• Korean Chemical Engineering Research
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• 제46권5호
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• pp.858-862
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• 2008

분리 당화발효(Separate Hydrolysis and Fermentation, SHF)는 당화와 발효공정을 따로 수행하는 방법으로 최종 생성물인 글루코오스에 의해 억제 영향을 받기 때문에 반응에 진행됨에 따라 축적된 글루코오스의 농도가 높아지면 반응이 종결되는 단점이 있다. 이를 극복하기 위해 효소의 양을 늘리는 방법이 있지만, 효소의 생산비용이 비싸기 때문에 경제적인 방법이 될 수 없다. 이러한 분리 당화발효 공정의 단점을 극복하기 위해서 동시당화발효 공정(Simultaneous Saccharification and Fermentation, SSF)은 하나의 반응기에서 당화와 발효를 동시에 수행한다. 동시당화발효 공정에서는 당화과정에서 글루코오스가 생성되자마자 효모가 발효과정을 통해 글루코오스를 바로 제거하기 때문에 반응기내에서 당의 축적을 최소화할 수 있다. 따라서 동시당화발효 공정은 최종 생성물의 억제 작용을 방지할 수 있고, 효소의 가수분해 반응을 향상시킬 수 있다. 본 연구에서는 동시당화발효에서 에탄올의 수율에 관여하는 조건들(pH, 반응온도, 효소 투입량, 반응시간)의 최적 조건을 찾는 연구를 수행하였다. 기질로는 감자전분을 사용하였고, 효소는 glucoamylase, 균주는 Saccharomyces cerevisiae가 각각 사용되었다. 동시당화발효의 최적의 조건은 pH 4, 온도 38로 나타났다. 최적의 조건으로 감자전분을 동시당화발효하였을 때 반응 18시간 후에 에탄올은 최대 수율 86%에 도달하였다.

• Korean Journal of Chemical Engineering
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• 제35권12호
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• pp.2403-2412
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• 2018

The present study was aimed at evaluating the effect of variable sodium carbonate ($Na_2CO_3$) loading during wet air oxidation (WAO) pretreatment of rice straw in reducing biomass recalcitrance. The research study was intended to increase the cellulose recovery, hemicellulose solubilization, lignin removal in the solid fraction and limiting the generation of inhibitors in the liquid fraction while reducing the chemical input. The operating condition of $169^{\circ}C$, 4 bar, 18 min and 6.5 g/L $Na_2CO_3$ loading resulted in maximum cellulose recovery of 82.07% and hemicellulose solubilization and lignin removal of 85.43% and 65.42%, respectively, with a total phenolic content of 0.36 g/L in the liquid fraction. The crystallinity index increased from 47.69 to 51.25 along with enzymatic digestibility with an increase in $Na_2CO_3$ loading from 0 to 6.5 g/L as a result of removal of barriers for saccharification via effective cleavage of ether and ester bonds cross-linking the carbohydrates and lignin as indicated by FT-IR spectroscopy. A further increase in the $Na_2CO_3$ loading to 9.5 g/L did not significantly increase the sugar release. Thus, it was concluded that 6.5 g/L $Na_2CO_3$ during WAO is sufficient to increase the delignification and deacetylation, leading to significant changes in apparent cellulose crystallinity inter alia improvement in cellulose accessibility and digestibility of rice straw.

• KSBB Journal
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• 제31권1호
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• pp.79-84
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• 2016

Biofuel has been considered as promising renewable energy to solve various problems that result from increasing usage of fossil fuels since the early 20th century. In terms of chemical and physical properties as fuel, biobutanol has more merits than bioethanol. It could replace gasoline for transportation and industrial demand is increasing significantly. Production of butanol can be achieved by chemical synthesis or by microbial fermentation. The water hyacinth, an aquatic macrophyte, originated from tropical South America but is currently distributed all over the world. Water hyacinth has excellent water purification capacity and it can be utilized as animal feed, organic fertilizer, and biomass feedstock. However, it can cause problems in the rivers and lakes due to its rapid growth and dense mats formation. In this study, the potential of water hyacinth was evaluated as a lignocellulosic biomass feedstock in biobutanol fermentation by using Clostridium beijerinckii. Water hyacinth was converted to water hyacinth hydrolysate medium through pretreatment and saccharification. It was found that productivity of water hyacinth hydrolysate medium on biobutanol production was comparable to general medium.

