Changes In Molecular Weight Distribution Research Articles

Molecular-level transformations of biomass burning-derived water-soluble organic carbon during dark aqueous OH oxidation: Insights from absorption, fluorescence, high-performance size exclusion chromatography and high-resolution mass spectrometry analysis

Biomass burning (BB) releases large amounts of water-soluble organic carbon (WSOC), which would undergo heterogenous oxidation processes that induce transformations in both molecular structures and compositions within BB WSOC. This study designed an aqueous oxidation initiated by OH radicals in the absence of light for WSOC extracted from smoke particles generated by burning of corn straw and fir wood. The BB WSOC was comprehensively characterized using a combination of UV–visible spectra, excitation-emission matrix fluorescence in conjunction with parallel factor analysis (EEM-PARAFAC), high-performance size exclusion chromatography (HPSEC), and high-resolution mass spectrometry (HRMS) analyses. Over the course of oxidation, both chromophores and fluorophores exhibited gradual decreases. Moreover, EEM-PARAFAC revealed a preferential degradation of larger-sized protein-like/phenol-like organic matters, accompanied by the accumulation and/or formation of humic-like substances in aged BB WSOC. HPSEC analysis showed notable changes in molecular weight (MW) distributions for both types of BB WSOC during oxidation. Specifically, high MW species (>1 kDa) displayed a tendency to form along with oxidation, possibly attributed to the formation of assemblies via intermolecular weak forces. After oxidation, evidence of CHO compound degradation and enrichment/formation of CHON compounds was observed for both types of BB WSOC. Remarkably, the resistant, degraded and produced molecules for BB WSOC were dominated by CHO (38–73 %) and lignin-like molecules (41–47 %), suggesting diverse responses to oxidation within these two groups. Furthermore, polyphenols experienced selective degradation, while CHON, aliphatic and poly-aromatic molecules tended to form during the oxidation process for both types of BB WSOC. In summary, this study provides a comprehensive understanding of the molecular-level transformations undergone by BB WSOC during dark aqueous OH oxidation. The findings significantly contribute to our insights into atmospheric evolution of BB WSOC, thereby playing a crucial role in accurately assessing their effects within climate models and informing policy decisions.

Fine molecular structure and digestibility changes of potato starch irradiated with electron beam and X-ray

The change of digestibility of starch irradiated with different types from the perspective of fine structure is not well understood. In this work, the change of internal structure, molecular weight and chain-length distribution, helical structure, lamellar structure, fractal structure and digestibility of native and treated potato starch with electron beam and X-ray was analyzed. Two irradiations caused the destruction of internal structure, the disappearance of growth rings and increase of pores. Irradiation degraded starch to produce short chains and to decrease molecular weight. Irradiation increased double helical content and the thickness and peak area of lamellar structure, resulting in the reorganization of amylopectin and increase of structure order degree. The protected glycosidic linkages increased starch resistance to hydrolase attack, thereby enhancing the anti-digestibility of irradiated starch. Pearson correlation matrix also verified the above-mentioned results. Moreover, X-ray more increased the anti-digestibility of starch by enhancing ability to change fine structure.

Study on the Performance and Mechanism of Cold-Recycled Asphalt Based on Permeable Recycling Agent.

In order to investigate the influence of recycling agent composition on the recycling effect of aged asphalt in the cold recycling process, the design and optimization of cold recycling agent composition were performed through the central composite design-response surface method combined with the dynamic shear rheometer (DSR) test and the bending beam rheometer (BBR) test. The molecular weight distribution and component changes in aged asphalt before and after the addition of a cold recycling agent were also analyzed by gel permeation chromatography (GPC) and hydrogen-flame ionization test. The results showed that the permeable cold recycling agent has a recycling effect on the aged asphalt, but its effectiveness is greatly affected by recycling agent composition. The best recycling effect was achieved when the ratio of aromatic oil and penetrant in the cold recycling agent was 61.2:38.8, respectively. In terms of the recycling agent and aromatic functional groups in the aromatic oil, the aromatics in the recycling agent are derived from the aromatic oils, and the penetrant is only fused and permeated with the aromatic oils. After the admixture of the cold recycling agent, the penetrant in the recycling agent allows the aromatic oil to enter the aged asphalt at room temperature. The light components volatilized by aging are replenished, allowing the aged asphalt to recover some of its properties.

