Global Structures of High Methoxyl Pectin from Solution and in Gels

Impact of adjustable swelling dynamics on the structural integrity of sunflower pollen microgels

Pollen is a renewable biomaterial found in seed-bearing plants, and the biocompatibility of pollen microgels is a key factor driving their use in drug delivery, biosensor development, and wound care applications. Herein, the microgel was synthesized from sunflower bee pollen by using a cost-effective process, and to examine its structural integrity under adverse acidic and alkaline conditions, digital microscopy and dynamic image particle analysis were carried out. Swelling dynamics of pollen microgels were regulated by varying pH conditions, and adding aqueous KOH to the solution, and the influence of swelling-deswelling on bulk rheology and local elastic properties were experimentally investigated and theoretically interpreted by using the Ross-Minton equation for the suspension viscosity. The present findings reveal how pollen microgels can be adapted to acidic to alkaline environments in order to modify mechanical and rheological properties.

Influence of pectin domains and protein on the viscosity and gelation properties of alkali-extracted pectin from green tea residue

Alkaline pectin extract (APE) from green tea residues has lower viscosity and gelation properties than commercial citrus pectin. To improve the viscosity and gelation properties of APE, four treatments, namely degradation of homogalacturonan (HG) or rhamnogalacturonan (RG) I domains, esterification, and protein removal and degradation, were applied. With proper degradation of the HG or RG I domains (arabinan or galactan), the viscosity of APE increased from 12 to 2.5×104 or 5.0×103 mPa·s, respectively, and the numbers further increased by approximately 500 times with the addition of Ca2+. Other treatments had slight effects on APE viscosity. The strongest gel (G' = 6.7 × 103 Pa and G″ = 930 Pa) was made using the polygalacturonase treated APE with Ca2+ addition. Degradation of the HG domain or protein enhanced APE's self-crosslink effect, while all methods except protein degradation improved the calcium bridging effect, potentially improving the market potential of pectin from biowaste.

Mechanism for gel formation of pectin from mealy and crisp lotus rhizome induced by Na+ and D-glucono-d-lactone

Lotus rhizome residue, a cell wall material produced during the production of lotus rhizome starch, has long been underutilized. This study aims to extract pectin-rich polysaccharides from the cell wall of lotus rhizome and investigate their gelation mechanism in order to improve their industrial applicability. The results indicated that both CP and MP (pectin extracted from crisp and mealy lotus rhizome) exhibited a highly linear low methoxyl pectin structure, with the primary linkage mode being →4)-GalpA-(1→. The pectin chains in MP were found to be more flexible than those in CP. Then the impact of Na+, D-glucono-d-lactone (GDL), urea, sodium dodecyl sulfate (SDS), either individually or in combination, on the rheological characteristics of gels was evaluated. The results indicated that gels induced by GDL exhibited favorable thermoreversible properties, whereas the thermoreversibility of Na+-induced gels is poor. In addition to hydrogen bonding and ionic interactions, hydrophobic interactions also play a significant role in the formation of pectin gels. This study offers theoretical guidance and methodologies to improve the utilization rate of lotus rhizome starch processing by-products, while also provides novel insights into the correlation between LMP structure and gelation mechanism.

Pectin gels based on H+/(NH4)2SO4 and its potential in sustained release of NH4. Int J Biol Macromol 2022;208:486-493. [PMID: 35304200 DOI: 10.1016/j.ijbiomac.2022.03.062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A gelling strategy for HP was proposed in this study, ammonium sulfate (AS) as a co-solute could induce the gelling of HP in acidic environment. The solubility and Zeta potential of HP dramatically decreased in AS solution, which indicated AS could promote the aggregation of HP. The rheological results confirmed the gelling of HP (G' > G″) with AS: 25-30 wt% and pH ≤ 3.0, and the gel strength is mainly depended on HP rather than AS concentration. Smaller AS crystals (SEM) and reduced T₂ values (LF-NMR) were observed in HP gels, suggested the gel network of HP could limit the migration of AS and water. Finally, it was found that the release process of NH₄⁺ in HP + AS gel was lagged behind that of pure AS, which verified the potential of HP + AS gel in the field of sustained-release fertilizers.

Tuning bio-aerogel properties for controlling theophylline delivery. Part 1: Pectin aerogels

A comprehensive study of release kinetics of a hydrophilic drug from bio-aerogels based on pectin was performed. Pectin aerogels were made by polymer dissolution, gelation (in some cases this step was omitted), solvent exchange and drying with supercritical CO₂. Theophylline was loaded and its release was studied in the simulated gastric fluid during 1 h followed by the release in the simulated intestinal fluid. Pectin concentration, initial solution pH and concentration of calcium were varied to tune the properties of aerogel. The kinetics of theophylline release was monitored and correlated with aerogel density, specific surface area, and aerogel swelling and erosion. Various kinetic models were tested to identify the main physical mechanisms governing the release.

