Conformational and configurational features of acidic polysaccharides and their interactions with calcium ions: a molecular modeling investigation

TBL38 atypical homogalacturonan-acetylesterase activity and cell wall microdomain localization in Arabidopsis seed mucilage secretory cells

Plant cell walls constitute complex polysaccharidic/proteinaceous networks whose biosynthesis and dynamics implicate several cell compartments. The synthesis and remodeling of homogalacturonan pectins involve Golgi-localized methylation/acetylation and subsequent cell wall-localized demethylation/deacetylation. So far, TRICHOME BIREFRINGENCE-LIKE (TBL) family members have been described as Golgi-localized acetyltransferases targeting diverse hemicelluloses or pectins. Using seed mucilage secretory cells (MSCs) from Arabidopsis thaliana, we demonstrate the atypical localization of TBL38 restricted to a cell wall microdomain. A tbl38 mutant displays an intriguing homogalacturonan immunological phenotype in this cell wall microdomain and in an MSC surface-enriched abrasion powder. Mass spectrometry oligosaccharide profiling of this fraction reveals an increased homogalacturonan acetylation phenotype. Finally, TBL38 displays pectin acetylesterase activity in vitro. These results indicate that TBL38 is an atypical cell wall-localized TBL that displays a homogalacturonan acetylesterase activity rather than a Golgi-localized acetyltransferase activity as observed in previously studied TBLs. TBL38 function during seed development is discussed.

Anionic species from multivalent metal salts are differentially retained during aqueous ionic gelation of sodium alginate and could fine-tune the hydrogel properties

The role of anionic counterions of divalent metal salts in alginate gelation and hydrogel properties has been thoroughly investigated. Three anions were selected from the Hofmeister series, namely sulphate, acetate and chloride, paired in all permutations and combinations with divalent metal cations like calcium, zinc and copper. Spectroscopic analysis revealed the presence of anions and their interaction with the respective metal cations in the hydrogel. The data showed that the gelation time and other hydrogel properties were largely controlled by cations. However, subtle yet significant variations in viscoelasticity, water uptake, drug release and cytocompatibility properties were anion dependent in each cationic group. Computational modelling based study showed that metal-anion-alginate configurations were energetically more stable than the metal-alginate models. The in vitro and in silico studies concluded that acetate anions preceded chlorides in the drug release, swelling and cytocompatibility fronts, followed by sulphate anions in each cationic group. Overall, the data confirmed that anions are an integral part of the metal-alginate complex. Furthermore, anions offer a novel option to further fine-tune the properties of alginate hydrogels for myriads of applications. In addition, full exploration of this novel avenue would enhance the usability of alginate polymers in the pharmaceutical, environmental, biomedical and food industries.

Self-assembled sodium alginate polymannuronate nanoparticles for synergistic treatment of ophthalmic infection and inflammation: Preparation optimization and in vitro/vivo evaluation

Frequent administrations are often needed during the treatment of ocular diseases due to the low bioavailability of the existing eye drops owing to inadequate corneal penetration and rapid drug washout. Herein, sodium alginate polymannuronate (SA) nanocarriers were developed using ionic gelation method that can provide better bioavailability through mucoadhesivity and sustained drug release by binding to the ocular mucus layer. This study disproves the common belief that only the G block of SA participates in the crosslinking reaction during ionic gelation. Self-assembly capability due to the linear flexible structure of the M block, better biocompatibility than G block along with the feasibility of controlling physicochemical characteristics postulate a high potential for designing efficient ocular drug delivery systems. Initially, four crosslinkers of varied concentrations were investigated. Taguchi design of experiment revealed the statistically significant effect of the crosslinker type and concentration on the particle size and stability. The best combination was detected by analyzing the particle size and zeta potential values that showed the desired microstructural properties for ocular barrier penetration. The desired combination was SA-Ca-1 that had particle size within the optimal corneal penetration range, that is 10-200 nm (135 nm). The drug carriers demonstrated excellent entrapment efficiency (∼89 % for Ciprofloxacin and ∼96 % for Dexamethasone) along with a sustained and simultaneous release of dual drug for at least 2 days. The nanoparticles also showed biocompatibility (4 ± 0.6 % hemolysis) and high mucoadhesivity (73 ± 2 % for 0.25 g) which was validated by molecular docking analysis. The prepared formulation was able to reduce the scleral inflammation of the rabbit uveitis models significantly within 3 days. Thus, the eye drop showed remarkable potential for efficient drug delivery leading to faster recovery.

Alginate biopolymeric structures: Versatile carriers for bioactive compounds in functional foods and nutraceutical formulations: A review

Alginate-based biopolymer products have gained attention for protecting and delivering bioactive components in nutraceuticals and functional foods. These naturally abundant anionic, unbranched, and linear copolymers are also produced commercially by microorganisms. Alone or in combination with other copolymers, they efficiently transport bioactive molecules in food and nutraceutical products. This review aims to provide an in-depth understanding of alginate-based products and structures, emphasizing their role in delivering functional molecules in various formulations and delivery systems. These include edible coatings/films, gels/emulsions, beads/droplets, microspheres/particles, and engineered nanostructures where alginates have been used potentially. By exploring these applications, readers gain insights into the benefits of these products. Because, alginate-based biopolymer products have shown promise in delivering bioactive compounds like vitamin C, vitamin D3, curcumin, β-carotene, resveratrol, folic acid, gliadins, caffeic acid, betanin, limonoids, quercetin, several polyphenols and essential oils, etc., which are chief contributors to treating specific/overall nutritional and chronic metabolic disorders. So, this review summarizes the potential of alginate-based structures/products in various forms for delivering a wide range of functional food ingredients and nutraceutical components that offer promising perspectives for future investigations.

The self-regulating on cohesion properties of calcium phosphate/ calcium sulfate bone cement improved by citric acid/sodium alginate

Calcium phosphate cement (CPC) has attracted extensive interest from surgeons and materials scientists. However, the collapsibility of calcium phosphate cement limits its clinical application. In this work, a gel network of SA-CA formed by the reaction of citric acid (CA) and sodium alginate (SA) was introduced into the α-TCP/α-CSH composite. Furthermore, a high proportion of α-CSH provided more calcium sources for the system to combine with SA forming a gel network to improve the cohesion property of the composite, which also played a regulating role in the conversion of materials to HA. The morphology, physicochemical properties, and cell compatibility of the composites were studied with SA-CA as curing solution. The results show that SA-CA plays an important role in the compressive strength and collapse resistance of bone cement, and its properties can be regulated by changing the content of CA. When CA is 10 wt%, the mechanical strength is the highest, reaching 12.49 ± 2.03 MPa, which is 265.80% higher than water as the solidifying liquid. In addition, the cell experiments showed that the samples were not toxic to MC3T3 cells. The results of ALP showed that when SA-CA were used as curing solution, the activity of ALP was higher than that of blank sample, indicating that the composite bone cement could be conducive to the differentiation of osteoblasts. In this work, the α-CSH/α-TCP based composite regulated by gel network of SA-CA can provide a promising strategy to improve the cohesion of bone cement.

