groups and nitrogen, oxygen, sulfur atoms in the side chain, which can provide lone-pair electrons to combine with metallic ions. Unidentate, bidentate, tridentate, bridging and α mode are regarded as common chelating modes. Moreover, the stability of peptide-mineral complexes in the gastrointestinal tract and possible transport pathways were summarized. This review is to present an overview of the latest research progress, existing problems and research prospects in the field of peptide-mineral complexes and to provide a more comprehensive theoretical basis for their exploitation in food industry.

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.

Enthalpy-entropy compensation in calcium binding to acid-base forms of glycine tyrosine dipeptides from hydrolysis of α-lactalbumin

Calcium binding to peptides formed by hydrolysis of whey proteins during digestion is important for calcium uptake in the intestines and affects the antioxidant function of the peptides. For the two dipeptides, Gly-Tyr and Tyr-Gly, potential hydrolysis products of α-lactalbumin, calcium binding to the three forms of each dipeptide in acid-base equilibrium at intestinal pH was determined electrochemically and compared to binding to tyrosine for aqueous 0.16 M NaCl for 5 < pH < 9 at 15 °C, 25 °C, and 37 °C. At milk pH at 25 °C, binding of calcium to the zwitterion of GlyTyr dominates, with an association constant K_ass2 = 22 M^-1 with ΔH⁰ = -46 kJ·mol^-1, while binding to the mononegative TyrGly dominates for TyrGly with K_ass3 = 32 M^-1 and ΔH⁰ = -38 kJ·mol^-1. At intestinal conditions, pH = 7 and 37 °C, binding of calcium has similar affinity for GlyTyr and TyrGly, while at higher pH and lower temperature, GlyTyr binds stronger. Density Functional Theory calculations confirmed a stronger binding to the zwitterion of GlyTyr than of TyrGly and an increasing affinity with increasing pH for both. Calcium binding to the acid/base forms of the dipeptides is at neutral pH strongly exothermic with ΔH⁰ becoming less negative at higher pH, and a linear enthalpy-entropy compensation (r² = 0.99) results in comparable binding important for calcium bioavailability along the changing distribution among acid-base forms. Calcium binding decreases radical scavenging rate and antioxidative activity of both dipeptides.

Purification and Identification of Novel Xanthine Oxidase Inhibitory Peptides Derived from Round Scad (Decapterus maruadsi) Protein Hydrolysates

The objective of the present study was to investigate the xanthine oxidase (XO) inhibitory effects of peptides purified and identified from round scad (Decapterus maruadsi) hydrolysates (RSHs). In this study, RSHs were obtained by using three proteases (neutrase, protamex and alcalase). Among them, the RSHs of 6-h hydrolysis by neutrase displayed the strongest XO inhibitory activity and had an abundance of small peptides (<500 Da). Four novel peptides were purified by immobilized metal affinity chromatography and identified by nano-high-performance liquid chromatography mass/mass spectrometry. Their amino acid sequences were KGFP (447.53 Da), FPSV (448.51 Da), FPFP (506.59 Da) and WPDGR (629.66 Da), respectively. Then the peptides were synthesized to evaluate their XO inhibitory activity. The results indicated that the peptides of both FPSV (5 mM) and FPFP (5 mM) exhibited higher XO inhibitory activity (22.61 ± 1.81% and 20.09 ± 2.41% respectively). Fluorescence spectra assay demonstrated that the fluorescence quenching mechanism of XO by these inhibitors (FPSV and FPFP) was a static quenching procedure. The study of inhibition kinetics suggested that the inhibition of both FPSV and FPFP was reversible, and the type of their inhibition was a mixed one. Molecular docking revealed the importance of π-π stacking between Phe residue (contained in peptides) and Phe⁹¹⁴ (contained in the XO) in the XO inhibitory activity of the peptides.

