• Journal of Microbiology and Biotechnology
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• 제18권7호
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• pp.1257-1265
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• 2008

To lower the cost of ethanol distillation of fermentation broths, a high initial glucose concentration is desired. However, an increase in the substrate concentration typically reduces the ethanol yield because of insufficient mass and heat transfer. In addition, different operating temperatures are required to optimize the enzymatic hydrolysis (50$^{\circ}C$) and fermentation (30$^{\circ}C$). Thus, to overcome these incompatible temperatures, saccharification followed by fermentation (SFF) was employed with relatively high solid concentrations (10% to 20%) using a portion loading method. In this study, glucose and ethanol were produced from Solka Floc, which was first digested by enzymes at 50$^{\circ}C$ for 48 h, followed by fermentation. In this process, commercial enzymes were used in combination with a recombinant strain of Zymomonas mobilis (39679:pZB4L). The effects of the substrate concentration (10% to 20%, w/v) and reactor configuration were also investigated. In the first step, the enzyme reaction was achieved using 20 FPU/g cellulose at 50$^{\circ}C$ for 96 h. The fermentation was then performed at 30$^{\circ}C$ for 96 h. The enzymatic digestibility was 50.7%, 38.4%, and 29.4% after 96 h with a baffled Rushton impeller and initial solid concentration of 10%, 15%, and 20% (w/v), respectively, which was significantly higher than that obtained with a baffled marine impeller. The highest ethanol yield of 83.6%, 73.4%, and 21.8%, based on the theoretical amount of glucose, was obtained with a substrate concentration of 10%, 15%, and 20%, respectively, which also corresponded to 80.5%, 68.6%, and 19.1%, based on the theoretical amount of the cell biomass and soluble glucose present after 48 h of SFF.

• KSBB Journal
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• 제7권4호
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• pp.258-264
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• 1992

효모를 이용한 에탄올 발효에서 세포 농도가 130g/L일 때 배양액은 약간의 가소성 유체의 성질을 보이며 세포 농도가 증가할수록 cell floc의 형성으로 인하여 세포 분리를 위한 막의 투과 성능은 향상되었다. 세포재순환 에탄올 발효에서 최적 세포농도를 발효액의 유변학적 성질, 막의 투과 성능, 그리고 에탄올 생산성을 고려하여 결정하였다. 또한 최적의 세포 농도에서 최대 에탄올 생산성과 최대 포도당 전환율을 위한 희석 속도를 최적화하였다. 최적의 세포 농도는 130g/L이었고 이 농도에서 최적의 희석 속도는 $1.3h^{-1}$이었다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제10권4호
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• pp.346-352
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• 2005

The chemical characteristics, enzymatic saccharification, and ethanol fermentation of autohydrolyzed lignocellulosic material that was exposed to steam explosion were investigated using bagasse as the sample. The effects of the steam explosion on the change in pH, organic acids production, degrees of polymerization and crystallinity of the cellulose component, and the amount of extractive components in the autohydrolyzated bagasse were examined. The steam explosion decreased the degree of polymerzation up to about 700 but increased the degree of crystallinity and the micelle width of the cellulose component in the bagasse. The steam explosion, at a pressure of 2.55 MPa for 3 mins, was the most effective for the delignification of bagasse. 40 g/L of glucose and 20 g/L of xylose were produced from 100 g/L of the autohydrolyzed bagasse by the enzymatic saccharification using mixed cellulases, acucelase and meicelase. The maximum ethanol concentration, 20 g/L, was obtained from the enzymatic hydrolyzate of 100 g/L of the autohydrolyzed bagasse by the ethanol fermentation using Pichia stipitis CBS 5773; the ethanol yield from sugars was 0.33 g/g sugars.

