Conformational Evolution Research Articles

De novo genome assemblies of two cryptodiran turtles with ZZ/ZW and XX/XY sex chromosomes provide insights into patterns of genome reshuffling and uncover novel 3D genome folding in amniotes.

Understanding the evolution of chromatin conformation among species is fundamental to elucidate the architecture and plasticity of genomes. Nonrandom interactions of linearly distant loci regulate gene function in species-specific patterns, affecting genome function, evolution, and, ultimately, speciation. Yet, data from nonmodel organisms are scarce. To capture the macroevolutionary diversity of vertebrate chromatin conformation, here we generate de novo genome assemblies for two cryptodiran (hidden-neck) turtles via Illumina sequencing, chromosome conformation capture, and RNA-seq: Apalone spinifera (ZZ/ZW, 2n = 66) and Staurotypus triporcatus (XX/XY, 2n = 54). We detected differences in the three-dimensional (3D) chromatin structure in turtles compared to other amniotes beyond the fusion/fission events detected in the linear genomes. Namely, whole-genome comparisons revealed distinct trends of chromosome rearrangements in turtles: (1) a low rate of genome reshuffling in Apalone (Trionychidae) whose karyotype is highly conserved when compared to chicken (likely ancestral for turtles), and (2) a moderate rate of fusions/fissions in Staurotypus (Kinosternidae) and Trachemys scripta (Emydidae). Furthermore, we identified a chromosome folding pattern that enables "centromere-telomere interactions" previously undetected in turtles. The combined turtle pattern of "centromere-telomere interactions" (discovered here) plus "centromere clustering" (previously reported in sauropsids) is novel for amniotes and it counters previous hypotheses about amniote 3D chromatin structure. We hypothesize that the divergent pattern found in turtles originated from an amniote ancestral state defined by a nuclear configuration with extensive associations among microchromosomes that were preserved upon the reshuffling of the linear genome.

Molecular regulation of lignin multi-level structure and conformational evolution for the self-powered fire alarm sensors

Many studies are still limited to focusing on the primary structure of biomass macromolecules, ignoring the impact of the multi-level structure of macromolecules and their conformational evolution on the high-value utilization of biomass. In this paper, a novel and clever strategy is designed and executed to regulate and immobilize the multi-level structure of lignin macromolecules. Lignin with different spatial conformations exhibits differences in physical properties and processability, despite their chemical primary structures being highly similar. In order to clearly and intuitively study the impact of multi-level structures, lignin-based carbon nanofibers (CFs) with high requirements for processing and precursor properties have been selected as the high-value utilization. The introduction of lignin with optimized multi-level structures effectively improves fiber morphology, uniform diameter, and flexibility. The resulting lignin-based CFs exhibit excellent refractoriness, stability, flame sensitivity (response time of only 1 s), and good energy storage properties (specific capacitance up to 226.1F/g). Furthermore, the CFs moist-electric generator has a high power generation efficiency, and the output voltage of a single device reaches 0.649 V and the output current is up to 160 μA. This work may explain a long-standing issue: why do lignin macromolecules with similar primary structures exhibit many differences in physical and processing properties, which is of great significance for promoting the industrial utilization of lignin macromolecules.

Unraveling the Mechanical Response of Short-Chain Branched Amorphous Polyethylene: Insights from Molecular Dynamics Simulations

The deformation behavior of short-chain branched, amorphous polyethylene (PE) was investigated using united atom molecular dynamics (MD) simulations under uniaxial stretching. Our research reported in this paper examined the internal mechanisms underlying the mechanical response of the PE by analyzing potential energies, dihedral angle distributions, chain orientation and entanglements. The findings indicated that the short-chain branching generally enhanced Young’s modulus, except for sample B60 with a critical ethyl branch content of 60/1000 (60 ethyl branches per 1000 backbone carbons). The Young’s modulus of B60 was the local minimum value in the various samples. Analysis of the evolution of dihedral angles shows that the short-chain branching hinders the transition from gauche to trans configurations, leading to a decrease in the trans population as the branch content increases. Regarding the sample B60 with critical branch content 60/1000, the orientation parameter and entanglement parameter of the molecular chains along the backbone were lowest in the initial structure, and the efficiency of chain disentanglement was at its lowest during deformation. The simulation results elucidated the deformation mechanism related to the conformational evolution of the molecular chains, which can provide atomic-scale insights into the mechanical properties and processability of branched polyethylene, thereby allowing for optimization in its design and application.

