Alcohol Precipitation of Xanthan Gum from Pure Solutions and Fermentation Broths

Abstract

Xanthan gum was precipitated from pure solutions and fermentation broths using either ethanol, isopropanol, or tert-butanol. The compositions of the precipitate and supernatant phases were determined as a function of alcohol concentration and used to construct binodal solubility curves with tie lines. Xanthan did not precipitate at bulk-mixture alcohol concentrations below 37.5% (wt) for ethanol, 35% for isopropanol, and 31% for tert-butanol. As the alcohol concentration increased beyond this point, the precipitates first were heavy gels with low xanthan concentrations. At higher alcohol concentrations, the precipitates were compact and fibrous. The maximum xanthan concentration in the precipitate was 14.5% at 60% ethanol, 23.5% at 50% isopropanol, and 33.5% at 40% tert-butanol in the pure solution precipitation experiments. At alcohol concentrations beyond 75%, the precipitates were brittle and needle-like, which made separation from the supernatant difficult. The results for the fermentation broth experiments were very similar to those of the pure solution experiments. Thus, precipitation using ethanol required the highest alcohol usage and resulted in the lowest xanthan concentration in the precipitate. Conversely, tert-butanol required the least alcohol for precipitation and formed the precipitates highest in xanthan concentration.     

Effect of fluid rheological properties on mass transfer in a bioreactor

Rheological properties and oxygen mass transfer coefficient (k_L a) were investigated in a stirred reactor (10 dm³) in the course of fermentations producing microbial polysaccharides—pullulan and xanthan. The fermentation broths behaved as pseudoplastic non-Newtonian fluids in both cases. Studies on the relationship between fluid rheological properties and k_L a were also carried out. The oxygen mass transfer coefficient decreases during the fermentation and exponential equations have been obtained to describe the relationship between the oxygen mass transfer coefficient, the agitation speed and the apparent viscosity of the broths. Furthermore, comparison of results between pullulan and xanthan fermentations was investigated. For the xanthan fermentation process, mixing and mass transfer in the reactor were more difficult than those for the pullulan fermentation.     

Performance of the scaba 6SRGT agitator in mixing of simulated xanthan gum broths

Power consumption under non-aerated and aerated conditions was measured in a 0.45 m diameter tank containing a range of xanthan gum solutions, using the Scaba 6SRGT impeller. Well-mixed caverns were measured in a transparent Carbopol solution. The data are compared with previous results obtained with a Rushton turbine in the range of Reynolds numbers, Re, between 1 and 2000. In each case, the non-aerated power numbers were similarly related to Re except that the Po values of the Scaba 6SRGT were 3 to 4 times smaller. Under aerated conditions, the aeration rate does not affect the power number, Po_g, with the actual value falling as a result of increasing xanthan concentration. The Po_g/Po vs Re curve passes through a minimum which is lower at higher xanthan concentrations. At the same Reynolds number, the decline in power consumption of the Scaba agitator due to aeration is 20 to 50% smaller than that observed with a Rushton turbine. Well-mixed cavern shapes and sizes are also very similar to those observed with Rushton turbines and can be predicted from equations available in literature. However, instabilities in torque could present a problem in broths containing xanthan in concentrations above 35 kg m^–3. Nevertheless, the Scaba agitator offers an interesting retrofitting possibility for xanthan fermentation, which could lead to improved performance.     

INTERIONIC AND INTERMOLECULAR INTERACTIONS IN ION-EXCHANGE AND SORPTION SYSTEMS INVOLVING PHYSIOLOGICALLY ACTIVE SUBSTANCE

ABSTRACT

This paper reviews the results obtained by studying the sorption of physiologically active substances (PAS) of different types such as, amino acids, nucleotides and melanoidins on ion exchangers and non-ionogenic sorbents. The review is mainly focused upon die mechanisms of interaction of PAS molecules in the sorbent phase. The contribution of ion-ionic, ion-molecular and intermolecular interactions to the overall sorption effect is discussed. The results of studying ion-exchange isothermal supersaturation of amino acid solutions on anion exchangers are reported and discussed. The mechanisms of aging of ion-exchange materials in the course of recovery of PAS from fermentation broths and hydrolysates are proposed.     

