Some chemical and physical properties of extracellular polysaccharides produced by Butyrivibrio fibrisolvens strains.

Most strains of Butyrivibrio fibrisolvens are known to produce extracellular polysaccharides (EPs). However, the rheological and functional properties of these EPs have not been determined. Initially, 26 strains of Butyrivibrio were screened for EP yield and apparent viscosities of cell-free supernatants. Yields ranged from less than 1.0 to 16.3 mg per 100 mg of glucose added to the culture. Viscosities ranged from 0.71 to 5.44 mPa.s. Five strains (CF2d, CF3, CF3a, CE51, and H10b) were chosen for further screening. The apparent viscosity of the EP from each of these strains decreased by only 50 to 60% when the shear rate was increased from 20 to 1,000 s-1. Strain CE51 produced the EP having the highest solution viscosity. A detailed comparison of shear dependency of the EP from strain CF3 with xanthan gum showed that this EP was less shear sensitive than xanthan gum and, at a shear rate of 1,000 s-1, more viscous. EPs from strains CF3 and H10b were soluble over a wide range of pH (1 to 13) in 80% (vol/vol) ethanol-water or in 1% (wt/vol) salt solutions. The pH of 1% EP solutions was between 4.5 and 5.5. Addition of acid increased solution viscosities, whereas addition of base decreased viscosity. EPs from strains CF3, CE51, and H10b displayed qualitatively similar infrared spectra. Calcium and sodium were the most abundant minerals in the three EPs. The amounts of magnesium, calcium, and iron varied considerably among the EPs, but the potassium contents remained relatively constant.     

Viscosity of locust bean, guar and xanthan gum solutions in the Newtonian domain: a critical examination of the log (ηsp)o-log c[η]o master curves

The viscosity in the low shear rate Newtonian domain of three biopolymers, locust bean gum, guar gum and xanthan gum was studied as a function of temperature and of polymer concentration in various aqueous solvents. The intrinsic viscosities [η]_o of both galactomannans are not modified in the presence of 10 or 40% sucrose. In this case, a master curve relating the Newtonian specific viscosity (η_sp)_o, to the reduced concentration c[η]_o is obtained and allows (in good agreement with theoretical conjectures), two critical concentrations C* and C** to be defined, from which the value of the expansion coefficient may be estimated. For xanthan, as expected for a polyelectrolyte, [η]_o depends strongly on salt concentration and on added sucrose and the results did not obey the above-mentioned master curve. However, it is shown that (η_sp)_o depends only on xanthan concentration whenC > C**, and then it is assumed that chain dimensions have attained their unperturbed values whatever the solvent. Considering that both types of chains, random coils (galactomannans) and semi-rigid (xanthan) should give the same (η_sp)_o-C[η]_o master curve for C > C** when [η]_o is replaced by its unperturbed counterpart [η]_θ, a method for estimating [η]_θ for the xanthan sample is proposed. In conclusion, the numerous exceptions to the widely accepted (η_sp)_o vs C[η]_o “universal” behaviour are mainly ascribed to significant differences in expansion coefficient values which depend on both the polymer and the solvent.     

Detection of red cell aggregation by low shear rate viscometry in whole blood with elevated plasma viscosity

The viscosity of whole blood measured at low shear rates is determined partly by shear resistance of the red cell aggregates present, stronger aggregation increasing the viscosity in the absence of other changes. Effects of cell deformability can confound interpretation and comparison in terms of aggregation, however, particularly when the plasma viscosity is high. We illustrate the problem with a comparison of hematocrit-adjusted blood from type 1 diabetes patients and controls in which it is found the apparent and relative viscosities at a true shear rate of 0.20 s-1 are lower in the patient samples than age matched controls, in spite of reports that aggregation is increased in such populations. Because the plasma viscosities of the patients were higher on average than controls, we performed a series of experiments to examine the effect of plasma protein concentration and viscosity on normal blood viscosity. Dilution or concentration by ultrafiltration of autologous plasma and viscosity measurements at low shear on constant hematocrit red cell suspensions showed (a) suspension viscosity at 0.25 and 3 s-1 increased monotonically with plasma protein concentration and viscosity but (b) the relative viscosity increased, in concert with the microscopic aggregation grade, up to a viscosity of approximately 1.25 mPa-s but above this the value the relative viscosity no longer increased as the degree of aggregation increased in concentrated plasmas. It is suggested that in order to reduce cell deformation effects in hyperviscous pathological plasmas, patient and control plasmas should be systematically diluted before hematocrit is adjusted and rheological measurements are made. True shear rates should be calculated. Comparison of relative viscosities at low true shear rates appears to allow the effects of red cell aggregation to be distinguished by variable shear rate viscometry in clinical blood samples.     

