Strategies of pH control and glucose‐fed batch fermentation for production of succinic acid by Actinobacillus succinogenes CGMCC1593

BACKGROUND: Succinic acid is an important precursor of numerous products, including pharmaceuticals, feed additives, green solvents, and biodegradable polymers. In this work, strategies of pH control and glucose‐fed batch fermentation for producing succinic acid using Actinobacillus succinogenes CGMCC1593 were carefully optimized. RESULTS: The production of succinic acid was stable within the pH range 6.0–7.2. Both cell growth and succinic acid production were inhibited by high concentrations of sodium and calcium ions, while there was no significant inhibition by magnesium ions. With an initial glucose concentration of 25 g L^?1, and glucose concentration was maintained between 10 and 15 g L^?1 during the course of fed batch fermentation, succinic acid concentration, productivity and yield were 60.2 g L^?1, 1.3 g L^?1 h^?1 and 75.1%, respectively. CONCLUSION: Of all the neutralization reagents used for pH control of A. succinogenes CGMCC1593, solid MgCO₃ was the most satisfactory. With increase of initial glucose concentration, the time course showed a longer growth lag period and the maximum biomass declined, while more carbon was diverted to succinate synthesis. The results obtained in this study should be helpful for the design of a highly efficient succinic acid production process. Copyright © 2008 Society of Chemical Industry     

Fermentative production of L(+)‐lactic acid from starch hydrolyzate and corn steep liquor as inexpensive nutrients by batch culture of Enterococcus faecalis RKY1

BACKGROUND: Attempts were made to determine the lactic acid production efficiency of novel isolate, Enterococcus faecalis RKY1 using four different starches (corn, tapioca, potato, and wheat starch) with different concentrations (50, 75, 100, and 125 g L^?1) and corn steep liquor as an inexpensive nitrogen source. RESULTS: The yield of lactic acid from each starch was higher than 95% based on initial starch concentrations. High lactic acid concentration (129.9 g L^?1) and yield (1.04 g‐lactic acid g^?1‐starch) were achieved faster (84 h) from 125 g L^?1 of corn starch. Among the starches used, tapioca starch fermentation usually completed in a shorter incubation period. The final dry cell weight was highest (7.0 g L^?1) for the medium containing 75 g L^?1 of corn starch, which resulted in maximum volumetric productivity of lactic acid (3.6 g L^?1 h^?1). The addition of 30 g L^?1 corn steep liquor supplemented with a minimal amount of yeast extract supported both cell growth and lactic acid fermentation. CONCLUSION: Enterococcus faecalis RKY1 was found to be capable of growing well on inexpensive nutrients and producing maximum lactic acid from starches and corn steep liquor as lower‐cost raw materials than conventionally‐used refined sugars such as glucose, and yeast extract as an organic nitrogen source in laboratory‐scale studies. These fermentation characteristics are prerequisites for the industrial scale production of lactic acid. Copyright © 2008 Society of Chemical Industry     

Efficient acetoin production by optimization of medium components and oxygen supply control using a newly isolated Paenibacillus polymyxa CS107

BACKGROUND: Acetoin is a natural flavor commonly used in wine, buffer, honey, garnet berry and strawberry as a food additive. It also has been widely applied in cosmetics, pharmacy and chemical synthesis. Culture medium optimization and process control were carried out for efficient production of acetoin by a newly isoliated P. polymyxa CS107. RESULTS: An acetoin high producing strain, designated as CS107, was newly isolated and identified as P. polymyxa based on its physiological and biochemical characteristics as well as the 16S rDNA sequence. The medium composition was optimized in shake flask fermentations by a sequential statistical experimental design. Under the optimized conditions, acetoin concentration of 30.98 g L^?1 was achieved with 71.83% of theoretical glucose conversion efficiency. Fed‐batch fermentation based on a suitable agitation speed was carried out in a 5 L jar, the maximum acetoin concentration of 55.3 g L^?1 was obtained with the productivity of 1.32 g L^?1 h^?1 and the yield of 75.62%. CONCLUSION: A new strain for efficient production of acetoin, designated as P. polymyxa CS107, was obtained. The optimization of fermentation variables and fed‐batch culture resulted in a maximum acetoin concentration of 55.3 g L^?1 in 5 L jar. Copyright © 2012 Society of Chemical Industry     