Solvent extraction of bacteriocins from model solutions and fermentation broths

A novel method for the extraction and purification of bacteriocins (small peptides with antimicrobial properties) from fermentation broths is described. Model solutions of nisin were prepared from Nisaplin®, a commercial whey‐based powder containing about 2.5% nisin and sold as a food preservative. These model solutions and fermentation broths from a culture of nisin‐producing Lactococcus lactis subsp lactis were cross‐flow filtered and stirred with toluene to obtain a white suspension in the toluene layer, which was back extracted with 10 mmol dm⁻³ HCl. Yields of the order of 90% for a single stage extraction were obtained followed by similar yields on back extraction. Yields dropped with decreasing pH, going through a minimum at pH 2. In larger scale experiments (11 dm³) at pH 6, a gel layer was formed which, on centrifugation and drying, gave a white solid containing about 50% nisin, the remainder being water and salt. Further process development would almost certainly bring this figure closer to the small‐scale value. The phase transfer technique was also applied to solutions containing variacin and carnocin (produced by Micrococcus varians and Carnobacterium piscicola, respectively). The mechanism of bacteriocin extraction probably involves concentration of the peptides, which are surface active, at the interface until their solubility is exceeded and they form reverse submicelles, which aggregate into reverse micelles to give a gel. © 2000 Society of Chemical Industry     

SELECTION OF A CATION EXCHANGE RESIN TO PRODUCE LACTIC ACID SOLUTIONS FROM WHEY FERMENTATION BROTHS

ABSTRACT

Lactic acid can be made by fermentation from inexpensive cheese whey. The acid is at present fairly costly, however, partly because of the costs of recovery and purification of the acid from the fementation broths. The present study has been undertaken to investigate a process that might reduce these costs. A number of commercial resins have been evaluated as ion exchangers for the production of lactic acid solutions. Amberlite IR-120, a gel strong cationic ion exchanger, was found to be the best resin. The loaded resin was regenerated efficiently. The results suggest that such a process is both technically and economically feasible.     

Increasing viscosity in entangled polyelectrolyte solutions by the addition of salt

The viscosity of several polyelectrolytes is measured in both salt free solutions and solutions in the high salt limit. At low polymer concentrations, the zero shear rate viscosity decreases as much as 100-fold upon addition of a monovalent salt, namely NaCl. However, as polymer concentration increases, the viscosity difference between polymer in salt free and in monovalent salt solution diminishes. Further, the zero shear rate viscosity becomes independent of added monovalent salt at the critical polyelectrolyte concentration c_D. Above c_D, the addition of monovalent salt increases the zero shear rate viscosity of the entangled polyelectrolyte solutions. The viscosity increase agrees with viscosity scaling theory for polyelectrolytes in the entangled regime. Polyelectrolytes exhibiting an increase in viscosity above c_D in the presence of monovalent salt include three natural anionic polyelectrolytes (xanthan, carrageenan, welan), one synthetic anionic polyelectrolyte (hydrolyzed polyacrylamide), and one natural cationic polyelectrolyte (chitosan). Generally, these polyelectrolytes are relatively high molecular weight (>1 M Dalton), which makes c_D experimentally accessible (e.g., c_D = 0.2 wt% for xanthan). The magnitude of the viscosity increase is as high as 300% for xanthan and nearly independent of monovalent salt concentration in the high salt limit. The increase in viscosity in monovalent salt solution and magnitude of c_D appear to be heavily influenced by the molecular characteristics of the polymers such as monomer weight, molecular structure, and chain conformation.     

Investigation of Polymer Adsorption on Rock Surface of Highly Saline Reservoirs

Blocking or reducing water production from oil wells is a serious problem in oil industry. Two types of polymers, namely, polyacrylamide (PAA) and polysaccharides (xanthan) have been investigated in this paper. The viscosity of both polymer solutions was first evaluated at different salinities, shear rates and concentrations. Afterwards, the solutions were injected into core samples to examine the adsorption on the rock surface by calculating the resistance factor as well as the residual resistance factor. Also, the effect of the injection rate of the polymer solutions has been studied. The results show that xanthan solution is tolerant of high salinity (20 %), while PAA solution is very sensitive to salt. Both polymer solutions show a pseudoplastic flow as a function of the shear rate. The core sample experiments show that both polymer solutions suffer a reduction in the adsorption rate with salinity increase. However, xanthan shows acceptable values even with a salinity up to 20 % and a temperature of 60 °C. Therefore, xanthan can be recommended to shut off water in high salinity and high temperature reservoirs. It was also found that the lower the injection rate the higher the adsorption on the rock surface.     

Extraction Processes for Bioproduct Separation

Abstract

The three-phase extraction process, a modification of reactive extraction, has been investigated for its applicability in the separation of organic acids from fermentation broth. It has been compared with reactive extraction, liquid membrane permeation, and supercritical fluid extraction.

These processes are based on the use of amine extractants, which have to be dissolved in nonpolar solvents, for the extraction of carboxylic acids, hydroxycarboxylic acids, and aminocarboxylic acids.