Multiscale investigation of viscoelastic properties of aqueous solutions of sodium alginate and evaluation of their biocompatibility

In order to get better knowledge of mechanical properties from microscopic to macroscopic scale of biopolymers, viscoelastic bulk properties of aqueous solutions of sodium alginate were studied at different scales by combining macroscopic shear rheology (Hz), diffusing-wave spectroscopy microrheology (kHz-MHz) and Brillouin spectroscopy (GHz). Structural properties were also directly probed by small-angle X-ray scattering (SAXS). The results demonstrate a change from polyelectrolyte behavior to neutral polymer behavior by increasing polymer concentration with the determination of characteristic sizes (persistence length, correlation length). The viscoelastic properties probed at the phonon wavelength much higher than the ones obtained at low frequency reflect the variation of microscopic viscosity. First experiments obtained by metabolic activity assays with mouse embryonic fibroblasts showed biocompatibility of sodium alginate aqueous solutions in the studied range of concentrations (2.5-10 g L-1) and consequently their potential biomedical applications.

Fabrication of cell-laden microbeads and microcapsules composed of bacterial polyglucuronic acid

In the past decades, the microencapsulation of mammalian cells into microparticles has been extensively studied for various in vitro and in vivo applications. The aim of this study was to demonstrate the viability of bacterial polyglucuronic acid (PGU), an exopolysaccharide derived from bacteria and composed of glucuronic acid units, as an effective material for cell microencapsulation. Using the method of dropping an aqueous solution of PGU-containing cells into a Ca²⁺-loaded solution, we produced spherical PGU microbeads with >93 % viability in the encapsulated human hepatoma HepG2 cells. Hollow-core microcapsules were formed via polyelectrolyte complex layer formation of PGU and poly-l-lysine, after which Ca²⁺, a cross-linker of PGU, was chelated, and this was accomplished by sequential immersion of microbeads in aqueous solutions of poly-l-lysine and sodium citrate. The encapsulated HepG2 cells proliferated and formed cell aggregates within the microparticles over a 14-day culture, with significantly larger aggregates forming within the microcapsules. Our results provide evidence for the viability of PGU for cell microencapsulation for the first time, thereby contributing to advancements in tissue engineering.

Comparative Electrokinetic Study of Alginate-Coated Colloidal Particles

Alginates are a family of natural polysaccharides with promising potential in biomedical applications and tissue regeneration. The design of versatile alginate-based structures or hydrogels and their stability and functionality depend on the polymer's physicochemical characteristics. The main features of alginate chains that determine their bioactive properties are the molar ratio of mannuronic and glucuronic residues (M/G ratio) and their distribution along the polymer chain (MM-, GG-, and MG blocks). The present study is focused on investigating the influence of the physicochemical characteristics of alginate (sodium salt) on the electrical properties and stability of the dispersion of polymer-coated colloidal particles. Ultrapure and well-characterized biomedical-grade alginate samples were used in the investigation. The dynamics of counterion charge near the vicinity of adsorbed polyion is studied via electrokinetic spectroscopy. The results show that the experimental values of the frequency of relaxation of the electro-optical effect are higher compared to the theoretical ones. Therefore, it was supposed that polarization of the condensed Na⁺ counterions occurs at specific distances according to the molecular structure (G-, M-, or MG-blocks). In the presence of Ca²⁺, the electro-optical behavior of the particles with adsorbed alginate molecules almost does not depend on the polymer characteristics but was affected by the presence of divalent ions in the polymer layer.

Description of the Wild Strain Rhizobium rosettiformans DSM26376, Reclassified under Peteryoungia rosettiformans comb.nov., for Producing Glucuronan

Glucuronan is a polysaccharide composed of β-(1,4)-linked d-glucuronic acids having intrinsic properties and biological activities recoverable in many fields of application. Currently, the description of Sinorhyzobium meliloti M5N1CS mutant bacterial strain as the sole source of glucuronan makes it relevant to the exploration of new microorganisms producing glucuronan. In this study, the Peteryoungia rosettifformans strain (Rhizobia), was identified as a wild producer of an exopolysaccharide (RhrBR46) related to glucuronan. Structural and biochemical features, using colorimetric assays, Fourier infrared spectroscopy, nuclear magnetic resonance, high pressure size exclusion chromatography coupled to multi-angle light laser scattering, and enzymatic assays allowed the characterization of a polyglucuronic acid, having a molecular mass (Mw¯) of 1.85 × 10⁵ Da, and being partially O-acetylated at C-2 and/or C-3 positions. The concentration of Mg²⁺ ions in the cultivation medium has been shown to impact the structure of RhrBR46, by reducing drastically its Mw¯ (73%) and increasing its DA (10%). Comparative structural analyses between RhrBR46 and the glucuronan from Sinorhyzobium meliloti M5N1CS strain revealed differences in terms of molecular weight, degree of acetylation (DA), and the distribution of acetylation pattern. These structural divergences of RhrBR46 might contribute to singular properties or biological activities of RhrBR46, offering new perspectives of application.

Temporary hydraulic barriers using organic gel for enhanced aquifer remediation during groundwater flushing: Bench-scale experiments

This study presents the use of organic gel-forming material for the construction of hydraulic barriers in aquifer, which can be easily removed after use. Experiments on the performance of the temporary hydraulic barrier during NAPL removal (aquifer flushing) were also conducted. An aqueous solution of sodium alginate was injected into the horizontally oriented, 2-dimensional flow chamber packed with sand, followed by gelation using a calcium solution. The alginate gel formed in the porous media produced a circular shape barrier (24 cm diameter, 1.3 cm thickness) that was successfully removed using sodium bicarbonate solution (1.0 M) in 72 h, whereas the gel was stable for 7 days during simulated groundwater flushing at the same flow rate as the sodium bicarbonate solution. When circular hydraulic barriers (12 cm diameter each, 14 cm apart) were set on either side of the NAPL (n-hexane and PCE mixture)-contaminated zone, the increased water flux during water flushing resulted in significantly increased PCE removal by almost 108%. When a surfactant solution (sodium dodecyl sulfate, 0.037%) was applied, the influenced groundwater flow controlled by hydraulic barriers on the NAPL removal was amplified by 196% removal.