Elucidating pathways of polypropylene chain cleavage and stabilization for multiple loop mechanical recycling

AbstractMechanical recycling is a decisive contribution for a sustainable circular economy of polypropylene (PP) but faces the challenge of processing‐induced and use‐phase accumulated molecular damage, exacerbated by multiple loop recycling. In this contribution, the molecular origin of degradation of PP under up to 30 repetitive reprocessing loops is analyzed together with the influence of stabilization, and processability data linked to changes of the entire molecular weight distribution. By comparison of experiments with simple Monte Carlo simulations, a coupled mechanism of random scission and shear‐induced cleavage can be inferred, while stabilizing additives effectively protect the material from progressing along this combined degradation pathway.

The Effect of Aging on the Molecular Distribution of Crumb Rubber Modified Asphalt Based on the Gel Permeation Chromatography Test

Asphalt aging is one of the main causes of asphalt pavement cracking, loosening and other issues. On a macro level, the asphalt hardens and becomes more brittle, while on a micro level, the chemical composition and molecular weight distribution change. This is a very complicated physicochemical process. Gel permeation chromatography (GPC) is a powerful technical tool for understanding the mechanism of asphalt aging and expressing the asphalt aging process. GPC can be used to measure the distribution and content of each component in the asphalt aging process. The mechanism of action of crumb rubber modified asphalt has not been fully elucidated due to its complex composition. This study investigated the molecular weight of crumb rubber modified asphalt before and after aging, and filtered asphalt based on gel permeation chromatography. The results indicated that crumb rubber itself experiences severe degradation following PAV aging and that a significant number of macromolecular materials are incorporated into the asphalt phase, causing changes in key parameters. The average molecular weight (Mw) and dispersion (D) of crumb rubber modified asphalt are directly related. At the same time, the Mw of crumb rubber modified asphalt has a positive correlation with LMS content, while SMS content has a negative correlation with Mw. The increase in crumb rubber content has a positive impact on the material interaction, and the molecular weight distribution of crumb rubber modified asphalt is affected by the reaction degree of the crumb rubber in asphalt. The complex physical and chemical reaction of crumb rubber in asphalt has a direct impact on the external macro rheological properties of asphalt.

Biodegradation and Carbon Resource Recovery of Poly(butylene adipate-co-terephthalate) (PBAT) by Mealworms: Removal Efficiency, Depolymerization Pattern, and Microplastic Residue

Poly(butylene adipate-co-terephthalate) (PBAT) waste biodegrades slowly under ambient conditions and typically ends up in incineration plants and landfills with great carbon emissions, and little is known about recovering carbon resources from PBAT waste in environmentally friendly ways. Here, we tested the biodegradation and resource recovery of PBAT using it as a supplementary feedstock for mealworms (Tenebrio molitor larvae). Over the 36-day test period, the PBAT removal was 49.2–54.9% depending on the ratio of PBAT in PBAT-containing feedstocks (100, 80, 60, 40, 20, and 10% PBAT). A low ratio of PBAT (10% PBAT content) in the PBAT–bran mixture feedstock was favorable for the growth and development of mealworms due to the highest final survival rate (96.3 ± 1.5%) and greatest larval weight growth (39.5 ± 1.5%). The biodegradation and depolymerization of PBAT were confirmed by chemical and thermal modifications as well as changes in molecular-weight distribution (MWD). Notably, the bran addition altered the depolymerization pattern of the ingested PBAT from broad depolymerization (a decrease in molecular weights) to limited-extent depolymerization (an increase in molecular weights) due to competitive digestion. Digestive biodegradation and removal resulted in a particle size reduction of the ingested PBAT material and generated residual PBAT particles within the range of microplastics (>9 μm). Based on the results, we provide a conceptual approach for management and resource recovery from PBAT waste via insect-mediated biodegradation.

Chemical Changes Over Time Associated with Protein Drying.

Upon drying, physical changes of the characteristics of proteins are observed by coagulation, but the nature and chronology of these changes have not been well studied. Coagulation changes the structure of protein from liquid to a solid or a thicker liquid by heat, mechanical action, or acids. Changes may have implications regarding the cleanability of reusable medical devices; therefore, an understanding of the chemical phenomena associated with drying of proteins is essential to ensuring adequate cleaning and mitigation of retained surgical soils. Using a high-performance gel permeation chromatography analysis with right-angle light-scattering detector at 90°, it was demonstrated that as soils dry, the molecular weight distribution changes. From the experimental evidence, the molecular weight distribution trends over time with drying to higher values. This is interpreted as a combination of oligomerization, degradation, and entanglement. As water is removed through evaporation, the distance between proteins decreases and their interactions increase. Albumin will polymerize into higher-molecular-weight oligomers, decreasing its solubility. Mucin, commonly found in the gastrointestinal tract to prevent infection, will degrade in the presence of enzymes releasing low-molecular-weight polysaccharides and leaving behind a peptide chain. The research described in this article investigated this chemical change.

