Acetone–butanol–ethanol (ABE) fermentation using Clostridium acetobutylicum XY16 and in situ recovery by PDMS/ceramic composite membrane

PDMS/ceramic composite membrane was directly integrated with acetone-butanol-ethanol (ABE) fermentation using Clostridium acetobutylicum XY16 at 37 °C and in situ removing ABE from fermentation broth. The membrane was integrated with batch fermentation, and approximately 46 % solvent was extracted. The solvent in permeates was 118 g/L, and solvent productivity was 0.303 g/(L/h), which was approximately 33 % higher compared with the batch fermentation without in situ recovery. The fed-batch fermentation with in situ recovery by pervaporation continued for more than 200 h, 61 % solvent was extracted, and the solvent in penetration was 96.2 g/L. The total flux ranged from 0.338 to 0.847 kg/(m(2)/h) and the separation factor of butanol ranged from 5.1 to 27.1 in this process. The membrane was fouled by the active fermentation broth, nevertheless the separation performances were partially recovered by offline membrane cleaning, and the solvent productivity was increased to 0.252 g/(L/h), which was 19 % higher compared with that in situ recovery process without membrane cleaning.     

An immobilized cell reactor with simultaneous product separation. II. Experimental reactor performance

The simultaneous separation of volatile fermentation products from product-inhibited fermentations can greatly increase the productivity of a bioreactor by reducing the product concentration in the bioreactor, as well as concentrating the product in an output stream free of cells, substrate, or other feed impurities. The Immobilized Cell Reactor-Separator (ICRS) consists of two column reactors: a cocurrent gas-liquid "enricher" followed by a countercurrent "stripper" The columns are four-phase tubular reactors consisting of (1) an inert gas phase, (2) the liquid fermentation broth, (3) the solid column internal packing, and (4) the immobilized biological catalyst or cells. The application of the ICRS to the ethanol-from-whey-lactose fermentation system has been investigated. Operation in the liquid continuous or bubble flow regime allows a high liquid holdup in the reactor and consequent long and controllable liquid residence time but results in a high gas phase pressure drop over the length of the reactor and low gas flow rates. Operation in the gas continuous regime gives high gas flow rates and low pressure drop but also results in short liquid residence time and incomplete column wetting at low liquid loading rates using conventional gas-liquid column packings. Using cells absorbed to conventional ceramic column packing (0.25-in. Intalox saddles), it was found that a good reaction could be obtained in the liquid continuous mode, but little separation, while in the gas continuous mode there was little reaction but good separation. Using cells sorbed to an absorbant matrix allowed operation in the gas continuous regime with a liquid holdup of up to 30% of the total reactor volume. Good reaction rates and product separation were obtained using this matrix. High reaction rates were obtained due to high density cell loading in the reactor. A dry cell density of up to 92 g/L reactor was obtained in the enricher. The enricher ethanol productivity ranged from 50 to 160 g/L h while the stripper productivity varied from 0 to 32 g/L h at different feed rates and concentrations. A separation efficiency of as high as 98% was obtained from the system.     

Recovery of endo-polygalacturonase using polyethylene glycol-salt aqueous two-phase extraction with polymer recycling

The partitioning behaviour of endo-polygalacturonase (endo-PG) and total protein from a clarified Kluyveromyces marxianus fermentation broth in polyethylene glycol (PEG)-ammonium sulfate and PEG-potassium phosphate (pH=7) aqueous two-phase systems was experimentally investigated. Both the enzyme and total protein partitioned in the bottom phase for these two kinds of systems. The enzyme partitioning coefficient can be lower than 0.01 in PEG8000-(NH₄)₂SO₄ ATPS with a large phase volume ratio and a moderate tie-line length, which implies the possibility of concentration operation using aqueous two phase partitioning. An ion-exchange separation of high purification efficiency was applied to analyze the clarified and dialyzed fermentation broth. A total purification factor of only 2.3 was obtained, which indicated the high enzyme protein content in the total protein of the fermentation broth. Consequently, the main purpose for separating endo-PG is concentration rather than purification. A separation scheme using an aqueous two-phase extraction process with polymer recycling and a dialysis was proposed to recover endo-PG from the fermentation supernatant of K. marxianus for commercial purpose. A high enzyme recovery up to 95% and a concentration factor of 5 to 8 with a purification factor of about 1.25 were obtained using the single aqueous two-phase extraction process. More than 95% polymer recycled will not affect the enzyme recovery and purification factor. Dialysis was used mainly to remove salts in the bottom phase. The dialysis step has no enzyme loss and can further remove small bulk proteins. The total purification factor for the scheme is about 1.7.     

