Exploration of Iron-Binding Mode, Digestion Kinetics, and Iron Absorption Behavior of Antarctic Krill–Derived Heptapeptide–Iron Complex

Effect of κ-carrageenan on the quality of crayfish surimi gels

The demand for crayfish surimi products has grown recently due to its high protein content. This study examined the effects of varying κ-carrageenan (CAR) and crayfish surimi (CSM) concentrations on the gelling properties of CAR-CSM composite gel and its intrinsic formation process. Our findings demonstrated that with the increasing concentration of carrageenan, the quality of CAR-CSM exhibited rising trend followed by subsequently fall. Based on the textural qualities, the highest quality CAR-CSM was achieved at 0.3% carrageenan addition. With the exception of chewiness, and the cooking loss of the gel system was 1.62%, whiteness was 82.35%, and the percentage of β-sheets increased to 57.18%. Further increase in CAR (0.4-0.5%) addition resulted in internal build-up of LCAR-CSM, conversion of intermolecular forces into disulfide bonds and gel breakage. This study exudes timely recommendations for extending the CAR application for the continuous development of crayfish surimi and its derivatives and its overall economic worth.

Molecular Mechanisms of Iron Transport and Homeostasis Regulated by Antarctic Krill-Derived Heptapeptide-Iron Complex

In this study, the molecular mechanisms of iron transport and homeostasis regulated by the Antarctic krill-derived heptapeptide-iron (LVDDHFL-iron) complex were explored. LVDDHFL-iron significantly increased the hemoglobin, serum iron, total iron binding capacity levels, and iron contents in the liver and spleen to normal levels, regulated the gene expressions of iron homeostasis, and enhanced in vivo antioxidant capacity in iron-deficiency anemia mice (P < 0.05). The results revealed that iron ions within LVDDHFL-iron can be transported via the heme transporter and divalent metal transporter-1, and the absorption of LVDDHFL-iron involved receptor-mediated endocytosis. We also found that the transport of LVDDHFL-iron across cells via phagocytosis was facilitated by the up-regulation of the high mobility group protein, heat shock protein β, and V-type proton ATPase subunit, accompanied by the regulatory mechanism of autophagy. These findings provided deeper understandings of the mechanism of LVDDHFL-iron facilitating iron absorption.

Effect of different iron ratios on interaction and thermodynamic stability of bound whey protein isolate

Whey protein isolates (WPI) are known to have mineral-binding capacity to promote iron absorption. The aim of this study was to investigate the effect of iron ratio on the conformational structure of iron-bound whey protein isolate (WPI-Fe) and its thermodynamic stability. It was shown that the iron to protein ratio affects both the iron binding capacity of WPI and the iron valence state on the surface of WPI-Fe complexes. As the iron content increases, aggregation between protein molecules occurs. In addition, WPI-Fe nanoparticles have thermodynamic stability and Fe2+ has a high affinity with WPI for spontaneous exothermic reactions. This study demonstrates that WPI-Fe complexes can be used to efficiently deliver high-quality iron source (Fe2+) for future iron supplements.

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.

Novel Ca-Chelating Peptides from Protein Hydrolysate of Antarctic Krill (Euphausia superba): Preparation, Characterization, and Calcium Absorption Efficiency in Caco-2 Cell Monolayer Model

Antarctic krill (Euphausia superba) is the world's largest resource of animal proteins and is thought to be a high-quality resource for future marine healthy foods and functional products. Therefore, Antarctic krill was degreased and separately hydrolyzed using flavourzyme, pepsin, papain, and alcalase. Protein hydrolysate (AKH) of Antarctic krill prepared by trypsin showed the highest Ca-chelating rate under the optimized chelating conditions: a pH of 8.0, reaction time of 50 min, temperature of 50 °C, and material/calcium ratio of 1:15. Subsequently, fourteen Ca-chelating peptides were isolated from APK by ultrafiltration and a series of chromatographic methods and identified as AK, EAR, AEA, VERG, VAS, GPK, SP, GPKG, APRGH, GVPG, LEPGP, LEKGA, FPPGR, and GEPG with molecular weights of 217.27, 374.40, 289.29, 459.50, 275.30, 300.36, 202.21, 357.41, 536.59, 328.37, 511.58, 516.60, 572.66, and 358.35 Da, respectively. Among fourteen Ca-chelating peptides, VERG presented the highest Ca-chelating ability. Ultraviolet spectrum (UV), Fourier Transform Infrared (FTIR), and scanning electron microscope (SEM) analysis indicated that the VERG-Ca chelate had a dense granular structure because the N-H, C=O and -COOH groups of VERG combined with Ca2+. Moreover, the VERG-Ca chelate is stable in gastrointestinal digestion and can significantly improve Ca transport in Caco-2 cell monolayer experiments, but phytate could significantly reduce the absorption of Ca derived from the VERG-Ca chelate. Therefore, Ca-chelating peptides from protein hydrolysate of Antarctic krill possess the potential to serve as a Ca supplement in developing healthy foods.