Thermal activation of kaolinite through potassium acetate intercalation: A structural and reactivity study

Calcined clays have emerged as a suitable alternative to partially replace conventional cement due to their high pozzolanic activity. This study explores a novel activation methodology for kaolinite, aiming to obtain metakaolin at lower temperatures than conventional thermal activation. This methodology involves a prior intercalation stage with potassium acetate (KAc) before thermal activation. The effectiveness of KAc intercalation was assessed through X-ray diffraction (XRD), indicating an intercalation ratio of approximately 90%. Several calcined temperatures were tested in accordance with the thermal behaviour analyzed through thermogravimetric analysis (TGA). Once calcined, the intercalated kaolinites exhibited enhanced reactivity compared to conventional calcined clays in the range between 400 °C to 550 °C, as demonstrated by modified Chapelle and Si/Al availability tests. A comprehensive structural characterization was conducted to facilitate a better understanding of the novel KAc-based metakaolin reactivity through various techniques (XRD, 27Al - 1H MAS NMR, and TGA). This focused on the crystalline changes in the kaolinite structure, the evolution of Al atoms conformation, and the OH behaviour at different thermal activation temperatures. Overall, this study highlights the potential of KAc intercalation as a strategy to obtain higher metakaolin content at lower temperatures than through conventional thermal treatments, offering insights into the development of its potential use as supplementary cementitious materials or alternative cementitious materials precursor.

Dynamic Evolution and Reversibility of a Single Au25 Nanocluster for the Oxygen Reduction Reaction.

Ultrasmall metallic nanoclusters (NCs) protected by surface ligands represent the most promising catalytic materials; yet understanding the structure and catalytic activity of these NCs remains a challenge due to dynamic evolution of their active sites under reaction conditions. Herein, we employed a single-nanoparticle collision electrochemistry method for real-time monitoring of the dynamic electrocatalytic activity of a single fully ligand-protected Au25(PPh3)10(SC2H4Ph)5Cl22+ nanocluster (Au252+ NC) at a cavity carbon nanoelectrode toward the oxygen reduction reaction (ORR). Our experimental results and computational simulations indicated that the reversible depassivation and passivation of ligands on the surface of the Au252+ NC, combined with the dynamic conformation evolution of the Au259+ core, led to a characteristic current signal that involves "ON-OFF" switches and "ON" fluctuations during the ORR process of a single Au252+ NC. Our findings reinvent the new perception and comprehension of the structure-activity correlation of NCs at the atomic level.

Dynamic changes of tenderness, moisture and protein in marinated chicken: the effect of different steaming temperatures.

The steam processing characteristics of chicken are a key factor in the simplicity and versatility of steamed chicken dishes. The aim of this study was to investigate in depth the changes in tenderness and water retention of marinated chicken at different slow steaming endpoint temperatures, and to further explore the effect of the evolution of protein conformations on the water status. The results showed that chicken samples' shear force peaked at 80 °C and decreased rapidly at 90 °C. As the steaming endpoint temperature increased between 50 and 90 °C, T21, T22, moisture content and centrifugal loss decreased, but P21, P22 and myofibril water-holding capacity showed regular changes. The electrophoretic bands and protein conformation changes showed that protein in marinated chicken underwent different degrees of denaturation, degradation and aggregation. And at 70 °C, with an increase of hydrophobic groups and crosslinking of disulfide bonds as well as an increase in the number of denatured sarcoplasmic proteins, the intermolecular network was enhanced, thus affecting the water retention. Water status of chicken meat heated at different steaming temperatures is closely related to the evolution of protein conformations. The present study serves as a robust theoretical foundation for enhancing the quality of steamed chicken products at an industrial scale. © 2024 Society of Chemical Industry.

Understanding the Impact of Chain Mobility on Conformational Evolution and Kinetics of Mesophase Formation in Poly(ʟ-lactide) under Low-Pressure CO2.

