• Journal of Microbiology and Biotechnology
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• v.24 no.5
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• pp.661-666
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• 2014

Both lactic acid productivity and cell growth were linearly correlated with yeast extract supplementation in batch fermentation. During conventional continuous operation, although fresh feed was introduced into the bioreactor with a significantly low dilution rate (0.04 $h^{-1}$), the amount of yeast extract employed was not enough to maintain the growth of microorganism. However, when the fresh feed contained 100 g/l glucose and 2 g/l yeast extract during cell-recycle continuous operation at a dilution rate of 0.04 $h^{-1}$, more than 90 g/l lactic acid was continuously produced, with the average productivity of 3.72 $g/l{\cdot}h$. In this experiment, 82 g of yeast extract (77% of reduction yield) could be reduced for the production of 1 kg of lactic acid compared with batch fermentation of a similar volumetric productivity.

• Microbiology and Biotechnology Letters
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• v.24 no.6
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• pp.717-725
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• 1996

We have developed an efficient immobilized cell separator for continuous operation of immobilized fungal cell cultures, and applied this separator to actual fermentation process for the production of cyclosporin A (CyA), a powerful immunosuppressant. In the experiments employing highly viscous polymer (carboxymethyl cellulose) solution, the decantor showed good separating performances at high solution viscosites and fast dilution rates. Air duct and cylindrical separator installed inside the decantor turned out to play key roles for the efficient separation of the immobilized cells. By installing the decantor in an immobilized perfusion reactor system (IPRS), continuous immobilized culture was stably carried out even at high dilution rate for a long period, leading to high productivities of free cells and CyA. Almost no immobilized biomass existed in effuluent stream of the IPRS, demonstrating the effectiveness of the decan- tor system for a long-term continuous fermentation. It was noteworthy that we could obtain these results despite of the unfavorable fermentation conditions, i.e., reduced density of the biosupports caused by overgrowth of cells inside the bead particles and existence of high density of suspended fungal cells (10g/l) in the fermentation broth.

• Journal of Microbiology and Biotechnology
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• v.18 no.5
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• pp.908-912
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• 2008

To achieve a higher succinic acid productivity and evaluate the industrial applicability, this study used Mannheimia succiniciproducens LPK7 (knock-out: ldhA, pflB, pta-ackA), which was recently designed to enhance the productivity of succinic acid and reduce by-product secretion. Anaerobic continuous fermentation of Mannheimia succiniciproducens LPK7 was carried out at different glucose feed concentrations and dilution rates. After extensive fermentation experiments, a succinic acid yield and productivity of 0.38 mol/mol and 1.77 g/l/h, respectively, were achieved with a glucose feed concentration of 18.0 g/l and $0.2\;h^{-1}$ dilution rate. A similar amount of succinic acid production was also produced in batch culture experiments. Therefore, these optimal conditions can be industrially applied for the continuous production of succinic acid. To examine the quantitative balance of the metabolism, a flux distribution analysis was also performed using the metabolic network model of glycolysis and the pentose phosphate pathway.

• Microbiology and Biotechnology Letters
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• v.19 no.4
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• pp.419-427
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• 1991

Ethanol fermentation of glucose by a strain of Saccharomyces cereuisiae was studied in membrane recycle bioreactor, where the fermentation vessel was coupled with cross flow hollow fiber membrane. The cell recycle system controlled backflushing with fresh medium was proven to be effective in alleviating membrane fouling and allowing long term operation of high-cell continuous fermentation. Using 100 g/l initial glucose concentration, the maximum productivity of about 9 5 g/$l \cdot h$ has been achieved at dilution rate 2.5 $h^{-1}$ and bleed stream ratio 0.05 with the corresponding ethanol concentration of 35g/l and glucose conversion of 100%. Increasing the glucose concentration to 200 g/$l \cdot h$ resulted in an increase in ethanol concentration to 48 g/l and productivity to 120 g1l.h. Substrate conversion, however, was only 69%. This productivity was the highest value in the study, and about 38 fold more than that of batch culture and 17 fold more that of single stage continuous culture without cell recycling. No further increase in the productivity was obtained when the glucose concentration was increased reased to 300g/l.

• KSBB Journal
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• v.13 no.4
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• pp.456-460
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• 1998

Fed-batch fermentations were carried out in order to improve the efficiency of hirudin production by recombinant Saccharomyces cerevisiae. A fed-batch fermentation done with the optimized semi-synthetic medium resulted in a maximum hirudin concentration of 342mg/$\ell$ by keeping a galactose concentrations between 10 and 30g/$\ell$ which corresponded to a 11.4-fold increase in hirudin concentration compared with the simple bach fermentation done with the same medium. Comparison of the chromatographic pattern of proteins in the growth medium clearly showed that the use of the semi-synthetic medium is more advantageous for separation of hirudin than the case o fusing the complex medium. Continuous cell recycle fermentation done at dilution rate of 0.1h-1 and an inlet galactose concentration of 100g/$\ell$ yielded a maximum hirudin productivity of 19.1mg hirudin/$\ell$$.$h.