Solvation and expansion of neutral and charged chains of a carbohydrate polyelectrolyte: Galacturonan in water. A critical revisiting

Experimental and theoretical data have been revisited to shed light onto the aspects of hydration and chain expansion of pectic acid (galacturonan) upon charging. The prediction of the variation of the number of solvation water molecules between the two limit ionization states from theoretical calculations was confirmed to a very high accuracy by the corresponding number evaluated form dilatometric measurements. The relevance of hydration to the mechanism of bonding of calcium ions by sodium pectate is discussed. Characterization of polymer expansion has been obtained by calculating the values of the characteristic ratio and/or the persistence length on the respective populations and comparing the theoretical predictions with experimental data. The results show that a charged chain in typical conditions of ionic strength is more expanded than its neutral counterpart, whereas the ideal limit (3₁ and 2₁) helical conformations in the uncharged and totally charged conditions, respectively, share the same value of the linear advance of the helical repeat, when the ionic strength tends to infinite. Total divergence between theoretical predictions and experimental evidence rules out the possibility that carboxylate charge reduction by protonation and by methyl esterification are equivalent in determining the solution behavior of galacturonan.

Doubling growth of egg-box structure during Calcium-mediated molecular assembly of alginate

Ca²⁺-mediated molecular assembly of alginate underpins its wide range of applications in foods, pharmaceutics, biomedicines, tissue engineering and environmental treatments. The mode of growth of egg-box structure of alginate in the presence of Ca²⁺ is a long-standing fundamental problem to be concluded. In this work, we investigate the Ca-induced structural evolution of alginate in dilute solution using atomic force microscopy and dilute solution viscometry. It is demonstrated that the structural evolution follows the three critical steps of monocomplexation, dimerization and multimerization, upon binding with Ca²⁺. Interestingly, the alginate single chains grow into dimers and multimers via a doubling mode, i.e., successive emerging of dimer, tetramer, octamer, and hexadecamer. Compared with lower guluronate (G) alginate, higher G alginate exhibits a more pronounced multimerization process occurring at a lower ratio of Ca/G. A mechanistic model depicting the evolution of egg-box structure is proposed. The results would add new knowledge to the current egg-box model regarding the molecular assembly and gelation of an important biopolymer alginate, and provide fundamental basis for molecular engineering of alginate for more advanced applications.

Exogenously applied melatonin alleviates the damage in cucumber plants caused by Aphis goosypii through altering the insect behavior and inducing host plant resistance

BACKGROUND

Aphis gossypii Glover is the main pest found in most cucumber-producing areas. Melatonin (MT) has been widely studied in protecting plants from environmental stresses and pathogens. However, little knowledge is available on the impact of MT on insect resistance.

RESULTS

The fecundity of aphids on MT-treated cucumber leaves was inhibited. Interestingly, MT-treated plants were more attractive to aphids, which would prevent the large-scale transmission of viruses caused by the random movement of aphids. Meanwhile, MT caused varying degrees of change in enzyme activities related to methylesterified HG degradation, antioxidants, defense systems and membrane lipid peroxidation. Furthermore, transcriptomic analysis showed that MT induced 2360 differentially expressed genes (DEGs) compared with the control before aphid infection. These DEGs mainly were enriched in hormone signal transduction, MAPK signaling pathway, and plant-pathogen interaction, revealing that MT can help plants acquire inducible resistance and enhance plant immunity. Subsequently, 2397 DEGs were identified after aphid infection. Further analysis showed that MT-treated plants possessed stronger JA signal, reactive oxygen species stability, and the ability of flavonoid synthesis under aphid infection, while mediating plant growth and sucrose metabolism.

CONCLUSION

In summary, MT as an environmentally friendly substance mitigated aphid damage to cucumbers by affecting the aphids themselves and enhancing plant resistance. This will facilitate exploring sustainable MT-based strategies for cucumber aphid control. © 2022 Society of Chemical Industry.

How Accurate Is the Egg-Box Model in Describing the Binding of Calcium to Polygalacturonate? A Molecular Dynamics Simulation Study

We performed molecular dynamics (MD) simulations of octameric galacturonate, GalA₈, chains in the presence of Ca²⁺ in a ratio of R = [Ca²⁺]/[GalA] = 0.25 in order to determine to which extent the popular "egg-box model" (EBM) is able to describe the association between Ca²⁺ cations and polygalacturonate (polyGalA) chains. To this aim, we slightly revised the empirical parameters for the interaction between Ca²⁺ and the carboxylate oxygen atoms of GalA units so as to reproduce the experimental Ca²⁺-GalA association constant. We also defined an ad hoc order parameter, referred to as the egg-box score (EBS), that quantifies any deviation of the local coordination geometry of calcium cations with respect to an "ideal" EBM coordination geometry. The results reveal that the local coordination geometry of Ca²⁺ cations bound to polyGalA chains differs from that of the EBM. Moreover, polyGalA chains exhibit significant conformational disorder, and the cross-link angles formed between polyGalA chain axes are broadly distributed. Overall, the present study suggests that the EBM fails to describe accurately the association modes between calcium and polyGalA chains at a molar ratio R of 0.25.

Interplay between biofilm microenvironment and pathogenicity of Pseudomonas aeruginosa in cystic fibrosis lung chronic infection

Pseudomonas aeruginosa (PA) is a highly, if not the most, versatile microorganism capable of colonizing diverse environments. One of the niches in which PA is able to thrive is the lung of cystic fibrosis (CF) patients. Due to a genetic aberration, the lungs of CF-affected patients exhibit impaired functions, rendering them highly susceptible to bacterial colonization. Once PA attaches to the epithelial surface and transitions to a mucoid phenotype, the infection becomes chronic, and antibiotic treatments become inefficient. Due to the high number of affected people and the severity of this infection, CF-chronic infection is a well-documented disease. Still, numerous aspects of PA CF infection remain unclear. The scientific reports published over the last decades have stressed how PA can adapt to CF microenvironmental conditions and how its surrounding matrix of extracellular polymeric substances (EPS) plays a key role in its pathogenicity. In this context, it is of paramount interest to present the nature of the EPS together with the local CF-biofilm microenvironment. We review how the PA biofilm microenvironment interacts with drugs to contribute to the pathogenicity of CF-lung infection. Understanding why so many drugs are inefficient in treating CF chronic infection while effectively treating planktonic PA is essential to devising better therapeutic targets and drug formulations.

Polyguluronate simulations shed light onto the therapeutic action of OligoG CF-5/20

Chronic mucoid P. aeruginosa cystic fibrosis (CF) lung infections are associated with the development of a biofilm composed of anionic acetylated exopolysaccharide (EPS) alginate, electrostatically stabilised by extracellular Ca2+ ions. OligoG CF-5/20, a low molecular weight guluronate rich oligomer, is emerging as a novel therapeutic capable of disrupting mature P. aeruginosa biofilms. However, its method of therapeutic action on the mucoid biofilm EPS is not definitively known at a molecular level. This work, utilising molecular dynamics (MD) and Density-Functional Theory (DFT), has revealed that OligoG CF-5/20 interaction with the EPS is facilitated solely through bridging Ca2+ ions, which are not liberated from their native EPS binding sites upon OligoG CF-5/20 dispersal, suggesting that OligoG CF-5/20 does not cause disruptions to mature P. aeruginosa biofilms through breaking EPS-Ca2+-EPS ionic cross-links. Rather it is likely that the therapeutic activity arises from sequestering free Ca2+ ions and preventing further Ca2+ induced EPS aggregation.

