Isoprene production by Rhodobacter sphaeroides and its antimicrobial activity.

Extensive studies on the antimicrobial activity of terpene-based substances, which are the main components of essential oils, are continuously underway. And some hydrocarbons constituting antimicrobial substances have been reported to exhibit the antimicrobial activity. This study confirmed the production of isoprene, the most basic constituent hydrocarbon of terpene, by Rhodobacter sphaeroides, and investigated the antimicrobial activity of isoprene and its mechanism. We developed an air-sharing culture system in which different bacterial cultures aseptically shared the same atmosphere, to evaluate the effect of volatile isoprene. Effects were tested on two Gram-negative bacteria, and on two Gram-positive bacteria. As a result, the isoprene released from R. sphaeroides showed the antimicrobial activity against all evaluated strains, especially against Gram-positive bacteria than Gram-negative bacteria. In addition, the microstructure of the bacteria was evaluated via FE-SEM. The FE-SEM images showed that isoprene has the antimicrobial activity mechanism that causes cell death by acting on the cell wall or the extracellular membrane.

Development and economic analysis of bioethanol production facilities using lignocellulosic biomass.

An integrated process for bioethanol production from Miscanthus sacchariflorus was used to construct a bench-scale plant constructed and an economic analysis was carried out to investigate the feasibility of its application to a commercial plant. The bench-scale plant was operated for 1 month and an economic analysis and sensitivity analysis was performed on the data acquired. In this study, 100,000 kL of bioethanol could be produced annually from 606,061 tons of M. sacchariflorus and the production cost was calculated to be US$1.76/L. However, the by-products of this process such as xylose molasses and lignin can be sold or used as a heat source, which can decrease the ethanol production costs. Therefore, the final ethanol production cost was calculated to be US$1.31/L, and is considerably influenced by the enzyme cost. The results and data obtained should contribute to the development of a commercial-scale lignocellulosic bioethanol plant.

Utilization of by-products derived from bioethanol production process for cost-effective production of lactic acid.

The by-products of bioethanol production such as thin stillage (TS) and condensed distillers solubles (CDS) were used as a potential nitrogen source for economical production of lactic acid. The effect of those by-products and their concentrations on lactic acid fermentation were investigated using Lactobacillus paracasei CHB2121. Approximately, 6.7 g/L of yeast extract at a carbon source to nitrogen source ratio of 15 was required to produce 90 g/L of lactic acid in the medium containing 100 g/L of glucose. Batch fermentation of TS medium resulted in 90 g/L of lactic acid after 48 h, and the medium containing 10 % CDS resulted in 95 g/L of lactic acid after 44 h. Therefore, TS and CDS could be considered as potential alternative fermentation medium for the economical production of lactic acid. Furthermore, lactic acid fermentation was performed using only cassava and CDS for commercial production of lactic acid. The volumetric productivity of lactic acid [2.94 g/(L·h)] was 37 % higher than the productivity obtained from the medium with glucose and CDS.

Pretreatment solution recycling and high-concentration output for economical production of bioethanol.

The purpose of this study was to enhance the economic efficiency of producing bioethanol. Pretreatment solution recycling is expected to increase economic efficiency by reducing the cost of pretreatment and the amount of wastewater. In addition, the production of high-concentration bioethanol could increase economic efficiency by reducing the energy cost of distillation. The pretreatment conditions were 95 °C, 0.72 M NaOH, 80 rpm twin-screw speed, and flow rate of 90 mL/min at 18 g/min of raw biomass feeding for pretreatment solution recycling. The pretreatment with NaOH solution recycling was conducted five times. All of the components and the pretreatment efficiency were similar, despite reuse. In addition, we developed a continuous biomass feeding system for production of high-concentration bioethanol. Using this reactor, the bioethanol productivity was investigated using various pretreated biomass feeding rates in a simultaneous saccharification and fermentation (SSF) process. The maximum ethanol concentration, yield, and productivity were 74.5 g/L, 89.5%, and 1.4 g/L h, respectively, at a pretreated biomass loading of approximately 25% (w/v) with an enzyme dosage of 30 FPU g/cellulose. The results presented here constitute an important contribution toward the production of bioethanol from Miscanthus.

Characterization of ethanol fermentation waste and its application to lactic acid production by Lactobacillus paracasei.

In this study, an ethanol fermentation waste (EFW) was characterized for use as an alternative to yeast extract for bulk fermentation processes. EFW generated from a commercial plant in which ethanol is produced from cassava/rice/wheat/barley starch mixtures using Saccharomyces cerevisiae was used for lactic acid production by Lactobacillus paracasei. The effects of temperature, pH, and duration on the autolysis of an ethanol fermentation broth (EFB) were also investigated. The distilled EFW (DEFW) contained significant amounts of soluble proteins (2.91 g/l), nitrogen (0.47 g/l), and amino acids (24.1 mg/l). The autolysis of the EFB under optimum conditions released twice as much amino acids than in the DEFW. Batch fermentation in the DEFW increased the final lactic acid concentration, overall lactic acid productivity, and lactic acid yield on glucose by 17, 41, and 14 %, respectively, in comparison with those from comparable fermentation in a lactobacillus growth medium (LGM) that contained 2 g/l yeast extract. Furthermore, the overall lactic acid productivity in the autolyzed then distilled EFW (ADEFW) was 80 and 27 % higher than in the LGM and DEFW, respectively.

A novel lactic acid bacterium for the production of high purity L-lactic acid, Lactobacillus paracasei subsp. paracasei CHB2121.

