Elucidation of interaction mechanisms between myofibrillar proteins and ethyl octanoate by SPME-GC-MS, molecular docking and dynamics simulation

Myofibrillar protein hydrolysis under hydroxyl radical oxidative stress: Structural changes and their impacts on binding to selected aldehydes

In this study, a hydroxyl radical oxidation system was established to simulate the oxidation process in fermented meat products. This system was employed to examine the structural changes in myofibrillar proteins (MPs) resulting from tryptic hydrolysis after a hydroxyl radical oxidative regime. The effect of these changes on the ability of MPs to bind selected aldehydes (3-methyl butanal, pentanal, hexanal, and heptanal) was also investigated. Moderate oxidation (H2O2 ≤ 1.0 mM) unfolded the structure of MPs, facilitating trypsin-mediated hydrolysis and increasing their binding capacity for the four selected aldehydes. However, excessive oxidation (H2O2 ≥ 2.5 mM) led to cross-linking and aggregation of MPs, inhibiting trypsin-mediated hydrolysis. The oxidised MPs had the best binding capacity for heptanal. The interaction of the oxidised trypsin-hydrolysed MPs with heptanal was driven by hydrophobic interactions. The binding of heptanal affected the structure of the oxidised trypsin-hydrolysed MPs and reduced their α-helix content.

Effect of ultrasound treatment on porcine myofibrillar protein binding furan flavor compounds at different salt concentrations

The effects of ultrasound (500 W) on the interaction of porcine myofibrillar protein (MP) with furan flavor compounds at different salt concentrations (0.6 %, 1.2 % and 2.4 %) were investigated. With the increase of salt concentration, the particle size of MP decreased, and the surface hydrophobicity and active sulfhydryl content increased due to the unfolding and depolymerization of MP. At the same time, ultrasound promoted the exposure of hydrophobic binding sites and hydrogen bonding sites of MP in different salt concentration systems, thus improving the binding ability of MP with furan compounds by 2 % to 22 %, among which MP had the strongest binding capacity of 2-pentylfuran. In conclusion, ultrasound could effectively promote the unfolding of the secondary structure of MP, which was beneficial to the combination of MP and furan flavor compounds under different salt concentrations.

Effects and mechanisms of different κ-carrageenan incorporation forms and ionic strength on the physicochemical and gelling properties of myofibrillar protein

The present work was aimed to investigate the effects of incorporating κ-carrageenan into myofibrillar protein (MP) as a dry powder (CP) or water suspension (CW) and the ionic strength (0.3 or 0.6 M sodium chloride (NaCl)) on MP physicochemical and gelling properties. The results indicated that incorporation of either CP or CW significantly increased turbidity, surface hydrophobicity, particle size and rheological behaviour of MP. In contrast, the protein solubility and fluorescence intensity of MP decreased when added with each form of κ-carrageenan (P < 0.05). These observed effects improved MP's gelling properties and produced a more compact and homogenous gel network after heating treatment. Moreover, the addition of CW rendered higher gel strength, water holding capacity and intermolecular interactions, such as ionic, hydrogen and disulphide bonds and hydrophobic interactions in MP gel compared with those added with CP, especially for 0.3 M NaCl (P < 0.05). Furthermore, addition of CW significantly decreased the α-helix content of MP gels (P < 0.05), which mainly contributing to the transformation from a random structure to an organised configuration. In addition, a higher NaCl concentration (0.6 M) enhanced the gelling properties of MP gels compared with 0.3 M NaCl concentration in the presence of each form of κ-carrageenan. Therefore, our present study indicated that incorporation form of κ-carrageenan and ionic strength have distinctive effects on regulating physicochemical characteristics and improves gelling properties of MP.

Influence of myoglobin on the antibacterial activity of carvacrol and the binding mechanism between the two compounds

BACKGROUND

Myoglobin (MB), a pigmentation protein, can adversely affect the antibacterial activity of carvacrol (CAR) and weaken its bacteriostasis effect. This study aimed to clarify the influence of MB on the antibacterial activity of CAR and ascertain the mechanism involved in the observed influence, especially the interaction between the two compounds.

RESULTS

Microbiological analysis indicated that the presence of MB significantly suppressed the antibacterial activity of CAR against Listeria monocytogenes. Ultraviolet-visible spectrometry and fluorescence spectroscopic analysis confirmed the interaction between CAR and MB. The stoichiometric number was determined as ~0.7 via double logarithmic Stern-Volmer equation analysis, while thermodynamic analysis showed that the conjugation of the two compounds occurred as an exothermal reaction (ΔH° = -32.3 ± 11.4 kJ mol-1 and ΔS° = -75 J mol-1  K-1 ). Circular dichroism, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy showed hydrogen bonding in the carvacrol-myoglobin complex (CAR-MB). Molecular docking analysis confirmed that amino acid residues, including GLY80 and HIS82, were most likely to form hydrogen bonds with CAR, while hydrogen bonds represented the main driving force for CAR-MB formation.