Estimation of Iron Availability in Modified Cereal β-Glucan Extracts by an in vitro Digestion Model

For cereal-based foods rich in dietary fibers, iron bioavailability is known to be poor. For native cereal β-glucan extracts, literature has demonstrated that the main factor impacting the bioavailability is phytic acid, which is often found in association with dietary fibers. During food processing, β-glucan can undergo modifications which could potentially affect the equilibrium between phytic acid, fiber, and iron. In this study, an in vitro digestion was used to elucidate the iron dialysability, and hence estimate iron availability, in the presence of native, chelating resin (Chelex)-treated, oxidised, or partially hydrolysed oat and barley β-glucan extracts (at 1% actual β-glucan concentration), with or without phytase treatment. It was confirmed that pure, phytic acid-free β-glucan polysaccharide does not impede iron availability in cereal foods, while phytic acid, and to a smaller extent, also proteins, associated to β-glucan can do so. Neither Chelex-treatment nor partial hydrolysis, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) or NaIO₄ oxidation significantly influenced the phytic acid content of the β-glucan extracts (ranging 2.0–3.9%; p > 0.05). Consequently, as long as intrinsic phytic acid was still present, the β-glucan extracts blocked the iron availability regardless of source (oat, barley) or Chelex-treatment, partial hydrolysis or NaIO₄-oxidation down to 0–8% (relative to the reference without β-glucan extract). Remarkably, TEMPO-oxidation released around 50% of the sequestered iron despite unchanged phytic acid levels in the modified extract. We propose an iron-mobilising effect of the TEMPO product β-polyglucuronan from insoluble Fe(II)/phytate/protein aggregates to soluble Fe(II)/bile salt units that can cross the dialysis membrane. In addition, Chelex-treatment was identified as prerequisite for phytase to dramatically diminish iron retention of the extract for virtually full availability, with implications for optimal iron bioavailability in cereal foods.

Microencapsulating Alginate-Based Polymers for Probiotics Delivery Systems and Their Application

Probiotics exhibit many health benefits and a great potential for broad applications in pharmaceutical fields, such as prevention and treatment of gastrointestinal tract diseases (irritable bowel syndrome), prevention and therapy of allergies, certain anticancer effects, and immunomodulation. However, their applications are limited by the low viability and metabolic activity of the probiotics during processing, storage, and delivery in the digestive tract. To overcome the mentioned limitations, probiotic delivery systems have attracted much attention. This review focuses on alginate as a preferred polymer and presents recent advances in alginate-based polymers for probiotic delivery systems. We highlight several alginate-based delivery systems containing various types of probiotics and the physical and chemical modifications with chitosan, cellulose, starch, protein, fish gel, and many other materials to enhance their performance, of which the viability and protective mechanisms are discussed. Withal, various challenges in alginate-based polymers for probiotics delivery systems are traced out, and future directions, specifically on the use of nanomaterials as well as prebiotics, are delineated to further facilitate subsequent researchers in selecting more favorable materials and technology for probiotic delivery.

Interaction-Induced Structural Transformations in Polysaccharide and Protein-Polysaccharide Gels as Functional Basis for Novel Soft-Matter: A Case of Carrageenans

Biocompatible, nontoxic, and biodegradable polysaccharides are considered as a promising base for bio-inspired materials, applicable as scaffolds in regenerative medicine, coatings in drug delivery systems, etc. The tunable macroscopic properties of gels should meet case-dependent requirements. The admixture of proteins to polysaccharides and their coupling in more sophisticated structures opens an avenue for gel property tuning via physical cross-linking of components and the modification of gel network structure. In this review recent success in the conformational studies of binary protein-polysaccharide gels is summarized with the main focus upon carrageenans. Future perspectives and challenges in rational design of novel polysaccharide-based materials are outlined.

Competing Effects of Hydration and Cation Complexation in Single-Chain Alginate

Alginic acid, a naturally occurring anionic polyelectrolyte, forms strong physically cross-linked hydrogels in the presence of metal cations. The latter engage in electrostatic interactions that compete with intra- and intermolecular hydrogen bonds, determining the gel structure and properties of the system in aqueous media. In this study, we use all-atom molecular dynamics simulations to systematically analyze the interactions between alginic acid chains and Na⁺ and Ca²⁺ counterions. The formed alginates originate from the competition of intramolecular hydrogen bonding and water coordination around the polyelectrolyte. In contrast to the established interpretation, we show that calcium cations strongly bind to alginate by disrupting hydrogen bonds within (1 → 4)-linked β-d-mannuronate (M) residues. On the other hand, Na⁺ cations enhance intramolecular hydrogen bonds that stabilize a left-hand, fourfold helical chain structure in poly-M alginate, resulting in stiffer chains. Hence, the traditionally accepted flexible flat-chain model for poly-M sequence is not valid in the presence of Na⁺. The two cations have a distinct effect on water coordination around alginate and therefore on its solubility. While Ca⁺ disrupts water coordination directly around the alginate chains, mobile Na⁺ cations significantly disrupt the second hydration layer.

Novel Surrogates for Membrane Fouling and the Application of Support Vector Machine in Analyzing Fouling Mechanism

It is difficult to recognize specific fouling mechanisms due to the complexity of practical feed water, thus the current studies usually employ foulant surrogates to carry out research, such as alginate and xanthan gum. However, the representativeness of these surrogates is questionable. In this work, the classical surrogates (i.e., alginate and xanthan gum) were systematically studied, and results showed that they behaved differently during filtration. For the mixture of alginate and xanthan gum, both filtration behaviors and adsorption tests performed by quartz-crystal microbalance with dissipation monitoring (QCM-D) indicated that alginate plays a leading role in fouling development. Furthermore, by examining the filtration behaviors of extracellular polymeric substances (EPS) extracted from practical source water, it turns out that the gel layer formation is responsible for EPS fouling, and the properties of gel layer formed by EPS share more similarities with that formed from pectin instead of alginate. In addition, with the use of experimental data sets extracted from this study and our previous studies, a modeling method was established and tested by the support vector machine (SVM) to predict complex filtration behaviors. Results showed that the small differences of fouling mechanisms lying between alginate and pectin cannot be recognized by Hermia's models, and SVM can show a discrimination as high as 76.92%. As such, SVM may be a powerful tool to predict complex filtration behaviors.

