Structural characterisation of thermoreversible anionic polysaccharide gels by their elastoviscous properties

Previously reported results obtained for the elastoviscous properties of some thermoreversible gels formed from anionic polysaccharides (high methoxyl pectin, furcellaran and κ-carrageenan) and also gelatin and maltodextrin are discussed and some conclusions about the structure of the gels are presented.The rate at which the relaxation processes take place in the gel is independent of the polymer concentration suggesting that the gels are structurally inhomogeneous.If the helical conformation of the individual macromolecule is stable the standard enthalpy change on crosslink breakdown is less than 45 kJ mol^?1. A relatively small decrease in standard enthalpy is sufficient for network stability because of the low standard entropy loss on gelation which is typical of semi-rigid chain polymers. If, however, the helical conformation is unstable the gelation process is cooperative and the standard enthalpy change on crosslink breakdown exceeds 200 kJ mol^?1.     

A study of some factors influencing amylose gelation

Amylose fractions were prepared by aqueous leaching from pea, maize and patato starch granules. The fractions were characterised by iodine binding, β-amylolysis and viscometry. Amylose starts to form a gel rather than a precipitate on cooling aqueous solutions to room temperature at concentrations above the coil overlap concentration C¹. Amylose gels are almost purely elastic, with negligible viscous flow at room temperature. The rigidity modulus is strongly dependent on concentration, c, in that above 1·5% w/w the modulus increases as a function of c⁷. The modulus of a matured gel falls only slightly with increasing temperature; at temperatures below 100°C the gel could not be melted. The non-equilibrium nature of the system is shown by the dependence of rigidity on thermal history. The shear modulus is also dependent on amylose type; higher molecular weight amylose fractions produced less rigid gels at a given concentration.     

Rheological characterization of neutral and anionic polysaccharides with reduced mucociliary transport rates

The purpose of this research was to compare the viscoelastic properties of several neutral and anionic polysaccharide polymers with their mucociliary transport rates (MTR) across explants of ciliated bovine tracheal tissue to identify rheologic parameters capable of predicting the extent of reduction in mucociliary transport. The viscoelastic properties of the polymer gels and gels mixed with mucus were quantified using controlled stress rheometry. In general, the anionic polysaccharides were more efficient at decreasing the mucociliary transport rate than were the neutral polymers, and a concentration threshold, where no further decreases in mucociliary transport occurred with increasing polymer concentration, was observed for several of the neutral polysaccharides. No single rheologic parameter (ν, G′, G″, tan δ, G^*) was a good predictor of the extent of mucociliary transport reduction, but a combination of the apparent viscosity (ν), tangent to the phase angle (tan δ), and complex modulus (G^*) was found to be useful in the identification of formulations capable of decreasing MTR. The relative values of each of the rheologic parameters were unique for each polymer, yet once the relationships between the rheologic parameters and mucociliary transport rate reduction were determined, formulations capable of resisting mucociliary clearance could be rapidly optimized. Published: April 20, 2007     

Water dynamics in charged and uncharged polysaccharide gels by quasi-elastic neutron scattering

Using a microeV neutron spectrometer we have studied the mobility of water in gels formed by two polysaccharides: agarose and hyaluronic acid. Agarose is a nearly uncharged polysaccharide; its gels are fairly stiff, quasi-random networks of fibre bundles. Hyaluronic acid is a highly charged polysaccharide capable of retaining large amounts of water in entangled meshworks with unusual rheological properties. We have analysed sets of quasi-elastic lineshapes broadened by two proton populations with different degrees of freedom. The resulting microscopic mobility parameters and their temperature dependence reveal a complex behaviour. The overall effect of the biopolymer network is to increase translational as well as rotational relaxation times, but the changes observed are not dramatic and cannot fully account for the strikingly different macroscopic properties of these gels. Local electrostatic interactions (over 3 to 20 A) do not appear to influence significantly the rheological behaviour.     