Anti-osteoporosis effect and purification of peptides with high calcium-binding capacity from walnut protein hydrolysates

The walnut protein hydrolysate (WPH) was prepared via simulated gastrointestinal digestion. The degree of hydrolysis (DH), amino acid composition, and relative molecular weight distribution of WPH were analyzed. The results showed that the DH of WPH was 11.6%, WPH was rich in Glu and Pro, and the relative average molecular weight of 572 Da accounted for 59.78%. The effects of WPH on osteoporosis were evaluated using a model of retinoic acid-induced osteoporosis rat. Treatment with WPH effectively increased the serum calcium and phosphorus contents, alleviated calcium loss, and reduced tartrate-resistant acid phosphate and alkaline phosphatase activities and bone gla protein content. WPH treatment significantly improved the biomechanical properties of the bone and increased the value of bone mineral density. In addition, WPH treatment improved the bone microstructure. WPH was isolated and purified by Sephadex G-25 gel filtration chromatography and semi-preparative reversed-phase high-performance liquid chromatography. A fraction with high calcium-binding activity was obtained and 15 peptides were identified.

Zinc delivery system constructed from food-borne nanoparticles derived from Undaria pinnatifida

Food-borne nanoparticles from Undaria pinnatifida (UPFNs) were prepared and successfully applied as nanocarriers for microelement zinc delivery. UPFNs were spherical nanoparticles with average sizes of about 4.07 ± 1.09 nm, which chelated with zinc ions through amino nitrogen and carboxyl oxygen atoms as characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and 1H nuclear magnetic resonance spectroscopy. Thermodynamic analysis revealed that the overall chelation process between UPFNs and zinc ions was a spontaneous enthalpy-driven endothermic reaction. Compared to zinc sulfate, UPFN-Zn2+ showed higher solubility both in phytic acid solution and the process of gastrointestinal digestion. Meanwhile, no obvious cytotoxicity was found in UPFNs and UPFN-Zn2+. Specifically, UPFN-Zn2+ could successfully rescue cell viability, DNA replication activity and restore cell proliferation ability in zinc-deficient cells induced by a specific zinc chelator TPEN. Overall, UPFNs might serve as efficient, stable, and safe nanocarriers for zinc delivery.

The Preparation, Antioxidant Activity Evaluation, and Iron-Deficient Anemic Improvement of Oat (Avena sativa L.) Peptides-Ferrous Chelate

Iron-chelating peptides have been widely considered as one of the best iron supplements to alleviate the iron deficiency. In this study, a novel oat peptides-ferrous (OP-Fe2+) chelate was prepared from antioxidant oat peptides obtained in the laboratory of the authors. The optimal preparation condition was obtained through the single-factor and response surface methodology, and the chelating rate could reach up to 62.6%. After chelation, the OP-Fe2+ chelate exhibited a significantly higher 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity than oat peptides. It was discovered that the hemoglobin concentration and the number of red blood cell levels in OP-Fe2+-treated iron-deficient anemic (IDA) rats were significantly higher than untreated IDA rats. The OP-Fe2+ chelate could also improve the hypertrophy of the spleen, serum iron (SI), total iron and binding capacity, and serum ferritin levels in the IDA rats. In addition, the OP-Fe2+ treatment significantly increased the antioxidant activities of super oxidase and glutathione in the liver homogenate of the IDA rats. Therefore, the OP-Fe2+ chelate is an effective type of iron supplement for IDA rats, which could be a promising source with anti-anemia and antioxidant activity.