Changes in biochemical properties and pectin nanostructures of juice sacs during the granulation process of pomelo fruit (Citrus grandis)

Postharvest granulation is a severe physiological disorder in citrus fruit that may be related to pectin metabolism. This study was designed to analyze the changes in fruit quality and pectin metabolism of pomelo fruit during granulation from expansion, gelation to lignification. Fruit quality showed a decrease starting from the gelation stage. Contents of water-soluble pectin, chelate-soluble pectin, sodium carbonate-soluble pectin and calcium, and activity of pectin methylesterase increased, while polygalacturonase activity decreased upon granulation. Atomic force microscopy analysis showed that both length and width of those three types of pectin molecules increased during granulation, accompanied by the decrease of linear structure molecules of pectin and the increase of pectin polymers, and multi-branched pectin tending to form cross-linked structure. Complex network of pectin might be remodeled during granulation process that immobilized the free water in juice sacs and induced the gelation occurrence, further promoted the granulation process.

Application of the Zimm-Bragg Model to the Removal of Azo Dyes with Pectin

In this work, the ability of pectin (Pec) to remove direct red 80 (DR80), Congo red (CR), methyl orange (MO), and methyl red (MR) was studied. The removal percentages under adequate pH and ionic strength conditions were as follows: DR80 (99.5%), CR (99.8%), MO (88.6%), and MR (68%), showing that this methodology is efficient to remove azo dyes. The proposed method included the addition of native Pec to the dye aqueous solution and the formation of a gel that occurred when a calcium salt solution was added. This gel retains the molecules adsorbed onto the molecular surface of Pec through hydrogen bonds and electrostatic and hydrophobic interactions. To our knowledge, it is the first time that the Zimm-Bragg model is used to describe the removal of azo dyes with native Pec. This model includes two parameters: $K_u$ (nucleation constant), which is related to the tendency exerted by a dye molecule attached to the Pec to bind to other molecules present in the aqueous phase, and $U$ (cooperativity parameter), which determines the aggregation capacity of the dye molecules already attached to the Pec. This model fits the experimental isotherms very well, suggesting that Pec binds single molecules and dye aggregates. The obtained results in the values of $K_u$ ranged from 922 mol/kg (MR) to 1,157,462 mol/kg (CR), and $U$ varied from 2.51 (MR) to 169.19 (MO). These results suggest that the use of Pec is a viable option to remove azo dyes from aqueous effluents and that the Zimm-Bragg model fits adequately the isotherms of dyes that have a high tendency to form aggregates.

On the Molecular Mechanism of the Calcium-Induced Gelation of Pectate. Different Steps in the Binding of Calcium Ions by Pectate

Pectic acid/sodium pectate is one of the most widespread hydrocolloid used in the food industry. It is able to form strong ionotropic gels by the addition of ions, in particular, calcium ions. The initial steps of binding Ca²⁺ ions to a sample of sodium pectate with a composition close to 90% of ideal Na⁺-poly(galacturonate) were investigated by means of circular dichroism (CD), microcalorimetry, dilatometry, viscosity, and membrane osmometry, as a function of increasing R_j, R_j being the ratio of the molar concentrations of Ca²⁺ and pectate repeating units. Data were collected in aqueous NaClO₄ at 25 °C. The key instrument of interpretation has been the counterion condensation theory (CCT) of linear polyelectrolytes, modified to include the presence of both specific affinity of the divalent counterion for the polysaccharide ("territorial binding"), and, very importantly, strong chemical bonding (not a covalent bonding, though) of Ca²⁺ on conformationally well-defined sites on the polymer, with local charge annihilation. Intrinsic viscosity and number-average molar mass data as a function of R_j showed that calcium bonding brings about chain association right from the beginning of addition to pectate. The analysis of the microcalorimetric curve using the modified CCT revealed two types of bonding. In the order of development as a function of R_j, the first mode (type 1) could be reconciled with the "tilted egg-box" type, recently proposed for Ca²⁺ binding to alginate and the second mode (type 2) with the "shifted egg-box" proposed for calcium pectate on the basis of conformational analysis investigation. Likewise, the two types of bonding turned out to be superimposable with similar bonding categories proposed for alginate and low-methoxyl pectin (LMP), on the one side, and for the association of semiflexible polyelectrolytes, on the other. The analysis allowed us to obtain standard Gibbs free energy, enthalpy, entropy, and volume molar values both for the affinity and the chemical bonding processes. Interestingly, the analysis of the dependence of the gelation temperatures, T_g, of LMP upon increasing additions of calcium ions provided the values of T_g and standard Gibbs free-energy of calcium-to-pectate association coinciding with those obtained from calorimetry for the type-2 bonding process. This finding corroborated previously reported evidence on the enthalpic nature of the elasticity of Ca²⁺-pectate gels. Finally, comparative analysis of different techniques, but of CD in particular, enabled proposing a "loose-2₁-helix" as the starting conformation of sodium pectate in aqueous solution.

Revisiting Cation Complexation and Hydrogen Bonding of Single-Chain Polyguluronate Alginate

Modifying the properties of bio-based materials has garnered increasing interest in recent years. In related applications, the ability of alginates to complex with metal ions has been shown to be effective in liquid-to-gel transitions, useful in the development of foodstuff and pharma products as well as biomaterials, among others. However, despite its ubiquitous use, alginate behavior as far as interactions with cations is not fully understood. Hence, this study presents a detailed comparison of alginate's complexation with Na⁺ and Ca²⁺ and the involved intramolecular hydrogen bonding and biomolecular chain geometry. Using all-atom molecular dynamics simulations, we find that in contrast to accepted models, calcium cations strongly bind to alginate chains by disruption of hydrogen bonds between neighboring residues, stabilizing a left-hand, 3-fold helical chain structure that enhances chain stiffness. Hence, while present, the traditionally accepted egg-box binding mode was a minor subset of possible conformations. For a single chain, most of the cation binding occurred as single-cation interaction with a carboxyl group, without the coordination of other alginate oxygens. The monovalent Na⁺ ions were found to be mostly nonlocalized around alginate and therefore do not compete with intramolecular hydrogen bonding. The different binding modes observed for Na⁺ and Ca²⁺ contribute toward explaining the different solubility of sodium and calcium alginate.

Cation complexation by mucoid Pseudomonas aeruginosa extracellular polysaccharide

Mucoid Pseudomonas aeruginosa is a prevalent cystic fibrosis (CF) lung colonizer, producing an extracellular matrix (ECM) composed predominantly of the extracellular polysaccharide (EPS) alginate. The ECM limits antimicrobial penetration and, consequently, CF sufferers are prone to chronic mucoid P. aeruginosa lung infections. Interactions between cations with elevated concentrations in the CF lung and the anionic EPS, enhance the structural rigidity of the biofilm and exacerbates virulence. In this work, two large mucoid P. aeruginosa EPS models, based on β-D-mannuronate (M) and β-D-mannuronate-α-L-guluronate systems (M-G), and encompassing thermodynamically stable acetylation configurations–a structural motif unique to mucoid P. aeruginosa–were created. Using highly accurate first principles calculations, stable coordination environments adopted by the cations have been identified and thermodynamic stability quantified. These models show the weak cross-linking capability of Na⁺ and Mg²⁺ ions relative to Ca²⁺ ions and indicate a preference for cation binding within M-G blocks due to the smaller torsional rearrangements needed to reveal stable binding sites. The geometry of the chelation site influences the stability of the resulting complexes more than electrostatic interactions, and the results show nuanced chemical insight into previous experimental observations.

