Chain Length Distribution Research Articles

Dynamics of Polymer Chains in Disperse Melts: Insights from Coarse-Grained Molecular Dynamics Simulations.

Synthetic polymers have a distribution of chain lengths which can be characterized by dispersity, Đ. Their macroscopic properties are influenced by chain mobility in the melt, and controlling Đ can significantly impact these properties. In this work, we present a detailed study of the static and dynamic behavior of fully flexible polymer chains that follow the Schulz-Zimm molecular weight distribution up to Đ = 2.0 using coarse-grained molecular dynamics simulations. We analyze the behavior of test chains with molecular weights that are equal to, above, or below the molecular weight (Mw) of the melt. Static analysis shows that the conformation of these test chains remains unaffected by the heterogeneity of the surrounding chains. To study the dynamics, we computed the mean-squared displacement of test chains in melts of the same Mw and different dispersities. The mobility of test chains with N > Mw steadily increases with dispersity, due to the shorter chains contributing to early onset of disentanglement of the long chains. However, the dynamics of test chains of length N < Mw is nonmonotonic with respect to dispersity; this behavior arises from a trade-off between the increased mobility of shorter chains and the corresponding slowdown caused by the presence of longer chains. We examine the dynamic structure factor and find a weakening of tube confinement, with the effects becoming less pronounced with increasing dispersity and Mw. These findings provide insights into the rich dynamic heterogeneity of disperse polymer melts.

Delayed Effect of Superheated Steam Treatment on Starch Retrogradation of Rice Cake After Storage by Modifying Starch Chain-Length Distribution in Rice Flour

This study investigated the effects of superheated steam (SS) treatment on the physicochemical properties of rice flour and the subsequent impact on rice cake quality. The SS-180 resulted in higher final viscosity and significantly increased pasting time and the temperature of rice flour (p &lt; 0.05). A significant enhancement in the water holding capacity of rice flour (p &lt; 0.05) was due to the rice starch aggregated in this SS process. SS treatment also led to an increase in the proportion of short chains of amylopectin in rice flour from 30.40% to 37.59%, while a decrease in long chains retarded retrogradation and improved rice cake texture. The hardness of the SS-treated rice cake was lower than that of the untreated one, but the specific volume was increased significantly (p &lt; 0.05). After 7 days of storage, rice cake with SS-180 treatment showed the lowest hardness, namely, the lowest retrograded process. These findings underscore the potential of SS treatment to enhance the physicochemical properties of rice flour and improve rice cake quality.

Chromatographic analysis of branched and debranched starch structure: Variability of their results

Starch structure determination is crucial for understanding its properties and applications. However, method-dependent variations in size determination can lead to ambiguous interpretations. This study investigates the ambiguities in starch structure determination by evaluating the variation in size of four commercial branched starches as determined by average molar mass, gyration radius, hydrodynamic radius, and chain-length distribution. The starches were analyzed using high-performance size-exclusion chromatography (HPSEC) coupled with multi-angle laser light scattering (MALLS) and refractive index detector (RI), and after debranching by HPSEC-RI and high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detector (PAD). MALLS-derived MW values for amylose and amylopectin were higher than those obtained using the hydrodynamic volume method. The molecular weight of amylopectin chains, determined by the degree of polymerization (DP), ranged between 2.1 and 2.9 × 103 g/mol for short chains, and between 4.1 × 103 and 1.1 × 104 g/mol for long chains. Differences in amylopectin chain content were observed between HPSEC-RI and HPAEC-PAD, highlighting the complementary nature of these techniques. The study underscores the need for standardizing chromatography-based methodologies in starch research, particularly with the advent of new technologies.

Determination of Chain Transfer Constants of Alcohols for High‐Pressure Polyethylene Polymerization

AbstractIn low‐density polyethylene (LDPE) production, low‐molecular‐weight species are used as chain transfer agents (CTAs). They reduce the degree of polymerization, which has an impact on the polymer properties, such as processability. To specifically adjust the product properties, a detailed understanding of the transfer kinetics to CTAs is indispensable. Thus, the transfer activity of various primary, secondary, and tertiary alcohols as well as diols was investigated experimentally between 120 °C and 250 °C at 2000 bar. The results were evaluated using the Mayo and chain length distribution (CLD) method, and the latter was found to give more reliable results. It was observed that the hydroxy group systematically increases transfer activity compared to alkanes. Additionally, a linear increase of transfer activity with the number of hydrogen atoms is found.