CONCLUSION

CAR antibacterial activity was significantly inhibited by the presence of MB in the environment due to the notable reduction in the effective concentration of CAR caused by CAR-MB formation. © 2023 Society of Chemical Industry.

Component stabilizing mechanism of membrane-separated hydrolysates on frozen surimi

This study investigated the cryoprotective mechanism of ultrafiltration membrane-separated fractions (>10 kDa, UF-1; 3-10 kDa, UF-2; and <3 kDa, UF-3) derived from silver carp hydrolysates on frozen surimi. The surimi gel incorporating UF-3 exhibited a compact, continuous structure with uniform pores, even after undergoing six freeze-thaw (F-T) cycle, with the minimal reduction in entrapped water (from 95.1 % to 91.1 %) and least increase in free water (from 4.5 % to 6.6 %) as revealed by SEM and LF-NMR analysis. Through molecular docking analysis, three major peptides in UF-3 were identified to form robust interactions with the myosin head pocket, facilitated by hydrogen bonds, electrostatic forces, and hydrophobic interactions. Furthermore, molecular dynamics simulations demonstrated that the three peptides effectively prevented myosin from unfolding and aggregating by tightly binding to basic amino acids (Arg, Lys) and hydrophobic amino acids (Phe, Leu, Ile, Met, and Val) residues in the myosin head pocket, primarily governed by electrostatic energies (-156.95, -321.38, and -267.53 kcal/mol, respectively) and van der Waals energies (-395.05, -347.46, and -319.16 kcal/mol, respectively). Notably, the key action site was identified as Lys599 on myosin. The hydrophilic and hydrophobic hotspot residues of the peptides worked synergistically to stabilize the myosin structure in frozen surimi.

Molecular simulation for food protein-ligand interactions: A comprehensive review on principles, current applications, and emerging trends

In recent years, investigations on molecular interaction mechanisms between food proteins and ligands have attracted much interest. The interaction mechanisms can supply much useful information for many fields in the food industry, including nutrient delivery, food processing, auxiliary detection, and others. Molecular simulation has offered extraordinary insights into the interaction mechanisms. It can reflect binding conformation, interaction forces, binding affinity, key residues, and other information that physicochemical experiments cannot reveal in a fast and detailed manner. The simulation results have proven to be consistent with the results of physicochemical experiments. Molecular simulation holds great potential for future applications in the field of food protein-ligand interactions. This review elaborates on the principles of molecular docking and molecular dynamics simulation. Besides, their applications in food protein-ligand interactions are summarized. Furthermore, challenges, perspectives, and trends in molecular simulation of food protein-ligand interactions are proposed. Based on the results of molecular simulation, the mechanisms of interfacial behavior, enzyme-substrate binding, and structural changes during food processing can be reflected, and strategies for hazardous substance detection and food flavor adjustment can be generated. Moreover, molecular simulation can accelerate food development and reduce animal experiments. However, there are still several challenges to applying molecular simulation to food protein-ligand interaction research. The future trends will be a combination of international cooperation and data sharing, quantum mechanics/molecular mechanics, advanced computational techniques, and machine learning, which contribute to promoting food protein-ligand interaction simulation. Overall, the use of molecular simulation to study food protein-ligand interactions has a promising prospect.

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.

Unravelling the interaction between α-SOH and myofibrillar protein based on spectroscopy and molecular dynamics simulation

This work systematically investigated the dose-response interaction between hydroxy-α-sanshool (α-SOH) and pork myofibrillar proteins (MPs) via spectroscopy, molecular docking, and molecular dynamics simulation methods. Results showed that MPs bound with low α-SOH can enhance the surface hydrophobicity and particle size of MPs, whereas high concentrations were exactly the opposite. The main interaction force in α-SOH/MPs complex changed from hydrophobic to hydrogen bonding with increased α-SOH. α-SOH causes tryptophan quenching and bring about a red shift at low concentration, as well as to promote α-helix conversion into β-sheet in MPs. Simultaneously, molecular docking and dynamics simulations verified that hydrogen bonding and hydrophobic forces were the main contributors to α-SOH/MPs complex, indicating that the binding of α-SOH with MPs proceeded spontaneously with high intensity, in which TYR286 contributed the most significant energy. Therefore, revealing the binding mechanism of α-SOH and MPs can contribute to the deep processing of numbing meat products.