• Korean Chemical Engineering Research
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• 제54권4호
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• pp.494-500
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• 2016

본 연구에서는 백합나무의 아세틸기 제거를 위해 전처리 전에 수산화나트륨을 이용하여 탈아세틸화를 수행하였다. 0.8%의 수산화나트륨을 첨가하여 $60^{\circ}C$에서 80분 동안 반응시켜 헤미셀룰로오스로부터 대부분의 아세틸기를 제거하였다. 탈아세틸화 처리된 바이오매스를 옥살산 전처리에 이용하였으며, 전처리된 바이오매스 투입량(10, 12.5, 15%) 및 효모 투입시간(0, 6, 12, 24시간)에 따라 동시당화발효 및 semi-동시당화발효를 수행하였다. 최대 에탄올 수율은 바이오매스 투입량 10%에서 효모를 당화시작과 동시에 첨가했을 때 120시간 후 26.73 g/L의 에탄올을 생산하였으며 이것은 88.14%의 에탄올 수율에 해당하였다. 바이오매스 투입량 12.5%와 15% 조건에서는 효모 투입시간 6시간 조건에서 각각 32.34 g/L, 27.15 g/L의 에탄올을 생산하였고, 이는 각각 85.58%와 59.87%의 에탄올 수율에 해당하였다. 옥살산 전처리 후 얻어진 액상 가수분해산물로부터 발효저해물질의 제거를 위해 수산화칼슘을 처리하였으며 발효 72시간 후 5.28 g/L의 최대 에탄올을 얻었다.

• Journal of Microbiology and Biotechnology
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• 제19권8호
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• pp.845-850
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• 2009

Bioethanol derived from lignocellulosic biomass has the potential to replace gasoline. Cellulose is naturally recalcitrant to enzymatic attack, and it also surrounded by the matrix of xylan and lignin, which enhances the recalcitrance. Therefore, lignocellulosic materials must be pretreated to make the cellulose easily degraded into sugars and further fermented to ethanol. In this work, hydrothermal pretreatment on corn stover at $195^{\circ}C$ for 15 min with and without lower concentration of formic acid was compared in terms of sugar recoveries and ethanol fermentation. For pretreatment with formic acid, the overall glucan recovery was 89% and pretreatment without formic acid yielded the recovery of 94%. Compared with glucan, xylan was more sensitive to the pretreatment condition. The lowest xylan recovery of 55% was obtained after pretreatment with formic acid and the highest of 75% found following pretreatment without formic acid. Toxicity tests of liquor parts showed that there were no inhibitions found for both pretreatment conditions. After simultaneous saccharification and fermentation (SSF) of the pretreated corn stover with Baker's yeast, the highest ethanol yield of 76.5% of the theoretical was observed from corn stover pretreated at $195^{\circ}C$ for 15 min with formic acid.

• Journal of Microbiology and Biotechnology
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• 제24권9호
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• pp.1245-1253
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• 2014

One-step sulfuric acid saccharification of the red alga Pterocladiella capillacea was optimized, and various detoxification methods (neutralization, overliming, and electrodialysis) of the acid hydrolysate were evaluated for fermentation with the thermotolerant yeast Kluyveromyces marxianus. A proximate composition analysis indicated that P. capillacea was rich in carbohydrates. A significant galactose recovery of $81.1{\pm}5%$ was also achieved under the conditions of a 12% (w/v) biomass load, 5% (v/v) sulfuric acid, $121^{\circ}C$, and hydrolysis for 30 min. Among the various detoxification methods, electrodialysis was identified as the most suitable for fermentable sugar recovery and organic acid removal (100% reduction of formic and levulinic acids), even though it failed to reduce the amount of the inhibitor 5-HMF. As a result, K. marxianus fermentation with the electrodialyzed acid hydrolysate of P. capillacea resulted in the best ethanol levels and fermentation efficiency.

• 한국해양바이오학회지
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• 제8권1호
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• pp.1-9
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• 2016

The hydrolysis of biomass to fermentable sugar (saccharification) and to oligosaccharide is an essential process in biotechnology including biorefinery and biofood. Various macroalgae are commercially cultivated in several Asian countries as a useful resource for food and agar production. Agar is a major component of the cell walls of red algae that can be hydrolyzed by agarase. Agarases are classified into ${\alpha}$-agarase (E.C. 3.2.1.158) and ${\beta}$-agarase (E.C. 3.2.1.81) according to the cleavage pattern and grouped in the glycoside hydrolase (GH) family (GH-16, GH-58, GH-86, GH-96, and GH-118) based on the amino acid sequences of the proteins. Agarases have been isolated from various bacteria found in seawater and marine sediments. To increase productivity of the enzyme, a research on recombinant enzymes has been done. The application of recombinant agarase can be possible in the various filed such as energy, food, cosmetics, medical and so on. This paper reviews the source, biochemical characteristics and production system of recombinant agarases for further study.