Kinetic Investigation of the Emulsion Polymerization of Vinylidene Fluoride

AbstractPoly(vinylidene fluoride) (PVDF) is among the most produced fluoropolymers, second only to polytetrafluoroethylene. Despite its popularity, the complex microstructural properties achieved during the polymerization are not well documented in the literature. In particular, available models only track the chain length distribution of the polymer, while neglecting the distribution of other important properties, affecting the final behavior of the product. In this work, a 2D kinetic model, evaluating not only the chain length but also the number of terminal double bonds (TDBs) per chain, is developed. The numerical solution of the model is achieved by fractionating the population of polymer chains into classes with a specific number of TDBs and using the method of moments for each class. The model results are compared with experimental evidences for the amount of produced polymer, moles of main chain‐ends, number, and weight average molecular weight as well as full molecular weight distribution. Based on this comparison, kinetic parameters are estimated by optimization using genetic algorithm. The model reliability is finally verified using additional experimental data at different temperatures and amounts of initiator.

Exploring the ring-opening metathesis polymerization process by kinetic Monte Carlo simulation

Investigating the kinetics of polymerization reactions is a powerful tool to obtain information for the engineering design of such processes. It provides insights into how the relative rates of elementary reactions which influence both the kinetics of the reactions and thus characteristics of the products as well, particularly when the reaction parameters of these reactions are unknown. Among polymerization processes, ring-opening metathesis polymerization (ROMP) has gained broad academic and industrial interest, due to its mild conditions to obtain a wide range of polymer products. In this study, kinetic Monte Carlo simulation was applied to reveal the effect of the elementary reactions of ROMP on the kinetics and product distribution. Both the propagation and the cross-metathesis reactions were considered, with the latter leading to the formation of various types of macrospecies whose population levels were also monitored. Relevant tendencies were observed regarding how the variations in the reaction parameters of the elementary reactions of this polymerization process, such as reaction probabilities, monomer addition method, catalyst-to-monomer ratio, and reaction time, affect the kinetics of the polymerization process and the product distributions. These variations also influence the key macromolecular parameters of the resulting polymeric materials, including chain length distribution (CLD), population levels, and polymer functionalities. The results of this study indicate that this simulation technique is a valuable tool for mapping the tailoring possibilities of modifying the reaction parameters of ROMP to achieve desired properties. These properties include number average molecular weight, polydispersity, chain end functionality, and macrocycle-free products.

Correlation analysis of starch molecular structure and film properties via rearrangements of glycosidic linkages by 1,4-α-glucan branching enzyme

The functional characteristics of starch films are significantly influenced by the amylose content and the distribution of the amylopectin chain length. This work used 1,4-α-glucan branching enzyme to molecularly reconstruct corn, pea, and cassava starch in order to examine the association. Films made of both natural and enzyme-modified starch were produced using the casting method. The study investigated the variations in starch films properties and explored the relationship between starch molecular structure and film qualities by correlation analysis. The results showed a significant positive connection (r = 0.954) between the tensile strength and amylose content, as well as a positive correlation (r = 0.939) between the A chains and the elongation at break. The average chain length (r = 0.932) and amylose content (r = 0.902) showed a positive correlation with the degradation temperature, whereas the amylose content (r = −0.946) showed an adverse correlation with the transparency. The B3 chain (r = 0.851) and the average chain length (r = 0.839) both exhibited a positive connection with its contact angle. As a result, our study thoroughly assesses how starch structure affects the characteristics of starch films and offers a fundamental modification pathway for the development of new application areas.