Modeling the Coal Tar Pitch Primary Carbonization Process

The properties of the carbon materials obtained as the final product of coal tar pitch carbonization process are a consequence of the type of chemical and physical phenomena occurring through the process. A new simplified approach for modeling of the primary carbonization is presented to provide the semi-quantitative knowledge about the process useful for improving the efficiency of the industries that deal with this process. The proposed approach is based on defining thermodynamic and kinetic equations simply representing numerous phenomena happening during primary carbonization. Partial pressures of emitted volatiles in a simple pitch system are studied. The model enables estimating the mass and enthalpy changes of pitch through thermal treatment consistent with experimental data for mass losses of pitch heat treated up to 550 °C. Application of the model to describe molecular weight distribution changes of pitch during primary carbonization is demonstrated, showing a good agreement between the presented results and the investigations reported by Greinke. For the first time, the effect of important parameters in pitch carbonization, such as the heating rate of the pitch and the carrier gas flow rate, on the emission rate of volatiles is successfully modeled. The present model is well able to estimate the energy requirement for thermal treatment of pitch up to 350 °C.

Pelletizing ultra-high molecular weight polyethylene (UHMWPE) powders with a novel tapered die and addition of high density polyethylene (HDPE): Processing, morphology, and properties

The extremely high molecular weight and molecular entanglement have rendered ultra-high molecular weight polyethylene (UHMWPE) superior properties. However, poor inter-particle diffusion makes it difficult to pelletize UHMWPE powders for easy processing/handling. A novel tapered die with air cooling was proposed to pelletize UHMWPE and a UHMWPE blend with 5 wt% high-density polyethylene (HDPE) for compression molding and material characterization. The tensile strength of samples prepared with the tapered die outperformed those by the regular die or from virgin powders. The addition of HDPE further improved the tensile strength. Fourier transform infrared spectroscopy (FTIR) revealed little chain scission and the lowest amount of oxidation from the tapered die. Intrinsic viscosity (IV) measurements confirmed the negligible chain scission and showed an increment in IV for the UHMWPE/HDPE blend. Multi-angle light scattering with size-exclusion chromatography (SEC-MALS) indicated no change in the UHMWPE molecular weight distribution, but some crosslinking in the blend. Polarized optical microscopy (POM) showed that the HDPE and extrusion led to a finer UHMWPE domain size and better fusion between UHMWPE and HDPE. The combined effect of enhanced molecular chain diffusion, improved consolidation, and lower oxidation using the tapered die led to 40% improvement of tensile strength for the UHMWPE/HDPE blend.

Oxidation-enhanced ferric coagulation for alleviating ultrafiltration membrane fouling by algal organic matter: A comparison of moderate and strong oxidation

Ultrafiltration is increasingly used in fields of water treatment and bio-energy for algae removal and algae harvest, respectively, but membrane fouling caused by extracellular organic matter is still a challenge. In this work, oxidation-enhanced ferric coagulation was assessed for alleviating membrane fouling by extracellular organic matter with Fe(II)/permanganate and Fe(II)/persulfate compared. Characterization of extracellular organic matter was performed before and after pretreatments to evaluate changes in molecular-weight distribution and hydrophilicity. Moreover, filtration tests were carried out to explore performance and mechanisms of fouling control by the enhanced ferric coagulation. The results indicated that both Fe(II)/permanganate and Fe(II)/persulfate could improve rejection of extracellular organic matter by 20%–40%, in particularly for humic-like acid and protein-like substances. Fe(II)/persulfate outperformed Fe(II)/permanganate in alleviating the flux reduction by extracellular organic matter. Simultaneous oxidation and coagulation, which were associated with in situ formed sulfate radicals and Fe(III), respectively, were the principal mechanism for fouling control. The enhanced ferric coagulation only slightly improved the fouling reversibility, and iron and manganese oxides deposited in the external cake layer rather than inside the membrane. Fe(II)/permanganate did not significantly changes pattern of fouling development, whereas Fe(II)/persulfate induced a shift of fouling mechanisms from dual pore blocking and cake filtration to single intermediate blocking. Overall, the strong oxidation (Fe(II)/persulfate) was more beneficial to the control of membrane fouling by extracellular organic matter than the moderate oxidation (Fe(II)/permanganate).