Nanoliposomes for encapsulation and calcium delivery of egg white peptide-calcium complex

Nanoliposomes and crude liposomes loaded with egg white peptide-calcium complex (EWP-Ca) were fabricated by thin-film dispersion with or without dynamic high-pressure microfluidization. Their physiochemical properties, in vitro stability, and calcium release profiles were investigated in this study. Results showed that the EWP-Ca-loaded nanoliposomes exhibited spherical structures with a lower particle size and polydispersity index as well as a higher thermal stability as compared to the corresponding crude liposomes. Further investigations revealed that EWP-Ca was embedded into the liposomes mainly through hydrogen bonding and present in an amorphous form within the liposomes. Additionally, the EWP-Ca-loaded nanoliposomes effectively slowed the release of calcium in gastric digestion, allowing more soluble calcium to enter the intestinal tract; in the subsequent intestinal digestion, the EWP-Ca-loaded nanoliposomes were more electrically and physically stable than the crude liposomes. Therefore, the EWP-Ca-loaded nanoliposomes could be used as a favorable dietary calcium delivery system to promote calcium bioavailability. PRACTICAL APPLICATION: Nanoliposomes were fabricated in this study to encapsulate the egg white peptide-calcium complex (EWP-Ca) for calcium delivery. The EWP-Ca-loaded nanoliposomes effectively slowed the release of calcium in gastric digestion, allowing more soluble calcium to enter the intestinal tract, and were more electrically and physically stable in the subsequent intestinal digestion. Therefore, the EWP-Ca-loaded nanoliposomes may be incorporated in calcium-fortified food to enhance calcium delivery for maintaining bone health.

Influence of ultrasound-assisted ionic liquid pretreatments on the functional properties of soy protein hydrolysates

In this work, the effect of dual-frequency ultrasound-assisted ionic liquids (ILs) pretreatment on the functional properties of soy protein isolate (SPI) hydrolysates was investigated. The degree of hydrolysis (DH) of SPI pretreated by ultrasound and [BMIM][PF₆] increased by 12.53% as compared to control (P < 0.05). More peptides with low molecular weight were obtained, providing support for the changes in DH. The trichloroacetic acid-nitrogen soluble index presented an increase, suggesting a better protein hydrolysate property. The increase in the calcium-binding activity showed the ultrasound-assisted ILs pretreatment could potentially improve bone health. The foaming capacity and stability of SPI hydrolysates pretreated by ultrasound-assisted [BMIM][PF₆] always increased remarkably as compared to ultrasound-assisted [BDMIM][Cl] pretreatment. However, the synergistic effect of ultrasound-assisted [BMIM][PF₆] on the emulsifying activity and antioxidant activities (DPPH and hydroxyl radical scavenging activity) was not as ideal as ultrasound-assisted [BDMIM][Cl] pretreatment, which may be affected by the structure of peptide. In conclusion, these results indicated the combination of dual-frequency ultrasound and ionic liquids would be a promising method to improve the functional properties of SPI hydrolysates and broaden the application scope of compound modification in proteolysis industry.

A Review on Health-Promoting, Biological, and Functional Aspects of Bioactive Peptides in Food Applications

Food-derived bioactive peptides are being used as important functional ingredients for health-promoting foods and nutraceuticals in recent times in order to prevent and manage several diseases thanks to their biological activities. Bioactive peptides are specific protein fractions, which show broad applications in cosmetics, food additives, nutraceuticals, and pharmaceuticals as antimicrobial, antioxidant, antithrombotic, and angiotensin-I-converting enzyme (ACE)-inhibitory ingredients. These peptides can preserve consumer health by retarding chronic diseases owing to modulation or improvement of the physiological functions of human body. They can also affect functional characteristics of different foods such as dairy products, fermented beverages, and plant and marine proteins. This manuscript reviews different aspects of bioactive peptides concerning their biological (antihypertensive, antioxidative, antiobesity, and hypocholesterolemic) and functional (water holding capacity, solubility, emulsifying, and foaming) properties. Moreover, the properties of several bioactive peptides extracted from different foods as potential ingredients to formulate health promoting foods are described. Thus, multifunctional properties of bioactive peptides provide the possibility to formulate or develop novel healthy food products.