The texture of potato mashes is impacted by blanching induced changes in their extracellular starch fractions

The texture of potato mash significantly influences consumer satisfaction. We here investigated the impact of blanching and different methods thereof on the texture and extractable extracellular fractions (EEFs) of potato mash when extracted with water or with dimethyl sulfoxide (DMSO) to seek determining factors of potato mash texture. Mashes prepared from potatoes blanched in 2.04 mM CaCl2 (CaB-M) exhibited hardness (24.9 N) and stickiness (1.0 N·s) readings intermediate to those from potatoes that were not blanched (NB-M, 19.2 N and 1.2 N·s), or blanched in deionized water (WaB-M, 30.5 N and 0.6 N·s), which aligned with their levels of intact cells. Starch was the main constituent (57.2 % – 64.4 %, w/w) in all EEFs and more starch was present in (1) NB-M and (2) the DMSO extracts. The chain length distributions of DMSO-extracted extracellular starch (DEES) revealed that the amylopectin content increased in the order WaB-M (46.3 %), CaB-M (55.1 %), and NB-M (76.6 %), which was attributed to more intracellular amylopectin being released to the extracellular phase of mashes. The relative contents of shorter chain amylose (degree of polymerization 110–1000) and the DEES yield were significantly correlated to the hardness while the yield of DEEFs was positively correlated with the stickiness.

Effects of amylose and amylopectin fine structure on the thermal, mechanical and hydrophobic properties of starch films

The fine structures of pumpkin, potato, wheat, cassava, and pea starches were determined, followed by an evaluation of how these structures affected the properties of starch films. The structures significantly influenced film properties. Starches with larger molecular weights exhibited greater thermal stability. The tensile strength of starch film was negatively associated with the amylose chain length (r = −0.88, p < 0.05). The chain length distributions of amylose and amylopectin affected the mechanical properties of starch films by influencing structure ordering, supported by the positive correlation between the double helix content and the tensile strength (r = 0.95, p < 0.05). The amylopectin B1, B2, and B3 chains increased film mechanical strength. Conversely, amylopectin A-chains reduced the mechanical strength. The water contact angle was negatively correlated with the B3 chain proportion (r = −0.93, p < 0.05). The pumpkin starch exhibited the highest tensile strength (14.29 MPa), while the wheat starch film showed the highest water contact angle (112°). This study offers valuable insights into the structure-function relationships of starch films, thereby facilitating the acquisition of starch films with enhanced strength and stability through screening or designing starch structures. Consequently, this will expand the application of starch films as packaging materials in various food products.

Exploring the potential of taro (Colocasia esculenta) starch: Recent developments in modification, health benefits, and food industry applications

AbstractTaro is a tropical plant and an underutilized root crop that has a good source of carbohydrate. Taro tuber contains 70%–80% of starch on dry basis. This review highlights the extraction of taro starch, latest advancements in the modification such as physical, chemical and enzymatic modification of taro starch. Furthermore, after modification of taro starch, molecular weight and amylopectin branch chain length distribution, granular shape, percentage crystallinity, swelling and solubilization, pasting and thermal properties and in vitro digestibility of taro starch were significantly affected. Additionally, researchers have explored novel methods to modify the physicochemical characteristics of taro starch, enhancing its functionality as a thickening, gelling, and stabilizing agent in various food formulations. However, fabrication of nanoparticles from taro starch was also studies. Various health benefits of taro starch have been reported in this study. One significant health benefit of taro starch is its potential to improve blood sugar management. Furthermore, the versatility of taro starch in food applications has expanded, ranging from traditional staples to modern convenience foods. Its gluten‐free nature makes it an attractive option for individuals with gluten sensitivity or celiac disease. Taro starch is increasingly incorporated into bakery products, snacks, noodles, and as a thickening agent in soups and sauces. The unique sensory attributes and nutritional profile of taro starch contribute to the development of novel, health‐conscious food products that cater to evolving consumer preferences.