• Journal of the Korean Wood Science and Technology
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• 제39권6호
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• pp.490-497
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• 2011

본 연구는 옥살산으로 전처리를 수행한 후 얻어진 옥수숫대를 이용하여 동시당화발효를 위한 최적조건을 탐색하였다. Pichia stipitis CBS 6054를 이용한 동시당화발효에서 독립변수인 반응온도($25.8{\sim}34.2^{\circ}C$)와 교반속도(80~220 rpm)에 대한 에탄올 생산량은 각각 99% 신뢰구간을 가졌다. 종속변수로 에탄올 생산량을 적용하였을 때 $30^{\circ}C$, 170 rpm에서 최대의 에탄올 생산을 예측할 수 있었다(22.5 g/L). 최적의 온도 및 교반속도에서 최적 질소원을 조사한 결과 yeast extract (1.25 g/L)와 urea (1.25 g/L)를 혼합하여 사용하였을 경우 에탄올 생산량은 증가하였으며 trace metal 성분과 비타민은 첨가하지 않았을 때 에탄올 생산이 촉진되었다. 동시당화 발효를 위한 $KH_2PO_4$, $MgSO_4{\cdot}7H_2O$의 최적 농도는 각각 1 g/L, 0.25 g/L로 나타났다.

• Journal of Microbiology and Biotechnology
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• 제31권10호
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• pp.1446-1454
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• 2021

Herein, we cloned and expressed an endo-β-1,4-glucanase gene (celA1805) from Bacillus subtilis B111 in Escherichia coli. The recombinant celA1805 contains a glycosyl hydrolase (GH) family 8 domain and shared 76.8% identity with endo-1,4-β-glucanase from Bacillus sp. KSM-330. Results showed that the optimal pH and temperature of celA1805 were 6.0 and 50℃, respectively, and it was stable at pH 3-9 and temperature ≤50℃. Metal ions slightly affected enzyme activity, but chemical agents generally inhibited enzyme activity. Moreover, celA1805 showed a wide substrate specificity to CMC, barley β-glucan, lichenin, chitosan, PASC and avicel. The K_m and V_max values of celA1805 were 1.78 mg/ml and 50.09 µmol/min/mg. When incubated with cellooligosaccharides ranging from cellotriose to cellopentose, celA1805 mainly hydrolyzed cellotetrose (G4) and cellopentose (G5) to cellose (G2) and cellotriose (G3), but hardly hydrolyzed cellotriose. The concentrations of reducing sugars saccharified by celA1805 from wheat straw, rape straw, rice straw, peanut straw, and corn straw were increased by 0.21, 0.51, 0.26, 0.36, and 0.66 mg/ml, respectively. The results obtained in this study suggest potential applications of celA1805 in biomass saccharification.

• Journal of Microbiology and Biotechnology
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• 제32권1호
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• pp.117-125
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• 2022

Until recently, four types of cellobiose-fermenting Saccharomyces cerevisiae strains have been developed by introduction of a cellobiose metabolic pathway based on either intracellular β-glucosidase (GH1-1) or cellobiose phosphorylase (CBP), along with either an energy-consuming active cellodextrin transporter (CDT-1) or a non-energy-consuming passive cellodextrin facilitator (CDT-2). In this study, the ethanol production performance of two cellobiose-fermenting S. cerevisiae strains expressing mutant CDT-2 (N306I) with GH1-1 or CBP were compared with two cellobiose-fermenting S. cerevisiae strains expressing mutant CDT-1 (F213L) with GH1-1 or CBP in the simultaneous saccharification and fermentation (SSF) of cellulose under various conditions. It was found that, regardless of the SSF conditions, the phosphorolytic cellobiose-fermenting S. cerevisiae expressing mutant CDT-2 with CBP showed the best ethanol production among the four strains. In addition, during SSF contaminated by lactic acid bacteria, the phosphorolytic cellobiose-fermenting S. cerevisiae expressing mutant CDT-2 with CBP showed the highest ethanol production and the lowest lactate formation compared with those of other strains, such as the hydrolytic cellobiose-fermenting S. cerevisiae expressing mutant CDT-1 with GH1-1, and the glucose-fermenting S. cerevisiae with extracellular β-glucosidase. These results suggest that the cellobiose-fermenting yeast strain exhibiting low energy consumption can enhance the efficiency of the SSF of cellulosic biomass.