Ca2+-Induced Conformational Changes of Myosin from Silver Carp (Hypophthalmichthys molitrix) in Gelation

Effect of partial substitution of NaCl by KCl on aggregation behavior and gel properties of beef myosin

Based on the three typical gels under KCl substitution groups, the effect of partial substitution of NaCl by KCl (groups: T 1:0.6 M NaCl; T 2: 0.3 M NaCl +0.3 M KCl; T 3: 0.2 M NaCl +0.4 M KCl; T 4:0.6 M KCl) on the aggregation behavior and gel characteristics of myosin was evaluated. The significant changes in hydrophobicity and sulfhydryl content (P < 0.05) indicate KCl substitution enhances myosin aggregation through hydrophobic interactions and disulfide bonds. According to Ca2+-ATP, scanning electron microscopes (SEM) and the rheological results, T2 had a smoother network structure at about 75 °C. Noticeably, T3 had high water holding capacity (WHC), but its gel had some visible cavities. T4 had a gel structure with several irregular aggregates due to a greater aggregation rate. Thus, appropriate partial substitution of NaCl by KCl could enhance beef myosin gel properties and heat-induced aggregation behavior.

Ultrasonic treatment enhanced the binding capacity of volatile aldehydes and pearl mussel (Hyriopsis cumingii) muscle: Investigation of underlying mechanisms

This study was aim to investigate the influencing mechanism of ultrasonic treatment on the interaction between volatile aldehydes and myosin. The results showed that when the mass concentration ratio of myosin to heptanal/hexanal was 1:0.3, ultrasonic treatment could enhance the binding capacity of myosin to heptanal/hexanal, especially the binding of myosin to hexanal. The entropy and enthalpy values of their interaction were negative, indicating that the interaction was mainly driven by hydrogen bond and van der Waals force. After ultrasonic treatment, the fluorescence wavelength of myosin-heptanal/hexanal complex was redshifted, the α-helix content was increased, while its roughness values, particle size and the polydispersity index were decreased. These demonstrated that ultrasonic treatment was conducive to myosin binding to heptanal/hexanal, thereby restraining the release of volatile flavor compounds from myosin, which could provide new insights for the regulation of volatile flavor compounds.

Insights into the interactions between etheric compounds and myofibrillar proteins using multi-spectroscopy, molecular docking, and molecular dynamics simulation

This study aimed to examine how the addition of etheric compounds (EC) affects the characteristics of myofibrillar proteins (MP) and to understand underlying interaction mechanisms. Fourier transform infrared spectroscopy confirmed that the EC-MP complex was formed through hydrogen bonding. The addition of EC resulted in an increase in the α-helix content and a decrease in the β-sheet content of MP, which would promote the protein unfolding. The unfolding of MP led to aggregation and formation of larger and non-uniform particles. As a result, the exposure of negative charge on the MP surface was enhanced, and zeta potential was decreased from -5.33 mV to -7.45 mV. Moreover, the EC-induced modification of MP conformation resulted in a less rigid three-dimensional network structure of MP gel and enhanced the discharge of aldehyde compounds (C > 6). Moreover, the rheological characteristics of MP were enhanced by the suppression of protein-protein interactions due to the MP unfolding. Molecular dynamics simulations revealed that anethole reduced the binding capacity of myosin to decanal by raising its binding energy from -22.22 kcal/mol to -19.38 kcal/mol. In the meantime, anethole competed for the amino acid residue (PHE165) where myosin connects to decanal. This caused the hydrogen bonds and hydrophobic contacts between the two molecules to dissolve, altering myosin's conformation and releasing decanal. The results might be useful in predicting and controlling the ability of proteins to release and hold onto flavors.

Structural changes induced by ultrasound improve the ability of the myofibrillar protein to bind flavor compounds from spices

Effects of ultrasound (UT) treatments on the structural, physicochemical, and functional properties of myofibrillar proteins (MPs), as well as their ability to bind to flavor compounds from spices, were investigated. The results demonstrated that UT treatment enhanced surface hydrophobicity, SH content, and absolute ζ-potential value of the MPs. Atomic force microscopy analysis displayed formation of MPs aggregates with small particle size in the UT-treated MPs samples. Meanwhile, UT treatment could improve the emulsifying properties and physical stability of MPs' emulsion. Additionally, the MPs gel network structure and stability significantly improved following UT treatment. Changes in the structural, physicochemical, and functional properties enhanced the ability of MPs to bind to flavor substances from spices depending on the duration of UT treatment. Furthermore, correlation analysis showed that the ability of myristicin, anethole, and estragole to bind to MPs was highly correlated with surface hydrophobicity, ζ-potential value, and α-helix content of MPs. The results of this study may help in understanding the relationship between the changes in MPs properties during the processing of meat products and their ability to bind to flavors from spices, thereby improving flavors retention and taste of processed meat products.