XM-6: A new gel-forming bacterial polysaccharide

A new extracellular microbial polysaccharide, XM-6, has been isolated from cultures of an Enterobacter species and shows unusual gelation properties of potential technological significance. The polysaccharide contains d-glucose, l-fucose and d-glucuronate in the approximate molar ratio 3:1:1. No significant amounts of acetate or pyruvate were detected. d-Glucuronate and some d-glucose are destroyed on periodate oxidation, but l-fucose and some d-glucose may be recovered intact, indicating the presence of some 1,3 linkages in the primary structure. The major oligosaccharide isolated from autohydrolysates was an aldobiuronic acid containing equal amounts of d-glucose and l-fucose.Thermally-reversible gels are formed on addition of salt to solutions of the polysaccharide. A preliminary investigation of the mechanism of gelation by optical rotation, circular dichroism, high resolution n.m.r. and mechanical spectroscopy suggests interchain association through conformationally ordered ‘junction zones’, with specific incorporation of site-bound cations within the ordered structures. In the sol state the polysaccharide shows the shear-rate and temperature dependence of viscosity typical of a disordered (‘random coil’) polymer solution. Divalent cations are, in general, more effective than monovalent cations in promoting gelation of XM-6, while trivalent cations normally cause precipitation. Within Groups I and II, optimum gelation is achieved with Na⁺ and Ca²⁺ (ionic radius ? 0·1 nm), with larger and smaller ions becoming progressively less effective. Both gel strength and melting temperature increase with increasing salt concentration.XM-6 forms gels of reasonable strength at unusually low concentrations of the polysaccharide. For example, gels comparable to those required for normal industrial or food applications may be obtained using 0·3% w/v XM-6 and 1% w/v NaCl. Gel strength increases with increasing polymer concentration but there is no systematic variation in melting point. The sol-gel transition of XM-6 is unusually sharp and, by suitable adjustment of salt concentration, can be made to occur just below body temperature (e.g. 30–35°C), with obvious implications for biomedical or food applications.     

Optimization of ultrasonic circulating extraction of polysaccharides from Asparagus officinalis using response surface methodology

Polysaccharides were extracted from Asparagus officinalis. A novel ultrasonic circulating extraction (UCE) technology was applied for the polysaccharide extraction. Three-factor-three-level Box-Behnken design was employed to optimize ultrasonic power, extraction time and the liquid-solid ratio to obtain a high polysaccharide yield. The optimal extraction conditions were as follows: ultrasonic power was 600 W, extraction time was 46 min, the liquid-solid ratio was 35 mL/g. Under these conditions, the experimental yield of polysaccharides was 3.134%, which was agreed closely to the predicted value. The average molecular weight of A. officinalis polysaccharide was about 6.18 × 10⁴ Da. The polysaccharides were composed of glucose, fucose, arabinose, galactose and rhamnose in a ratio of 2.18:1.86:1.50:0.98:1.53. Compared with hot water extraction (HWE), UCE showed time-saving, higher yield and no influence on the structure of asparagus polysaccharides. The results indicated that ultrasonic circulating extraction technology could be an effective and advisable technique for the large scale production of plant polysaccharides.     

Red blood cell rouleaux formation in dextran solution: dependence on polymer conformation

The velocity of rouleaux formation (RF), as previously shown, increases with increasing dextran concentration up to a critical concentration (C_a), beyond which the addition of dextran reduces the RF velocity (RFV). de Gennes' model for polymer solutions suggests that dextrans exist in two conformations: a coil structure at low concentrations, which changes to a network beyond a critical concentration (C^*). In the present study we examined the relation between C_a and C^* for dextrans of different molecular weight, and found that they coincide. This suggests that the change in dextran behavior, from increasing to decreasing RFV, occurs when their conformation changes from coil to network. In addition, it has been reported that in dilute dextran solutions the intercellular distance (D) between RBC in rouleaux increases with the molecular weight of the dextran. We found that D correlates with R_f, the end-to-end distance of the polymer molecule, and for all dextrans D ≤ 1.5 R_f. In accord with de Gennes' Model for polymers between surfaces, this corresponds to intercellular interaction with two overlapping surface-associated polymer layers, which may extend “tails” to interact with the opposing cells. Received: 8 August 1997 / Accepted: 28 November 1997     

Physical characteristics of calcium induced κ- carrageenan networks

The presence of an optimum counter-ion concentration in calcium-induced κ-carrageenan gels at low polymer concentrations of 5 and 10 g/l is observed. At approximately the stoicheometric molar ratio of 1 calcium per carrageenan sulphate, a gel with high elastic modulus, high optical clarity and fine network structure is observed. On further increase of counter-ion concentration beyond this optimum, elastic modulus decreases significantly associated with sharp increase in the gels turbidity together with a network characterised with coarse and large-pore mesh.