Natural and anthropogenic forcing of ecological and environmental changes at Lake Qilu, SW China, since the last deglaciation

The ecological evolution of lakes and their watersheds and the driving mechanisms are a key topic in paleoenvironmental research. However, the relative impacts of human activities and climate change on lake ecosystems since the last deglaciation remain unclear. We conducted a high-resolution study of the chain length distribution and concentration of n-alkanes in a sediment core from Lake Qilu in SW China, to reveal the ecological changes and their controlling factors since 14.6 cal kyr BP. Based on studies of modern samples, short-chain, medium-chain, and long-chain n-alkanes are associated with bacteria/algae, aquatic plants, and terrestrial plants, respectively. Combining the ACL17–33, Paq, and Σn-alkane indices, we found that both aquatic and terrestrial plants proliferated at Lake Qilu from 14.6 to 6 cal kyr BP, which was associated with a relatively warm and wet climate and dynamic strong winds. During the interval from 6 to 2 cal kyr BP, aquatic plants flourished, accompanied by a rapid surge in the regional productivity, primarily due to human activities. After 2 cal kyr BP, anthropogenic eutrophication was the primary cause of the increase in bacteria and algae populations. These results suggest that, before 6 cal kyr BP, climatic factors dominated the n-alkanes distribution; whereas after 6 cal kyr BP, human activities became the primary factor controlling the n-alkanes and ecological changes in Lake Qilu.

Phenotypic Analysis and Gene Cloning of Rice Floury Endosperm Mutant wcr (White-Core Rice).

The composition and distribution of storage substances in rice endosperm directly affect grain quality. A floury endosperm mutant, wcr (white-core rice), was identified, exhibiting a loose arrangement of starch granules with a floury opaque appearance in the inner layer of mature grains, resulting in reduced grain weight. The total starch and amylose content remained unchanged, but the levels of the four component proteins in the mutant brown rice significantly decreased. Additionally, the milled rice (inner endosperm) showed a significant decrease in total starch and amylose content, accompanied by a nearly threefold increase in albumin content. The swelling capacity of mutant starch was reduced, and its chain length distribution was altered. The target gene was mapped on chromosome 5 within a 65 kb region. A frameshift mutation occurred due to an insertion of an extra C base in the second exon of the cyOsPPDKB gene, which encodes pyruvate phosphate dikinase. Expression analysis revealed that wcr not only affected genes involved in starch metabolism but also downregulated expression levels of genes associated with storage protein synthesis. Overall, wcr plays a crucial role as a regulator factor influencing protein synthesis and starch metabolism in rice grains.

Enzymatic advances in starch modification: Creating functional derivatives and exploring applications

Enzyme based starch modification has attracted much attention form recent years due to formation various functional derivatives with novel processing and functional properties such as resistant to digestion, thermos-reversible gel formation, etc. It has emerges as a promising method due to their high specificity, safety, and eco-friendly nature. Starch-modifying enzymes hydrolyse or form glycosidic bonds causing alteration in the amylose/amylopectin ratio, molecular weight and distribution of branch chain-length that has reduced limitation possessed by NSs i.e., low water-holding capacity, insolubility, syneresis retrogradation, etc. The review delves into the key enzymes used for modifying starch, affecting the structural and functional properties of starch. These alteration in starch properties provide guidelines in designing a new starch-based products with desired structure and properties for the food industry.

Structure and digestibility changes of Indica and japonica waxy rice starch during in vitro pre-digestion

The digestion of starch have been of great interest, yet little is known about the structure changes and structure-digestibility relationships of waxy rice starch during digestion. In this study, waxy rice starch from Indica and Japonica cultivars were in vitro pre-digested for different times, and the changes in their structure and properties were investigated, including granule morphology, chain length distribution, short-range ordered structure, crystallinity, thermal properties, and digestibility. Pre-digested Indica and Japonica waxy rice starch had the characteristics of porous starch, showing similar surface erosion and pores. With the prolongation of pre-digestion time, the amylose content decreased by 0.74 %–2.69 %, the proportion of amylopectin short A chain (DP6–12) and B1 chain (DP13–24) decreased, and the proportion of long B2 (DP25–36) and B3 chain (DP ≥ 37) increased, especially in pre-digested Indica waxy rice starch. The short- and long-range ordered structure of pre-digested starch increased, manifested by an increase in the absorbance ratio at 1047/1022 cm−1, a decrease at 1022/995 cm−1, and an increase in relative crystallinity, leading to higher gelatinization temperature and enthalpy. Pre-digested waxy rice starch had a reduced rapidly digestible starch of 18.27 %–33.93 % and an increased resistant starch of 29.51 %–41.32 %, which will be applied in functional starch and healthy starchy foods.