Development of reduced-fat mayonnaise using 4αGTase-modified rice starch and xanthan gum

In this study a disproportionating enzyme, 4-α-glucanotransferase (4αGTase), was used to modify the structural properties of rice starch to produce a suitable fat substitute in reduced-fat (RF) mayonnaise. The mayonnaise fat was partially substituted with the 4αGTase-treated starch paste at levels up to 50% in combination with xanthan gum and the physical and rheological properties of the modified RF mayonnaise samples were investigated. All mayonnaises prepared in this study exhibited shear thinning behavior and yield stress. Viscoelastic properties of mayonnaise were characterized using dynamic oscillatory shear test and it was observed that mayonnaises exhibited weak gel-like properties. The magnitude of elastic and loss moduli was also affected by 4αGTase-treated starch concentration and presence of xanthan gum. In relation to microstructure, RF mayonnaise prepared with 3.8 or 5.6 wt% of 4αGTase-treated starch and xanthan gum showed smaller droplets. The use of 5.6 wt% of 4αGTase-treated starch and 0.1 wt% of xanthan gum produced a RF mayonnaise with similar rheological properties and appearances as FF mayonnaise with gum. This study demonstrated a high feasibility for using 4αGTase-treated rice starch as a viable fat replacer in mayonnaise.     

Modified xanthan—its preparation and viscosity

Xanthan with various pyruvic acid and acetate contents has been prepared from a single commercial polysaccharide sample using optimised chemical conditions (acid and alkali hydrolysis, respectively) for removal of acetal and acyl groups. The only significant change found on analysis of the modified xanthans was loss of pyruvic acid and/or acetate; no low moleculur weight carbohydrate-containing material was released. Contrary to some previous reports, evidence is presented to show that the pyruvic acid acetal and o-acetyl contents of xanthan do not affect solution viscosity. The viscosities of native, pyruvate-free and pyruvate/acetate-free xanthan solutions (0·3% w/v) were similar at shear rates 8·8–88·3 s^?1 in both distilled water and 1% KCl. Over the concentration range 0·2-1·5%, the viscosities of native and pyruvate-free xanthan at 10 s^?1 were similar. The viscosity increase on addition of 1% KCl to salt-free xanthan solutions was independent of pyruvic acid acetal substitution. Our results suggest that xanthan samples with various pyruvic acid acetal and o-acetal contents, prepared under different fermentation conditions of Xanthomonas campestri should not normally be used for assessing the contribution of these groups to solution viscosity.     

Yield stress components of waxy corn starch–xanthan mixtures: Effect of xanthan concentration and different starches

Yield stress of 6% (w/w) waxy maize (WXM), cross-linked waxy maize (CLWM), and cold water swelling (CWS) starches in xanthan gum dispersions: 0%, 0.35%, 0.50%, 0.70%, and 1.0% was measured with the vane method at an apparent shear rate of 0.05 s⁻¹. The intrinsic viscosity of the xanthan gum was determined to be: 112.3 dL/g in distilled water at 25 °C. Values of the static (σ_0s) and dynamic (σ_0d) yield stress of each dispersion were measured before and after breaking down its structure under continuous shear, respectively. The WXM and CWS starches exhibited synergistic behavior, whereas the CLWM starch showed antagonistic effect with xanthan gum. The difference (σ_0s − σ_0d) was the stress required to break the inter-particle bonding (σ_b). The contributions of the viscous (σ_v) and network (σ_n) components were estimated from an energy balance model. In general, values of σ_b of the starch–xanthan gum dispersions decreased and those of σ_n increased with increase in xanthan gum concentration.     

Inter- and Intra-Manufacturer Variability in Pharmaceutical Grades and Lots of Xanthan Gum

A pharmaceutical formulation typically contains one or more excipients in addition to the active pharmaceutical ingredient(s). Though excipients have been considered inert components of a formulation, variability in their properties has been shown to affect the performance of drug dosage forms and delivery systems. This study investigates the inter- and intra-manufacturer variability among different NF grades and lots of xanthan gum made by two manufacturers. As many formulators rely on compendial standards to monitor and control the variability of excipients, this study focuses on the adequacy of the NF specifications, in particular the viscosity specification, to discern the variability in solution properties of different pharmaceutical grades and lots of xanthan gum. All the grades and lots in this study were NF grade materials. Xanthan gum solutions were prepared in accordance with NF test methodology and were rheologically evaluated using a rotational rheometer. Both steady shear measurements and small amplitude oscillatory measurements were carried out on 1% w/w xanthan gum solutions. Results showed significant inter- and intra-manufacturer variability among the NF grades and lots of xanthan gum that was not reflected in the NF viscosity test specifications.     