Research advances of molecular docking and molecular dynamic simulation in recognizing interaction between muscle proteins and exogenous additives

During storage and processing, muscle proteins, e.g. myosin and myoglobin, will inevitably undergo degeneration, which is thus accompanied by quality deterioration of muscle foods. Some exogenous additives have been widely used to interact with muscle proteins to stabilize the quality of muscle foods. Molecular docking and molecular dynamics simulation (MDS) are regarded as promising tools for recognizing dynamic molecular information at atomic level. Molecular docking and MDS can explore chemical bonds, specific binding sites, spatial structure changes, and binding energy between additives and muscle proteins. Development and workflow of molecular docking and MDS are systematically summarized in this review. Roles of molecular simulations are, for the first time, comprehensively discussed in recognizing the interaction details between muscle proteins and exogenous additives aimed for stabilizing color, texture, flavor, and other properties of muscle foods. Finally, research directions of molecular docking and MDS for improving the qualities of muscle foods are discussed.

Cryoprotective effect of soybean oil on surimi gels and the mechanism based on molecular dynamics simulation

The effect of soybean oil (SO) on freeze-thaw (F-T)-treated surimi was investigated and its related mechanism was revealed by molecular dynamics (MD) simulations. The results displayed that SO has a disrupting effect on the structure of fresh samples. However, in the F-T-treated samples, surimi gels supplemented with SO had a more uniform microstructure. Simultaneously, when SO was added from 0% to 7% in the F-T-treated samples, the gel strength increased from46.66 to 51.86 N · mm $$ 46.66\ \mathrm{to}\ 51.86\;\mathrm{N}\cdotp \mathrm{mm} $$ (p < .05), the physically bound water was increased from 92.90% to 94.15% (p < .05), and storage modulus was increased from 5939 to 6523 Pa. Triglycerides of SO generated hydrophobic interactions with myosin mainly in carbon chains. Computational results from MD simulations illustrated that the structure of myosin combined with triglycerides was more stable than that of myosin alone during temperature fluctuations (-20 to 4°C). During ice crystal growth, triglycerides absorbed on the myosin surface inhibited the growth of surrounding ice crystals and mitigated the ice crystal growth rate (from 7.54 to 5.99 cm/s). The addition of SO during the F-T treatments allowed myosin to be less negatively affected by ice crystal formation and temperature fluctuations and ultimately contributed to the formation of a more uniform network gel structure.

Ionic liquid as hydrogen bond acceptor in the extraction of nutritional natural products

In-depth studies of the extraction mechanism using deep eutectic solvents (DES), especially extraction through the formation of a deep eutectic system (DESys), revealed commonalities between the DES- and ionic liquids (IL)-based extraction systems. New applications of ILs and DES for extraction of nutritional natural products were presented. In this study, the extraction behavior of choline chloride (ChCl) and 1-(2-hydroxyethyl)-3-methylimidazolium chloride ([HMIm][Cl]) in DES and IL, respectively, in mechanochemical extraction of target compounds from Moringa oleifera leaves was systematically studied. The results suggested that both extraction methods were based on the formation of a DESys, either a normal DESys or an IL DESys. Considering the DESys-based one-step extraction improves the extraction efficiency and reduces the preparation time, the same idea can be used in IL for performance improvement. By formation of a new IL deep eutectic system based on hydrogen bond interaction in extraction, similar improvement was obtained.

Flavor-protein interactions for four plant proteins with ketones and esters

The interaction between flavors and proteins results in a reduced headspace concentration of the flavor, affecting flavor perception. We analyzed the retention of a series of esters and ketones with different chain lengths (C4, C6, C8, and C10) by protein isolates of yellow pea, soy, fava bean, and chickpea, with whey as a reference. An increase in protein concentration led to a decrease in flavor compound in the headspace as measured with atmospheric pressure chemical ionization time-of-flight mass spectroscopy (APCI-TOF-MS). Flavor retention was described with a flavor-partitioning model. It was found that flavor retention could be well predicted with the octanol-water partitioning coefficient and by fitting the hydrophobic interaction parameter. Hydrophobic interactions were highest for chickpea, followed by pea, fava bean, whey, and soy. However, the obtained predictive model was less appropriate for methyl decanoate, possibly due to its solubility. The obtained models and fitted parameters are relevant when designing flavored products with high protein concentrations.