Fermentation-derived lactic acid has several potential industrial uses as an intermediate carbon chemical and a raw material for biodegradable polymer. We therefore undertook the identification of a novel bacterial strain that is capable of producing high concentrations of lactic acid and has potential commercial applications. A novel L(+)-lactic acid producing bacterium, Lactobacillus paracasei subsp. paracasei CHB2121 was isolated from soil obtained near an ethanol production factory and identified by 16S rRNA gene sequence analysis and characterization using an API 50 CHL kit. L. paracasei subsp. paracasei CHB2121 efficiently produced 192 g/L lactic acid from medium containing 200 g/L of glucose, with 3.99 g/(L·h) productivity, and 0.96 g/g yield. In addition, the optical purity of the produced lactic acid was estimated to be 96.6% L(+)-lactic acid. The newly identified L. paracasei subsp. paracasei CHB2121 efficiently produces high concentrations of lactic acid, and may be suitable for use in the industrial production of lactic acid.

Simultaneous saccharification and continuous fermentation of sludge-containing mash for bioethanol production by Saccharomyces cerevisiae CHFY0321.

A continuous process was employed to improve the volumetric productivity of bioethanol production from cassava mash containing sludge and to simplify the process of ethanol production from cassava. After raw cassava powder was liquefied, it was used directly in a continuous process without sludge filtration or saccharification. A fermentor consisting of four linked stirrer tanks was used for simultaneous saccharification and continuous fermentation (SSCF). Although the mash contained sludge, continuous fermentation was successfully achieved. We chose the dilution rate on the basis of the maximum saccharification time; the highest volumetric productivity and ethanol yield were observed at a dilution rate of 0.028 h⁻¹. The volumetric productivity, final ethanol concentration, and % of theoretical ethanol yield were 2.41 g/Lh, 86.1g/L, and 91%, respectively. This SSCF process using the self-flocculating yeast Saccharomyces cerevisiae CHFY0321 illustrates the possibility of realizing cost-effective bioethanol production by eliminating additional saccharification and filtration processes. In addition, flocculent CHFY0321, which our group developed, showed excellent fermentation results under continuous ethanol production.

Continuous ethanol production from cassava through simultaneous saccharification and fermentation by self-flocculating yeast Saccharomyces cerevisiae CHFY0321.

In this study, a fermentor consisting of four linked stirred towers that can be used for simultaneous saccharification and fermentation (SSF) and for the accumulation of cell mass was applied to the continuous production of ethanol using cassava as the starchy material. For the continuous process with SSF, the pretreated cassava liquor and saccharification enzyme at total sugar concentrations of 175 g/L and 195 g/L were continuously fed to the fermentor with dilution rates of 0.014, 0.021, 0.031, 0.042, and 0.05 h(-1). Considering the maximum saccharification time, the highest volumetric productivity and ethanol yield were observed at a dilution rate of 0.042 h(-1). At dilution rates in the range of 0.014 h(-1) to 0.042 h(-1), high production rates were observed, and the yeast in the first to fourth fermentor showed long-term stability for 2 months with good performance. Under the optimal culture conditions with a feed sugar concentration of 195 g/L and dilution rate of 0.042 h(-1), the ethanol volumetric productivity and ethanol yield were 3.58 g/L x h and 86.2%, respectively. The cell concentrations in the first to fourth stirred tower fermentors were 74.3, 71.5, 71.2, and 70.1 g dry cell/L, respectively. The self-flocculating yeast, Saccharomyces cerevisiae CHFY0321, developed by our group showed excellent fermentation results under continuous ethanol production.

Repeated-batch fermentation using flocculent hybrid, Saccharomyces cerevisiae CHFY0321 for efficient production of bioethanol.

In this study, the repeated-batch fermentation of liquefied cassava medium using the flocculent hybrid Saccharomyces cerevisiae CHFY0321 was investigated for semicontinuous, high-throughput production of bioethanol. Cassava medium was selected due to the industrial requirement for a cheap starchy substrate. Fermentations were performed by simultaneous saccharification and fermentation (SSF) with a set of ten batches successfully completing a series within the repeated fermentation process. In addition, pH of the culture medium was not controlled to simplify ethanol production for future use in industry. Optimal recycling volume was found to be 5%. Volumetric productivity, final ethanol concentration, and ethanol yield were measured at 3.34 g l(-1) h(-1), 84.5 g l(-1), and 90.7%, respectively. Cell recycling (24.5 g DCW l(-1)) resulted in 1.8-fold decrease in fermentation time (24 h) and 1.8-fold increase in volumetric productivity compared with the ordinary batch fermentation. Therefore, repeated-batch SSF using flocculent CHFY0321 demonstrates the possibility of cost-effective bioethanol production by eliminating additional saccharification and inoculation steps.

Production of fumaric acid using rice bran and subsequent conversion to succinic acid through a two-step process.

The fungal production of fumaric acid using rice bran and subsequent bacterial conversion of succinic acid using fungal culture broth were investigated. Since the rice bran contains abundant proteins, amino acids, vitamins, and minerals, it is suitable material that fungi use as a nitrogen source. The effective concentration of rice bran to produce fumaric acid was 5 g/L. A large amount of rice bran caused excessive fungal growth rather than enhance fumaric acid production. In addition, we could produce fumaric acid without the addition of zinc and iron. Fungal culture broth containing approx 25 g/L of fumaric acid was directly employed for succinic acid conversion. The amount of glycerol and yeast extract required for succinic acid conversion was reduced to 70 and 30%, respectively, compared with the amounts cited in previous studies.