Simultaneous saccharification and fermentation of sludge‐containing cassava mash for batch and repeated batch production of bioethanol by Saccharomyces cerevisiae CHFY0321

BACKGROUND: The aim of this study was to examine the repeated batch production of bioethanol from sludge‐containing cassava mash as starchy substrate by flocculating yeast to improve volumetric bioethanol productivity and to simplify the process of a pre‐culture system. RESULTS: For the repeated batch production of bioethanol using cassava mash, the optimal recycling volume ratio was found to be 5%. The repeated batch fermentation was completed within 36 h, while the batch fermentation was completed after 42 h. Volumetric productivity, final ethanol concentration, and ethanol yield were attained to 2.15 g L^?1 h^?1, 83.64 g L^?1, and 85.15%, respectively. Although cell accumulation in the repeated batch process is difficult due to the cassava mash, the repeated batch process using Saccharomyces cerevisiae CHFY0321 could exhibited 10‐fold higher initial viable cell number (1.7 × 10⁷ CFU mL^?1) than that of the batch process. CONCLUSION: The liquefied cassava powder was directly used for the repeated batch process without removal of sludge. Repeated batch bioethanol production by simultaneous saccharification and fermentation using self‐flocculating yeast could reduce process costs and accelerate commercial applications. This result was probably due in part to the effect of the initial viable cell density. Copyright © 2008 Society of Chemical Industry     

Production of L‐lactic acid with very high gravity distillery wastewater from ethanol fermentation by a newly isolated Enterococcus hawaiiensis

BACKGROUND: A great amount of wastewater with high contents of chemical oxygen demand (COD) are produced by ethanol production. It would be useful to utilize distillery wastewater to produce L‐lactic acid, which could be a high additional value byproduct of ethanol production. The fermentation process of L‐lactic acid production by a newly isolated Enterococcus hawaiiensis CICIM‐CU B0114 is reported for the first time. RESULTS: The strain produced 56 g L^?1 of L‐lactic acid after cultivation for 48 h in optimized medium consisting of (g L^?1) 80 glucose, 10 peptone, 10 yeast extract, 1.5 Na₂HPO₄ and 0.2 MgSO₄. E. hawaiiensis CICIM‐CU B0114 was isolated and purified by subculture for growing and producing L‐lactic acid in distillery wastewater of very high gravity (VHG) from ethanol fermentation. L‐lactic acid fermentation was further studied with distillery wastewater substrate in 7 L and 15 L fermentors. The results showed that L‐lactic acid concentrations of 52 g L^?1 and 68 g L^?1 was achieved in 7 L and 15 L fermentors with the initial sugar concentrations of 67 g L^?1 and 87 g L^?1, respectively. CONCLUSION: The production of L‐lactic acid by the newly isolated E. hawaiiensis CICIM‐CU B0114 was carried out and the fermentation medium was optimized by orthogonal experimental design. This new strain holds the promise of L‐lactic acid production utilizing distillery wastewater from VHG ethanol fermentation. Copyright © 2010 Society of Chemical Industry     

Production of bioethanol by immobilized Saccharomyces Cerevisiae onto modified sodium alginate gel