Oxygen-transfer strategy and its regulation effects in serine alkaline protease production by Bacillus licheniformis

The effects of oxygen transfer on the production and product distribution in serine alkaline protease (SAP) fermentation by Bacillus licheniformis and oxygen-transfer strategy in relation to the physiology of the bacilli were investigated on a defined medium with citric acid as sole carbon source in 3.5-dm(3) batch bioreactor systems. By forming a 3 x 3 matrix with the parameters air-inlet rates of Q(O)/V(R) = 0.2, 0.5, 1.0 vvm, and agitation rates of N = 150, 500, 750 min(-1), the effects of oxygen transfer were investigated at nine different conditions. The concentrations of the product SAP and by-products, i.e., neutral protease, alpha-amylase, amino acids, and organic acids, and SAP activities were determined throughout the bioprocess. Among the constant air-flow and agitation-rate fermentations, Q(O)/V(R) = 0.5 vvm, N = 750 min(-1) oxygen-transfer conditions produced maximum SAP activity that was 500 U cm(-3), at t = 37 h. With the increase in Q(O)/V(R) and/or N, Damk?hler number that is the oxygen-transfer limitation decreases; and the process passes from oxygen-transfer limited conditions to biochemical-reaction limited conditions. Further increase in SAP activity, A = 680 U cm(-3) was achieved by applying an oxygen-transfer strategy based on the analysis of the data obtained with the constant oxygen-transfer condition experiments, with a step increase in air-inlet rate, from Q(O)/V(R) = 0.2 to Q(O)/V(R) = 0.5 vvm at N = 750 min(-1) constant agitation rate at t = 24 h. Organic acids and amino acids that were excreted to the fermentation medium varied depending on the oxygen-transfer conditions. With the increase in oxygen-transfer rate acetic acid concentration increased; contrarily, with the decrease in the oxygen-transfer rate the TCA-cycle organic acids alpha-ketoglutaric and succinic acids, and gluconic acid were excreted to the fermentation broth; nevertheless, the application of the oxygen-transfer strategy prevented the increase in acetic acid concentration between t = 35-38 h. Under all the oxygen-transfer conditions, the amino acid having the highest concentration and the amino acid that was not excreted to the fermentation broth were lysine and asparagine, respectively; both of which belong to the aspartic acid-group amino acids. Further, this result indicates the requirement of the genetic regulation directed to the aspartic acid-group enzymes for the progress in SAP production in B. licheniformis.     

Simultaneous solid–liquid separation and primary purification of clavulanic acid from fermentation broth of Streptomyces clavuligerus using salting‐out extraction system