Preparation, structure characterization, and stability analysis of peptide-calcium complex derived from porcine nasal cartilage type II collagen

BACKGROUND

Porcine nasal cartilage type II collagen-derived peptides (PNCPs) may be complexed with calcium to provide a highly bioavailable, low-cost, and effective calcium food supplement. However, the calcium-binding characteristics of PNCPs have not yet been investigated. In the present study, calcium-binding peptides were derived from porcine nasal cartilage type II collagen and the resulting PNCPs-Ca complex was characterized.

RESULTS

The study reveals that the calcium-binding capacity of PNCPs is closely related to enzymatic hydrolysis conditions. The highest calcium-binding capacity of PNCPs was observed at a hydrolysis time of 4 h, temperature of 40 °C, enzyme dosage of 1%, and solid-to-liquid ratio of 1:10. Scanning electron microscopy and energy dispersive X-ray spectroscopy revealed that the PNCPs had a pronounced capacity for calcium binding, with the PNCPs-Ca complex exhibiting a clustered structure consisting of aggregated spherical particles. Fourier-transform infrared spectroscopy, fluorescence spectroscopy, X-ray diffraction, dynamic light scattering, amino acid composition, and molecular weight distribution analyses all indicated that the PNCPs and calcium complexed via the carboxyl oxygen and amino nitrogen atoms, leading to the formation of a β-sheet structure during the chelation process. In addition, the stability of the PNCPs-Ca complex was maintained over a range of pH values consistent with those found in the human gastrointestinal tract, facilitating calcium absorption.

CONCLUSION

These research findings suggest the feasibility of converting by-products from livestock processing into calcium-binding peptides, providing a scientific basis for the development of novel calcium supplements and the potential reduction of resource waste. © 2023 Society of Chemical Industry.

Mechanism for improving the gel properties of transglutaminase-mediated porcine myofibrillar protein by ultrasonic pretreatment combined with carrageenan

To improve the limitation of transglutaminase on the quality of myofibrillar protein (MP) gel, this study investigated the synergistic effect of ultrasonic pretreatment in combination with carrageenan on the gel properties of transglutaminase-mediated MP gels. The synergistic effect generated gel with lower surface hydrophobicity and fluorescence intensity. Combined with the secondary structure results, it can be hypothesized that the synergistic effect caused the rearrangement of the proteins and the formation of aggregates wrapping hydrophobic groups, which changed the structure and phase behavior of the proteins. The synergistic effect also improved the formation of dense and interpenetrating gel networks, which reduced cooking loss and produced composite MP gels with optimal gel strength. Moreover, FTIR spectroscopy revealed the presence of electrostatic interactions in the hybrid gel system. This study provides a theoretical basis and experimental foundation for the effective use of high-tech composite functional components to improve the quality of gel products.

Iron Complexes with Antarctic Krill-Derived Peptides Show Superior Effectiveness to Their Original Protein-Iron Complexes in Mice with Iron Deficiency Anemia

Antarctic krill protein-iron complex and peptide-iron complex were acquired to investigate their iron bioavailability, expression of iron-regulated genes, and in vivo antioxidant capacity. Results indicated that the Antarctic krill peptide-iron complex significantly increased the hemoglobin (Hb), serum iron (SI), and iron contents in the liver and spleen in iron-deficiency anemia (IDA) mice (p < 0.05) compared with those of the Antarctic krill protein-iron complex. Despite the gene expressions of the divalent metal transporter 1(DMT1), the transferrin (Tf), and the transferrin receptor (TfR) being better regulated by both Antarctic krill peptide-iron complex and protein-iron complex, the relative iron bioavailability of the Antarctic krill peptide-iron complex group (152.53 ± 21.05%) was significantly higher than that of the protein-iron complex group (112.75 ± 9.60%) (p < 0.05). Moreover, Antarctic krill peptide-iron complex could enhance the antioxidant enzyme activities of superoxidase dismutase (SOD) and glutathione peroxidase (GSH-Px), reduce the malondialdehyde (MDA) level in IDA mice compared with the protein-iron complex, and reduce the cell damage caused by IDA. Therefore, these results indicated that Antarctic krill peptide-iron complex could be used as a highly efficient and multifunctional iron supplement.