Structural insights into the mechanism of pH-selective substrate specificity of the polysaccharide lyase Smlt1473

Polysaccharide lyases (PLs) are a broad class of microbial enzymes that degrade anionic polysaccharides. Equally broad diversity in their polysaccharide substrates has attracted interest in biotechnological applications such as biomass conversion to value-added chemicals and microbial biofilm removal. Unlike other PLs, Smlt1473 present in the clinically relevant Stenotrophomonas maltophilia strain K279a demonstrates a wide range of pH-dependent substrate specificities toward multiple, diverse polysaccharides: hyaluronic acid (pH 5.0), poly-β-D-glucuronic (celluronic) acid (pH 7.0), poly-β-D-mannuronic acid, and poly-α-L-guluronate (pH 9.0). To decode the pH-driven multiple substrate specificities and selectivity in this single enzyme, we present the X-ray structures of Smlt1473 determined at multiple pH values in apo and mannuronate-bound states as well as the tetra-hyaluronate-docked structure. Our results indicate that structural flexibility in the binding site and N-terminal loop coupled with specific substrate stereochemistry facilitates distinct modes of entry for substrates having diverse charge densities and chemical structures. Our structural analyses of wild-type apo structures solved at different pH values (5.0–9.0) and pH-trapped (5.0 and 7.0) catalytically relevant wild-type mannuronate complexes (1) indicate that pH modulates the catalytic microenvironment for guiding structurally and chemically diverse polysaccharide substrates, (2) further establish that molecular-level fluctuation in the enzyme catalytic tunnel is preconfigured, and (3) suggest that pH modulates fluctuations resulting in optimal substrate binding and cleavage. Furthermore, our results provide key insight into how strategies to reengineer both flexible loop and regions distal to the active site could be developed to target new and diverse substrates in a wide range of applications.

Seaweed-Derived Alginate-Cellulose Nanofiber Aerogel for Insulation Applications

The next generation of green insulation materials is being developed to provide safer and more sustainable alternatives to conventional materials. Bio-based cellulose nanofiber (CNF) aerogels offer excellent thermal insulation properties; however, their high flammability restricts their application. In this study, the design concept for the development of a multifunctional and non-toxic insulation material is inspired by the natural composition of seaweed, comprising both alginate and cellulose. The approach includes three steps: first, CNFs were separated from alginate-rich seaweed to obtain a resource-efficient, fully bio-based, and inherently flame-retardant material; second, ice-templating, followed by freeze-drying, was employed to form an anisotropic aerogel for effective insulation; and finally, a simple crosslinking approach was applied to improve the flame-retardant behavior and stability. At a density of 0.015 g cm-3, the lightweight anisotropic aerogels displayed favorable mechanical properties, including a compressive modulus of 370 kPa, high thermal stability, low thermal conductivity (31.5 mW m-1 K-1), considerable flame retardancy (0.053 mm s-1), and self-extinguishing behavior, where the inherent characteristics were considerably improved by crosslinking. Different concentrations of the crosslinker altered the mechanical properties, while the anisotropic structure influenced the mechanical properties, combustion velocity, and to some extent thermal conductivity. Seaweed-derived aerogels possess intrinsic characteristics that could serve as a template for the future development of sustainable high-performance insulation materials.

Novel synthesis of natural cation exchange resin by crosslinking the sodium alginate as a natural polymer with 1,6-hexamethylene diisocyanate in inert solvents: Characteristics and applications

Novel synthesis of natural polymeric cation exchanger from sodium alginate reagent as natural polymer (CAlg-Na)_n has been developed. This procedure takes place by crosslinking the solid sodium alginate with 1,6-hexamethylene diisocyanate (HDI) in dryness benzene as inert solvent (DB). The experimental results for crosslinking the alginate using different degrees of crosslinking of HDI/DB (w/w) showed that the capacity of the synthesized resin for binding the polyvalent metal ions reached its maximum at 30% of (HDI/D) ratio. This work aims to present a novel synthesis of cation exchange resin from natural polymers as an alternative promising competitor of low-cost, high performance and non-toxicity for removal of the toxic heavy metal ions in wastewater remediation and radionuclide pollutants from environmental contaminated media. The results obtained from various applied techniques for determining the bounded metal ion concentrations with (CAlg-Na)_n indicated that the resin capacity was followed the order U(VI) > Cu(II) > Sr(II) > Ca(II) at 25 °C, respectively. The factors influenced the alginate affinity for chelating the metal ions were explained in some correlation terms between the alginate capacity and some physicochemical properties of chelated metal ions and its respective formed complexes. Speculated geometrical configurations for chelation were suggested and discussed.

Spray-drying encapsulation of microwave-assisted extracted polyphenols from Moringa oleifera: Influence of tragacanth, locust bean, and carboxymethyl-cellulose formulations

In this work, polyphenols from Moringa oleifera (Mor) leaves were extracted by microwave-assisted extraction (MAE) and encapsulated by spray-drying (SD). Particularly, we explored the influence of tragacanth gum (TG), locust bean gum (LBG), and carboxymethyl-cellulose (CMC) as wall-materials on the physicochemical behavior of encapsulated Mor. Single or combined wall-material treatments (100:00 and 50:50 ratios, and total solid content 1%) were tested. The results showed the wall-material had a significant effect on the process yield (55.7-68.3%), encapsulation efficiency (24.28-35.74%), color (yellow or pale-yellow), total phenolic content (25.17-27.49 mg GAE g^-1 of particles), total flavonoid content (23.20-26.87 mg QE g^-1 of particles), antioxidant activity (DPPH^• = 5.96-6.95 mg GAE g^-1; ABTS^•+ = 5.61-6.18 mg TE g^-1 of particles), and particle size distribution (D₅₀ = 112-1946 nm) of the encapsulated Mor. On the other hand, SEM analysis showed smooth and spherical particles, while TGA and DSC analyses confirmed the encapsulation of bioactive compounds based on the changes in thermal peaks. Finally, XRD analysis showed that the particles have an amorphous behavior. The encapsulated Mor produced with individual TG or CMC demonstrated better properties than those obtained from mixed gums. Thus, TG or CMC might be feasible wall materials for manufacturing encapsulated Mor that conserve the phenolic content and antioxidant activity.