This paper considers the comparison of the above-mentioned processes. Furthermore, the extractability of acids from synthetic aqueous solutions and fermented broths has been compared. Principal consideration has been paid to the extraction of lactic acid, gluconic acid, citric acid, and L-leucine.     

Modification of Single‐walled Carbon Nanotubes for Enhancing Isopropyl Alcohol Vapor Adsorption from Air Streams

Abstract

Single‐walled carbon nanotubes (SWCNTs) were oxidized by HCl, HNO₃ and NaClO solutions and were selected as adsorbents to study their characterizations and adsorption properties of isopropyl alcohol (IPA) vapor from air streams. The physicochemical properties of SWCNTs were greatly changed after oxidation by HNO₃ and NaClO solutions. These modifications include the increase in surface functional groups and surface basic sites, which enhance the chemisorption capacity of IPA, and the decrease in pore size and the increase in surface area of micropores, which improve the physisorption capacity of IPA. The maximum IPA adsorption capacities of SWCNTs, SWCNTs(HCl), SWCNTs(HNO₃) and SWCNTs(NaClO) calculated by Langmuir model are 63.48, 54.34, 72.99, and 103.56 mg/g, respectively. The SWCNTs(NaClO) show the best performance of IPA removal and their adsorption mechanism appears mainly attributable to physical force with a relatively low influent IPA concentration but appears attributable to both physical and chemical forces with a relatively high influent IPA concentration.     

Studies on the Separation of Cadmium from Solutions by Foam Separation. II. Precipitate Flotation of Cadmium Hydroxide

Abstract

Foam separation of cadmium in relation to pH from solutions of different metal concentrations was carried out by means of lauryl sulfate. The effect of inert salt on the removal of cadmium hydroxide and cadmium cations by adsorbing colloid floation was also studied. The precipitate flotation results reflect the precipitation of the metal in the form of a hydroxide. The precipitation pH values calculated are approximately those at which cadmium removal over 50% is obtained. The presence of electrolyte has a negative effect on the results of precipitate flotation of cadmium hydroxide and adsorbing colloid flotation of cadmium cations with lauryl sulfate.     

Rheological properties of progesterone microemulsions: Influence of xanthan and chitosan biopolymer concentration

In this preformulations study, rheological properties of microemulsions with progesterone (1%) were studied to analyze the effect of xanthan and chitosan at different concentrations (0.5–3%). Steady shear and oscillatory rheological properties were analyzed using a controlled stress rheometer. Steady shear data were satisfactorily adjusted to the Carreau model. For all preparations, shear‐thinning behavior was observed. Zero shear viscosity (η₀) increased with the biopolymer concentration. The results from dynamic experiments showed the behavior of all preparations with xanthan gum and those of chitosan to be characteristic of weak gels and liquid‐like solutions, respectively. The correlation between dynamic and steady‐shear properties (extended Cox‐Merz rule) was satisfactory for the two polymers. The recovery analysis of microemulsions with xanthan showed a total recovery percentage of 90% for the highest concentrations of this polymer. However, microemulsions with chitosan showed practically no recovery. Progesterone release was greater for the microemulsions with chitosan. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Downstream Processing of Lactic Acid by Membrane-Based Solvent Extraction∗

Abstract

Lactic acid has extensive use in the food and chemical industry. About half the lactic acid used in the world is produced by fermentation of carbohydrates using lactic acid bacteria. The recovery of lactic acid from the fermentation broth is more difficult than the fermentation itself. In the present work a study of membrane-based solvent extraction as a separation unit for the continuous downstream processing of lactic acid from fermentation broth was carried out. The experiments were performed using simulated fermentation broths made of lactic acid in acetate buffer or distilled water as the feed solution. The effects of membrane material, organic carrier, and pH of the feed solution on membrane extraction efficiency were investigated. A separation degree of 35% was obtained by using a polyether-etherketone (PEEK-WC 14%) membrane with 5% trioctylamine as the organic carrier in n-heptane. The experimental results obtained with the simulated system encourage the use of membrane-based solvent extraction with a real fermentation broth.

     

Studies on fermentation-broth rheology of a penicillium strain with cellulose as substrate

The rheological behaviour of cellulose fermentation broths of Penicillium funiculosum culture has been investigated. The shear stress-shear rate behaviour is explained satisfactorily by a power law model, although there appear to be small yield stresses, particularly at high substrate concentrations.     