Comprehensive Multi-Spectroscopy and Molecular Docking Understanding of Interactions between Fermentation-Stinky Compounds and Mandarin Fish Myofibrillar Proteins

The release of flavor compounds is a critical factor that influences the quality of fermented foods. A recent study investigated the interactions between four fermentation-stinky compounds (indole, isovaleric acid, dimethyl disulfide, and dibutyl phthalate) and myofibrillar proteins (MPs). The results indicated that all four fermentation-stinky compounds had different degrees of binding to MPs, with dibutyl phthalate and dimethyl disulfide exhibiting stronger interactions. Reduced hydrophobicity enhanced these interactions. Multi-spectroscopy showed that static fluorescence quenching was dominant in the MPs-fermentation-stinky compound complexes. The interaction altered the secondary structure of MPs, predominantly transitioning from β-sheets to α-helix or random coil structures via hydrogen bond interactions. Molecular docking confirmed that these complexes maintained steady states due to stronger hydrogen bonds, van der Waals forces, ionic bonds, conjugate systems, and lower hydrophobicity interactions. Hence, it is a novel sight that the addition of hydrophobic bond-disrupting agents could improve the flavor of fermented foods.

Understanding interactions among flavor compounds from spices and myofibrillar proteins by multi-spectroscopy and molecular docking simulation

Influence of the constant heating treatment on structural and adsorption properties of myofibrillar proteins (MPs) of chicken was investigated. The results showed that heat treatment enhanced the exposure of sulfhydryl groups and improved hydrophobicity of MPs surface. Particle size distribution of MPs significantly varied depending on heat treatment duration. Also, heat treatments resulted in significant changes in the α-helix and β-sheet structures of MPs. Besides, the MPs formed larger, irregular, and cluster-like aggregates after heat treatments. Moreover, heat treatments increased viscosity and surface roughness of MPs, while zeta potential value was reduced after heat treatments. Furhthermore, binding interactions between the MPs and spices flavors signifcanlty varied relying on nature of MPs and flavor compounds, as well as heat treatments duration. Amino acid residues were interacted with flavor compounds of spices via a variety of bonds and a stable MPs-flavors complex was performed. The obtained results provide a basis for understanding structural and physicochemical changes that occur in MPs during cooking and the interactions between MPs and flavors of spices.

Study on the Interaction Mechanism of Methoxy Polyethylene Glycol Maleimide with Sweet Potato β-Amylase

In this study, sweet potato β-amylase (SPA) was modified by methoxy polyethylene glycol maleimide (molecular weight 5000, Mal-mPEG5000) to obtain the Mal-mPEG5000-SPA modified β-amylase and the interaction mechanism between SPA and Mal-mPEG5000 was investigated. the changes in the functional groups of different amide bands and modifications in the secondary structure of enzyme protein were analyzed using infrared spectroscopy and circular dichroism spectroscopy. The addition of Mal-mPEG5000 transformed the random curl in the SPA secondary structure into a helix structure, forming a folded structure. The Mal-mPEG5000 improved the thermal stability of SPA and protected the structure of the protein from breaking by the surrounding. The thermodynamic analysis further implied that the intermolecular forces between SPA and Mal-mPEG5000 were hydrophobic interactions and hydrogen bonds due to the positive values of ΔH^θ and ΔS^θ. Furthermore, the calorie titration data showed that the binding stoichiometry for the complexation of Mal-mPEG5000 to SPA was 1.26, and the binding constant was 1.256 × 10⁷ mol/L. The binding reaction resulted from negative enthalpy, indicating that the interaction of SPA and Mal-mPEG5000 was induced by the van der Waals force and hydrogen bonding. The UV results showed the formation of non-luminescent material during the interaction, the Fluorescence results confirmed that the mechanism between SPA and Mal-mPEG5000 was static quenching. According to the fluorescence quenching measurement, the binding constant (K_A) values were 4.65 × 10⁴ L·mol^-1 (298K), 5.56 × 10⁴ L·mol^-1 (308K), and 6.91 × 10⁴ L·mol^-1 (318K), respectively.

Hydrophobic bonds-dominated key off-odors/silver carp myofibrillar protein interactions, and their binding characteristics at cold storage and oral temperatures

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Off-odors binding to MP via hydrophobic forces is a spontaneous process.

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Nonanal had the strongest binding ability to MP among the three off-odors.

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MD method provided a structural basis for the fluorescence spectroscopic analysis.

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Three off-odors, especially nonanal, could change the conformation of MP.

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Compared with others, nonanal formed more binding sites to Trp residues in Myosin1.

