• Journal of Microbiology and Biotechnology
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• 제14권4호
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• pp.665-672
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• 2004

D-Ribose is a five-carbon sugar used for the commercial synthesis of riboflavin, antiviral agents, and flavor enhancers. Batch fermentations with transketolase-deficient B. subtilis JY1 were carried out to optimize the production of D-ribose from xylose. The best results for the fermentation were obtained with a temperature of $37^{\circ}C$ and an initial pH of 7.0. Among various sugars and sugar alcohols tested, glucose and sucrose were found to be the most effective for both cell growth and D-ribose production. The addition of 15 g/l xylose and 15 g/l glucose improved the fermentation performance, presumably due to the adequate supply of ATP in the xylose metabolism from D-xylulose to D-xylulose-5-phosphate. A batch culture in a 3.7-1 jar fermentor with 14.9 g/l xylose and 13.1 g/l glucose resulted in 10.1 g/l D-ribose concentration with a yield of 0.62 g D-ribose/g sugar consumed, and 0.25 g/l-h of productivity. Furthermore, the sugar utilization profile, indicating the simultaneous consumption of xylose and glucose, and respiratory parameters for the glucose and sucrose media suggested that the transketolase-deficient B. subtilis JY1 lost the glucose-specific enzyme II of the phosphoenolpyruvate transferase system.

• 한국미생물·생명공학회지
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• 제7권2호
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• pp.91-95
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• 1979

Cellulose 및 hemicellulose 를 함유하는 볏짚 등 농산폐자원을 Trichoderma로 만든 Koui와 효모를 동시에 처리하여 단일공정으로 ethanol과 xylose 를 생산할 수 있었다. 볏짚 50g을 처리하여 ethanol 18mι와 xylose 2.7g 을 생산할 수 있었으며 옥수수속대 50g에서 ethanol 3.8mι와 xylose 10.8 g을 얻을 수 있었다. 이 처리에서 토양 분리균 Tri-choderma sp. KI 7-2로 만든 Koji가 T. reesei 의 그것보다 높은 효모활성을 보였다. 볏짚의 alkali 전처리는 ethanol 및 xylose의 생산에 큰 효과가 없었으며 이에 대하여 논하였다

• Journal of Microbiology and Biotechnology
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• 제13권5호
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• pp.725-730
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• 2003

Three recombinant Saccharomyces cerevisiae strains showing different levels of xylose reductase activity were constructed to investigate the effects of xylose reductase activity and glucose feed rate on xylitol production. Conversion of xylose to xylitol is catalyzed by xylose reductase of Pichia stipitis with cofactor NAD(P)H. A two-substrate fermentation strategy has been employed where glucose is used as an energy source for NADPH regeneration and xylose as substrate for xylitol production. All recombinant S. cerevisiae strains Yielded similar specific xylitol productivity, indicating that xylitol production in the recombinant S. cerevisiae was more profoundly affected by the glucose supply and concomitant It generation of cofactor than the xylose reductase activity itself. It was confirmed in a continuous culture that the elevation of the glucose feeding level in the xylose-conversion period enhanced the xylitol productivity in the recombinant S. cerevisiae.

• 한국식품과학회지
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• 제28권5호
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• pp.970-973
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• 1996

Candida parapsilosis KFCC-10875를 사용하여 균체농도가 xylose로부터 xylitol의 생산에 미치는 영향을 조사하였다. Xylitol 생산속도는 균체농도 20 g/l에서 최대값 2.8 g/l-h를 보여주었으며 비 xylitol 생산속도는 농축된 균제에 의한 산소제한으로 균체농도가 증가할수록 감소하였다. 약 20 g/l로 농축된 균체를 사용하여 초기 xylose농도가 xylitol 생산에 미치는 영향을 살펴본 결과 xylitol 생산속도, 비 xylitol 생산속도 및 xylose에 대한 xylitol의 수율은 xylose의 농도 170 g/l에서 최대값을 보여주었다. 고농도의 균체를 사용하려면 xylose의 배지에서 배양된 균체를 다시 농축하여야 한다. 이러한 단점을 해결하기 위하여 발효과정 중에 균체를 농축하는 방법을 시도하였다. 고농도 균체를 얻기위하여 지수증식기인 배양 초기에는 용존산소의 농노를 충분히 유지시켜 18시간 배양하여 약 20 g/l의 고농도 균체를 얻을 수 있었다. 고농도 균체를 이용하여 xylitol을 생산하기 위하여 용존산소의 농도를 0.7-1.5%로 낮추어 유지하였다. 이때, 기질의 농도는 xylose 농도가 170 g/l 이상에서는 xylitol 생산성이 비교적 크게 감소하므로 xylitol 생산성의 향상을 위하여 고농도의 xylose를 피하는 유가식 배양을 수행하였다. 그 결과 56시간 배양하여 200 g/l xylose로부터 약 140 g/l의 xylitol을 생산할 수 있었다.