Different combined systems with Fenton-like oxidation and ultrafiltration for industrial wastewater treatment

Combining Fenton-like oxidation with ultrafiltration by membranes seems promising for wastewater treatment, while it still has defects in comprehensive comparison of different combinations for industrial wastewater treatment. To fill in these gaps, mixed matrix Fe3O4/polyvinylidene fluoride membranes were used for setting up three combined systems, i.e., sequential oxidation and filtration (Seq-O&F), simultaneous oxidation and filtration (Sim-O&F), and sequential filtration and oxidation (Seq-F&O) systems. Performance on industrial wastewater decontamination was evaluated, and anti-fouling property of membranes was measured by flux decline and recovery efficiency. Characterizations of membranes and change of molecular weight distribution were also investigated for auxiliary analysis. Furthermore, the stability of membrane matrix and catalyst was investigated for time-equivalent of 10,000 L/m2 wastewater treatment. The results indicate that Seq-O&F system shows the best decontamination and anti-fouling performance, but with multi-units and low stability of the catalyst. Sim-O&F system shows acceptable decontamination and anti-fouling performance, yet the stability for long-term operation needs to be further improved. Seq-F&O can effectively save the oxidant and prolong operational life, but performs worse in decontamination and anti-fouling. We believe this study gives a new understanding of Fenton-like oxidation and ultrafiltration combined systems for industrial wastewater treatment, and provides guidance for further application.

The photostability and peel strength of ethylene butyl acrylate copolymer blends for use in conservation of cultural heritage

Materials, both natural and synthetic, are used as adhesives or consolidants during the conservation of cultural objects. However, few adhesives have been formulated specifically for the needs of cultural heritage. This article describes a study of the stability of ethylene butyl acrylate copolymers as well as blends of these polymers with low molecular weight resins, which may be used as consolidating adhesives for flaking and fragile paint layers. The materials were aged under simulated museum conditions. Fourier-transform infrared spectroscopy and size exclusion chromatography were used to analyze changes in chemical structure and molecular weight distribution, respectively. The degree of degradation was found to be dependent on the specific blend composition. With the addition of a hindered amine light stabilizer, minimal changes occurred in the molecular weight distribution and no loss in polymer solubility were noted. Therefore, it is suggested to incorporate a stabilizer into ethylene butyl acrylate polymer blends to extend their life and safe use in cultural heritage. Differential scanning calorimetry was employed to investigate the miscibility of the binary blends and the temperature window of their application. Furthermore, adhesive peel strength for the individual components and the binary mixtures revealed values comparable to that of Paraloid™ B-72, a frequently used consolidant. Consolidation tests on the blends were done by professional conservators on mock up and dummy paintings.

Levan from Leuconostoc citreum BD1707: production optimization and changes in molecular weight distribution during cultivation

BackgroundLevan is a well-known homopolymer of fructose composed predominantly of β-(2, 6) fructofuranosyl linkages in the backbone with occasional β-(2, 1) linkages in the branch chains with varied applications. However, high production cost due to low yield of microbial levan has become a bottleneck for its practical applications. Furthermore, factors affecting the molecular mass of the synthesized levan by Leuconostoc spp. during prolonged cultivation is not fully elucidated.MethodsThe cultivation condition for Leuconostoc citreum BD1707 to synthesize levan was optimized by single-factor experiments and subsequently with response surface methodology (RSM). The average molecular weight (Mw) of levan synthesized by the strain L.citreum BD1707 under the optimized cultivation conditions was monitored by high-performance size exclusion chromatography (HPSEC). Finally, the enzyme with levan-degrading activity was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE).ResultsThe levan yield of BD1707 reached 34.86 g/L with a corresponding productivity of 7.47 g/L/d under the optimal cultivation conditions deduced by RSM, i.e., cultivation at 26 °C and 200 rpm for 112 h in tomato juice supplemented with 172 g/L sucrose with an initial pH value of 6.12. The Mw of levan reached a peak value of 2.320 × 107 Da at 6 h of cultivation under the optimized cultivation conditions and then gradually decreased to 8.809 × 106 Da after 120 h of cultivation.ConclusionThe levan yield of the strain L.citreum BD1707 could be sufficiently enhanced via cultivation condition optimization. The decrease in molecular mass of the synthesized levan was attributed predominantly to the hydrolytic activity of levansucrase secreted by L.citreum BD1707 during cultivation, with an estimated Mw of 130 KD by SDS-PAGE, while the effect of acid hydrolysis could be nearly neglected.