Improvement of functional characteristics of Hypophthalmichthys molitrix protein by modification with chitosan oligosaccharide

In the food processing field, it is very often that fish proteins are denatured affecting the nutritional value of the product which is vital to be solved. By using appropriate sugar donors for glycosylation with protein, improving the stability and emulsification properties of fish proteins can be achieved. This research looks into the impacts of enzymatic chitosan oligosaccharide (CO) at various concentration (0.15%, 0.30%, 0.45%, 0.60%, w/v) upon the molecular makeup and function of silver carp myofibrillar protein (MP) in an attempt to comprehend the impact of electrostatic binding among MP as well as CO on protein conformation. Analysis was done on the impact of various CO concentrations upon MP's secondary structure, conformational changes, and functional characteristics. Twelve sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) assays were implemented to monitor MP; Fourier transform infrared spectroscopy, endogenous fluorescence spectroscopy, and UV absorption spectra were carried out to investigate the influence of CO on MP; Particle size distribution, emulsifying activity index (EAI), solubility, turbidity, sulfhydryl content, carbonyl content, foaming capacity, surface hydrophobicity, emulsifying stability index (ESI), and foam persistence were all investigated. In addition, we used dynamic light scattering, scanning electron microscope, and atomic force microscope to analyze myosin (MO) and 0.60% CO-MO complex. The results demonstrated that CO and MP form complexes through hydrogen bonding and electrostatic interactions. CO modification not only delayed the oxidation of MP but also promoted MP to show better solubility, foaming, and foaming stability. In addition, CO modified myosin particle size decreased, reducing myosin's roughness and making myosin's structure more compact. To sum up, molecular interaction could change functional characteristics, and products with special properties could be developed after modification with chitosan oligosaccharide.

Effects of CaCl2 on 3D Printing Quality of Low-Salt Surimi Gel

In order to develop low-salt and healthy surimi products, we limited the amount of NaCl to 0.5 g/100 g in this work and studied the effect of CaCl₂ (0, 0.5, 1.0, 1.5, and 2.0 g/100 g) on the 3D printing quality of low-salt surimi gel. The results of rheology and the 3D printing showed that the surimi gel with 1.5 g/100 g of CaCl₂ added could squeeze smoothly from the nozzle and had good self-support and stability. The results of the chemical structure, chemical interaction, water distribution, and microstructure showed that adding 1.5 g/100 g of CaCl₂ could enhance the water-holding capacity and mechanical strength (the gel strength, hardness, springiness, etc.) by forming an orderly and uniform three-dimensional network structure, which limited the mobility of the water and promoted the formation of hydrogen bonds. In this study, we successfully replaced part of the salt in surimi with CaCl₂ and obtained a low-salt 3D product with good printing performance and sensory properties, which could provide theoretical support for the development of healthy and nutritious surimi products.

Study on the interactions between the screened polyphenols and Penaeus vannamei myosin after freezing treatment

The denaturation of proteins (particularly myosin) due to freezing can lead to the deterioration of Penaeus vannamei. The purpose of this study was to verify the antifreeze protective effects of polyphenols screened by a molecular docking technique, and to explore their interactions with myosin after freezing treatment. It was found that the screened polyphenols could significantly increase the freezing rate and unfreezable water content of shrimp paste. The results of fluorescence spectra indicated that the hesperetin to myosin quenching process included both dynamic and static quenching, and it was primarily bound to myosin through hydrophobic interactions; The quenching of myosin by both dihydroquercetin and mangiferin was static quenching, and they were bound to myosin mainly by hydrogen bonds and van der Waals forces; All three of these polyphenols had only one binding site on myosin. Surface hydrophobicity indicated that all four polyphenols were engaged in non-covalent binding (hydrophobic interactions) with myosin. Infrared spectra demonstrated that the addition of these four polyphenols significantly increased the α-helix content of myosin. They also reduced the myosin particle size, zeta potential, and protein degeneration degree. Scanning electron microscopy revealed that the four polyphenols reduced the degree of aggregation, while more uniformly distributing the myosin particles. These observations provide a basis for the screening of polyphenols and further research into the protective mechanism of polyphenols on frozen myosin.