BACKGROUND: Microbial bioethanol production is an important option in view of the finite global oil reserves. Bioethanol fermentation was carried out using immobilized microorganisms (Saccharomyces cerevisiae, Zymomonas mobilis, Pichia stipitis, etc.), which has many advantages compared with the use of free cells. Various support materials have been used for bioethanol fermentation, and alginate gels have been one of the most widely used matrices for cell entrapment. The aim of this study was increased bioethanol production by Saccharomyces cerevisiae immobilized on alginate gels. First, N‐vinyl‐2‐pyrrolidone was grafted onto sodium alginate. Then, the properties of ethanol production were investigated using the matrix obtained. RESULTS: The performance of ethanol fermentation was affected by calcium chloride concentration, N‐vinyl‐2‐pyrrolidone grafted onto the sodium alginate, sugar concentration and the percentage of immobilized cell beads. These effects were optimized to give maximum ethanol production. Ethanol production was accelerated when sodium alginate polymer was modified with N‐vinyl‐2‐pyrrolidone. The maximum concentration, productivity and yield of ethanol were 69.68 g L^?1, 8.71 g L^?1 h^?1 and 0.697 g g^?1, respectively. CONCLUSION: The new polymeric matrix, when compared with sodium alginate, showed better ethanol production due to the hydrophilic property of N‐vinyl‐2‐pyrrolidone. The results suggest that the proposed method for immobilization of Saccharomyces cerevisiae has potential in industrial applications of the ethanol production process. Copyright © 2011 Society of Chemical Industry     

Nisin expression production from Lactococcus lactis in milk whey medium

BACKGROUND: Nisin is a commercially available bacteriocin produced by Lactococcus lactis ATCC 11454 and used as a natural agent in the biopreservation of food. In the current investigation, milk whey, a byproduct from dairy industries was used as a fermentation substrate for the production of nisin. Lactococcus lactis ATCC 11454 was developed in a rotary shaker (30 °C/36 h/100 rpm) using two different media with milk whey (i) without filtration, pH 6.8, adjusted with NaOH 2 mol L^?1 and without pH adjustment, both autoclaved at 121 °C for 30 min, and (ii) filtrated (1.20 µm and 0.22 µm membrane filter). These cultures were transferred five times using 5 mL aliquots of broth culture for every new volume of the respective media. RESULTS: The results showed that culture media composed of milk whey without filtration supplied L. lactis its adaptation needs better than filtrated milk whey. Nisin titers, in milk whey without filtration (pH adjusted), was 11120.13 mg L^?1 in the second transfer, and up to 1628‐fold higher than the filtrated milk whey, 6.83 mg.L^?1 obtained in the first^t transfer. CONCLUSIONS: Biological processing of milk byproducts (milk whey) can be considered a profitable alternative, generating high‐value bioproducts and contributing to decreasing river disposals by dairy industries. Copyright © 2008 Society of Chemical Industry     

Statistical optimization of fermentation conditions for the improved production of poly-β-hydroxybutyrate from Bacillus subtilis

Poly-β-hydroxybutyrate (PHB) has been an effective biodegradable plastic obtained by microbial fermentation. Batch fermentation of Bacillus subtilis features an attractive system for the production of PHB. Identification of appropriate media components and cultivation conditions are extremely important for the optimal production of biomass and/or PHB production. Statistical media design was utilized for the optimization of different fermentation variables (glucose, peptone, sodium chloride, K₂HPO₄, KH₂PO₄, ammonium sulfate, ammonium chloride, sodium sulfate, temperature, inoculum size, and pH). The optimized media predicted the optimal dry cell weight of 7.54?g?L^?1 and PHB production of 77.2?mg?L^?1 at 1?g?L^?1 of peptone, 1.46?g?L^?1 sodium sulfate, and pH 6.8 in 24?h. Glucose utilization, batch growth, and PHB production kinetics of B. subtilis were determined experimentally. The effect of substrate inhibition on specific growth rate was also determined experimentally for B. subtilis. The values of kinetic and substrate inhibition parameters obtained from this study shall be utilized to develop a mathematical model for PHB production for further improving the production of PHB.     