Genetic engineering of polysaccharide structure: production of variants of xanthan gum in Xanthomonas campestris.

Xanthan gum is an extracellular heteropolysaccharide produced by the bacterium Xanthomonas campestris. Xanthan has wide commercial application as a viscosifier of aqueous solutions. Previously, through genetic engineering, a set of mutants defective in the xanthan biosynthetic pathway has been obtained. Certain mutants were shown to synthesize and polymerize structural variants of the xanthan repeating unit and thus produce "variant xanthans". Initial studies of solution viscosities of these polymers, presented here, indicate that the variants have rheological properties similar to, but not identical with, xanthan. These results indicate that acetylation and pyruvylation can affect the viscometric properties of xanthan. Specifically, the presence of pyruvate increases viscosity, whereas acetate decreases viscosity. In addition, the elimination of sugar residues from xanthan side chains also has a major effect on viscosity. Compared to wild-type xanthan, polymer lacking the terminal mannose (polytetramer) is a poor viscosifier. In contrast, polymer lacking both the terminal mannose and glucuronic acid (polytrimer) is a superior viscosifier, on a weight basis. There is a negative effect of acetylation on the viscosity of polytetramer xanthan, but there is seemingly no effect of acetylation on polytrimer xanthan viscosity. The further study of these materials should provide insight into the relationship between xanthan structure and rheological behavior.     

改性黄原胶酯化条件的优化及结构的表征

为了提高黄原胶的速溶性和粘度,将黄原胶进行改性处理。将黄原胶与马来酸酐进行酯化反应,探讨了黄原胶与马来酸酐摩尔比、反应时间和反应温度等因素的影响,以取代度为指标,利用响应面方法确定,该酯化反应的最优条件为:黄原胶与马来酸酐摩尔比1∶11.5、反应时间24.4 h、反应温度66℃。对改性黄原胶进行红外光谱、光散射和X-射线衍射等结构表征,表明酯化改性成功,且进一步解释了速溶性和粘度提高的原因。改性黄原胶细胞毒性实验,显示无毒性。结果表明,改性黄原胶的速溶性和粘度有很大提高,0.2%改性黄原胶的速溶性和粘度较对照提高了近3倍,在食品、药品等领域具有潜在的应用价值。     

Synthetic media for production of quality xanthan gum in 20 liter fermentors

Xanthan gum is a heteropolysaccharide synthesized by Xanthomonas campestris NRRL B-1459 and is composed of D -glucose, D -mannose, and D -glucuronic acid, in addition to acetic and pyruvic acids. Different amounts of pyruvic acid ketal are found in various preparations which can influence the viscosities of dilute xanthan solutions. Polysaccharide production on synthetic media was studied in small-scale fermentors. Fermentation conditions were established for production of both high and low pyruvic acid gums (about 4 and 2% pyruvic acid, respectively). Low nitrogen [0.1% (NH₄)₂HPO₄] and air (0.25 vol/liter/min) levels favor production of low pyruvate gum; increasing (NH₄)₂HPO₄ to 0.15%, adding K₂HPO₄, and increasing the air flow to 1.5 vol/liter/min favored production of normal gum. Both processes gave xanthan yields of 50 to 60%, based on 2.5% initial D -glucose substrate, in two to three days. Differences in pyruvic acid content and in the quantity of gum produced under a given set of conditions were attributed to strain variability. Substrains were isolated that have desirable characteristics for production of xanthan gum; i.e., the ability to give good yields of high-pyruvate gum when grown on both complex and synthetic media.     

Utilization of Glucose and Xylose in Ruminal Strains of Butyrivibrio fibrisolvens

The dual-substrate utilization pattern in cultures of five ruminal strains of Butyrivibrio fibrisolvens growing on glucose and xylose was investigated. Strains ATCC 19171 and 86 utilized glucose and xylose simultaneously. Other strains exhibited diauxic growth. Strains X1 and CE 51 exhibited classical diauxic growth in which glucose was utilized during the first phase. Strain X2D62 displayed atypical diauxic growth in which slow utilization of xylose was followed by rapid utilization of glucose after the xylose depletion. The ATP-dependent phosphorylation of glucose was found in all strains tested. The phosphoenolpyruvate-dependent phosphorylation of glucose was detected only in B. fibrisolvens CE 51.     