Clavulanic acid (CA) is usually used together with other β‐lactam antibiotics as combination drugs to inhibit bacterial β‐lactamases, which is mainly produced from the fermentation of microorganism such as Streptomyces clavuligerus. Recently, it is still a challenge for downstream processing of low concentration and unstable CA from fermentation broth with high solid content, high viscosity, and small cell size. In this study, an integrated process was developed for simultaneous solid–liquid separation and primary purification of CA from real fermentation broth of S. clavuligerus using salting‐out extraction system (SOES). First, different SOESs were investigated, and a suitable SOES composed of ethanol/phosphate was chosen and further optimized using the pretreated fermentation broth. Then, the optimal system composed of 20% ethanol/15% K₂HPO₄ and 10% KH₂PO₄ w/w was used to direct separation of CA from untreated fermentation broth. The result showed that the partition coefficient (K) and recovery yield (Y) of CA from untreated fermentation broth were 29.13 and 96.8%, respectively. Simultaneously, the removal rates of the cells and proteins were 99.8% and 63.3%, respectively. Compared with the traditional method of membrane filtration or liquid–liquid extraction system, this developed SOES showed the advantages of simple operation, shorter operation time, lower process cost and higher recovery yield of CA. These results demonstrated that the developed SOES could be used as an attractive alternative for the downstream processing of CA from real fermentation broth.     

盐析萃取生物基化学品的研究进展

廉价生物质的生物炼制研究主要集中在菌种和发酵方面,对下游分离研究较少。廉价生物质资源的利用导致发酵液中引入更多杂质,成分较单糖发酵更复杂,致使生物基化学品的下游分离过程成为其工业化生产亟需解决的关键问题。文中介绍了一种基于两相分配差异分离亲水性生物基化学品的盐析萃取技术及其在生物基化学品分离方面的应用,重点阐述了短链醇和盐对双水相形成的影响,并对1,3-丙二醇、2,3-丁二醇、乙偶姻、乳酸等的盐析萃取研究进展进行了总结和展望。盐析萃取技术可有效地回收发酵液中的小分子亲水性产品,同时除去大多数的杂质 (细胞和蛋白质等),在生物基化学品的分离过程中将是一种有前景的分离技术。     

Reactive extraction of penicillin G from mycel-containing broth in a countercurrent extraction decanter

Penicillin was recovered from mycel-containing fermentation broth by direct reactive extraction into a counter-current extraction decanter, Type CA 226-290 of the Westfalia Separator Co., at room temperature via steady state operation. Penicillin concentrations in the feed varied from 3 to 41 g L(-1), Amberlite LA-2 carrier concentrations from 7 to 20 g L(-1)and/or DITDA carrier concentrations from 7.2 to 84 g L(-1), the LA-2-to-penicillin mole concentration ratio from 4 to 6.4, and/or the DITDA-to-penicillin mole concentration ratio was maintained at 2. The throughputs of the fermentation broth (520 to 880 L h(-1)) of the solvent phase (200 to 860 L h(-1)) and the over all throughput (800 to 1750 L h(-1)) were high. Extraction degrees of 72 to 96% were achieved between pH 4.6 and 5.1. Without carriers in the same pH range, extraction degrees of only 17 to 19% were attained. By reducing the pH to 2.3 and in the absence of carriers, the degree of extraction was increased to 61%. However, during the extraction, 6.5% of the penicillin decomposed. At these high throughputs, the steady state was attained within 1 to 4 min. Through the mechanical stress, the length of the hyphae was reduced and the protein content of the broth was increased by 50 to 100%. However, this protein content had no appreciable influence on the phase separation.     

A new integrated membrane filtration and chromatographic device

To improve protein separation, a novel integrated device combining membrane filtration and chromatography has been developed. The device basically consists of a hollow fiber filtration module whose shell side is filled with chromatographic resin beads. However, there is an essentially impermeable coated zone near the hollow fiber module outlet. The integrated device enjoys the advantages of both membrane filtration and chromatography; it also allows one to load the chromatographic media directly from the fermentation broth or lysate and separate the adsorbed proteins through the subsequent elution step in a cyclic process. Interfacial polymerization was carried out to coat the bottom section of the hollow fiber membrane; the rest of the hollow fiber membrane remained unaffected. Myoglobin (Mb) and alpha-lactalbumin (alpha-LA) were primarily used as model proteins in a binary mixture; binary mixtures of Mb and bovine serum albumin (BSA) were also investigated. Separation behaviors of binary protein mixtures were studied in devices having either an ultrafiltration (UF) or a microfiltration (MF) membrane. Experimental results show that the breakthrough time and the protein loading capacities were dramatically improved after introducing the impermeable coating in both UF and MF modules. For a synthetic yeast fermentation broth feed, four loading-washing-elution-reequilibration-based cyclic runs for separation of Mb and alpha-LA were performed in the device using a MF membrane with a coated zone without cleaning in between. The Mb and alpha-LA elution profiles for the four consecutive runs were almost superimposable. Due to lower transmembrane flux in this device plus the periodical washing-elution during the chromatographic separation, fouling was not a problem, unlike in conventional microfiltration.     