Changes in molecular weight distribution caused by main-chain scission of electron beam resists

Main-chain-scission-type resists have attracted much attention as the next-generation electron beam (EB) resist used for photomask fabrication. In this study, the gel permeation chromatography (GPC) charts of irradiated EB resists (ZEP series of ZEON) were analyzed by simulation to clarify the changes in the molecular weight distribution caused by the main-chain scission of a resist polymer. In the low-exposure-dose region, the molecular weight distribution obtained by GPC was well reproduced by the simulation using a random-scission model. In the high-exposure-dose region, the calculated molecular weight distribution deviated from the experimental one because of crosslinking and the generation of stable components.

ЧИСЕЛЬНЕ МОДЕЛЮВАННЯ ТЕЧІЇ В'ЯЗКОПРУЖНОЇ РІДИНИ З ІНТЕГРАЛЬНИМ РЕОЛОГІЧНИМ ЗАКОНОМ У ПЛОСКОМУ АБО ЦИЛІНДРИЧНОМУ КАНАЛАХ

The viscoelastic liquid may be a melt of a polymeric material from a rheological point of view. Therefore, emphasis will place on the practical application of the results of the solution of the mathematical model of the flow of viscoelastic fluid in the study of the process of filling the cavity of the mold with polymeric material. High shear stresses can occur in flat or cylindrical channels. During the flow of viscoelastic fluid, in which the carbon bonds of macromolecules are broken, which leads to a decrease in the average molecular weight, and this leads to a change in molecular weight distribution, which significantly reduces the performance product. Therefore, it is important, in our opinion, to create a method for determining the stress field that arises in the process of forming products. The article is devoted to the development of a mathematical model of the flow of viscoelastic fluid in flat or cylindrical channels and its implementation by numerical methods. The calculation of this model will allow to determine the stress field in the middle of the viscoelastic fluid during its movement in flat or cylindrical channels under certain initial and boundary conditions. The paper proposes to introduce the concept of "memory" into the model and to assume that the stress determined by the complete history of polymer deformation. This assumption allowed us to express the stress tensor as an isotropic functional of the deformation history. To solve the developed numerical model of viscoelastic fluid flow with integrated rheological law, a procedure for calculating its finite difference method proposed. Numerical mathematical model of viscoelastic fluid in its implementation by the finite difference method (MAC method) allows determine the stress field in the middle of the entire flow region. The results of this modeling can used in the development of injection molding equipment and improvement of equipment for injection molding of polymer products.

Detailed studies on microbial adhesion and degradation of polystyrene foam wastes (PSFW) for clean environment.

The present study explores the efficient management of non-degradable polystyrene foam wastes (PSFW) by transforming into a microbial responsive material for an effective biodegradation process. In brief, the study involves three steps, viz., (i) preparation of citrus fruit peel extract from peel wastes; (ii) dissolution of PSFW using the extract and transform to polystyrene sheet (PSS) and characterization of the sheet formed and (iii) finally the microbial adhesion and biofilm formation on PSS. Results revealed that the maximum yield of the peel extract identified as D-limonene was obtained from Citrus sinensis (8.2 ± 0.06ml/100g fresh waste). Characterization studies on PSS suggested that there are appreciable changes in the infrared spectrum, thermo gravimetric analysis, gel permeation chromatography analyses, and contact angle measurements in comparison with PSFW. Observations on significant variations in the glass transition temperature of PSFW (100°C) and PSS (60°C); decomposition temperature of PSFW (310.93°C) and PSS (78.18°C), and molecular weight distribution changes in PSFW (2.00Mw/Mn) and PSS (1.03Mw/Mn) suggested the occurrence of structural and molecular changes in PSS. Studies on microbial adhesion and biofilm formation on PSS suggested that amongst six microbial species isolated from the waste dump yard, WD03 strain identified as Lysinibacillus sp., displayed a maximum adhesion and biofilm formation on the surface of the PSS as evidenced through biofilm characterizations, SEM, and fluorescence microscopic analyses respectively. In conclusion, the transformation of PSFW to PSS and the appreciable microbial adhesion and biofilm formation suggested the possibility of the effective management of white nuisance (PSFW) wastes in the environment.