Strain isolation and optimization of process parameters for bioconversion of glycerol to lactic acid

BACKGROUND: The crude glycerol from biodiesel production represents an abundant and inexpensive source which can be used as raw material for lactic acid production. The first aim of this investigation was to select a strain suitable for producing lactic acid from glycerol with a high concentration and productivity. The second aim was to obtain the optimum fermentation conditions, as a basis for large‐scale lactate production in the future. RESULTS: Eight bacterial strains, which could aerobically convert glycerol to lactic acid, were screened from soil samples. One of the strains, AC‐521, which synthesized lactic acid with a higher concentration, was identified based on its 16S rDNA sequences and physiological characteristics. These results indicated that this strain was a member of Escherichia coli. The optimal fermentation conditions for Escherichia coli AC‐521 were 42 °C, pH 6.5, 0.85 min^?1 (K_La). CONCLUSION: Escherichia coli AC‐521 suitable for producing lactic acid from glycerol with high concentration and productivity was identified. After 88 h of fed‐batch fermentation, both the lactic acid concentration and glycerol consumption reached maximum, giving 85.8 g L^?1 of lactic acid with a productivity of 0.97 g L^?1 h^?1 and a yield of 0.9 mol mol^?1 glycerol. Copyright © 2009 Society of Chemical Industry     

Ammonium fumarate production by free or immobilised Rhizopus arrhizus in bench‐ and laboratory‐scale bioreactors

Ammonium fumarate production from glucose‐based media by Rhizopus arrhizus NRRL 1526 with mycelial growth controlled by phosphorus limitation exhibited mixed‐growth‐associated product formation kinetics, with growth‐associated production related to secondary mycelial growth only. The contribution of the primary mycelial growth phase was minimised by resorting to prolonged batch production using free mycelia under intermittent glucose feeding or repeated batch production using immobilised mycelia. The metabolic activity of free or immobilised mycelia was limited by fumarate accumulation or by oxygen diffusion phenomena, respectively. For batch cultures in a 15 dm³ stirred bioreactor the peripheral impeller speed (v_I) was increased from 1.88 to 3.3 m s^?1, and the fumarate yield coefficient on glucose increased from 0.25 ± 0.01 to 0.42 ± 0.02 g g^?1, while the malate yield coefficient on fumarate (Y_M/F) reduced from 0.46 ± 0.01 to 0.14 ± 0.01 g g^?1. With a net increase in the fumarate‐to‐malate ratio from 2 to 6.5, a v_I value of 3.3 m s^?1 gave the best fermentation performance and provided a basis for further scale‐up studies. © 2002 Society of Chemical Industry     

Optimization of the culture conditions for production of glutamate decarboxylase by Streptococcus salivarius ssp. thermophilus

The culture conditions for glutamate decarboxylase (GAD) production under submerged fermentation by Streptococcus salivarius ssp. thermophilus were investigated. The results indicated the optimum culture medium was composed as follows: 15.0 g L^?1 of peptone, 12.5 g L^?1 of beef extract, 12.5 g L^?1 of sucrose, 1.03 g L^?1 of dipotassium hydrogen phosphate, 5 g L^?1 of sodium acetate, 2 g L^?1 of ammonium dibasic citrate, 2.12 g L^?1 of calcium chloride, 1 g L^?1 of Tween 80, and initial pH 6.79. The optimum culture temperature and time were 37 °C and 12 h, respectively. Under these conditions, GAD production was 257.46 ± 5.12 U, which was about 1.45‐fold that of Man–Rogosa–Sharpe broth. Copyright © 2008 Society of Chemical Industry     

Xylitol production by Candida tropicalis from corn cob hemicellulose hydrolysate in a two‐stage fed‐batch fermentation process

BACKGROUND: Xylitol, a sugar alcohol widely used in food and pharmaceutical industries, can be produced through biological reduction of xylose present in hemicellulose hydrolysates by Candida tropicalis. However, the aeration rate and by‐products originating from hemicellulose hydrolysis strongly inhibit the production of xylitol in a fermentation process. A two‐stage fed‐batch fermentation system was developed to reduce these inhibitory effects and to improve xylitol production from corn cob hemicellulose hydrolysates by C. tropicalis. RESULTS: Results of batch fermentations indicated that high xylitol production could be obtained from C. tropicalis at an initial xylose concentration of 80 g L^?1 in corn cob hydrolysate medium at an aeration rate of 0.4 vvm at the micro‐aeration stage. In the two‐stage fed‐batch fermentation process, 96.5 g L^?1 xylitol was obtained after 120 h, giving a yield of 0.83 g g^?1 and a productivity of 1.01 g L^?1 h^?1, which were 12.16% and 65.57% higher than those in a batch fermentation. CONCLUSION: High xylitol production can be achieved in a two‐stage fed‐batch fermentation process, in which the negative effects of aeration rate and inhibitory compounds on xylitol formation can be considerably reduced. Copyright © 2011 Society of Chemical Industry     