Aggregation and weak gel formation by pectic polysaccharide homogalacturonan

This study presents a novel model of homogalacturonan (HG) based on the dissipative particle dynamics (DPD). The model was applied to investigate the mechanism of self-aggregation of low-methoxylated homogalacturonan in aqueous solutions in the absence of cations. The coarse-grained model provided new insights into the structural features of HG aggregates and networks in aqueous solutions. Depending on the properties and concentration of polysaccharides, two major patterns of self-assembly were observed for HG - ellipsoidal aggregates and a continuous three-dimensional network. Simulations showed that a decrease in the degree of dissociation of HG results in a higher rate of self-aggregation, as well as facilitating the formation of larger assemblies or thicker nanofilaments depending on the type of final self-assembly. Simulations of polysaccharides of different chain lengths suggested the existence of a structural threshold for the formation of a spatial network for HG consisting of less than 35 GalA units.

Interfacial properties of ultrahigh methoxylated pectin

The interfacial properties of ultrahigh methoxylated pectin (UHMP) prepared via esterification of citrus pectin (CP) were investigated. The intrinsic viscosity ([η]) of pectin was significantly decreased from 1211.5 mL/g to 294.9 mL/g as the degree of methylation (DM) increased from 63.18 ± 0.08% to 91.52 ± 0.11%. Surface tension (γ) analysis indicated that UHMP had a critical micelle concentration (CMC) of 0.8 g/L, which was slightly smaller than that of sugar beet pectin (SBP) (1.0 g/L). The morphology of the UHMP aggregation presented a network structure and irregular clusters at 10 μg/mL and 1 μg/mL based on atomic force microscopy (AFM). Transmission electron microscopy (TEM) observations further confirmed the self-aggregation behaviours and rod-like micelles of UHMP. The surface excess (Γ) was 1.69 ± 0.17 μmol/m² for UHMP, which was lower than the values of SBP (1.88 ± 0.21 μmol/m²) and CP (2.91 ± 0.57 μmol/m²). Correspondingly, UHMP possessed the highest molecular area (A) of 0.99 ± 0.10 nm². Thus, UHMP was proposed to be more flexible and extendable at the interface. The interfacial shear rheology study suggested that UHMP was able to form an elastic-dominant interfacial film to stabilize the oil/water interface.

Structural characterization and rheological properties of a pectin with anti-constipation activity from the roots of Arctium lappa L

A new pectin (ALP-2) was extracted from the roots of Arctium lappa L. with the molecular weight of 1.84 × 10⁶ Da. ALP-2 was composed of rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, xylose and arabinose. Results of NMR revealed that the dominant linkage types of ALP-2 were →4-α-GalpA-6-OMe-(1→, →2-α-Rha-(1→, →5-α-Araf-(1→ and →3,6-β-Galp-(1→. The ELISA results indicated ALP-2 was a typical pectin with HG chain and RG-I chain. The rheological experiments showed that ALP-2 fluid exhibited shear thinning behavior. The viscosity of ALP-2 was mainly affected by concentration, temperature, and pH. The ALP-2 fluid with elastic properties at high frequencies could be used as a thickener in the food industry. Moreover, ALP-2 with the dosages of 200 mg/kg and 400 mg/kg exhibited strong anti-constipation activity in vivo. ALP-2 treated groups could improve small intestinal movement rate and increase the weight of feces significantly in constipation mice. Therefore, ALP-2 could be considered as the active component for functional food or therapeutic agent in constipation therapy.

Fruit softening and pectin disassembly: an overview of nanostructural pectin modifications assessed by atomic force microscopy

BACKGROUND

One of the main factors that reduce fruit quality and lead to economically important losses is oversoftening. Textural changes during fruit ripening are mainly due to the dissolution of the middle lamella, the reduction of cell-to-cell adhesion and the weakening of parenchyma cell walls as a result of the action of cell wall modifying enzymes. Pectins, major components of fruit cell walls, are extensively modified during ripening. These changes include solubilization, depolymerization and the loss of neutral side chains. Recent evidence in strawberry and apple, fruits with a soft or crisp texture at ripening, suggests that pectin disassembly is a key factor in textural changes. In both these fruits, softening was reduced as result of antisense downregulation of polygalacturonase genes. Changes in pectic polymer size, composition and structure have traditionally been studied by conventional techniques, most of them relying on bulk analysis of a population of polysaccharides, and studies focusing on modifications at the nanostructural level are scarce. Atomic force microscopy (AFM) allows the study of individual polymers at high magnification and with minimal sample preparation; however, AFM has rarely been employed to analyse pectin disassembly during fruit ripening.

SCOPE

In this review, the main features of the pectin disassembly process during fruit ripening are first discussed, and then the nanostructural characterization of fruit pectins by AFM and its relationship with texture and postharvest fruit shelf life is reviewed. In general, fruit pectins are visualized under AFM as linear chains, a few of which show long branches, and aggregates. Number- and weight-average values obtained from these images are in good agreement with chromatographic analyses. Most AFM studies indicate reductions in the length of individual pectin chains and the frequency of aggregates as the fruits ripen. Pectins extracted with sodium carbonate, supposedly located within the primary cell wall, are the most affected.