The quite complete characterisation of the various gel networks both mechanically by ways of oscillatory and static rheology and optically by turbidimetry and cryo-SEM shows that the extensive structural charge neutralisation of the polysaccharide by divalent calcium ions is responsible for a marked aggregation of the polymer strands reminiscent of precipitation. At lower counter-ion to polymer ratios, onset of gelation might prevent such phase separation.     

陕甘花楸果实多糖的结构表征及抗氧化活性研究

陕甘花楸(Sorbus koehneana)是我国西北地区特有的灌木之一,主要被用于观赏和制作家具,但对其有效成分的研究却鲜见报道,从而限制了陕甘花楸产业的进一步开发和利用。该研究以陕甘花楸果实为原料,经石油醚脱脂后,采用超声辅助水提醇沉法提取、Sevag法脱蛋白,得到了较纯的花楸果实多糖(SSP),并对其进行结构表征和抗氧化活性研究。结果表明:(1)经苯酚-硫酸法测得多糖纯度为65.8%;FT-IR检测官能团,发现在3 420 cm~(-1)、2 929 cm~(-1)和1 733 cm~(-1)处存在多糖的典型吸收峰;用SEC-LLS测得重均分子量(Mw)为1.739×105,数均分子量(Mn)为5.052×104,多分散系数为3.443,表明分子量分布较为均一;经三氟乙酸酸解、糖腈衍生化等处理及气相-质谱联用法测定SSP的单糖组成,表明SSP由甘露糖、葡萄糖和未知单糖等3种单糖组成,摩尔比为2.2∶1.4∶6.4。(2)体外抗氧化活性实验表明:SSP具有很好的DPPH清除活性、超氧阴离子清除活性以及较强的还原力;当SSP浓度为2 mg·mL-1时,SSP对DPPH自由基的清除能力相当于BHT的96%,对超氧阴离子自由基清除能力为Vc的76.07%,还原能力等价于Vc的92%。以上表明该多糖可以用于抗衰老和抗炎等方面,是一种优良的天然抗氧化剂,为花楸资源的进一步开发利用提供了更为广阔的前景。     

Partial Chemical and Physical Characterization of Two Extracellular Polysaccharides Produced by Marine, Periphytic Pseudomonas sp. Strain NCMB 2021

The marine bacterium Pseudomonas sp. strain NCMB 2021, which can attach to solid, and especially hydrophobic, surfaces, elaborates two different extracellular polysaccharides in batch cultures. One (polysaccharide A) was produced only during exponential growth and contained glucose, galactose, glucuronic acid, and galacturonic acid in a molar ratio of 1.00:0.81:0.42:0.32. It produced viscous solutions, formed gels at high concentrations, and precipitated with several multivalent cations. The other (polysaccharide B) was released at the end of the exponential phase and in the stationary phase. It contained equimolar amounts of N-acetylglucosamine, 2-keto-3-deoxyoctulosonic acid, an unidentified 6-deoxyhexose, and also O-acetyl groups. Despite its high molecular weight (10⁵ to 10⁶ as judged by gel filtration), the polysaccharide produced aqueous solutions with very low viscosities and was also soluble in 90% aqueous phenol, 80% methanol, and 80% ethanol.     

Orientation of DNA Molecules in Agarose Gels By Pulsed Electric Fields

Abstract

The electric birefringence of DNA restriction fragments of three different sizes, 622,1426, and 2936 base pairs, imbedded in agarose gels of different concentrations, was measured. The birefringence relaxation times observed in the gels are equal to the values observed in free solution, if the median pore diameter of the gel is larger than the effective hydrodynamic length of the DNA molecule in solution. However, if the median pore diameter is smaller than the apparent hydrodynamic length, the birefringence relaxation times increase markedly, becoming equal to the values expected for the birefringence relaxation of fully stretched DNA molecules. This apparent elongation indicates that end-on migration, or reptation is a likely mechanism for the electrophoresis of large DNA molecules in agarose gels. The relaxation times of the stretched DNA molecules scale with molecular weight (or contour length) as N^2.8, in reasonable agreement with reptation theories.     