Bioconversion of residual soybean oil into polyhydroxyalkanoates

The aim of this study is to evaluate the bioconversion of residual soybean oil (RSO) into polyhydroxyalkanoates (PHAs) by selecting microorganism and fermentation condition in order to increase PHAs production. PHAs production by Cupriavidus necator IPT 026 using glucose (PHA 1) and RSO (PHA 2) as substrate is 1.15 ± 0.21 and 2.84 ± 0.04 g L^?1, respectively. FTIR spectra of PHAs were similar to data reported in literature. PHAs presented low crystallinity (PHA 1: 42.69%; PHA 2: 46.44%), high thermal stability (PHA 1: 271.78 °C; PHA 2: 272.52 °C), and low M_W (PHA 1: 140.69 kDa; PHA 2: 254.54 kDa). PHAs produced by RSO are potential candidates for industrial applications, especially ones that demand higher temperatures. This is the first study on the production and characterization of PHAs obtained by C. necator IPT 026 in culture with RSO. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46255.     

Modulated gluconic acid production from immobilized cells of Aspergillus niger ORS‐4.410 utilizing grape must

BACKGROUND: Gluconic acid (GA) production by immobilized cells of mutant Aspergillus niger ORS‐4.410 on polyurethane sponge (PUS) and calcium‐alginate (Ca‐alginate) was evaluated in repeated batches of solid state surface fermentation (SSF) and submerged fermentation (SmF) conditions, respectively, utilizing rectified grape must as carbon source. RESULTS: The passive immobilization of cells in fermentation medium solid support of having 0.4 cm³ cube size, 4% spore suspension, 0.6 g inoculum of PUS immobilized cells at 32 °C and 2.0 L min^?1 resulted in the maximum GA production (88.16 g L^?1) with a 92.8% yield, while the Ca‐alginate matrix with a 0.5 cm diameter bead size, 2–3% spore suspension, 15 g inoculum at 34 °C and 150 rpm agitation speed revealed 67.19 g L^?1 GA with a 85.2% yield. Repeated use of PUS showed higher levels of GA (110.94 g L^?1) in the third–fourth fermentation cycles with 95–98% yield and 22.50 g L^?1 d^?1 productivity under SSF that was 2.5‐fold higher than the productivity obtained from a typical fermentation cycle, and 54% greater than the productivity obtained with repetitive use of Ca‐alginate immobilized cells of A. niger under SmF. CONCLUSION: Using immobilized cells of A. niger in PUS, the rectified form of grape must can be utilized for GA production as an alternative source of carbohydrate by replacing the conventional fermentation conditions. Copyright © 2008 Society of Chemical Industry     

The effects of dilution rate and glucose concentration on continuous acetone–butanol–ethanol fermentation by Clostridium acetobutylicum immobilized on bricks

BACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of butanol through biological routes has attracted increasing attention. However, low butanol productivity severely impedes its potential industrial production. It is known that the immobilization of whole cells can enhance productivity in the acetone‐butanol‐ethanol (ABE) continuous fermentation process. Therefore, the objective of this study was to develop a low‐cost continuous operation for butanol production. RESULTS: Bricks were chosen as cell support because of their low cost and ease of use for immobilization. The solvent productivity for the bricks with immobilized cells was 0.7 g L^?1 h^?1, 1.89 times that of free cells (0.37 g L^?1 h^?1) at a dilution rate of 0.054 h^?1. The productivity improvement can contribute to greater retention of biomass inside the reactor due to immobilization. The increase in glucose feed concentration raised total solvent production. However, it resulted in a decrease in yield (grams of solvents produced per gram of glucose introduced). Continuous operation with immobilized cells at a dilution rate of 0.107 h^?1 resulted in a solvent productivity of 1.21 g L^?1 h^?1, 2.1 times that of the operation at 0.027 h^?1. However, the yield (butanol produced per glucose consumed) was decreased to 0.19 from 0.29 under the same glucose feeding condition of 60 g L^?1. CONCLUSION: The increase in dilution rate and feed glucose concentration enhanced productivity, but decreased the utilization of substrates and the final solvent concentration. Therefore, a balance between productivity and glucose utilization is required to ensure continuous process operation. Copyright © 2011 Society of Chemical Industry     