Lactose consuming strains of Xanthomonas citri subsp. citri (Xcc) insight into the emergence of natural field resources for xanthan gum production

Xanthomonas genus possesses a low level of β-galactosidase gene expression and is therefore unable to produce xanthan gum in lactose-based media. In this study, we report the emergence of some natural field strains of Xanthomonas citri subsp. citri (Xcc) capable to use lactose as a sole carbon source to produce xanthan gum. From 210 Xcc strains isolated from key lime (C. aurantifolia), 27 showed the capacity to grow on lactose containing medium. Xcc lactose consuming strains demonstrated a good level of xanthan production. Amongst all, NIGEBK37 produced the greatest (14.62 g/l) amount of xanthan gum in experimental laboratory conditions. By evaluating the viscosity of the biopolymer at 25 °C, it was demonstrated that xanthan synthesized by strain NIGEBK37 has the highest viscosity (44,170.66 cP). Our results were indicative for the weakness of a commercial strain of Xanthomonas campestris pv. Campestris DSM1706 (Xcc/DSM1706) to produce xanthan in lactose containing medium.     

Anaerobic Production of Extracellular Polysaccharide by Butyrivibrio fibrisolvens nyx

Anaerobic production of extracellular polysaccharide (EP) was examined, using a previously uncharacterized, obligately anaerobic rumen isolate, Butyrivibrio fibrisolvens nyx, which produced an EP that was rheologically similar to xanthan gum. The main objectives were to determine the nutritional requirements and conditions which promoted EP production by strain nyx. Strain nyx was grown anaerobically in defined and semidefined media. In addition to carbohydrate and nitrogen sources, strain nyx required acetic acid, folic acid, biotin, and pyridoxamine. Strain nyx produced similar amounts of EP at 35 to 40°C. Conditions that improved growth usually improved EP production. Of the carbohydrates tested, glucose supported the fastest growth and most EP production, followed by sucrose, xylose, and lactose. Strain nyx utilized ammonium sulfate, urea, or vitamin-free casein hydrolysate as nitrogen sources for growth and EP production. At 2 and 20 g/liter, respectively, ammonium sulfate and vitamin-free casein hydrolysate supported about the same rates of growth and EP production. EP was not produced in the lag or stationary phases, and EP production was exponential during exponential cell growth. Based on the results of this work, anaerobic EP production with B. fibrisolvens nyx could reduce energy costs for industrial EP production compared with the cost of aerated systems. Finally, this work demonstrated that, under appropriate growth conditions, a gastrointestinal tract (ruminal) microorganism produced high levels of EP.     

Extracellular microbial polysaccharides: Generalized power law for biopolysaccharide solutions

A generalized power low model, \documentclass{article}\pagestyle{empty}\begin{document}$ \eta \, = \,\eta _0 [1\, + \,(\dot \gamma /\gamma _0 )];{N - 1} $\end{document}, is shown to described satisfactorily the shear viscosity data for xanthan gum solutions from 0.18 g/L to nearly 4 g/L and low to intermediate shear rates. Since mixing, mass and heat transfer, residence time distributions, and power input for agitation and aeration all depend on shear viscosity, this equation provides a simple prediction of this important quantity over the shear rate ranges characteristic of fermentations.     

Fermentation of glucose and xylose in ruminal strains of Butyrivibrio fibrisolvens

Metabolism of glucose and xylose and parameters of growth were investigated in strains of Butyrivibrio fibrisolvens ATCC 19171 and CE 51. In the strain ATCC 19171, the composition of fermentation end-products was the same in cultures supplied with glucose and xylose. The strain CE 51 produced more volatile fatty acids and less lactate from xylose than from glucose. Cells of this strain grown on xylose possessed phosphoketolase activity (EC 4.1.2.9). In both strains the production of cell dry matter and growth rate were higher in cultures supplied with glucose. In xylose-grown cultures butyrivibrios tended to convert more substrate carbon into metabolites and less into cellular material than in cultures grown on glucose.     