Nucleation and growth of microbial lipase crystals from clarified concentrated fermentation broths

Bulk crystallization is emerging as a new industrial operation for protein recovery. Characterization of bulk protein crystallization is more complex than protein crystallization for structural study where single crystals are grown in flow cells. This is because both nucleation and crystal growth processes are taking place while the supersaturation falls. An algorithm is presented to characterize crystallization using the rates of the two kinetic processes, nucleation and growth. The values of these rates allow ready comparison of the crystallization process under different operating conditions. The crystallization, via adjustment to the isoelectric pH of a fungal lipase from clarified fermentation broth, is described for a batch stirred reactor. A maximum nucleation rate of five to six crystals formed per microliter of suspension per second and a high power dependency ( approximately 11) on the degree of supersaturation were found. The suspended protein crystals were found to grow at a rate of up to 15-20 nm/s and also to exhibit a high power dependency ( approximately 6) of growth rate on the degree of supersaturation.     

Downstream separation and purification of bio-based alpha-ketoglutaric acid from post-fermentation broth using a multi-stage membrane process

In this study, a multi-stage membrane process, assisted by vacuum evaporation and crystallization, for recovery of bio-based alpha-ketoglutaric acid from the actual post-fermentation broth was designed and investigated. In the first part of this study, pre-treatment of crude fermentation broth (centrifugation-ultrafiltration-nanofiltration) was carried out to remove biomass, proteins, sugars, part of inorganic ions and color compounds. The commercial ceramic UF membrane (15 kDa) and nanofiltration ceramic membrane (200 Da or 450 Da) were applied. Electrodialysis with a bipolar membrane was proposed for separation of ionic compounds and simultaneous electro-acidification to the acid form. During bipolar membrane electrodialysis carried out under acidic conditions, it was possible to remove close to 90 % of alpha-ketoglutaric acid. Moreover, the migration of other acids present in the fermentation broth (lactic and acetic) was significantly limited. The calculated specific energy consumption was low and equal to 0.6 kW h/kg. The final purification using crystallization assisted vacuum evaporation allowed obtaining alpha-ketoglutaric acid in solid form. Analysis of the final product showed that the proposed method of alpha-ketoglutaric acid recovery gives the acid of high purity equal to 94.8 %. Furthermore, the presented results have practical relevance and may in future be the basis for the development of separation technologies of alpha-ketoglutaric acid from the fermentation broth on industrial scale.     

Fermentation and recovery of glutamic acid from palm waste hydrolysate by Ion-exchange resin column

Glutamic acid produced from palm waste hydrolysate by fermentation with Brevibacterium lactofermentum ATCC 13869 is produced with a remarkably high yield compared with that produced from pure glucose as a carbon source. The produce yield is 70 g/L with glucose, wherease, when palm waste hydrolysate is the fermentation medium in the same bioreactor under same conditions, it is 88 g/L. The higher yield may be attributed to the fact that this organism has the ability to convert sugars other than only glucose present in the hydrolysate. Bioreactor conditions most conducive for maximum production are pH 7.5, temperature of 30 degrees rmentation period of 48 h, inoculum size 6%, substrate concentration of 10 g per 100 mL, yeast extract 0.5 g per 100 mL as a suitable N source, and biotin at a concentration of 10 pg/L. Palm waste hydrolysate used in this study was prepared by enzymic saccharification of treated palm press fiber under conditions that yielded a maximum of 30 g/L total reducing sugars. Glutamic acid from fermentation broth was recovered by using a chromatographic column (5cm x 60 cm) packed with a strong ion-exchange resin. The filtered broth containing glutamic acid and other inorganic ions was fed to the fully charged column. The broth was continuously recycled at a flow rate of 50 mL/min (retention time of 55 min) until glutamic acid was fully adsorbed on the column leaving other ions in the effluent. Recovery was done by eluting with urea and sodium hydroxide for total displacement of glutamic acid from the resin. The eluent containing 88 g/L of glutamic acid was concentrated by evaporation to obtain solid crystals of the product. (c) 1995 John Wiley & Sons, Inc.     