• 신재생에너지
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• 제9권1호
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• pp.25-32
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• 2013

It is indispensable to increase the conversion rate of a reducing sugars such as pentose and hexose derived from cellulosic wastes for a highly efficient bioethanol fermentation from food wastes. The saccharification liquid from cellulosic substrates such as vegetable food wastes contained lots of hexose like glucose and pentose like xylose. Since Saccharomyces-based yeasts could not convert xylose to bioethanol, Pichia stipitis which could directly ferment xylose to ethanol was chosen. After selecting Saccharomyces coreanus and P. stipitis, fermentation characteristics by mixture of two yeasts were investigated. As a result, it was verified the production of ethanol was enhanced by the co-fermentation, although there were somewhat differences between the fermentation characteristics by the aeration methods. Moreover, the consumption of pentose, hexose and disaccharide was obviously observed, and aeration in the process of fermentation seemed to stimulate the activity of P. stipitis.

• 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.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2005년도 생물공학의 동향(XVII)
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• pp.272-276
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• 2005

Candida tropicalis, an osmophilic strain isolated from honeycomb, produced xylitol at a maximal volumetric production rate of 3.5 g $l^{-1}$ $h^{-1}$ from an initial xylose concentration of 200 g $l^{-1}$. Even with a very high xylose concentration, e.g., 350 g $l^{-1}$, this strain produced xylitol at a moderate rate of 2.07 g $l^{-1}$ $h^{-1}$. In a fed-batch fermentation of xylose and glucose, 260 g $l^{-1}$ of xylose was added, and xylitol production was 234 g $l^{-1}$ for 48 h, corresponding to a rate of 4.88 g $l^{-1}$ $h^{-1}$. To increase the xylitol production rate, cells were recycled in a submerged membrane bioreactor with suction pressure and air sparging. In cell-recycle fermentation, the average concentration of xylitol produced per recycle round, total fermentation time, volumetric production rate, and product yield for ten rounds were 180 g $l^{-1}$, 195 h, 8.5 g $l^{-1}$ $h^{-1}$, and 85%, respectively. When cell-recycle fermentation was started with the cell mass contratrated two-fold after batch fermentation and was performed for ten recycle rounds, we achieved a very high production rate of 12 g $l^{-1}$ $h^{-1}$. The production rate and total amount of xylitol produced in cell-recycle fermentation were 3.4 and 11 times higher than in batch fermentation, respectively.

• 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.

• Biotechnology and Bioprocess Engineering:BBE
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• 제10권6호
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• pp.587-592
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• 2005

Hydrolyzates from lignocellulosic biomass contain a mixture of simple sugars; the predominant ones being glucose, cellobiose and xylose. The fermentation of such mixtures to ethanol or other chemicals requires an understanding of how each of these substrates is utilized. Candida lusitaniae can efficiently produce ethanol from both glucose and cellobiose and is an attractive organism for ethanol production. Experiments were performed to obtain kinetic data for ethanol production from glucose, cellobiose and xylose. Various combinations were tested in order to determine kinetic behavior with multiple carbon sources. Glucose was shown to repress the utilization of cellobiose and xylose. However, cellobiose and xylose were simultaneously utilized after glucose depletion. Maximum volumetric ethanol production rates were 0.56, 0.33, and 0.003 g/L h from glucose, cellobiose and xylose, respectively. A kinetic model based on cAMP mediated catabolite repression was developed. This model adequately described the growth and ethanol production from a mixture of sugars in a batch culture.

• KSBB Journal
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• 제21권6호
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• pp.493-497
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• 2006

볏짚 가수분해물의 조성과 유사한 xylose/glucose 혼합배지를 이용하여 Candida mogii ATCC 18364에 의한 xylitol 생산성 및 수율에 관한 연구를 수행하였다. 통기량을 생육단계 (약 10시간)는 호기적인 2 vvm, 300 rpm에서, 생산단계는 반호기적 조건인 1 vvm, 300 rpm으로 조절한 결과 균체의 농도가 10시간 만에 약 $4.7\;g/{\ell}$까지 증가하여 농축균을 사용한 것과 같은 효과를 얻을 수 있었으며, 4일 후에 $0.58\;g/{\ell}$의 수율과 $0.25\;g/{\ell}{\cdot}h$의 생산성으로 약 $24\;g/{\ell}$의 자일리톨이 생산되어 농축균을 이용한 것보다 약간 더 우수하였다. 또한 생산단계에서 xylose를 이용한 세포의 성장을 감소시키기 위해 생산단계에서 포도당을 $6.8\;g/{\ell}{\cdot}day$로 공급한 결과 4일 후에 0.8 g/g의 수율과 $0.31\;g/{\ell}{\cdot}h$의 생산성으로 약 $29.4\;g/{\ell}$의 자일리톨을 생산하여, 포도당 공급을 하지 않았을 때보다 약 $20{\sim}30%$의 증가를 보여주었다.