Effect of feed composition on PHB production from methanol by HCDC of Methylobacterium extorquens (DSMZ 1340)

BACKGROUND: Poly‐β‐hydroxybutyrate (PHB), produced by several species of bacteria, has attracted great attention as a biodegradable and biocompatible compound with similar properties to polypropylene. Unfortunately, its use is currently limited due to high production costs. One of the most common methods for overcoming this constraint is the use of inexpensive substrates, like methanol, in high cell density cultivations (HCDC). RESULTS: Fermentation was carried out with optimized feed composition (639 g l^?1 methanol, 4 g l^?1 MgSO₄.7H₂O, 41 mL L^?1 trace elements, 5.6 g L^?1 NaH₂PO₄.H₂O and 24.3 g L^?1 K₂HPO₄) and a feeding strategy based on the detection of substrate limitation by dissolved oxygen (DO). After 35 h, at which dry cell weight (DCW) reached a value of 70 g L^?1, PHB production was stimulated, and biomass and PHB productivities of 2.8 and 0.98 g L^?1 h^?1 were obtained, respectively. These results surpassed those reported in the literature for PHB production from methanol by Methylobacterium species. CONCLUSION: The proposed feed composition and feeding strategy for PHB production from methanol by Methylobacterium extorquens 1340 in fed‐batch cultivation resulted in high biomass and PHB productivity. They can be implemented for recombinant bioproducts (proteins) produced by M. extorquens due to the lack of PHB accumulation in the growth phase. Copyright © 2009 Society of Chemical Industry     

High cell density fermentation via a metabolically engineered Escherichia coli for the enhanced production of succinic acid

BACKGROUND: Succinic acid is a valuable four‐carbon organic chemical with applications in many fields. It was found that cell mass was an important factor in succinic acid production by metabolically engineered Escherichia coli strains. In this work, high cell density fermentation was investigated for succinic acid production by a metabolically engineered strain SD121 with ldhA, pflB, ptsG mutation and heterogenous cyanobacterial ppc overexpression. RESULTS: Under two‐stage cultivation, the controlled DO feeding strategy during the aerobic growth phase facilitated biomass up to a dry cell weight of 19.6 g L^?1, and enhanced succinic acid production in the following anaerobic fermentation phase to a concentration of 116.2 g L^?1. A near theoretical maximum succinic acid yield of 1.73 mol mol^?1 glucose was achieved with an average productivity of 1.55 g L^?1 h^?1. CONCLUSION: The results indicated the potential advantage of high cell density fermentation for improvement of succinic acid production by E. coli. Copyright © 2010 Society of Chemical Industry     

Continuous production of poly‐β‐hydroxybutyrate by high‐cell‐density cultivation of Wautersia eutropha

BACKGROUND: Poly‐β‐hydroxybutyrate (PHB) accumulation is triggered by limitation of a nutrient other than carbon. The production cost of PHB is very high. In order to reduce this cost, continuous cultivation for the accumulation of PHB was investigated. The culture was first allowed to grow under fed‐batch conditions to yield a significant increase in biomass and PHB accumulation. Thereafter this high‐cell‐density biomass containing PHB was allowed to grow and maintained under conditions of continuous cultivation so that the overall process could be simplified and economised. RESULTS: For continuous cultivation a medium containing 90 g L^?1 fructose and 2.5 g L^?1 nitrogen (as urea) was fed continuously at a dilution rate of 0.1 h^?1. A steady state biomass of 27.7 g L^?1 with a PHB concentration of 5.5 g L^?1 was established in the bioreactor. This resulted in a continuous PHB productivity of 0.55 g L^?1 h^?1. CONCLUSION: The experiments have resulted in the development of a novel production technology involving the integration of batch, fed‐batch and continuous processes. At the same time the production of PHB under continuous cultivation increases the overall industrial importance of the system. Copyright © 2008 Society of Chemical Industry     