Numerical simulations of equilibrium, kinetics, and chain length distribution in linear polycondensation proceeding in nano-scale small volumes: An apparent violation of the law of mass action

A simple polycondensation process Mi + Mj ⇄ Mi+j + Z, proceeding in dispersion of nano-scale droplets was described by analytical solutions and differential equations giving insight into equilibrium and kinetics of the process. Stochastic and deterministic simulations show that the statistical nature of polycondensation, both irreversible and reversible one, affects the way the macromolecules of different lengths are formed and distributed among droplets. The droplet distributions in respect to the number of reacting chains and the chain length distributions depend, for the given conversion, on the polycondensation equilibrium constant Kcond and the initial conditions: monomer concentration and the number of its molecules in a droplet. The apparent equilibrium constants of condensation K¯ij=[Mi+j]¯e[Z]¯e/[Mi]¯e[Mj]¯e depend on oligomer/polymer sizes as well as on the initial number of monomer molecules in a droplet. This apparent violation of the law of mass action was explained by stochasticity of involved processes. Moreover, when the polycondensation byproduct Z is being removed reversibly from the system, K¯ij depends also on average equilibrium concentration [Z]¯e. The indicated effects are observed not only for ideally dispersed systems (all droplets contain initially the same number of monomer molecules), but also when the initial numbers of monomer molecules conform the Poisson distribution. However, the chain length distribution as well as kinetics and K¯ij differ here from those observed for systems with uniform distribution.

Mutations in starch BRANCHING ENZYME 2a suppress the traits caused by the loss of ISOAMYLASE1 in barley

Key messageThe hvbe2a mutations restore the starch-deficient phenotype caused by the hvisa1 and hvflo6 mutations in barley endosperm.The genetic interactions among starch biosynthesis genes can be exploited to alter starch properties, but they remain poorly understood due to the various combinations of mutations to be tested. Here, we isolated two novel barley mutants defective in starch BRANCHING ENZYME 2a (hvbe2a-1 and hvbe2a-2) based on the starch granule (SG) morphology. Both hvbe2a mutants showed elongated SGs in the endosperm and increased resistant starch content. hvbe2a-1 had a base change in HvBE2a gene, substituting the amino acid essential for its enzyme activity, while hvbe2a-2 is completely missing HvBE2a due to a chromosomal deletion. Further genetic crosses with barley isoamylase1 mutants (hvisa1) revealed that both hvbe2a mutations could suppress defects in endosperm caused by hvisa1, such as reduction in starch, increase in phytoglycogen, and changes in the glucan chain length distribution. Remarkably, hvbe2a mutations also transformed the endosperm SG morphology from the compound SG caused by hvisa1 to bimodal simple SGs, resembling that of wild-type barley. The suppressive impact was in competition with floury endosperm 6 mutation (hvflo6), which could enhance the phenotype of hvisa1 in the endosperm. In contrast, the compound SG formation induced by the hvflo6 hvisa1 mutation in pollen was not suppressed by hvbe2a mutations. Our findings provide new insights into genetic interactions in the starch biosynthetic pathway, demonstrating how specific genetic alterations can influence starch properties and SG morphology, with potential applications in cereal breeding for desired starch properties.

Effect of twin-screw extrusion pretreatment on starch structure, rheological properties and 3D printing accuracy of whole potato flour and its application in dysphagia diets

Twin-screw extrusion pretreatment has great potential for the development of three-dimensional (3D) printed food as dysphagia diets. This study aimed to investigate the effect of twin-screw extrusion pretreatment on starch structure, rheological properties and 3D printing accuracy of whole potato flour and its application in dysphagia diets. The results indicated that twin-screw extrusion pretreatment was found to change chain length distributions, short-range ordered structure and relative crystallinity of whole potato flour (WPF), thereby improving its 3D printing performance. With the increasing proportion of long linear chains (DP > 12), the intensity of hydrogen bonds, linear viscoelastic region, storage modulus (G′), loss modulus (G″), viscosity and n of whole potato flour paste were increased, enhancing high printing accuracy and shape retention of 3D printed samples with a denser microstructure and smaller pore diameter distribution. The whole potato flour paste extruded with a peristaltic pump speed at 5.25 mL/min (WPF-4) displayed the highest printing accuracy with excellent rheological properties, good water distribution state and dense network structure, which classified as class 5 level dysphagia diets. This research provides an effective guidance for the modification of whole potato flour using twin-screw extrusion pretreatment as 3D printed food inks for dysphagia patients.