Rheological characterization of acid pectin samples in the absence and presence of monovalent ions

Pectins are traditionally divided into two groups, high methoxy and low methoxy. The groupings determine the charge of the pectin and the gelation mechanism. However, not as yet extensively studied is the impact on gelation of the distribution of the charges as characterized by an absolute degree of blockiness (DBabs). The aim of this study was to characterize rheologically the acid gelation of a pectin with a high DBabs and a degree of methyl esterification of ∼ 37%, in the absence and presence of monovalent ions. The results obtained suggest that a pectin with a blocky charge distribution at pH conditions close to or below the pKa exhibits weak gel-like properties at intermediate frequencies, despite the absence of a permanent network structure. The addition of monovalent ions changed the rheological behavior to resemble that of a strong gel whose properties depended on the type and concentration of the ions.

Viscometric study of pectin. Effect of temperature on the hydrodynamic properties

Hydrodynamic properties are important parameters affecting the performance of pectin. This polysaccharide is used as a thickening and gelling agent in food and pharmaceutical industries. The most common and economical of the hydrodynamic properties is the determination of viscosity, in which are determined the intrinsic viscosity and the diffusion coefficient. They indirectly measure the molecular weight (M(w)); hydrodynamic radius (R(H)); number of Simha, (ν(a/b)); Perrin parameter (P); Scheraga-Mandelkern parameter (β); and Flory parameters (ϕ(0) and P(0)). All the hydrodynamic parameters are dependent on temperature. Normally these parameters are reported at a temperature of 25°C, which limits their application to different temperatures. This work studies pectin dependence on temperature, finding that this biopolymer in aqueous solution presents a conformation of rod-like with ν(a/b)=10.5, and a value from 0.8232 to 0.8129. Pectin behavior in this system indicates that it behaves like a colloidal particle that tends to compact with increasing temperature (R(H) decrease). The molecular weight calculated for pectin is 180,000 g/mol. Mark-Houwink-Sakurada (M-H-S) equation constants, a and k, for pectin in water solvent-temperature systems have been already reported.

Identification of extensin protein associated with sugar beet pectin

Several studies have suggested that the emulsification properties associated with pectin obtained from sugar beet (Beta vulgaris) are due to the presence of a protein-pectin complex. Nevertheless, the identity of the protein has remained elusive. Pectin, extracted from sugar beet pulp by microwave-assisted extraction, and a commercial sample were both subjected to protease digestion with trypsin. The resulting peptides were separated from the pectin solution by ultrafiltration using a 3 kDa molecular weight cutoff (MWCO) membrane and analyzed using matrix-assisted laser desorption ionization with tandem time-of-flight mass spectrometry. The partial sequences derived from the mass spectrometry analyses of the resulting tryptic peptides are found to be highly consistent with extensin protein matched from the B. vulgaris Genetic Index database and also correspond to previously reported extensin peptides found in sugar beet cell suspension cultures. Further attempts were made to disassociate the protein from pectin using 1 M NaCl and a 100 kDa MWCO membrane; however, no peptides were observed following trypsin digestion of the permeate solution. This evidence suggests the existence of a complex between the pectin and extensin that is not due to ionic interactions. Trypsin digestion of commercial sugar beet pectin also produced the peptide profile observed with the microwave-assisted extracted pectin sample. Atomic force microscopy established that the number of rod-like elements decreased following protease treatment compared to the untreated sample.

AFM imaging of RGD presenting synthetic extracellular matrix using gold nanoparticles

Several high-resolution imaging techniques such as FESEM, TEM and AFM are compared with respect to their application on alginate hydrogels, a widely used polysaccharide biomaterial. A new AFM method applicable to RGD peptides covalently conjugated to alginate hydrogels is described. High-resolution images of RGD adhesion ligand distribution were obtained by labeling biotinylated RGD peptides with streptavidin-labeled gold nanoparticles. This method may broadly provide a useful tool for sECM characterization and design for tissue regeneration strategies.

Global structure of microwave-assisted flash-extracted sugar beet pectin

The global structure of microwave-assisted flash-extracted pectins isolated from fresh sugar beet pulp has been studied. The objective was to minimize the disassembly and possibly the degradation of pectin molecules during extraction. These pectins have been characterized by high-performance size exclusion chromatography with light scattering, viscometric detection, and atomic force microscopy (AFM). Analysis of molecular parameters was performed on 15 and 8 microm size column packings. Samples analyzed with 15 microm packing gave weight-average molar masses that ranged from 532,000 to 1.2 million Da, radii of gyration from about 35 to 51 nm, polydispersities from 1.78 to 2.58, intrinsic viscosities from about 3.00 to 4.30 dL/g, and recoveries from 8.40 to 14.81% of dry weight. Chromatography revealed that a bimodal distribution of high molar mass spherical particles and lower molar mass coils was obtained. AFM images of pectin corroborated this conclusion and further revealed that these strands and spherical particles were integrated into networks. It is demonstrated that microwave-assisted extraction of sugar beet pulp under moderate pressure and at relatively low temperature could extract under acid conditions high molar mass, moderate-viscosity pectin in minutes rather than hours as required by conventional heating.