Effect of Enzymatic Hydrolysis on the Zinc Binding Capacity and in vitro Gastrointestinal Stability of Peptides Derived From Pumpkin (Cucurbita pepo L.) Seeds

Zinc is a crucial micronutrient for maintaining body immune system and metabolism function. However, insufficient intake from diet may lead to zinc deficiency and impair normal body function. In addition, conventional zinc salts supplementation has the disadvantage of low bioavailability since the zinc ions may be easily chelated by dietary fiber or phytate commonly found in diets rich in plants, and form precipitates that cannot be absorbed. Therefore, the objective of the present study is to prepare pumpkin seed derived peptides and to evaluate the effect of structure and surface properties on the zinc binding behavior of the pumpkin seed protein hydrolysate (PSPH), as well as their gastrointestinal stability. Briefly, different PSPHs were prepared using enzymatic hydrolysis method with bromelain, papain, flavourzyme, alcalase, and pepsin. The particle size, zeta potential, surface hydrophobicity, degree of hydrolysis, ATR-FTIR spectra, and zinc binding capacity were determined. The representative samples were chosen to characterize the binding energy and surface morphology of PSPH-Zn. At last, the in vitro gastrointestinal stability of PSPH and PSPH-Zn were evaluated. Our results showed that peptides hydrolyzed by papain had the largest average molecular weight, smallest particle size, highest hydrophobicity, and the greatest zinc binding capacity. Zinc showed better gastrointestinal stability in PSPHs chelates than in its salt. Meanwhile, PSPH-Zn with higher zinc binding capacity showed better stability. The result of this study indicated pumpkin seed hydrolyzed by papain may be used as a potential source for zinc fortification. The findings in this study may provide important implications for developing plant-based zinc chelating peptides.

Extraction optimization and screening of angiotensin-converting enzyme inhibitory peptides from Channa striatus through bioaffinity ultrafiltration coupled with LC-Orbitrap-MS/MS and molecular docking

Channa striatus is high-protein food with many health functions. This study aimed to prepare, screen and identify the angiotensin-converting enzyme inhibition peptides (ACEIPs) from C. striatus hydrolysates by response surface methodology and bioaffinity ultrafiltration coupled with LC-Orbitrap-MS/MS and molecular docking. The optimal conditions for preparing ACEIPs were hydrolysis temperature 55 °C, hydrolysis time 3 h, pH 9, solid-liquid ratio 1:20 g/mL, and enzyme addition 5%, the ACE inhibition and molecular weight distribution of obtained hydrolysate was 54.35% and 8770-160 Da, respectively. Seven novel ACEIPs were screened through the established high-throughput screening approach, among which, EYFR and LPGPGP showed the strongest ACE inhibition with the IC₅₀ value of 179.2 and 186.3 μM, respectively (P > 0.05). Molecular docking revealed that three and ten hydrogen bonds were formed between ACE and LPGPGP and EYFR, respectively, S1 and S2 were the major active pockets, but the major driving forces varied.

Electro-deposition synthesis of tube-like collagen-chitosan hydrogels and their biological performance

Electro-deposition is a smart, safe and efficient method for biomaterial manufacturing. Collagen, a functional protein with excellent biocompatibility and biosafety, is a promising candidate for tissue engineering and biomedical applications. However, there are few reports on electro-deposition of biomaterials using collagen without electrically or magnetically active nanoparticles. In this study, electro-deposition was employed to swiftly fabricate tube-like collagen-chitosan hydrogels in a mild environment. Fourier transform infrared spectroscopy was employed to analyze the ingredients of the tube-like hydrogels. The result showed that the hydrogels contained both collagen and chitosan. The distribution and content of collagen in the hydrogels was further measured by hematoxylin-eosin staining and hydroxyproline titration. Collagen was distributed homogeneously and its content was related to the initial collagen:chitosan ratio. The tension resistance of the composite gels and the thermal stability of collagen in the composites were obviously enhanced by the chitosan doping. Meanwhile, the tube-like hydrogels retained a good ability to promote cell proliferation of collagen. This method offers a convenient approach to the design and fabrication of collagen-based materials, which could effectively retain the bioactivity and biosafety of collagen and furnish a new way to enhance the stability of collagen and the tensile strength of collagen-based materials.

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, 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.