This study revealed the interaction mechanism between silver carp myofibrillar protein (MP) and key off-odors by combining fluorescence spectroscopy with molecular dynamics (MD) simulation. Spectroscopic results exhibited a dynamic quenching mechanism between MP and off-odors. Thermodynamic analysis indicated that the MP/off-odors interaction was spontaneous (ΔG° < 0) and dominated by hydrophobic interactions (ΔH° > 0, ΔS° > 0). Meanwhile, the binding affinity was in the order of nonanal (n = 1.38) > hexanal (n = 0.89) > 1-octen-3-ol (n = 0.65), which was further verified by the MD results. Among off-odors, nonanal had the highest binding energy with myosin (8105.66 kJ/mol) and formed more hydrophobic binding sites to Trp residues in myosin head (e.g., Trp820 and Trp822), thereby changing myosin conformations via both physical and chemical interactions. Additionally, higher binding energies of myosin/off-odors were observed at oral temperature (37 °C) than at cold storage temperature (4 °C), implying that less off-odors were released at 37 °C.

The Changes Occurring in Proteins during Processing and Storage of Fermented Meat Products and Their Regulation by Lactic Acid Bacteria

Protein, which is the main component of meat, is degraded and oxidized during meat fermentation. During fermentation, macromolecular proteins are degraded into small peptides and free amino acids, and oxidation leads to amino acid side chain modification, molecular crosslinking polymerization, and peptide chain cleavage. At different metabolic levels, these reactions may affect the protein structure and the color, tenderness, flavor, and edible value of fermented meat products. Lactic acid bacteria are currently a research hotspot for application in the fermented meat industry. Its growth metabolism and derivative metabolites formed during the fermentation of meat products regulate protein degradation and oxidation to a certain extent and improve product quality. Therefore, this paper mainly reviews the changes occurring in proteins in fermented meat products and their effects on the quality of the products. Referring to studies on the effects of lactic acid bacteria on protein degradation and oxidation from all over the world, this review aims to provide a relevant reference for improving the quality of fermented meat products.

Studies on Flavor Compounds and Free Amino Acid Dynamic Characteristics of Fermented Pork Loin Ham with a Complex Starter

Staphylococcus simulans and Lactobacillus plantarum screened from Guizhou specialty food were used to prepare fermented pork loin ham. The sensory qualities and flavor profiles of fermented pork loin hams from 0 to 42 days were investigated in order to reveal the dynamics of fermented pork loin ham. The results show that total free amino acids (TFAA) content reached the highest value on the 35th day, and the umami amino acids, including aspartic acid (ASP), glutamic acid (GLU), glycine (GLY), and alanine (ALA), were the main amino acids in all periods. Notably, the RV coefficient (0.875) indicates that free amino acids (FAA) are highly correlated with the sensory score of the E-tongue. In terms of the volatile compounds identified, the esters content gradually increased between 7 and 42 days, and ethyl octanoate was the most abundant compound during all periods. These esters imparted a characteristic aroma component to the fermented pork loin ham. The most important finding was that the increase in the content of esters represented by octanoic acid-ethyl ester might be related to the increase in the content of FAA with the increase in fermentation time. Both the E-nose and E-tongue showed good discrimination ability for fermented tenderloin ham with different fermentation times, which was crucial in cases with large clusters. In addition, the multiple factor analysis (MFA) indicated that the E-nose aroma value might be the key factor in distinguishing fermented pork loin ham with different fermentation times.

Influence of Proteolysis on the Binding Capacity of Flavor Compounds to Myofibrillar Proteins

Proteolysis occurs extensively during postmortem aging, enzymatic tenderization and fermentation of meat products, whereas less is understood regarding how proteolysis affects meat flavor. Myofibrillar proteins (MP) were extracted from beef longissimus dorsi muscle and subsequently treated with three commercial proteases. The effect of proteolysis on the interactions between the treated MP and butyraldehyde, 2-pentanone, octanal and 2-octanone was investigated. The progress of proteolysis increased the degree of hydrolysis (DH) and the surface hydrophobicity but decreased the turbidity and particle size. Fluorescence-quenching analysis results indicated that the enzymatic treatment generally increased the quenching constant (Ksv) between the treated MP and ketones but decreased the Ksv between the treated MP and aldehydes, and the papain treatment changed the Ksv value to a larger degree than treatment with proteinase K and bromelain. The adsorption assay showed that the proteinase K treatment largely increased the adsorption capacity of the MP to octanal (by 15.8−19.3%), whereas the bromelain treatment significantly reduced the adsorption capacity of the treated MP to butyraldehyde (by 6.0−7.9%) and 2-pentanone (by 9.7−11.9%). A correlation analysis demonstrated a strong positive correlation (0.859, p < 0.05) between the DH of the MP and the adsorption ability of the treated MP to octanal. This study highlighted the significant but complex influence of proteolysis on MP binding capacity to flavor compounds.