Although the mesomorphic phase as an intermediate state has been introduced to understand polymer crystallization, the understanding of the mesomorphic phase is far from complete. Here, the effect of chain mobility on the mesophase structuring in melt-quenched poly(ʟ-lactide) (PLLA) treated in low-pressure CO2 at 1.6-2.0 MPa and 0 °C was investigated using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and atomic force microscopy (AFM). The IR and AFM results demonstrated that the final degree of order and the kinetics of structural evolution during the CO2-induced mesophase formation were critically dependent on the CO2 pressure. This was attributed to the distinct dynamics of conformational evolution (gg to gt conformer transition) due to the different CO2 pressures. The thermal behavior from the DSC results showed that CO2 pressure dominated both the scale and dynamics of the chain motion of PLLA. At a lower CO2 pressure of 1.6 MPa, smaller-scale segmental motion was not replaced by the larger-scale cooperative motion that occurred at a relatively higher CO2 pressure of 2 MPa, which was favorable for faster mesophase formation. Consequently, by inhibiting direct crystallization under limited mobility conditions, it was demonstrated that different chain mobility controlled by CO2 pressure and thus CO2 solubility impacted the dynamics of the mesophase formation of PLLA. The present results have implications for understanding the role of chain mobility in determining the intermediate structural phases in semicrystalline polymers.

Experimental measurement and molecular dynamics simulation analysis of thermal aging performance in composite solid propellants

As a complex mixed system, the aging mechanism of high-energy composite materials involves the aging of each component itself, interactions between components, and transformation of microstructural and thermodynamic properties. The study of a single component or performance parameter has great limitations for elaborating the cognitive complexity of aging processes, making it difficult to reveal the underlying principles of physicochemical property transformation. Thus, it can only be applied as an empirical summary. In view of this, this study comprehensively utilized numerical analysis and experimental detection to explore the evolution of micromolecular conformation and changes in macro aging performance from four aspects of composite systems, including binder aging, plasticizer migration, bond interface debonding, and mechanical property transformation. There was good consistency observed between molecular simulation and thermal aging experiments, indicating that there was basically no post curing process for HTPB propellants using TDI as the curing agent. In the early stage of aging, scission chain was the main process and, in the later stage of aging, oxidation crosslinking the main process. Oxidative crosslinking increased the mean square radius of gyration and glass transition temperature of the binder system, reduced the peak value of radial distribution function, and revealed the reason for the change of propellant hardness and CC and CO double bond content. However, chain degradation increased the number of polar groups, enhanced intermolecular polarity, reduced the solubility parameter, and increased the free volume fraction of the mixed system and the dioctyl sebacate diffusion coefficient. This resulted in an increase in the tangent value of the HTPB propellant loss angle from 0.43 to 0.44° and a decrease in the glass transition temperature from 203.3 to 202.0 K. The binding energy at the interfaces of AP/HTPB and Al/HTPB increased first and then decreased, which was consistent with SEM images of bonding interfaces. The joint effect of binding energy and mechanical properties of the binder system promoted the transformation of the stress-strain curve of aging propellant.

Understanding the Fast-Triggering Unfolding Dynamics of FK-11 upon Photoexcitation of Azobenzene.

Photoswitchable molecules can control the activity and functions of biomolecules by triggering conformational changes. However, it is still challenging to fully understand such fast-triggering conformational evolution from nonequilibrium to equilibrium distribution at the molecular level. Herein, we successfully simulated the unfolding of the FK-11 peptide upon the photoinduced trans-to-cis isomerization of azobenzene based on the Markov state model. We found that the ensemble of FK-11 contains five conformational states, constituting two unfolding pathways. More intriguingly, we observed the microsecond-scale conformational propagation of the FK-11 peptide from the fully folded state to the equilibrium populations of the five states. The computed CD spectra match well with the experimental data, validating our simulation method. Overall, our study not only offers a protocol to study the photoisomerization-induced conformational changes of enzymes but also could orientate the rational design of a photoswitchable molecule to manipulate biological functions.

Exploring the binding mechanisms of thermally and ultrasonically induced molten globule-like β-lactoglobulin with heptanal as revealed by multi-spectroscopic techniques and molecular simulation

This work employed the model protein β-lactoglobulin (BLG) to investigate the contribution of microstructural changes to regulating the interaction patterns between protein and flavor compounds through employing computer simulation and multi-spectroscopic techniques. The formation of molten globule (MG) state-like protein during the conformational evolution of BLG, in response to ultrasonic (UC) and heat (HT) treatments, was revealed through multi-spectroscopic characterization. Differential MG structures were distinguished by variations in surface hydrophobicity and the microenvironment of tryptophan residues. Fluorescence quenching measurements indicated that the formation of MG enhanced the binding affinity of heptanal to protein. LC-MS/MS and NMR revealed the covalent bonding between heptanal and BLG formed by Michael addition and Schiff-base reactions, and MG-like BLG exhibited fewer chemical shift residues. Molecular docking and molecular dynamics simulation confirmed the synergistic involvement of hydrophobic interactions and hydrogen bonds in shaping BLG-heptanal complexes thus promoting the stability of BLG structures. These findings indicated that the production of BLG-heptanal complexes was driven synergistically by non-covalent and covalent bonds, and their interaction processes were influenced by processes-induced formation of MG potentially tuning the release and retention behaviors of flavor compounds.