Changes in Myosin from Silver Carp (Hypophthalmichthys molitrix) under Microwave-Assisted Water Bath Heating on a Multiscale

To further prove the advantages of microwave-assisted water bath heating (MWH) in low-value fish processing, the effects of different heating methods (two heating stage method, high temperature section respectively using MWH1, MWH2, MWH3, WH—water heating, MH—microwave heating) on secondary and tertiary myosin structures, SDS-PAGE, surface morphology, scanning electron microscopy (SEM), and particle size distribution were compared and analyzed. The findings revealed that MH and MWH aided in the production of gel formations by promoting myosin aggregation. Myosin from silver carps demonstrated enhanced sulfhydryl group and surface hydrophobicity after MWH treatment, as well as a dense network structure. The distribution of micropores becomes more uniform when the microwave time is increased. Actually, the total effect of microwave time on myosin is not substantially different. The correlation between particle size distribution and protein aggregation was also studied, in terms of time savings, the MWH of short microwave action is preferable since it not only promotes myosin aggregation but also avoids the drawbacks of a rapid warming rate. These discoveries give a theoretical foundation for understanding silver carp myosin under microwave modification, which is critical in the food industry.

Changes in the structure and digestibility of myoglobin treated with sodium chloride

Myoglobin is a protein not easily broken down by digestive enzymes due to its rigid structure. This study evaluated the structural characteristics of myoglobin under various sodium chloride treatments (0.4-0.8 mol/L for 5-10 h) and the impacts on its digestibility using spectroscopic and molecular dynamics simulation techniques. Myoglobin digestibility was 40% following pepsin digestion and 60% after being sequentially digested by pepsin and trypsin. The α-helix content of myoglobin did not change significantly following sodium chloride treatment but hydrophobic amino acids were exposed and the binding of phenylalanine targeted by some digestive enzymes became more stable, leading to the reduced digestibility.

Low-temperature combined with high-humidity thawing improves the water-holding capacity and biochemical properties of Portunus trituberculatus protein

This study compared the effects of conventional thawing methods (water immersion thawing (WIT, (25±1) °C), natural air thawing (AT, (25±1) °C, relative humidity (RH) (65±2) per cent), refrigerator thawing (RT, 4 °C, RH (80±2) per cent) and low-temperature (LT) combined with high-humidity thawing (LT, –1 °C to 1 °C (LT–1–1), 2–4 °C (LT2–4), 5–7 °C (LT5–7) and 8–10 °C (LT8–10), RH≥95 per cent) on the water-holding capacity, lipid oxidation and biochemical properties of Portunus trituberculatus (P. trituberculatus) myofibrillar protein. The results showed that WIT and AT significantly decreased the water-holding capacity while dramatically increasing lipid oxidation, protein oxidation and degeneration, resulting in serious P. trituberculatus quality deterioration. High humidity was beneficial for P. trituberculatus thawing. The thawing time of P. trituberculatus under the conditions of LT2–4 was only 39.39 per cent of that of conventional air thawing at 4 °C (RT), and the LT2–4 samples not only maintained better water-holding capacity but also had an obviously reduced degree of lipid oxidation, protein oxidation and denaturation. Thawed samples LT2–4 and LT5–7 provided better maintenance of P. trituberculatus quality than the LT–1–1 and LT8–10 samples. The best quality was exhibited after thawing at 2–4 °C. The levels of thiobarbituric acid reacting substances, carbonyl content and surface hydrophobicity observably decreased in these samples, while the total sulfhydryl contents dramatically increased compared to those of conventionally thawed samples, indicating lower lipid oxidation and protein oxidation. Moreover, the Ca2+-ATPase activity of the sample thawed at 2–4 °C (2.06 μmol Pi/mg prot/h) was markedly higher than that of samples subjected to WIT and AT. The product qualities observed after thawing at –1 °C to 1 °C, 5–7 °C and 8–10 °C under LT were comparable to that observed by RT. Considering its thawing efficiency and product quality, LT is a suitable method for the thawing of P. trituberculatus, and the ideal thawing conditions were LT at 2–4 °C.