A Stochastic Model for Adsorption Kinetics

A novel stochastic model is proposed to characterize the adsorption kinetics of pollutants including dyes (direct red 80 and direct blue 1), fluoride ions, and cadmium ions removed by calcium pectinate (Pec-Ca), aluminum xanthanate (Xant-Al), and reed leaves, respectively. The model is based on a transformation over time following the Ornstein–Uhlenbeck stochastic process, which explicitly includes the uncertainty involved in the adsorption process. The model includes stochastic versions of the pseudo-first-order (PFO), pseudo-second-order (PSO), and pseudo- $n$ -order (PNO) models. It also allows the estimation of the adsorption parameters, including the maximum removal capacity ( $q_e$ ), the adsorption rate constant ( $k_n$ ), the reaction pseudoorder ( $n$ ), and the variability $\left({\sigma }^2\right)$ . The model fitted produced $R^2$ values similar to those of the nonstochastic versions of the PFO, PSO, and PNO models; however, the obtained values for each parameter indicate that the stochastic model better reproduces the experimental data. The $q_e$ values of the Pec-Ca-dye, Xant-Al-fluoride, and reed leaf-Cd+2 systems ranged from 2.0 to 9.7, 0.41 to 1.9, and 0.04 and 0.29 mg/g, respectively, whereas the values of $k_n$ ranged from 0.051 to 0.286, 0.743 to 75.73, and 0.756 to 8.861 (mg/g)1-n/min, respectively. These results suggest a variability in the parameters $q_e$ and $k_n$ inherent to the natures of the adsorbate and adsorbent. The obtained $n$ values ranged from 1.13 to 2.02 for the Pec-Ca-dye system, 1.0–3.5 for the Xant-Al-fluoride system, and 1.8–3.8 for the reed leaf-Cd+2 system. These ranges indicate the flexibility of the stochastic model to obtain fractional $n$ values, resulting in high $R^2$ values. The variability in each system was evaluated based on ${\sigma }^2$ . The developed model is the first to describe pollutant removal kinetics based on a stochastic differential equation.

The influence of calcium on pectin's impact on TLR2 signalling

High intake of dietary fibres and calcium has been correlated to a lower frequency of Western disease such as allergy, asthma and obesity. How the combined higher intake of dietary fibres and calcium reduces the incidence of these diseases is unknown. Dietary fibre pectin can interact with Toll-like receptor (TLR) 2 and calcium in a degree of methyl-esterification (DM)-dependent manner. Low DM pectins interact stronger with TLR2 than high DM pectins. Since low DM pectin are known to bind calcium strongly, we investigated how calcium influences the DM-dependent impact of pectins on TLR2 signalling. We tested TLR2 activating, inhibiting and binding properties of pectins with DM18, DM52 and DM69 under 0 mM, 1 mM and 10 mM calcium conditions. None of the pectins activated TLR2, but pectins inhibited TLR2. Under 0 mM calcium conditions, especially DM18 and DM52 strongly inhibited TLR2 and bound strongly to TLR2. Addition of 1 and 10 mM calcium to these pectins reduced TLR2 inhibition and TLR2 binding. Our study shows that calcium reduces inhibition of TLR2 by low and intermediate DM pectins, but calcium has lower impact on TLR2 inhibition by high DM pectins. Calcium may therefore beneficially influence the impact of pectin on TLR2 signalling and contribute to an improved intestinal barrier function. A combined higher intake of pectin and calcium may therefore contribute to a lower incidence of Western diseases.

How alginate properties influence in situ internal gelation in crosslinked alginate microcapsules (CLAMs) formed by spray drying

Alginates gel rapidly under ambient conditions and have widely documented potential to form protective matrices for sensitive bioactive cargo. Most commonly, alginate gelation occurs via calcium mediated electrostatic crosslinks between the linear polyuronic acid polymers. A recent breakthrough to form crosslinked alginate microcapsules (CLAMs) by in situ gelation during spray drying ("CLAMs process") has demonstrated applications in protection and controlled delivery of bioactives in food, cosmetics, and agriculture. The extent of crosslinking of alginates in CLAMs impacts the effectiveness of its barrier properties. For example, higher crosslinking extents can improve oxidative stability and limit diffusion of the encapsulated cargo. Crosslinking in CLAMs can be controlled by varying the calcium to alginate ratio; however, the choice of alginates used in the process also influences the ultimate extent of crosslinking. To understand how to select alginates to target crosslinking in CLAMs, we examined the roles of alginate molecular properties. A surprise finding was the formation of alginic acid gelling in the CLAMs that is a consequence of simultaneous and rapid pH reduction and moisture removal that occurs during spray drying. Thus, spray dried CLAMs gelation is due to calcium crosslinking and alginic acid formation, and unlike external gelation methods, is insensitive to the molecular composition of the alginates. The 'extent of gelation' of spray dried CLAMs is influenced by the molecular weights of the alginates at saturating calcium concentrations. Alginate viscosity correlates with molecular weight; thus, viscosity is a convenient criterion for selecting commercial alginates to target gelation extent in CLAMs.

Identification and characterization of cellouronate (β-1,4-linked polyglucuronic acid) lyase from the scallop Mizuhopecten yessoensis

The semisynthetic polysaccharide cellouronate is a β-1,4-linked polyglucuronic acid prepared from regenerated cellulose by chemical oxidation. Here, we isolated a novel enzyme, MyAly, as a cellouronate lyase from a scallop Mizuhopecten yessoensis. Its optimum temperature, pH, and NaCl concentration for cellouronate degradation were determined to be 30 °C, 6.9, and 200-500 mM, respectively. MyAly endolytically degraded cellouronate into unsaturated di-, tri-, and tetrasaccharides with k_cat of 31.1 s^-1. MyAly also showed an alginate-degradation activity with a k_cat value of 0.58 s^-1. However, there was no significant difference in K_m values between cellouronate and alginate. MyAly consisted of 280 amino acids and shared 36.5-44.1 % identity with known marine gastropod alginate lyases belonging to the polysaccharide lyase family 14. This is the first study to identify and characterize a cellouronate-degrading lyase from a marine organism, providing a better understanding of the biodegradability of the industrially important polysaccharide, cellouronate, in marine environments.

Seaweed-Based Compounds and Products for Sustainable Protection against Plant Pathogens

Sustainable agricultural practices increasingly demand novel, environmentally friendly compounds which induce plant immunity against pathogens. Stimulating plant immunity using seaweed extracts is a highly viable strategy, as these formulations contain many bio-elicitors (phyco-elicitors) which can significantly boost natural plant immunity. Certain bioactive elicitors present in a multitude of extracts of seaweeds (both commercially available and bench-scale laboratory formulations) activate pathogen-associated molecular patterns (PAMPs) due to their structural similarity (i.e., analogous structure) with pathogen-derived molecules. This is achieved via the priming and/or elicitation of the defense responses of the induced systemic resistance (ISR) and systemic acquired resistance (SAR) pathways. Knowledge accumulated over the past few decades is reviewed here, aiming to explain why certain seaweed-derived bioactives have such tremendous potential to elicit plant defense responses with considerable economic significance, particularly with increasing biotic stress impacts due to climate change and the concomitant move to sustainable agriculture and away from synthetic chemistry and environmental damage. Various extracts of seaweeds display remarkably different modes of action(s) which can manipulate the plant defense responses when applied. This review focuses on both the similarities and differences amongst the modes of actions of several different seaweed extracts, as well as their individual components. Novel biotechnological approaches for the development of new commercial products for crop protection, in a sustainable manner, are also suggested.