Optimization of sulfated modification conditions of tremella polysaccharide and effects of modifiers on cellular infectivity of NDV

Based on our previous research, sulfated modification conditions of Tremella polysaccharide (TPS), the chlorosulfonic acid to pyridine (CSA-Pry) ratio, reaction temperature and time, were optimized by L₉ (3⁴) orthogonal design taking the yield and degree of sulfation (DS) of modifiers as indexes. Two TPSs, TPS_tp and TPS_70c, were modified under optimized conditions. The effects of two modifiers, sTPS_tp and sTPS_70c, on cellular infectivity of NDV were determined by MTT method taking the non-modified TPS_tp, TPS_tc and TPS_70c as controls. The results showed that the optimized modification conditions were reaction temperature of 80 °C, CSA-Pry ratio of 1:6 and reaction time of 1.5 h. Five polysaccharides at proper concentrations could significantly inhibit the infectivity of NDV to CEF. The virus inhibitory rates of sTPS_tp at 1.563 μg mL⁻¹ group were the highest and significantly higher than those of other three non-modified polysaccharide groups in three sample-adding modes. This indicated that sulfated modification could significantly improve the antiviral activity of TPS. sTPS_tp possessed the best efficacy and would be as a component of antiviral polysaccharide drug.     

Comparative flexibility,extension, and conformation of some simple polysaccharide chains

Realistic polymer chain models are developed for several polysaccharides to illustrate, using perspective drawings of representative chain conformations, the wide range of configuration, extension, and flexibility found in chains of the polysaccharide class. A method for incorporating the gauche or exo-anomeric effect into polysaccharide conformational energy functions is described, and a novel measure of directional correlation and pseudohelical persistence is utilized to help distinguish the differences in chain configuration observed among the polysaccharides compared.     

Structural characterization and solution properties of a galacturonate polysaccharide derived from Aloe vera capable of in situ gelation

A series of highly purified galacturonate polysaccharides have been extracted from the Aloe vera plant and analyzed in terms of chemical composition and molecular weight. This Aloe vera polysaccharide (AvP) has been found to exist as a high molecular weight species and possess a unique chemical composition, including a high galacturonic acid (GalA) content and low degree of methyl ester substitution. These factors facilitate gel formation upon exposure to low concentrations of calcium ions, leading to potential application in formulations designed for in situ nasal or subcutaneous protein delivery. Thorough examination of classic dilute solution properties, the [eta]-M(w), and R(g)-M(w) relationships, persistence length (L(p)), and inherent chain stiffness (B parameter), indicate an expanded random coil in aqueous salt solutions. The critical concentration for transition from dilute to concentrated solution, C(e), was determined by measuring both the zero shear viscosity (eta(o)) and fluorescence emission of the probe molecule 1,8-anilino-1-naphthalene sulfonic acid (1,8-ANS) as a function of polymer concentration. Examination of zeta potential and C(e) as a function of ionic strength indicates that the shift in C(e) from 0.60 to 0.30 wt % is related to an increased occurrence of intermolecular interactions at high salt concentrations. Additionally, dynamic rheology data are presented highlighting the ability of AvP to form gels at low polymer and calcium ion concentrations, exemplifying the technological potential of this polysaccharide for in situ drug delivery.     

Quasielastic light-scattering study of polyadenylic acid solutions. II

Quasielastic light scattering is used to study saline solutions of polyadenylic acid with varying polymer concentrations and molecular masses. These experiments clearly show the existence of two relaxation times. For dilute solutions, when the chains are mutually independent, the fast mode is due to the free diffusion of the polymer chains. For concentrations above the overlap concentration C*, the fast mode is due to the propagation of collective excitations of the pseudolattice of polymer chains. The slow modes are observed when the polymer concentration is in the vicinity of the overlap concentration C*. A series of experiments shows that both their relaxation time and amplitude depend only on the polymer concentration and not on the polymer molecular mass. This result rules out any previous explanation based on individual chain motion. Furthermore, since the amplitudes depend on the time elapsed from the preparation of the solution, the slow modes are due to the diffusion of concentration inhomogeneities in the pseudolattice.     

Impact of incorporations of various polysaccharides on rheological and microstructural characteristics of heat-induced quinoa protein isolate gels

This study aimed to investigate the properties of heat-induced gels (85 °C for 30 min) of quinoa protein isolate (QPI) in the presence and absence of various polysaccharides including guar gum (GG), locust bean gum (LBG), and xanthan gum (XG) at pH 7. For this purpose, samples with three gum concentrations (0.05, 0.1, and 0.2 wt%) at a fixed QPI concentration (10 wt%) and a fixed ionic strength (50 mM NaCl) were studied in terms of their gelation behaviour, small and large deformation rheological properties, water holding capabilities, and microstructural characteristics. Rheological measurements revealed that all polysaccharides incorporation could improve gel strength (complex modulus, G*) and breaking stress, accelerate gel formations, and more stiffer gels were obtained at greater polysaccharide concentrations. The XG exhibited the most gel strengthening effect followed by LBG and GG. Incorporation of 0.2 wt% XG led to a 15 folds increase in G* compared to the control. Confocal laser scanning microscopy observation revealed that the polysaccharides also altered gel microstructures, with the gels containing XG showing the most compact gel structures. The findings of this study may provide useful information for the fabrication of novel QPI based food gel products with improved texture.