• Journal of Microbiology and Biotechnology
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• v.17 no.2
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• pp.297-304
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• 2007

The effect of yeast propagated at different aeration conditions on yeast physiology, fermentation ability, and beer quality was investigated using three strains of Saccharomyces cerevisiae. It was shown that yeast cells grown under continuous aeration conditions during propagation were almost two times higher as compared with discontinuous aeration conditions. The maximum of cell growth of all samples reached between 36 hand 48 h. The concentration of trehalose was increased under continuous aerated yeasts, whereas glycogen was decreased. It was also observed that the concentration of glycogen and trehalose in yeast cells had no direct effect on subsequent fermentation ability. The effect of yeast propagated under different aeration conditions on subsequent fermentation ability was different from yeast strains, in which the influence will be most pronounced at the first fermentation. Later, the yeasts might regain its original characteristics in the following fermentations. Generally, continuously propagated yeast had a positive effect on beer quality in subsequent fermentation. Hence, the concentration of aroma compounds obtained with yeast propagated under 6 1/h for 48 h aeration was lower than those grown under other aeration conditions in the bottom yeasts; in particular, the amounts of phenylethyl alcohol, ester, and fatty acids were decreased.

• KSBB Journal
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• v.14 no.2
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• pp.181-187
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• 1999

We have investigated industrial media for lactic acid fermentation to reduce the cost of nitrogen sources. Corn steep liquor (CSL) was successfully used at 5% (v/v) in batch fermentations. Use of soluble CSL improved the productivity about 20% with an advantage of clearer fermentation broth. Yeast extract-complemented CSL improved the productivity about 20% with an advantage of clearer fermentation broth. Yeast extract-complemented CSL media further increased the increased the productivity. It was found that 3.1 g/L yeast extract and 5% CSL could be an effective substitute for 15 g/L yeast extract in 10% glucose medium. Brewing yeast was also used as a sole nitrogen source equivalent to 5% CSL. A continuous culture coupled with cell-recycle by microfiltration at the dilution rate of 0.05-0.065 h-1 led to the highest lactic acid productivity. Lactic acid was recovered by electrodialysis from the cell free broth. Depleted cell free broth supplemented with 5-10 g/L of yeast extract performed reasonably in batch and continuous cultures. Reuse of the fermentation broth may reduce the cost of raw materials as well as minimize the fermentation wastes.

• Microbiology and Biotechnology Letters
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• v.23 no.3
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• pp.346-351
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• 1995

To produce ethanol from Jerusalem artichoke powder efficiently, Kluyveromyces marxianus F043 cells were encapsulated in 2% sodium alginate and were cultured in a countinuous reactor to investigate the fermentation properties. Immobilized K. marxianus F043 cells were activated for 48 hours in a fermentor for continuous ethanol production. The culture in a CSTR using a Jerusalem artichoke substrate treated with 2% cellulase showed a decrease in ethanol concentration and an increase in residual saccharide concentration with a increasing dilution rate. Optimum conditions for high ethanol productivity and low residual saccharide output were clarified to be given at a dilution rate of 0.2 h$^{-1}$ and a Jerusalem artichoke medium concentration of 75 g/l. Ethanol productivity of 3.1 g/l-h and saccharide utilization of 62.6% were obtained under the optimum condition. When the fermentation was performed for 3 weeks under these conditions, the effluent medium showed stable ethanol concentrations of 16.3 - 17.9 g/l and viable cells of 6.60-7.16 log cells/ml without contamination. Trace amounts of methyl, n-propyl, iso-butyl, isoamyl alcohols besides ethanol were detected.

• Microbiology and Biotechnology Letters
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• v.19 no.4
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• pp.398-404
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• 1991

- Ethanol production by calcium alginate-immobilized baker's yeast was studied in the continuous shaked-flask reactor (CSFR) using glucose medium as a feed. Immobilized cells were stable at 30~$37^{\circ}C$ and pH 4~8. Fermentation characteristics of immobilized baker's yeast were examined changing the initial glucose concentration employed were 50, 100 and 150 g/l, respectively. It was investigated that the influent glucose concentration and the dilution rate have an influence on the ethanol fermentation characteristics at steady state in continuous culture of immobilized baker's yeast. The optimum conditions for high ethanol productivity and low residual glucose output in ethanol prodution were shown to be 0.2 h ' for the dilution rate and 150 g/l for the influent glucose concentration. The maximum ethanol productivity, ethanol yield, specific growth rate and glucose conversion rate were around 7.12 g/$l\cdot h$, 0.23, 0.366 g/$l\cdot h$ and 78.43, respectively.

• KSBB Journal
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• v.23 no.3
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• pp.213-218
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• 2008

The present study was to investigate the continuous production of alcohol using immobilized carrier manufactured by polymeric materials. Fermentation runs with a crushed rice, with constituents recovered from batch culture and with ones from continuous culture were thus compared. The performances of immobilized carrier were governed by sandwitched synthetic polymers, the evolution of the continuous culture was steadily governed by the production of alcohol in the lag time of batch culture. The main focus was set on the enhancement of the alcohol production by an newly-developed polymeric forms. This polymeric form led to a drastic increase of the microorganism and the production cost in the continuous reactor was thereby reduced. The sandwitched polymeric-formed carrier, which was resistant to external environments, serves as an interesting alternative to maintain the stability of biological process. These whole results were discussed with the aim to better understand the continuous process implied in the microorganism's build-up during cultivation of fermentation broth.