Rheological properties of barley β-glucan

Health benefits of cereal β-glucan are linked to its high viscosity. Although viscosity of β-glucan gum solutions has been reported previously, there are conflicting reports about its behavior at elevated temperatures. Therefore, the viscosity behavior of barley β-glucan gum obtained in a pilot plant (PP) or in a laboratory (LAB) was determined at different shear rates (1.29–129 s⁻¹) and temperatures (0.1–75 °C) in this study. Viscosity decrease with temperature was demonstrated for both gums and activation energy E_a was calculated from the Arrhenius equation. None of the fresh gum solutions exhibited thixotropic behavior at ≤1% (w/w) concentration, but the measurement demonstrated that increased shear rate is not applicable to polymer solutions of low viscosity. Information about rheological properties of β-glucan will lead to better understanding of its behavior under physiological and processing conditions.     

Guar Gum,Xanthan Gum,and HPMC Can Define Release Mechanisms and Sustain Release of Propranolol Hydrochloride

The objectives were to characterize propranolol hydrochloride-loaded matrix tablets using guar gum, xanthan gum, and hydroxypropylmethylcellulose (HPMC) as rate-retarding polymers. Tablets were prepared by wet granulation using these polymers alone and in combination, and physical properties of the granules and tablets were studied. Drug release was evaluated in simulated gastric and intestinal media. Rugged tablets with appropriate physical properties were obtained. Empirical and semi-empirical models were fit to release data to elucidate release mechanisms. Guar gum alone was unable to control drug release until a 1:3 drug/gum ratio, where the release pattern matched a Higuchi profile. Matrix tablets incorporating HPMC provided near zero-order release over 12 h and erosion was a contributing mechanism. Combinations of HPMC with guar or xanthan gum resulted in a Higuchi release profile, revealing the dominance of the high viscosity gel formed by HPMC. As the single rate-retarding polymer, xanthan gum retarded release over 24 h and the Higuchi model best fit the data. When mixed with guar gum, at 10% or 20% xanthan levels, xanthan gum was unable to control release. However, tablets containing 30% guar gum and 30% xanthan gum behaved as if xanthan gum was the sole rate-retarding gum and drug was released by Fickian diffusion. Release profiles from certain tablets match 12-h literature profiles and the 24-h profile of Inderal^® LA. The results confirm that guar gum, xanthan gum, and HPMC can be used for the successful preparation of sustained release oral propranolol hydrochoride tablets.     

A rheological study on plasma lipoproteins (author's transl)]

Lipoproteins of the types LpB and LP-X are studied in a microviscometer to measure intrinsic viscosity. Up to a shear rate of 1700s-1 no shear dependence of viscosity is observed. Intrinsic viscosities are 3.5 and 4.0 for LpB, and 8.5 ml/g for LP-X. Density measurements are used to calculate apparent specific volumes. The results are compatible with a spherical model. An upper limit of 0.45 is estimated for the hydration.     

改善吞咽功能食品增稠剂的研究

为了提供一种适合老年吞咽障碍患者使用的增稠剂,以黄原胶和罗望子胶及麦芽糊精为原料,粘度及溶解时间为指标,采用单因素实验和正交实验相结合的方法确定胶体最适的复配比例。结果表明:复配后的胶体粘度均大于单一胶体的粘度,且三种胶体复配后的溶解速度得到了显著地提高。黄原胶、罗望子胶和麦芽糊精的最适复配比例为3∶1∶30,粘度为611mPa·s,溶解时间为3min。随后通过流变仪对复配溶液的流变特性及粘度进行分析验证。最后将最适配方的增稠剂与市面上具有代表性的国内外增稠剂进行对比,表明该配方的增稠剂不仅具有成本低及速溶的优势,还能应用于医学钡餐造影。     

Effect of salts on pasting, thermal, and rheological properties of rice starch in the presence of non-ionic and ionic hydrocolloids

Effects of salts on pasting, thermal, and rheological properties of rice starch (RS) in the presence of non-ionic (guar gum; GG) or ionic (xanthan; XT) hydrocolloid were studied. Rapid visco-analysis (RVA) showed that addition of salts significantly increased peak, breakdown, and final viscosities, and pasting temperatures of RS/XT blends, whereas those of RS/GG blends were varied depending on the type of salts added. Differential scanning calorimetry (DSC) demonstrated that salt addition significantly increased gelatinization temperatures of either RS/GG or RS/XT blend, whereas gelatinization enthalpy was less affected. Dynamic viscoelastic tests revealed that addition of salts had a more pronounced effect on enhancing structure formation of RS/XT gels than that of RS/GG gels. The steady shear viscosity was generally in line with the values of final viscosity obtained during pasting. These results would be used as a guideline for developing starch-based food products containing salts.