Oil Detachment Mechanism in Natural Surfactant Flooding from Silica Surface: Molecular Dynamics Simulation

Summary International regulations have compelled Europe and the United States to phase out certain traditional surfactants to mitigate the use of toxic and nonbiodegradable chemicals. Sodium cocoyl propionate (SCA), as a natural surfactant with high performance, has been proved to have the potential to replace traditional surfactants in previous studies. However, its performance has not fully met practical application requirements. Therefore, in this paper, molecular dynamics (MD) simulation was used to study the detachment behavior and mechanism of SCA, lauryl dimethylamine oxide (OA-12), emulsifier OP-10, and SOO (combination of SCA, OA-12, and OP-10) on crude oil (dodecane, C12) at different temperatures (80–120°C) and salinities (20 000–200 000 mg/L). The complex interaction mechanism between surfactant molecules and C12 molecules was revealed by analyzing the simulated snapshot, radial distribution function (RDF), mean square displacement (MSD), and interaction energy. The simulated snapshot captures the conformational evolution of surfactant molecules at different time points, emphasizing the spatiotemporal and spatial changes of their dynamic behavior. A comparison of two desorption modes reveals that dispersive adsorption displacement and concentrated adsorption displacement are two possible desorption mechanisms. RDF analysis shows that the probability of SOO molecules near C12 remains high even at high-salinity and -temperature conditions. MSD analysis showed that the diffusion capacity of SOO was the highest at 100°C, reaching 1.52867×10 –5 cm2/ps. The calculation of interaction energy results reveals that SOO has a strong adsorption capacity for C12, which is mainly due to the effect of van der Waals (vdW) force. This is because the C12 molecules are inert, and their molecular movement is mainly determined by the polar groups of the surfactant. The main contribution of this study is to provide a natural surfactant with superior performance as a viable alternative, offering experimental settings for further improvement in SCA performance. This research provides theoretical guidance for on-site applications of SCA and SOO to enhance oil recovery.

Deciphering the adaptive conformational evolution of dihydrophenazine derivatives in the confined space of a semi-rigid macrocyclic host

Exploring the conformational evolution of organic molecules is a long-pursuit theme in the field of chemistry. Herein, interests are endeavored to unveil the conformational evolution of conformationally flexible dihydrophenazines with environment-sensitive and continuously-changeable fluorescence in the confined space exerted by the semi-rigid macrocyclic host ExBox4+. Co-crystals of the ExBox4+ and dihydrophenazines are obtained via vapor diffusion, facilitating direct clarification of the structural variations of the host and guests. The adaptive ground-state conformational evolution of the guests is fully deciphered via 1H NMR titration, crystallography analysis as well as systematic theoretical calculations. In contrast to the much smaller structural change of the well-noted conformationally adaptive host, the conformational variation in the central dihedral angle of the guest can be up to 22° in the crystal of the host-guest complex, which is completely different from the cases when ExBox4+ interacting with the rigid guests. Dynamic information encryption has been further achieved by harnessing the distinct fluorescence behaviors before and after host-guest complexation. This work not only provides new insights into the understanding of mutual interactions between a semi-rigid host and conformationally flexible guests, but also offers an alternative scheme for advanced information encryption based on the luminescent host-guest complexes.

Recent advances in organic molecule reactions on metal surfaces.

Chemical reactions of organic molecules on metal surfaces have been intensively investigated in the past decades, where metals play the role of catalysts in many cases. In this review, first, we summarize recent works on spatial molecules, small H2O, O2, CO, CO2 molecules, and the molecules carrying silicon groups as the new trends of molecular candidates for on-surface chemistry applications. Then, we introduce spectroscopy and DFT study advances in on-surface reactions. Especially, in situ spectroscopy technologies, such as electron spectroscopy, force spectroscopy, X-ray photoemission spectroscopy, STM-induced luminescence, tip-enhanced Raman spectroscopy, temperature-programmed desorption spectroscopy, and infrared reflection adsorption spectroscopy, are important to confirm the occurrence of organic reactions and analyze the products. To understand the underlying mechanism, the DFT study provides detailed information about reaction pathways, conformational evolution, and organometallic intermediates. Usually, STM/nc-AFM topological images, in situ spectroscopy data, and DFT studies are combined to describe the mechanism behind on-surface organic reactions.