Chromatography of hen egg-white proteins on anion-exchange cellulose at high flow rates using a radial flow column.

The influence of column configuration on the separation of hen egg-white proteins using Whatman DE52 and QA52 anion-exchange cellulose has been investigated. Using a 100 ml volume axial flow column (6.6 cm x 4.4 cm i.d.) we achieved flow rates of up to 25 ml/min i.e. 15 bed volumes/h after which higher flow was restricted due to pressure constraints within the system. Under radial flow conditions using a 100 ml column flow rates of up to 150 ml/min i.e. 90 bed volumes/h were achieved using DE52 and QA52. While chromatographic resolution was superior under axial flow at the lower flow rates excellent resolution was maintained at up to 150 ml/min using the radial flow column. This is a consequence of the fast kinetics of adsorption/desorption exhibited by DE52 and QA52. The data indicate that it is the column configuration and not the cellulose matrix which influences flow performance.     

Protein separations using colloidal magnetic nanoparticles

Phospholipid-coated colloidal magnetic nanoparticles with mean magnetite core size of 8 nm are shown to be effective ion exchange media for the recovery and separation of proteins from protein mixtures. These particles have high adsorptive capacities (up to 1200 mg protein/mL adsorbent, an order of magnitude larger than the best commercially available adsorbents) and exhibit none of the diffusional resistances offered by conventional porous ion exchange media. Protein-laden particles are readily recovered from the feed solution using high-gradient magnetic filtration.     

微生物发酵-膜分离法制备褐藻胶寡糖及其产物分析

比较褐藻胶裂解酶产生菌Alteromonassp .在摇瓶和发酵罐培养过程中生物量、褐藻胶寡糖含量以及褐藻胶裂解酶活性的变化 ,根据其变化确立了通过微生物发酵 膜分离技术结合制备褐藻胶寡糖的条件 ,并对寡糖进行凝胶过滤色谱和薄层色谱分析。用组成为每升含酵母粉 5g、蛋白胨 10g、FeSO4 0 1g、褐藻酸钠 12g、NaCl 1 5g ,pH为7 5的培养基 ,在 2 8℃培养褐藻胶裂解酶产生菌 ,结果表明 ,发酵罐培养 30h ,发酵液寡糖含量达到最大。发酵液通过超滤 纳滤两级膜分离 ,得到褐藻胶寡糖 ,寡糖的回收率和脱盐率分别为 94 0 %和 93 3%。通过凝胶柱分离和TLC分析 ,得到 5个褐藻胶寡糖组分。     

Recovery of penicillin by reactive extraction in centrifugal extractors

Penicillin V and/or G were extracted from fermentation broth by Amberlite LA-2 in n-butylacetate at pH 5 in a laboratory centrifugal extractor, Type SA 01 of Westfalia, up to an overall phase throughput rate of 30 L/h, in a bench-scale four-stage extraction system, consisting of Type TA 1 of Westfalia, up to an overall phase throughput rate of 110 L/h, and in a pilot-plant three-stage extraction unit, consisting of Type TA 7 extractors of Westfalia, up to a phase throughput rate of 990 L/h with very high degrees of extraction (up to 99%). The reextraction from the ion-pair complex, which contained organic solvent, was performed by phosphate, borate, or carbonate buffer at pH 7.5-8.5 in all three extractor systems with degrees of extraction up to 98%, but at considerably lower overall phase throughput rates than those of the extraction, since no satisfactory phase separation is possible at higher throughput rates.     