     

Investigation of the state and dynamics of water in hydrogels of cellulose ethers by 1H NMR spectroscopy

The aim of this work was to study the effect of the type of substituent of the cellulose ethers and the molecular mass on the state and dynamics of water in the respective hydrogels to specify the quantity of adsorbed water on the polymers or, more explicitly, to calculate the average number of water molecules bound to a polymer repeating unit (PRU).¹H NMR relaxation experiments were performed on equilibrated systems of cellulose ether polymers (HEC, HPC, HPMC K4M, and HPMC K100M) with water. In particular, the water proton spinlattice (T ₁) and spin-spin (T ₂) relaxation times were measured in these systems at room temperature. The observed proton NMRT ₁ andT ₂ of water in hydrogels at different cellulose ether concentrations at room temperature were shown to decrease with increasing polymer concentration. The relaxation rate 1/T ₁ is sensitive to the type of polymer substituent but insensitive to the polymer molecular mass. The rate 1/T ₂ appears much less influenced by the polymer substitution. The procedure developed for calculating the amount of water bound per PRU, based on the analysis of theT ₁ andT ₂ data, shows that this amount is the largest for HPC followed by HEC, HP MC K4M, and HPMC K100M. The results correlate well with the degree of hydrophilic substitution of the polymer chains. This NMR analysis deals with a single molecular layer of adsorbed water for the investigated cellulose ether polymers at all concentrations, while the rest of the water in the hydrogel is bulk-like. Therefore, the mesh size of polymer network in the view of a single molecular layer is not effectively changed.     

Ultrasonic degradation, purification and analysis of structure and antioxidant activity of polysaccharide from Porphyra yezoensis Udea

The chemical structure and antioxidant of natural and ultrasonic degraded polysaccharides from Porphyra yezoensis Udea was investigated. The degraded polysaccharide (PYPS_UD) was purified, and F2 (a homogeneous fraction) was obtained. FT-IR, ¹H and ¹³C NMR spectral analysis revealed that F2 have typical porphyran structure. It has a backbone of alternating (1 → 4)-3,6-anhydro-α-l-galactopyranose) units and (1 → 3)-linked β-d-galactose or (1 → 4)-linked α-l-galactose 6-sulfate units. The result ascertained ultrasound degradation did not change the main structure of polysaccharides in the test conditions. Antioxidant proved that the activity of scavenging superoxide and hydroxyl radical is F₂ > V_C > PSPY_UD > PSPY. It was possible that ultrasonic treatment is an effective way for enhancing PSPY's antioxidant activity ascribing to decreasing molecular weight of polysaccharides.     

Sulfation of fucoidan in Fucus embryos. I. Possible role in localization

Zygotes of the brown alga Fucus distichus L. Powell divide into two cells which are structurally and biochemically different from each other. Cytochemical staining and autoradiography indicate that a sulfated polysaccharide is localized in only one of the two cells. Up to 10 hr after fertilization, no localization of sulfated polysaccharides is detectable in zygotes, and little ³⁵S (Na₂³⁵SO₄) is incorporated into an acid-soluble carbohydrate fraction. Between 10 and 16 hr, during rhizoid initiation and several hours before the first cell division, there is a large increase in the amount of ³⁵S incorporated into this fraction. The label is found associated with the sulfated fucose polymer fucoidan. Various extraction techniques and labeling experiments demonstrate that fucoidan is unsulfated at fertilization and undergoes little metabolic activity or turnover during the first 24 hr. Thus, the incorporation of sulfate into this carbohydrate fraction appears to involve a sulfation of a preexisting, unsulfated fucan polymer. The degree of sulfation achieved at this time in vivo is sufficient for migration of fucoidan through an electric field in agarose or acrylamide gels. The possible role of sulfation as a mechanism for the localization of fucoidan in the rhizoid cell by means of an intracellular electrical gradient is discussed.