Structural and physicochemical properties of enzymatically modified rice starch as influenced by the degree of enzyme treatment

The structure and physicochemical properties of rice starch modified with 4-α-glucanotransferase (4αGTase) were compared for different enzyme treatment times (1, 24, and 96 h). Specifically, the gelation properties of native rice starch and 4αGTase-treated rice starch (GS) were analyzed regarding their structural characteristics. The average molecular weight of GS decreased with increasing treatment time, and was 4.73 × 104 g/mol after 96 h of treatment. The chain length distribution was also broadened with the enzyme treatment, as 4αGTase transferred α-glucan from one chain to another. The enzyme treatment also altered the gelation properties and decreased the viscosity of the starch depending on the treatment time, perhaps due to the changes in molecular weight distribution and branched chain length distribution. Moreover, the overall characteristics of GS differed significantly from those of maltodextrin. The physicochemical characteristics of GS with different degrees of 4αGTase treatment suggest that it can be used in the food and pharmaceutical industries.

Direct Monte-Carlo simulation of dry e-beam etching of resist

Novel model of e-beam interaction with PMMA, based on Direct Monte-Carlo simulation algorithm, is presented. It takes into account valence bond structure in PMMA monomers and could be easily applied for the study of e-beam-induced PMMA at higher temperatures due to various PMMA degradation pathways. The model was verified by the simulation of changes in PMMA molecular weight distribution and comparison of simulated and experimental G(S) values for e-beam irradiation of PMMA. Simulation algorithm of dry e-beam etching of resist (DEBER) is provided, including simulation of most significant processes: e-beam-induced PMMA degradation above glass transition, PMMA chain depropagation with subsequent released monomer diffusion and structure profile melting due to low PMMA viscosity at higher temperatures. Only 70% of DEBER profile depth is expected to be caused by monomer evacuation from the specimen, while the remaining 30% are supposed to be a result of PMMA swelling. Simulation of DEBER profile obtained by PMMA exposure at 160 °C in series of parallel lines was carried out. PMMA chain scissions are suggested to originate from ionization events on C–С backbone atoms and hydrogen abstraction. PMMA zip length at 160 °C was determined from the comparison of simulated and experimental profiles and comprised 3400. Experimental DEBER profiles were reproduced basing on the assumption of gaussian profile nature.

Digestibility of squash polysaccharide under simulated salivary, gastric and intestinal conditions and its impact on short-chain fatty acid production in type-2 diabetic rats

In vitro digestive conditions were simulated to investigate the digestibility of polysaccharides prepared from squash (SPS). A small amount of free glucose monosaccharide was released after salivary and intestinal digestion due to the breakdown of α-(1 → 4)-glucose linkages and may form SPS or a starch impurity. At the same time, there was no obvious change in molecular weight distribution and reducing sugar content throughout this digestion period, demonstrating that the main structure of SPS was relatively stable under the simulated digestive conditions. Thus, most SPS can be transported intact to the large intestine. In addition, SPS alleviated type 2 diabetes (T2D) in rats. Moreover, the content of short-chain fatty acids (SCFAs) in the colon significantly increased after treatment with SPS. The present research provides insight into the non-digestibility of SPS, and suggests its utility to alleviate T2D by promoting the production of SCFA in the colon.

Change in physicochemical characteristics and molecular weight distribution of glutenin macropolymer induced by postharvest wheat maturation

The present study was aimed to investigate change in physicochemical characteristics and glutenin macropolymer (GMP) molecular weight distribution during postharvest wheat maturation. The freshly harvested wheat was stored under four different conditions (WT1, WT2, WT3 and WT4) for specified times. During maturation, the strengthening of wheat gluten structure was observed by increase in gluten index, swelling index of glutenin and sodium dodecyl sulphate (SDS) sedimentation value. The postharvest maturation resulted in contents increase of glutenin, glutenin/gliadin ratio, and GMP, and the decline of gliadin content. The contents of free sulfhydryl in GMP reduced, and S-S content rose during the whole maturation. Visible aggregates of GMP were observed in SDS-PAGE patterns for WT3 and WT4 samples after 4 weeks of storage. Moreover, in these two samples, polymerisation of gluten proteins into GMP was observed in size-exclusion high performance liquid chromatography patterns during storage. Some low molecular weight glutenin subunits (LMW-GS) incorporated into the aggregate, or combination of high molecular weight glutenin subunits and LMW-GS formed large polymeric glutenins by S-S linkage, and then assembled into GMP in postharvest wheat maturation. GMP polymerisation probably results in the improvement of wheat quality.