• 한국미생물·생명공학회지
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• 제23권4호
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• pp.479-484
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• 1995

The effect of initial cell concentration on the characteristics of ethanol fermentation was investigated in the batch fermentation of Saccharomyces cerevisiae ATCC 24858. The characteristics were investigated in the range of 60 to 230 g/l of the initial sugar concentrations and 0.5 to 85 g/l of the initial cell concentrations. When the initial cell concentrations were 27 g/l for 60 g/l of the initial sugar and 85 g/l for 230 g/l, the fermentation time required for the complete consumption of the initial sugar was one hour, respectively. The ethanol productivity increased with the initial cell concentration so that, in the case of 100 g/l of initial sugar, the productivity rose up to 55 g/l/hr at 55 g/l of the initial cell concentration. The specific growth rate decreased according to the increase in the initial biomass concentration and finally became zero at around 25 g/l of the cell concentration regardless of the initial sugar concentration. The specific ethanol production rate was constant as 1.02 g/l/hr up to 150 g/l of the initial sugar. However, the rates decreased sharply with the augmentation of concentration of the initial sugar above 160 g/l. The overall ethanol yield represented a constant value, 0.475 g/g irrespective of the initial cell and sugar concentrations. The overall biomass yietd showed a trend to diminish in values with the biomass and ultimately to reach zero more than 25 g/l of the initial cell concentration.

• 한국미생물·생명공학회지
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• 제19권4호
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• pp.390-397
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• 1991

효모를 Ca-alginate에 고정화하여 회분발효에서 glucose로부터 에탄올을 생산하여 다음의 결과를 얻었다. 100g wet weight/l($4.3 \times 10^9$ cell/l)의 효모를 pH 7.0, 2% 농도의 Ca-alginate에 고정화하였다. 10 beads volume이 에탄올 생산에 최적이었고 30일 (720 시간) 동안 bead의 수명이 지속되었다. 회분식 발효에서 온도안정성은 고정화 효모의 경우 30~$40^{\circ}C$였으며 free cell의 경우 30~$37^{\circ}C$였다. pH 안정성은 pH 4.0~9.0였으며, 에탄올생산 최적 당농도는 15%였다. 최적조건에서 에탄올수율은 0.45, 생산된 에탄올 농도는 67.6g/l 그리고 에탄올 생산성은 1.99g/l.h로 각각 나타났다.

• 생명과학회지
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• 제21권3호
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• pp.335-340
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• 2011

포도당과 자일로스는 자연계에서 가장 풍부한 물질이며 이들은 효모에 의해 에탄올로 전환될 수 있다. 본 연구에서는 Saccharomyces cerevisiae와 Pichia stipitis을 이용하여 분리배양, 공동배양 그리고 순차배양 등의 조합을 통해 가장 효과적인 발효의 방법을 찾고자 하였다. 분리배양에서 S. cerevisiae은 29.4 g/l의 포도당을 발효하여 14.5 g/l의 에탄올을 생산한 반면에 자일로스를 이용하지 못했다. 그렇지만 P. stipitis은 포도당뿐만 아니라 자일로스도 분해하여 각각 포도당 29.4 g/l로부터 11.9 g/l의 에탄올을, 자일로스 29.0 g/l로부터 11.6 g/l의 에탄올을 생산하였다. 포도당과 자일로스 혼합배양에서, S. cerevisiae은 13.4 g/l의 에탄올을 생산한 반면에 P. stipitis은 21.1 g/l의 에탄올을 생산하였다. 공동배양과 순차배양에서, 공동배양이 18.6 g/l, 순차배양이 12.4 g/l의 에탄올을 생산하여 공동배양이 더 효과적인 것으로 나타났다. 두 효모의 생장에서 영양분의 효과를 보기 위해 yeast nitrogen base (YNB)을 S. cerevisiae가 포도당을 소모한 시점에 첨가하니 자일로스의 소비량과 미생물의 성장이 증가하였고 54.6 g/l의 당 혼합배양액에서 22.5 g/l의 에탄올을 생산하여 0.41 g/g의 수득율을 나타내었다.