Improved cultivation conditions for polysaccharide production by H. influenzae type b

Haemophilus influenzae b (Hib), an encapsulated Gram‐negative cocco‐bacillus, is one of the most common agents of meningitis worldwide. The capsular polysaccharide conjugated to a carrier protein is the antigen of the vaccine against Hib. An optimized cultivation process that could lead to an increase in the polysaccharide production would be of great interest for mass vaccination programs. The aim of this work was to evaluate different culture conditions in attempt to improve the capsular polysaccharide yield. Hib was cultivated in a bioreactor with modified soy‐peptone and yeast‐extract (MP) medium and optimal hemin and nicotinamide adenine dinucleotide (NAD) concentration in the culture medium was established at 30 mg L^?1 and 15 mg L^?1, respectively. The batch experiments were carried out as follows: (a) overlay aeration without pH control; (b) air‐sparged with dissolved oxygen tension (DOT) controlled at 10 and 30% air saturation, with and without pH control. The cultures with air‐sparged aeration, without pH control, showed values for the specific production (SP_p/x) of 180–190 mg PRP g^?1 dry cell weight (DCW) and overall polysaccharide productivity of 22–29 mg L^?1 h^?1, accounting for an increase of ca 47% over the polysaccharide production with overlay aeration. Batch cultivations with air sparged aeration led to an improvement in the poly(ribosylribitol phosphate) (PRP) production for both conditions (DOT at 10 and 30% air saturation) investigated upon pH control, achieving up to 980 PRP mg L^?1. The SP_p/x and overall polysaccharide productivity were 280–300 mg PRP g^?1 DCW and 45–41 mg L^?1h^?1, respectively. The best production of capsular polysaccharide was obtained in the modified MP‐medium, with 30 mg L^?1 hemin and 15 mg L^?1 NAD, upon sparged aeration and pH control. Copyright © 2005 Society of Chemical Industry     

Performance evaluation of batch and unsteady state fed‐batch reactor operations for the production of a marine microbial surfactant

BACKGROUND: Biosurfactants are microbially derived surface‐active and amphipathic molecules produced by various microorganisms. These versatile biomolecules can find potential applications in food, cosmetics, petroleum recovery and biopharmaceutical industries. However, their commercial use is impeded by low yields and productivities in fermentation processes. Thus, an attempt was made to enhance product yield and process productivity by designing a fed‐batch mode reactor strategy. RESULTS: Biosurfactant (BS) production by a marine bacterium was performed in batch and fed‐batch modes of reactor operation in a 3.7 L fermenter. BS concentration of 4.61 ± 0.07 g L^?1 was achieved in batch mode after 22 h with minimum power input of 33.87 × 10³ W, resulting in maximum mixing efficiency. The volumetric oxygen flow rate (K_La) of the marine culture was about 0.08 s^?1. BS production was growth‐associated, as evident from fitting growth kinetics data into the Luedeking‐Piret model. An unsteady state fed batch (USFB) strategy was employed to enhance BS production. Glucose feeding was done at different flow rates ranging from 3.7 mL min^?1 (USFB‐I) to 10 mL min^?1 (USFB‐II). USFB‐I strategy resulted in a maximum biosurfactant yield of 6.2 g l^?1 with an increment of 35% of batch data. The kinetic parameters of USFB‐I were better than those from batch and USFB‐II. CONCLUSION: Comparative performance evaluation of batch and semi‐continuous reactor operations was accomplished. USFB‐I operation improved biosurfactant production by about 35% over batch mode. USFB‐I strategy was more kinetically favorable than batch and USFB‐II. © 2012 Society of Chemical Industry