Physicochemical properties and release behavior of indomethacin-loaded polysaccharide membranes

Abstract

Polyelectrolyte complex based on chitosan and xanthan gum and containing the anti-inflammatory indomethacin at three different concentrations were developed with the intent of using these drug-loaded membranes as bioactive wound dressings. The resulting incorporation efficiency of indomethacin into the membranes was above 95%. The drug-loaded membranes were quite stable and exhibited a high degree of swelling in aqueous solutions. Studies of drug release in phosphate buffer saline solutions indicated that the formulation containing 20?mg of drug per gram of biopolymer is able to release the expected topical dosage in 6?h, thus showing a potential for biomedical application.     

A REVIEW OF THE INDUSTRIAL AND RECENT POTENTIAL APPLICATIONS OF TRIOCTYLPHOSPHINE OXIDE

ABSTRACT

The industrial applications of trioctylphosphine oxide, more commonly known as TOPO, make use of its complexing powers with metals and with hydrogen donor organic compounds. Commercial uses as a solvent extraction reagent are in the recovery of uranium from wet process phosphoric acid and in the recovery of byproduct acetic acid and furfural generated during sulphite wood pulping. Recently investigated potential uses include the separation of niobium from tantalum and the extraction of organic compounds, such as citric acid, from fermentation broths. Each process is discussed briefly.     

The prediction of transport parameters in filamentous fermentation broths based on results obtained in pseudoplastic polymer solutions

Transport phenomena studies on single phase “model” fluids are of limited value in biochemical engineering if they cannot be translated to the heterogeneous systems encountered in real fermentation processes. In this paper we discuss the utility of polymer solutions as models of filamentous fermentation broths for evaluation of: pipeline friction factors and impeller power numbers (turbine and helical ribbon). To a first approximation, polymer solutions can serve as suitable models for the prediction of laminar flow pressure drop in pipelines and turbulent power consumption in stirred tanks. However, results obtained on polymer solutions do not directly apply to filamentous fermentation broths for predictions of laminar flow impeller power consumption and the transition point for turbulent flow in stirred tanks. These discrepancies are believed to result from the existence of a time dependent yield stress in filamentous fermentation broths.     

放线菌AF1发酵液提取物对病原微生物的抑菌作用和稳定性分析

对放线菌菌株AFI乙酸乙酯提取物的抑菌谱做了研究。抑菌活性试验表明:AF1发酵液提取物对8种植物病原真菌和10种革兰氏阳性病原菌都具有抑制活性,对4种革兰氏阴性致病菌无抑制作用。在供试的8种植物病原菌中,放线菌AF1发酵液提取物对香蕉枯萎病菌(fusarium oxysporum f.sp.cubense)和苦瓜枯萎病菌(fusarium oxysporum f.sp.momodicae)的抑菌率达到85%以上。稳定性试验结果表明:菌种AF1发酵液对紫外线、热和酸碱较稳定,室温至80℃时稳定,90℃时活性丧失,在pH 2~10范围内稳定,耐受紫外线照射。试验表明该菌株发酵液提取物对革兰氏阳性致病菌的抑制作用较好,有较强的稳定性,具有一定的开发价值。     

Sorption and desorption of cadmium and lead on pectin-based biosorbents – batch and column studies

ABSTRACT

The hybrid pectin-based beads containing carob, gellan and xanthan gum were studied to be suitable for removing the Cd(II) and Pb(II) from aqueous solution in column system. Desorption of the ions from studied materials was also determined in batch and continuous studies. It was possible to remove the Cd(II) and Pb(II) ions from solution of concentration ca. 130 and 250 mg/L, respectively, to the level permissible by law. Both ions may be completely removed from our biosorbents using mineral acid solutions (confirmed by mass balance). The minimal lifetime of sorbent was also determined to be at least 10 cycles.     

Reversed Micellar Extraction of Vancomycin: Effect of pH,Salt Concentration,and Affinity Ligands

Abstract

Vancomycin was extracted from an aqueous feed solution into a reverse micellar solution of bis(2-ethylhexyl)sulfosuccinate sodium salt in isooctane. A low pH and salt concentration of aqueous feed solutions favors forward extraction. The backward extraction efficiency of vancomycin from reverse micelles into an aqueous phase, on the other hand, increases with pH. Affinity cosurfactants prepared by attaching a dipeptide d-alanyl-d-alanine or a racemic dipeptide dl-alanyl-dl-alanine to cholesteryl-chloroformate was employed for affinity reverse micellar extraction of vancomycin. The forward extraction efficiency increases significantly in the presence of an affinity cosurfactant. The recovery of vancomycin from fermentation broth with high selectivity was also achieved by employing this affinity cosurfactant.