Impact of freeze-thaw cycles on the physicochemical properties and structure-function relationship of potato starch with varying granule sizes in frozen dough

Starch, as a critical component of dough, significantly influences quality preservation during the freezing process. In particular, the fine structure of potato (B-type) starch in frozen processing is a subject of considerable interest. This study aims to investigate the intrinsic differences of B-type starch and the impact of freeze-thaw (F/T) treatment on its molecular structure and physicochemical properties. Chain length distribution and X-ray photoelectron spectroscopy were utilized to examine the structural characteristics of natural potato starch with different granule sizes. Furthermore, the fine structure, thermal properties, and rheological properties of the isolated starches after F/T treatment were analyzed. The results indicate that potato starch with smaller particle sizes exhibits higher surface CC and PO content along with a higher proportion of very short chains (DP < 6, 8.17 %) and long B chains (DP > 25, 20.68 %). The study found that after F/T treatment, the surface of small-sized starch granules was initially damaged, exhibiting threads on the surface centered on the umbilical point. Following F/T treatment, both the crystallinity (very large (VL): 24.52–18.36 %; small (S): 17.03–16.69 %) and short-range order (VL: 2.97–2.61; S: 2.71–2.35) of starch particle size decreased. Both the amylose content (20.88–14.57 %) and ΔH (10.15–8.62 J/g) of isolated starch after freeze-thaw-treated dough exhibited a decrease to varying degrees. With the exception of the fifth cycle, small-size starch particles exhibited relatively higher G' and G" values and showed significant changes as a result of F/T treatment, demonstrating high hardness and complex viscosity. Clarifying the physicochemical properties of potato starches with different granule sizes is expected to expand their applications in frozen dough.

High-Resistant Starch Based on Amylopectin Cluster via Extrusion: From the Perspective of Chain-Length Distribution and Structural Formation.

Resistant starch (RS) has the advantage of reshaping gut microbiota for human metabolism and health, like glycemic control, weight loss, etc. Among them, RS3 prepared from pure starch is green and safe, but it is hard to achieve structural control. Here, we regulate the crystal structure of starch with different chain-length distributions (CLDs) via extrusion at low/high shearing levels. The change in CLDs in extruded starch was obtained, and their effects on the fine structure (Dm, dBragg, dLorentz, degree of order and double helix, degree of crystal) of RS and its physicochemical properties were investigated by SAXS, FTIR, XRD and 13C NMR analyses. The results showed that the RS content under a 250 r/min extrusion condition was the highest at 61.52%. Furthermore, the crystalline system induced by high amylopectin (amylose ≤ 4.78%) and a small amount of amylose (amylose ≥ 27.97%) was favorable for obtaining a high content of RS3-modified products under the extruding environment. The control of the moderate proportion of the A chains (DP 6-12) in the starch matrix was beneficial to the formation of RS.

Structural characterization and physicochemical properties of grain amaranth starch

With potato starch (PS) and corn starch (CS) as the controls, the structure and physicochemical properties of grain amaranth starch (GAS) and its binding with dihydromyricetin were investigated in this study. The results indicated that GAS granules were small in size (3.21 ± 0.13 μm) and had a low amylose content (11.57 ± 0.91%). GAS exhibited low paste clarity, solubility, and swelling power, but demonstrated good freeze-thaw stability and resistance to retrogradation. Although the pasting temperature of GAS was high (75.88 ± 0.03 °C), its peak viscosity, breakdown viscosity, and setback viscosity were significantly lower than those of PS and CS. GAS was classified as A-type starch, with a high molecular weight and broad distribution (Mw, 3.96 × 107 g/mol; PDI, 2.67). For its chain length distribution, chain B1 had the highest proportion (50.09%), while chain B3 had the lowest proportion (13.50%). The complexation of GAS with dihydromyricetin effectively enhanced its ABTS and DPPH free radical scavenging capacities.