Production of butanol and isopropanol with an immobilized <Emphasis Type="Italic">Clostridium</Emphasis>

Clostridium beijerinckii optinoii is a Clostridium species that produces butanol, isopropanol and small amounts of ethanol. This study compared the performances of batch and continuous immobilized cell fermentations, investigating how media flow rates and nutritional modification affected solvent yields and productivity. In 96-h batch cultures, with 80 % of the 30 g L^?1 glucose consumed in synthetic media, solvent concentration was 9.45 g L^?1 with 66.0 % as butanol. In a continuous fermentation using immobilized C. beijerinckii optinoii cells, also with 80 % of 30 g L^?1 glucose utilization, solvent productivity increased to 1.03 g L^?1 h^?1. Solvent concentration reached 12.14 g L^?1 with 63.0 % as butanol. Adjusting the dilution rate from 0.085 to 0.050 h^?1 to allow extended residence time in column was required when glucose concentration in fresh media was increased from 30 to 50 g L^?1. When acetate was used to improve the buffer capacity in media, the solvent concentration reached 12.70 on 50 g L^?1 glucose. This continuous fermentation using immobilized cells showed technical feasibility for solvent production.     

Kinetics of growth and ethanol formation from a mix of glucose/xylose substrate by Kluyveromyces marxianus UFV-3

The fermentation of both glucose and xylose is important to maximize ethanol yield from renewable biomass feedstocks. In this article, we analyze growth, sugar consumption, and ethanol formation by the yeast Kluyveromyces marxianus UFV-3 using various glucose and xylose concentrations and also under conditions of reduced respiratory activity. In almost all the conditions analyzed, glucose repressed xylose assimilation and xylose consumption began after glucose had been exhausted. A remarkable difference was observed when mixtures of 5 g L^?1 glucose/20 g L^?1 xylose and 20 g L^?1 glucose/20 g L^?1 xylose were used. In the former, the xylose consumption began immediately after the glucose depletion. Indeed, there was no striking diauxic phase, as observed in the latter condition, in which there was an interval of 30 h between glucose depletion and the beginning of xylose consumption. Ethanol production was always higher in a mixture of glucose and xylose than in glucose alone. The highest ethanol concentration (8.65 g L^?1) and cell mass concentration (4.42 g L^?1) were achieved after 8 and 74 h, respectively, in a mixture of 20 g L^?1 glucose/20 g L^?1 xylose. When inhibitors of respiration were added to the medium, glucose repression of xylose consumption was alleviated completely and K. marxianus was able to consume xylose and glucose simultaneously.     

Enhancing ethanol production from cellulosic sugars using <Emphasis Type="Italic">Scheffersomyces (Pichia) stipitis</Emphasis>

Studies were performed on the effect of CaCO₃ and CaCl₂ supplementation to fermentation medium for ethanol production from xylose, glucose, or their mixtures using Scheffersomyces (Pichia) stipitis. Both of these chemicals were found to improve maximum ethanol concentration and ethanol productivity. Use of xylose alone resulted in the production of 20.68 ± 0.44 g L^?1 ethanol with a productivity of 0.17 ± 0.00 g L^?1 h^?1, while xylose plus 3 g L^?1 CaCO₃ resulted in the production of 24.68 ± 0.75 g L^?1 ethanol with a productivity of 0.21 ± 0.01 g L^?1 h^?1. Use of xylose plus glucose in combination with 3 g L^?1 CaCO₃ resulted in the production of 47.37 ± 0.55 g L^?1 ethanol (aerobic culture), thus resulting in an ethanol productivity of 0.39 ± 0.00 g L^?1 h^?1. These values are 229 % of that achieved in xylose medium. Supplementation of xylose and glucose medium with 0.40 g L^?1 CaCl₂ resulted in the production of 44.84 ± 0.28 g L^?1 ethanol with a productivity of 0.37 ± 0.02 g L^?1 h^?1. Use of glucose plus 3 g L^?1 CaCO₃ resulted in the production of 57.39 ± 1.41 g L^?1 ethanol under micro-aerophilic conditions. These results indicate that supplementation of cellulosic sugars in the fermentation medium with CaCO₃ and CaCl₂ would improve economics of ethanol production from agricultural residues.     

Production of flavonoids and polysaccharide by adding elicitor in different cellular cultivation processes of Glycyrrhiza uralensis Fisch