Inhibitory effect of microwave heating on cathepsin l-induced degradation of myofibrillar protein gel

This work was aimed to compare the effect of microwave (MW) heating on the cathepsin L (Cat L)-induced degradation of myofibrillar protein (MP) gels with that of water bath (WB) heating. First, Cat L from silver carp was purified and determined to be 45 kDa. The gel strength of the MW-heated MP gels were significantly higher than those of the WB-heated when Cat L was added (P < 0.05). The gel electrophoresis pattern and scanning electron microscopy analysis indicated that MW heating inhibited the Cat l-induced hydrolysis of MP gels. In addition, the number of sulfhydryl groups and surface hydrophobicity of MW-heated gels were lower than those of WB-heated gels when Cat L was added. These results indicated that MW heating could effectively weaken the degradation of Cat L on MP gels by manipulating disulfide bonds and hydrophobic amino acids, resulting in good gel properties and a compact protein network.

Effects of partial substitution of NaCl on myofibrillar protein properties from pearl mussel Hyriopsis cumingii muscle: Structural characteristics and aggregation behaviors

The effects of NaCl and its partial substitutes (KCl, MgCl₂ and CaCl₂) on solubility, structural characteristics and aggregation behaviors of myofibrillar protein (MP) from pearl mussel muscle were investigated and compared. MP at 0.6 M NaCl was beneficial to protein unfolding and showed excellent potential functional properties. When NaCl was substituted in low level, MPs also showed good solubility and ordered microstructure as well as NaCl, especially MgCl₂ and CaCl₂, due to the unfolding of α-helical structures and subsequently exposed tyrosine residues and hydrophobic groups. However, the obviously increased disulfide bonds and hydrophobic interactions in high substitution level indicated the excessive non-sodium salts had negative effects on molecular rearrangement, leading to irregular and overly tight of microstructure. Thus, NaCl partially substituted by KCl, MgCl₂ and CaCl₂ in low substitution level is promising to improve functional properties of MP in low-sodium meat products.

Effect of high intensity ultrasound on gelation properties of silver carp surimi with different salt contents

Surimi from silver carp with different salt contents (0-5%) was obtained treated by high intensity ultrasound (HIU, 100 kHz 91 W·cm-2). The gelation properties of samples were evaluated by puncture properties, microstructures, water-holding capacity, dynamic rheological properties and intermolecular interactions. As the salt content increased from 0 to 5%, gel properties of surimi without HIU significantly improved. For samples with low-salt (0-2% NaCl) content, HIU induced obvious enhancement in breaking force and deformation. HIU promoted the protein aggregation linked by SS bonds, hydrophobic interactions and non-disulfide covalent bonds in surimi gels with low-salt content. Moreover, microstructures of HIU surimi gels with low-salt content were more compact than those of the corresponding control samples. HIU also improved the gelation properties of surimi with 3% NaCl to an extent. However, for high-salt (4-5% NaCl) samples, HIU decreased the breaking force and deformation of surimi gels due to the degradation of proteins suggested by increased TCA-soluble peptides. In conclusion, HIU effectively improved the gelation properties of surimi with low-salt content (0-2% NaCl), but was harmful for high-salt (4-5% NaCl) surimi. This might provide the theoretical basis for the production of low-salt surimi gels.

Aggregation and conformational changes of silver carp myosin as affected by the ultrasound-calcium combination system

BACKGROUND

Ultrasound and Ca²⁺ have been used separately to increase myosin properties in fish processing. However, little is know about how myosin changes are affected by Ca²⁺ and ultrasound in combination. The present study aimed to investigate the effects of the ultrasound-calcium combination system on aggregation and conformational changes of silver carp myosin.

RESULTS

Ultrasound facilitated a Ca²⁺ -induced increase in turbidity. As the Ca²⁺ concentration increased from 0 to 100 mmol L^-1 , there was an obvious increase in the turbidity, solubility and mean hydrated particle size of myosin after ultrasound treatment compared to without treatment. Moreover, changes of total and reactive SH contents depended on the ultrasound-calcium combination conditions. Under this combination system, myosin surface hydrophobicity significantly increased for the synergistic effect of ultrasound and Ca²⁺ . Furthermore, the ultrasound-calcium combination conditions could affect myosin gelation, with better gelation properties being observed for myosin treated with a combination of 60 mmol L^-1 Ca²⁺ and 9 min of ultrasound.

CONCLUSION

The combination system reported in the present study was beneficial for myosin unfolding, facilitating intermolecular interactions between Ca²⁺ and myosin. Ultrasound treatment promoted myosin aggregation via the induction of Ca²⁺ and reduced the critical concentration of Ca²⁺ required to aggregate myosin. In the fish processing industry, this combination system can enhance the gelation properties of surimi-based products. © 2018 Society of Chemical Industry.