Exploring conformational landscapes and binding mechanisms of convergent evolution for the SARS-CoV-2 spike Omicron variant complexes with the ACE2 receptor using AlphaFold2-based structural ensembles and molecular dynamics simulations.

In this study, we combined AlphaFold-based approaches for atomistic modeling of multiple protein states and microsecond molecular simulations to accurately characterize conformational ensembles evolution and binding mechanisms of convergent evolution for the SARS-CoV-2 spike Omicron variants BA.1, BA.2, BA.2.75, BA.3, BA.4/BA.5 and BQ.1.1. We employed and validated several different adaptations of the AlphaFold methodology for modeling of conformational ensembles including the introduced randomized full sequence scanning for manipulation of sequence variations to systematically explore conformational dynamics of Omicron spike protein complexes with the ACE2 receptor. Microsecond atomistic molecular dynamics (MD) simulations provide a detailed characterization of the conformational landscapes and thermodynamic stability of the Omicron variant complexes. By integrating the predictions of conformational ensembles from different AlphaFold adaptations and applying statistical confidence metrics we can expand characterization of the conformational ensembles and identify functional protein conformations that determine the equilibrium dynamics for the Omicron spike complexes with the ACE2. Conformational ensembles of the Omicron RBD-ACE2 complexes obtained using AlphaFold-based approaches for modeling protein states and MD simulations are employed for accurate comparative prediction of the binding energetics revealing an excellent agreement with the experimental data. In particular, the results demonstrated that AlphaFold-generated extended conformational ensembles can produce accurate binding energies for the Omicron RBD-ACE2 complexes. The results of this study suggested complementarities and potential synergies between AlphaFold predictions of protein conformational ensembles and MD simulations showing that integrating information from both methods can potentially yield a more adequate characterization of the conformational landscapes for the Omicron RBD-ACE2 complexes. This study provides insights in the interplay between conformational dynamics and binding, showing that evolution of Omicron variants through acquisition of convergent mutational sites may leverage conformational adaptability and dynamic couplings between key binding energy hotspots to optimize ACE2 binding affinity and enable immune evasion.

Dimerized small molecular acceptors: Regulation of dimer conformation realizes binary organic solar cells with highly comprehensive performance

Dimerized small-molecular-acceptors (DSMA)-based organic solar cells have gained much progress but insufficient flexibility of the rigid DSMAs limits application in wearable electronics. By regulating dimer conformation, a series of DSMAs (2BOHD-T, 2BOHD-TCxT (x = 4, 6)) are synthesized through microwave-assist-reaction. Conformation evolution from 2-dimension planarity to 3-dimension architecture evoked by linkage engineering from rigidity to flexibility precisely controls the electronic structures, intermolecular interactions, film-forming processes, and flexibility of DSMAs. The rigid terminal-linked 2BOHD-T performs best in small-area devices with efficiency of 17.68%. The 3-dimensional flexible terminal-linked 2BOHD-TC4T achieves a record efficiency of 16.50% with a notable VOC of 0.980 V among the reported flexible DSMAs. 2BOHD-TC4T-based large-area printing device obtains the best efficiency (14.53%) among these acceptors. Furthermore, PM6:2BOHD-TC4T not only improves thermal stability close to the all-polymer system but also achieves an excellent crack onset strain, producing the large-area flexible device with excellent bending tolerance. An updated evaluation parameter, efficiency-stretchability-thermal stability-factor (ESSTF), is proposed. 2BOHD-TC4T-based device yields the highest ESSTF, demonstrating the most balanced large-area device efficiency, thermal stability, and mechanical robustness.

Theoretical exploration of the molecular stacking and charge transfer mechanism of PBQx:Y6 OSCs

The stacking morphology of the active layer molecules of organic solar cells is closely related to the PCE performance. However, experimental techniques are difficult to observe the molecular conformation and dynamic evolution at the atomic scale, which limits the understanding of the active layer charge transfer mechanism and the design of high-performance material molecules. DFT and AIMD methods can simulate the dynamic evolution of molecules at the atomic scale, and we obtained the local molecular stacking morphology of the active layers of PBQx:Y6 (x = 5,6,7) systems by AIMD simulations. The results reveal that PBQ6:Y6 exhibits the highest number of continuous π-π stacking molecules and the best ordering. The relatively high ΔES1CTx (> 0.1 eV) of PBQ7:Y6 results in increased open-circuit voltage loss. Interestingly, we found that the near-overlapping stacking of the D/A interface not only enables S1/CTX hybridization to reduce ΔES1CTx, but also enables energy level inversion of T1 and 3CT1 state to inhibit the non-geminate exciton recombination pathway. This work provides a systematic theoretical exploration of the molecular stacking and charge transfer mechanisms in PBQx:Y6 OSCs, which offer valuable theoretical insights for the development of high-performance photovoltaic devices.