Application of continuous zone electrophoresis to preparative separation of proteins

A comprehensive study of the application of continuous zone electrophoresis to preparative separation of proteins in free solution is presented. First, the influence of electric field strength, buffer residence time in the chamber, sample flow rate, and sample concentration on separation resolution and throughput were studied. Using multiple injections of sample into the electrophoresis chamber, a throughput of 500 mg protein/h was achieved for partially purified model proteins. Experiments on Escherichia coli crude extracts yielded a fivefold purification of beta-galactosidase along with a simultaneous separation of proteins from cell debris in a single step. Experiments correlating the electrophoretic mobility in continuous electrophoresis with the elution behavior in ion-exchange chromatography were performed on more than a dozen proteins which conclusively showed that separation of proteins in continuous zone electrophoresis is governed by net surface charge. Based on these results, the fraction numbers in which the proteins eluted could be correctly predicted. Proteins and enzymes with differences >0.5 M elution molarities in ion-exchange chromatography were separated by continuous zone electrophoresis on a preparative scale (mg/h or g/h) with >90% recovery. This corresponds to a preparative scale separation of proteins and enzymes which differ in apparent electrophoretic mobility by only 0.70 x 10(-5) cm(2)/V . s. (c) 1993 John Wiley & Sons, Inc.     

Hydrogen production with immobilized sewage sludge in three-phase fluidized-bed bioreactors

Municipal sewage sludge was immobilized with a modified alginate gel entrapment method, and the immobilized cells were used to produce hydrogen gas in a three-phase fluidized bed. The hydrogen-producing fluidized beds were operated at different liquid velocity (U(0)) and hydraulic retention time (HRT). The results show that in response to operating liquid velocities, the fluidized-bed system had three flow regimes, namely, plug flow, slug flow, and free bubbling. Pressure fluctuation analysis was used to analyze the hydrodynamic properties in this three-phase fluidized bed when it was under a steady-state production of biogas. With a steady-state biogas production rate (U(g)) of 0.196 mL/s/L, a transition state occurred at a liquid velocity (U(0)) of 0.85 cm/s. As U(0) < 0.85 cm/s, the system was basically a nonhomogeneous fluidized bed, whereas the bed became homogeneous when U(0) was higher than 0.85 cm/s. The fluidized bed can be stably carried out at high loading rates (HRT as low as 2 h). Hydrogen fermentation results show that the maximal hydrogen production rate was 0.93 L/h/L and the best yield (Y(H)2(/sucrose)) was 2.67 mol H(2)/mol sucrose.     

Studies on the interaction of fermentation and microfiltration operations: erythromycin recovery from Saccharopolyspora erythraea fermentation broths