Impact of Alginate Mannuronic-Guluronic Acid Contents and pH on Protein Binding Capacity and Complex Size

Alginates, serving as hydrocolloids in the food and pharma industries, form particles at pH < 4.5 with positively charged proteins, such as β-lactoglobulin (β-Lg). Alginates are linear anionic polysaccharides composed of 1,4-linked β-d-mannuronate (M) and α-l-guluronate (G) residues. The impact of M and G contents and pH is investigated to correlate with the formation and size of β-Lg alginate complexes under relevant ionic strength. It is concluded, using three alginates of M/G ratios 0.6, 1.1, and 1.8 and similar molecular mass, that β-Lg binding capacity is higher at pH 4.0 than at pH 2.65 and for high M content. By contrast, the largest particles are obtained at pH 2.65 and with high G content. At pH 4.0 and 2.65, the stoichiometry was 28-48 and 3-10 β-Lg molecules bound per alginate, respectively, increasing with higher M content. The findings will contribute to the design of formation of the desired alginate-protein particles in the acidic pH range.

The primary, secondary, and structures of higher levels of pectin polysaccharides

Pectin is a heteropolysaccharide abundant in the cell wall of plants and is obtained mainly from fruit (citrus and apple), thus its properties are particularly prone to changes occurring during ripening process. Properties of pectin depend on the string-like structure (conformation, stiffness) of the molecules that determines their mutual interaction and with the surrounding environment. Therefore, in this review the primary, secondary, and structures of higher levels of pectin chains are discussed in relation to external factors including crosslinking mechanisms. The review shows that the primary structure of pectin is relatively well known, however, we still know little about the conformation and properties of the more realistic systems of higher orders involving side chains, functional groups, and complexes of pectin domains. In particular, there is lack of knowledge on the influence of postharvest changes and extraction method on the primary and secondary structure of pectin that would affect conformation in a given environment and assembly to higher structural levels. Exploring the above-mentioned issues will allow to improve our understanding of pectin functionality and will help to tailor new functionalities for the food industry based on natural but often biologically variable source. The review also demonstrates that atomic force microscopy is a very convenient and adequate tool for the evaluation of pectin conformation since it allows for the relatively straightforward stretching of the pectin molecule in order to measure the force-extension curve which is directly related to its stiffness or flexibility.

Acidic Monosaccharides become Incorporated into Calcite Single Crystals*

Carbohydrates, along with proteins and peptides, are known to represent a major class of biomacromolecules involved in calcium carbonate biomineralization. However, in spite of multiple physical and biochemical characterizations, the explicit role of saccharide macromolecules (long chains of carbohydrate molecules) in mineral deposition is not yet understood. In this study, we investigated the influence of two common acidic monosaccharides (MSs), the two simplest forms of acidic carbohydrates, namely glucuronic and galacturonic acids, on the formation of calcite crystals in vitro. We show here that the size, morphology, and microstructure of calcite crystals are altered when they are grown in the presence of these MSs. More importantly, these MSs were found to become incorporated into the calcite crystalline lattice and induce anisotropic lattice distortions, a phenomenon widely studied for other biomolecules related to CaCO₃ biomineralization, but never before reported in the case of single MSs. Changes in the calcite lattice induced by MSs incorporation were precisely determined by high-resolution synchrotron powder X-ray diffraction. We believe that the results of this research may deepen our understanding of the interaction of saccharide polymers with an inorganic host and shed light on the implications of carbohydrates for biomineralization processes.

Dissipative particle dynamics model of homogalacturonan based on molecular dynamics simulations

In this study we present an alternative dissipative particle dynamics (DPD) parametrization strategy based on data extracted from the united-atom molecular simulations. The model of the homogalacturonan was designed to test the ability of the formation of large-scale structures via hydrogen bonding in water. The extraction of coarse-grained parameters from atomistic molecular dynamics was achieved by means of the proposed molecule aggregation algorithm based on an iterative nearest neighbour search. A novel approach to a time-scale calibration scheme based on matching the average velocities of coarse-grained particles enabled the DPD forcefield to reproduce essential structural features of homogalacturonan molecular chains. The successful application of the proposed parametrization method allowed for the reproduction of the shapes of radial distribution functions, particle velocities and diffusivity of the atomistic molecular dynamics model using DPD force field. The structure of polygalacturonic acid molecules was mapped into the DPD force field by means of the distance and angular bond characteristics, which closely matched the MD results. The resulting DPD trajectories showed that randomly dispersed homogalacturonan chains had a tendency to aggregate into highly organized 3D structures. The final structure resembled a three-dimensional network created by tightly associated homogalacturonan chains organized into thick fibres.

Physicochemical and swelling properties of composite gel microparticles based on alginate and callus cultures pectins with low and high degrees of methylesterification

Composite gel microparticles based on alginate and callus culture pectins with low and high degrees of methylesterification or apple pectin were produced. By varying the chemical composition of the pectic samples and the ratio of alginate to pectin, the gel strength, morphology, and swelling properties of composite microparticles can be altered. The inclusion of increasing concentrations of alginate in gel formulations promoted an increase in the microparticle gel strength and the formation of a smoother surface microrelief independently of the pectin chemical composition. Microparticles based on the pectin with a low degree of methylesterification (DM) and a higher concentration of alginate exhibited an increased swelling degree in the simulated digestive fluids. Microparticles based on the pectin with high DM and low alginate concentration were destroyed in the simulated intestinal fluid within 1 h due to the low Ca²⁺ content, gel strength, and grooved and rough surface of these microparticles. An increase in alginate concentration of gel formulations based on pectin with high DM led to increased stability of the microparticles in the simulated intestinal and colonic fluids due to increased Ca²⁺ content, microparticle gel strength and degree of crosslinking.

Acetic acid reducing the softening of lotus rhizome during heating by regulating the chelate-soluble polysaccharides

Lotus rhizomes were used to study on the relationship between the cell wall polysaccharides and cooked texture by adding acetic acid. Hardness and scanning electron microscopy results showed that acetic acid treatment can maintain higher hardness and the integrity of the cell wall. Then, the cell walls were sequentially extracted and divided into water-soluble fraction, chelate-soluble fraction (CSF), sodium carbonate-soluble fraction and hemicellulose fraction. The pectin fraction contents, monosaccharides composition, esterification degree and sugar ratios in different groups were evaluated, the results showed that acetic acid increased the total amount of CSF, decreased the esterification degree and less side chain compared that in the solely thermal treatment group. The nanostructures showed that acetic acid treatment maintained longer chain and destroy helical structure of CSF backbone. This work helps us to demonstrate the relationship between polysaccharides structure and cooked texture, and further control the plant-based vegetables processing texture in food industry.