In this study, callus and cell suspension were induced from seedlings of licorice (G. uralensis). In addition, it was revealed that the appropriate concentration of sucrose could promote the callus growth and increase the content of polysaccharide. The methyl jasmonate (MJ) and phenylalanine (PHE) could enhance the callus growth and content of flavonoids for G. uralensis. For producing more flavonoids and polysaccharide, two-stage cultivation was performed. In the first step, 30 g L^?1 sucrose was fed into a 5-L balloon-type bubble bioreactor on 8th day of culture to enhance cell production and metabolite production. In a two-stage cultivation process, PHE (2 mM) and MJ (5 mg L^?1) were added into a 5-L balloon-type bubble bioreactor after 10 days of culture. Using a fed-batch cultivation strategy (30 g L^?1 sucrose was fed into a 5-L balloon-type bubble bioreactor on 8th day), polysaccharide production was enhanced to 1.19 g L^?1, which was 2.12-fold greater than that in batch cultivation. The flavonoids yield (55.42 mg L^?1) which was about 22 % higher than that in batch cultivation was obtained on 21st day. In a two-stage cultivation process, the polysaccharide content was increased by 1.14- and 2.12-fold compared with fed-batch cultivation and batch cultivation on 15th day. Meanwhile, total flavonoids yield (132.36 mg L^?1) on 15th day, was increased by 2.26- and 2.67-fold compared with fed-batch cultivation and batch cultivation. In conclusion, two-stage cultivation process combined with the sucrose and elicitor treatment could promote both the callus growth and the secondary metabolites accumulation.     

Microbial production of a biofuel (acetone–butanol–ethanol) in a continuous bioreactor: impact of bleed and simultaneous product removal

Acetone butanol ethanol (ABE) was produced in an integrated continuous one-stage fermentation and gas stripping product recovery system using Clostridium beijerinckii BA101 and fermentation gases (CO₂ and H₂). In this system, the bioreactor was fed with a concentrated sugar solution (250–500 g L^?1 glucose). The bioreactor was bled semi-continuously to avoid accumulation of inhibitory chemicals and products. The continuous system was operated for 504 h (21 days) after which the fermentation was intentionally terminated. The bioreactor produced 461.3 g ABE from 1,125.0 g total sugar in 1 L culture volume as compared to a control batch process in which 18.4 g ABE was produced from 47.3 g sugar. These results demonstrate that ABE fermentation can be operated in an integrated continuous one-stage fermentation and product recovery system for a long period of time, if butanol and other microbial metabolites in the bioreactor are kept below threshold of toxicity.     

<Emphasis Type="Italic">In vitro</Emphasis> sucrose concentration influences microtuber production and diosgenin content in white yam (<Emphasis Type="Italic">Dioscorea rotundata</Emphasis> Poir)

Dioscorea spp. is an important food crop in many countries and the source of the phytochemical diosgenin. Efficient microtuber production could provide source materials for farm-planting stock, for food markets, and for the production of high-diosgenin-producing cultivars. The first step in this study was optimizing the plant growth regulators for plantlet production, followed by a study of the effects of sucrose concentration on microtuber induction and diosgenin production. Significantly, more shoots (3.5) were produced at 4.65 μM (1 mg L^?1) kinetin (KIN), longer shoots (4.1 cm) were obtained at 2.46 μM (0.5 mg L^?1) indole-3-butyric acid (IBA), and root number (3.9) was significantly higher at 5.38 μM (1 mg L^?1) naphthalene acetic acid (NAA) than in other treatments. Increased sucrose concentrations in the optimized growth medium with 4.65 μM KIN and 5.38 μM NAA had significant effects on microtuber production (p < 0.01) and diosgenin content (p < 0.05). The most microtubers (6.2) were obtained with 100 g L^?1 sucrose, while those on 80 g L^?1 sucrose were the heaviest (0.7 g) and longest (7.4 mm). Microtubers formed in medium with 80 g L^?1 sucrose had significantly higher diosgenin content (3.64% [w/w]) than those in other sucrose treatments (< 2%) and was similar to that of field-grown parent tubers (3.79%). This result indicates an important role for sucrose in both microtuber growth and diosgenin production. Medium containing 4.65 μM KIN and 5.38 μM NAA is recommended for plantlet production, and medium containing 80 g L^?1 sucrose is recommended for microtuber and diosgenin production.     

Effect of controlled oxygen limitation on Candida shehatae physiology for ethanol production from xylose and glucose

Carbon distribution and kinetics of Candida shehatae were studied in fed-batch fermentation with xylose or glucose (separately) as the carbon source in mineral medium. The fermentations were carried out in two phases, an aerobic phase dedicated to growth followed by an oxygen limitation phase dedicated to ethanol production. Oxygen limitation was quantified with an average specific oxygen uptake rate (OUR) varying between 0.30 and 2.48 mmolO₂ g dry cell weight (DCW)^?1 h^?1, the maximum value before the aerobic shift. The relations among respiration, growth, ethanol production and polyol production were investigated. It appeared that ethanol was produced to provide energy, and polyols (arabitol, ribitol, glycerol and xylitol) were produced to reoxidize NADH from assimilatory reactions and from the co-factor imbalance of the two-first enzymatic steps of xylose uptake. Hence, to manage carbon flux to ethanol production, oxygen limitation was a major controlled parameter; an oxygen limitation corresponding to an average specific OUR of 1.19 mmolO₂ g DCW^?1 h^?1 allowed maximization of the ethanol yield over xylose (0.327 g g^?1), the average productivity (2.2 g l^?1 h^?1) and the ethanol final titer (48.81 g l^?1). For glucose fermentation, the ethanol yield over glucose was the highest (0.411 g g^?1) when the specific OUR was low, corresponding to an average specific OUR of 0.30 mmolO₂ g DCW^?1 h^?1, whereas the average ethanol productivity and ethanol final titer reached the maximum values of 1.81 g l^?1 h^?1 and 54.19 g l^?1 when the specific OUR was the highest.     