• 한국미생물·생명공학회지
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• 제20권4호
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• pp.451-458
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• 1992

에탄올발효에서 에탄올은 세포의 성장 및 에탄올생합성에 저해작용을 하는 것으로 알려져 있다. 이러한 저해작용을 감소시켜주기 위하여 에탄올을 선택적으로 분리하는 투과증발법을 이용하였다. 실리콘폴리슬폰 복합막을 제조하여 사용하였는데, 이 막은 유입액의 에탄올 농도가 25g/l, 온도가 30'C, 막하부의 압력이 10mmHg일 때 에탄올의 선택도가 약 4 이었으며, 총 투과유속은 300g/m2h이었다. 에탄올 발효는 Saccharomyces cerevisiae를 Ca-alginate에 고정화시켜 유동층 생물반응기에 접종하여 수행하였고, 이 반응기를 투과증발장치와 연결한 혼합공정을 구성하였는데, 혼합공정의 경우 발효배지의 에탄올농도는 막을 연결하지 않았을 때보다 감소하여 저해작용을 감소시키고 생산성을 향상시켰다.

• 한국미생물·생명공학회지
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• 제24권3호
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• pp.331-335
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• 1996

Characteristics of ethanol fermentation were investigated during the stationary culture of a killer yeast, Saccharomyces cerevisiae B15-1. Specific ethanol production rate reached the maximum level, 1.203 g-EtOH/g-cell-hr, at 150 g/l of the initial glucose concentration. No big differences were obtained in ethanol fermentability based on the initial sugar concentration below 150 g/l. When 200 g/l of sugar was used, fermentability dropped significantly. Although the final cell mass and the amount of ethanol produced were increased, their increase rates were declined according to the increase of initial sugar concentration. It was found that most of the sugar used below 150 g/l of concentration could be changed to ethanol. However, when 200 g/l of sugar was used, some of them remained in the media even after increase of cell mass and fermentation stopped. The ethanol yield was decreased when initial sugar concentration was high, and were increased when the amount of ethanol produced was increased and finally reached the plateau over 60 g/l of ethanol concentration.

• 미생물학회지
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• 제29권2호
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• pp.136-142
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• 1991

The selection of ethanol-tolerant strains was applied to enrichment culture of YPD broth medium containing various concentrations of ethanol. Isolates were identified to be Saccharomyces cerevisiae, the others as S. dairensis, S. exiguus, S. telluris, Saccharomycodes ludwigii, Schwanniomyces occidentalis var. occidentalis and Zygosaccharomyces florentinus. Among isolates S. cerevisiae YO-1 was screened as having the highest ethanol tolerance and produced 18% (v/v) ethanol after 4 days fermentation. The change of fatty-acyl residues represents that a progressive decrease in fatty-acyl unsaturation and a proportional increase in saturation in phospholipids of yeast cells during fermentation affected the yeast viability. Supplementation ethanol to the cultures led to an increase of unsaturated fatty-acyl residues, especially $C_{16}$ or $C_{18}$ residues, along with a decrease in the proportion of saturated residues in cellular phospholipids. Increasing the amount of soy flour led to an increase in the maximum number of viable yeast cells and ethanol production. It was possible in 4 days to reach 21% (v/v) ethanol by adding 4% soy flour as source of unsaturated fatty-acyl residues to the fermentation medium. Soy flour not only increased yeast population but also enhanced the physiological properties of yeast cells to be ethanol tolerant in the anaerobic culture.

• Journal of Microbiology and Biotechnology
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• 제4권1호
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• pp.56-62
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• 1994

A yeast strain, BT001, which can directly ferment D-xylose to ethanol was isolated from forest soils, and then identified as Candida sp. Cultural conditions for the optimum ethanol production, along with the effects of aeration on cell growth and ethanol production were investigated. Aeration stimulated the cell growth and the volumetric rate of ethanol production, but decreased the ethanol yield. Optimum temperature and initial pH for the ethanol production were $33{\circ}^C$ and 6.0, respectively. In a shake flask culture, this strain produced 52.3 g ethanol per liter from 12%(w/v) D-xylose after incubation for 96 hours. Ethanol yield was 0.436 g per g D-xylose consumed. This corresponds to 85.8% of theoretical yield. Also, this yeast strain produced ethanol from D-galactose, D-glucose and D-mannose, but not from L-arabinose and L-rhamnose. Among these sugars, D-glucose was the fastest in being converted to ethanol sugars.