Structural and Functional Insights into the Biomineralized Zeolite Imidazole Frameworks.

Biomineralization is a natural process of mineral formation mediated by biomacromolecules, allowing access to hierarchical structures integrating biological, chemical, and material properties. In this contribution, we comprehensively investigate the biomineralization of zeolite imidazole frameworks (ZIFs) for one-step synthesis of an enzyme-MOF biocomposite, in terms of differential crystallization behaviors, fine microstructure of resultant ZIF biominerals, the enzyme's conformation evolution, and protective effect of ZIF mineral. We discover that the biomineralization ability is ZIF organic linker dependent and the biocatalytic function is highly related to the ZIF mineral species and their distinguishable topologies and defect structures. Importantly, a side-by-side analysis suggests that the protective effect of ZIF mineral toward the hosted enzyme is highly associated with the synergistic effect of size dimension and chemical microenvironment of the ZIF pores. This work provides important insight into the ZIF-dependent biomineralization behaviors and highlights the important role of the ZIF microstructure in its biocatalytic activity and durability, which has been underestimated previously.

Molecular dynamic simulations of deformation behaviour of blended polyethylene

ABSTRACT The tensile deformation behaviour of blended polyethylene (PE) was studied using molecular dynamic methods. The blended PE was modeled by blending linear chains with different molecular weights based on a united atom model. The mechanical response and microscopic conformational behaviours of blended PE were investigated at different strain rates and temperatures. The interatomic energy evolution displayed a similar trend to the stress–strain curve showing the stiffness of blended PE increase with a higher fraction of chain with high molecular weight. The microstructure metrics associated with free volume, orientation, entanglement and crystallisation were recorded as a function of strain in detail to obtain insight into the role of PE chains with different molecular weights for blended PE during deformation. The conformation evolution indicates that orientation and disentanglement are more noticeable in the short chain with low molecular weight in a blended PE system, while the long chain promotes the crystallisation of the initial chain structure. The chain entanglement evolution clearly shows some new flexion nodes created to entangle short chains again, implying that re-entanglement might exist during the tensile deformation.

Regular double-helix self-assembled from two poly(p_phenylene) chains under the inducement of metal nanoclusters

Molecular dynamics simulations demonstrate that metal nanoclusters (NCs) can induce two poly(p_phenylene) (PP) chains to self-assemble into regular double-helix through noncovalent interactions. In the process, the van der Waals (vdW) energy dominates the helically self-assembly of PP chains. The corresponding mechanism is revealed from the evolution of atomic conformations and the variation of total potential energy including its energy components. When adsorption energy of PP and NCs between 1.32 and 12.87 kcal/mol·Å, NCs can induce the helical self-assembly of two PP chains to form regular double-helix. The NC diameter and relative position of PP and NCs have a great influence on the formation of the double helix. Furthermore, the PP chain interacting with different number of Ni NCs are also studied.

Changes in physicochemical and structural properties of pea protein during the high moisture extrusion process: Effects of carboxymethylcellulose sodium and different extrusion zones

This study investigated effects of carboxymethylcellulose sodium (CMC) on the conformational evolution of pea protein during the high moisture extrusion process. The morphological observation showed that the addition of CMC facilitated the formation of fibrous structure of pea protein. In comparison with the pea protein in the melting zone and extrudate, the combination of CMC increased the denaturation enthalpy of pea protein by 2.09 % and 2.34 %. Compared with the material in the mixing zone, the degree of grafting between CMC and pea protein in the die was enhanced by 98.95 %. In general, the supplementation of CMC depressed the exposure of hydrophobic groups in the pea protein. In the extrusion barrel, the CMC increased the unfolding of protein molecular chains while it promoted the refolding of protein chains in the die. For the extrudate, the addition of CMC decreased the contents of α-helix and β-sheet of pea protein by 9.67 % and 6.93 % while the contents of β-turn and random coil were increased, leading to changes in the molecular weight distribution of protein molecules. In conclusion, these results provided new strategies toward producing the high-quality pea protein-based meat analogues by adding CMC.