Changes in fermentation media not only affect the performance of the fermentation itself (with regard to the kinetics of biomass and product formation and the yields obtained) but also the initial product-recovery operations downstream of the fermentor. In this work, microfiltration experiments to remove Saccharopolyspora erythraea biomass from fermentation broth and to recover erythromycin were carried out using two fundamentally different media; a soluble complex medium (SCM) and an oil-based process medium (OBM). Small-scale batch fermentations of 14-L working volume were carried out in triplicate using both media. Broth samples were taken from each fermentation at regular intervals from the end of the exponential-growth phase onwards. These were then processed using a Minitan II (acrylic), tangential crossflow-filtration module, fitted with a single 60 cm(2) Durapore hydrophilic 0.2 microm membrane, operated in concentration mode. The OBM fermentations produced higher titers of erythromycin but required longer fermentation times due to increased lag phases and slower maximum-growth rates. The OBM also increased the loading on the membrane; at maximum product titers residual oil concentrations of 3 g. L(-1), antifoam concentrations of 2 g. L(-1) and flour concentrations estimated at approximately 10 g/L(-1) were typical. It was found that both the permeate flux and erythromycin transmission were affected by the choice of medium. The OBM had significantly lower values for both parameters (12.8 Lm(-2) h(-1) and 89.6% respectively) than the SCM (35.9 Lm(-2) h(-1) and 96.7% respectively) when the fermentations were harvested at maximum erythromycin titers. Transmission of erythromycin stayed approximately constant as a function of fermentation time for both media, however, for the OBM the permeate flux decreased with time which correlated with an increase in broth viscosity. The relatively poor microfiltration performance of the OBM medium was, however, offset by the higher titers of erythromycin that were achieved during the fermentation. The filtration characteristics of the SCM broth did not show any correlation with either broth viscosity or fermentation time. Image-analysis data suggested that there was a correlation between hyphal morphology (main hyphal length) and permeate flux (no such correlation was found for the OBM broth). Moreover, it has been shown for the OBM broth that the residual flour had a profound effect on the microfiltration characteristics. The influence of the residual flour was greater than that imposed by the morphology and concentration of the biomass. The understanding of the factors governing the interaction of the fermentation and microfiltration operations obtained in this work provides a first step towards optimization of the overall process sequence.     

A novel cell modification method used in biotransformation of glycerol to 3-HPA by Lactobacillus reuteri

The aim of the present study was to develop a new cell modification method to facilitate the cell separation from broth. In order to reduce the transfer limitation of substrate and product caused by general immobilization methods in the following biotransformation of glycerol, the carboxyl-functioned superparamagnetic nanoparticle (MNP) was directly attached to the surface of Lactobacillus reuteri for 3-hydroxypropionealdehyde producing. The modification process could be finished in several minutes by just adding MNP fluid into the bulk fermentation broth. The modified cells could be rapidly separated from the solution with the aid of magnetic field. The interaction between cell and MNP was shown by electron microscopy. The efficiency of the cells attached by MNPs for transformation of various concentrations of glycerol (100–400 mM) was studied at various temperatures (25–40 °C) and pH levels (5.8–7.5) with different cell concentrations (7.5–30 g/L). The 3- hydroxypropionealdehyde (HPA)/glycerol molar conversion under optimal condition (30 °C and pH 7) reached 70 %. The inactive modified cell could be reactivated easily by fresh medium and recovered the ability of glycerol conversion. MNPS distributing on cell surface had little adverse effect on cell activity. The modification method simplified the two-step production of 3-HPA by resting L. reuteri. The method of MNPs attached to cell surface is totally different from the traditional immobilization method in which the cell is attached to or entrapped in big carrier. The results obtained in this study showed that carboxyl-functioned MNP could be directly used as cell modification particle and realized cell recycle with the aid of magnetic field in bioprocess.     

Separation of bio‐based chemicals from fermentation broths by salting‐out extraction

The possibility of creating a biorefinery using inexpensive biomass has attracted a great deal of attention, which is mainly focused on the improvement of strains and fermentation, whereas few resources have been spent on downstream processing. Bio‐based chemical downstream processing can become a bottleneck in industrial production because so many impurities are introduced into the fermentation broth. This review introduces a technique referred to as salting‐out extraction, which is based on the partition difference between chemicals in two phases consisting of salts and polymers or hydrophilic solvents, hydrophobic solvents, and amphipathic chemicals. The effects of solvents and salts on the formation of two phases were discussed, as was the use of this method to recover bio‐based chemicals. This review focused on the separation of hydrophilic chemicals (1,3‐propanediol, 2,3‐butanediol, acetoin, and lactic acid) from fermentation broths. Diols could be recovered at a high yield from fermentation broths without pretreatment especially with a hydrophilic solvent‐based system, whereas the recovery of organic acids was slightly lower. Most of the impurities (cells and proteins) were removed during the same step. Extractive fermentations were also used for polymer‐based aqueous two‐phase systems.