Contribution of κ-/ι-carrageenan on the gelling properties of shrimp myofibrillar protein and their interaction mechanism exploration

BACKGROUND

The contribution and mechanism of κ-/ι-carrageenan (CG) with different hydration characteristics on the gelling properties of shrimp myofibrillar protein (MP) gelation was studied.

RESULTS

The gel strength, water-holding capacity and viscoelastic properties of MP gels were significantly enhanced by 1.0% κ-/ι-CG (P < 0.05), but the microstructure showed that excessive carrageenan caused fragmentation of the gel network and a corresponding decrease in gel properties. Compared to MP-ιCG, MP-κCG showed larger breaking force and shorter breaking distance, thus enhancing the hardness and brittleness of the gel, which might be ascribed to a reinforced network skeleton and a tighter binding of κCG-myosin. However, MP-ιCG stabilized more moisture in the gel network, thereby improving the tenderness of the gel, which might be related to the electrostatic repulsion observed between the sulfate groups of ιCG and the myosin observed by molecular docking. In addition, the β-sheet content and intermolecular interactions might be positively correlated with gel properties.

CONCLUSION

In this study, a composite gel system was constructed based on the interaction of MP and CG. The quality differences of two kinds of CG-MP gels were clarified, which will provide guidance for the application of different kinds of carrageenan and the development of recombinant meat products with specific quality. © 2022 Society of Chemical Industry.

Insight into the Gel Properties of Antarctic Krill and Pacific White Shrimp Surimi Gels and the Feasibility of Polysaccharides as Texture Enhancers of Antarctic Krill Surimi Gels

Antarctic krill is a potential and attractive resource for consumption. However, most Antarctic krill meat is used to produce primary products with low commercial value, with few highly processed products. This study aimed to evaluate and improve the gelling properties of Antarctic krill surimi, with Pacific white shrimp surimi as control. Compared with Pacific white shrimp surimi, the lower β-sheet content and protein aggregation degree had a severe impact on the formation of the gel network of Antarctic krill surimi, which resulted in weaker breaking force, gel strength, and viscoelasticity (p < 0.05). Moreover, water retention capacity and molecular forces had a positive effect on the stability of the gel matrix of shrimp surimi. Thus, the high α-helix/β-sheet ratio, weak intermolecular interactions, and low level of protein network cross-linkage were the main reasons for the poor quality of Antarctic krill surimi. On this basis, the effects of six polysaccharides on the texture properties of Antarctic krill surimi were studied. Chitosan, konjac glucomannan, sodium carboxyl methyl cellulose, and waxy maize starch resulted in no significant improvement in the texture properties of Antarctic krill surimi (p > 0.05). However, the addition of ι-carrageenan (2%) or κ-carrageenan (1~2%) is an effective way to improve the texture properties of Antarctic krill surimi (p < 0.05). These findings will contribute to the development of reconstituted Antarctic krill surimi products with high nutritional quality and the promotion of deep-processing products of Antarctic krill meat.

Iron delivery systems for controlled release of iron and enhancement of iron absorption and bioavailability

Iron deficiency is a global nutritional problem, and adding iron salts directly to food will have certain side effects on the human body. Therefore, there is growing interest in food-grade iron delivery systems. This review provides an overview of iron delivery systems, with emphasis on the controlled release of iron during gastrointestinal digestion, as well as the enhancement of iron absorption and bioavailability. Iron-bearing proteins are easily degraded by digestive enzymes and absorbed through receptor-mediated endocytosis. Instead, protein aggregates are slowly degraded in the stomach, which delays iron release and serves as a potential iron supplement. Amino acids, peptides and polysaccharides can bind iron through iron binding sites, but the formed compounds are prone to dissociation in the stomach. Moreover, peptides and polysaccharides can deliver iron by mediating the formation of ferric oxyhydroxide which is absorbed through endocytosis or bivalent transporter 1. In addition, liposomes are unstable during gastric digestion and iron is released in large quantities. Complexes formed by polysaccharides and proteins, and microcapsules formed by polysaccharides can delay the release of iron in the gastric environment and prolong iron release in the intestinal environment. This review is conducive to the development of iron functional ingredients and dietary supplements.