Enhancing isomaltulose production by recombinant Escherichia coli producing sucrose isomerase: culture medium optimization containing agricultural wastes and cell immobilization

Isomaltulose is a structural isomer of sucrose commercially used in food industries. In this work, recombinant Escherichia coli producing sucrose isomerase (SIase) was used to convert sucrose into isomaltulose. To develop an economical industrial medium, untreated cane molasses (10.63 g l^?1), yeast extract (25.93 g l^?1), and corn steep liquor (10.45 g l^?1) were used as main culture compositions for SIase production. The relatively high SIase activity (14.50 ± 0.11 U mg DCW^?1) was obtained by the recombinant cells. To the best of our knowledge, this is the first investigation on SIase production by engineered E. coli using untreated cane molasses. The recombinant E. coli cells expressing the SIase gene were immobilized in calcium alginate gel in order to improve the efficiency of recycling. The immobilization was most effective with 2 % (w/v) sodium alginate and 3 % (w/v) calcium chloride. The optimal initial biomass for immobilization was 20 % (w/v, wet wt.), with a hardening time of 8 h for cell immobilization. The immobilized E. coli cells exhibited good stability for 30 batches with the productivity of 0.45 g isomaltulose g pellet^?1 h^?1. A continuous isomaltulose formation process using a column reactor remained stable for 40 days with 83 ± 2 % isomaltulose yield, which would be beneficial for economical production of isomaltulose.     

Selective fengycin production in a modified rotating discs bioreactor

Production of lipopeptides fengycin and surfactin in rotating discs bioreactor was studied. The effects of rotation velocity and the addition of agitators between the discs on volumetric oxygen transfer coefficient k _L a were firstly studied in model media. Then the production of lipopeptides was also studied at different agitation conditions in the modified bioreactor (with agitators). The effect of agitation on dissolved oxygen, on submerged and immobilized biomass, on lipopeptide concentrations and yields and on the selectivity of the bioreaction was elucidated and discussed. The proposed modified rotating discs bioreactor allowed to obtain high fengycin concentrations (up to 787 mg L^?1), but also better selectivity of the bioreaction towards fengycin (up to 88 %) and better yields of fengycin per glucose (up to 62.9 mg g^?1), lipopeptides per glucose (up to 71.5 mg g^?1), fengycin per biomass (up to 309 mg g^?1) and lipopeptides per biomass (up to 396 mg g^?1) than those reported in the literature. Highest fengycin production and selectivity were obtained at agitation velocity of 30 min^?1. The proposed non-foaming fermentation process could contribute to the scale-up of lipopeptide fermentors and promote the industrial production of fengycin. The proposed bioreactor and bioprocess could be very useful also for the production of other molecules using bioprocesses requiring bubbleless oxygen supply.     

Enhanced citric acid production by a yeast <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> over-expressing a pyruvate carboxylase gene

In this study, after the expression of a pyruvate carboxylase gene (PYC) cloned from Meyerozyma guilliermondii in a marine-derived yeast Yarrowia lipolytica SWJ-1b, a transformant PG86 obtained had much higher PYC activity than Y. lipolytica SWJ-1b. At the same time, the PYC gene expression and citric acid (CA) production by the transformant PG86 were also greatly enhanced. When glucose concentration in the medium was 60.0 g L^?1, CA concentration formed by the transformant PG86 was 34.02 g L^?1, leading to a CA yield of 0.57 g g^?1 of glucose. During a 10-L fed-batch fermentation, the final concentration of CA was 101.0 ± 1.3 g L^?1, the yield was 0.89 g g^?1 of glucose, the productivity was 0.42 g L^?1 h^?1 and only 5.93 g L^?1 reducing sugar was left in the fermented medium within 240 h of the fed-batch fermentation. HPLC analysis showed that most of the fermentation products were CA.     

Evaluation of the tolerance of acetic acid and 2-furaldehyde on the growth of Pichia stipitis and its respiratory deficient

The use of lignocellulosic residues for ethanol production is limited by toxic compounds in fermenting yeasts present in diluted acid hydrolysates like acetic acid and 2-furaldehyde. The respiratory deficient phenotype gives the cell the ability to resist several toxic compounds. So the aim of this work was to evaluate the tolerance to toxic compounds present in lignocellulosic hydrolysates like acetic acid and 2-furaldehyde in Pichia stipitis and its respiratory deficient strains. The respiratory deficient phenotype was induced by exposure to chemical agents such as acriflavine, acrylamide and rhodamine; 23 strains were obtained. The selection criterion was based on increasing specific ethanol yield (g ethanol g^?1 biomass) with acetic acid and furaldehyde tolerance. The screening showed that P. stipitis NRRL Y-7124 ACL 2-1RD (lacking cytochrome c), obtained using acrylamide, presented the highest specific ethanol production rate (1.82 g g^?1 h^?1). Meanwhile, the ACF8-3RD strain showed the highest acetic acid tolerance (7.80 g L^?1) and the RHO2-3RD strain was able to tolerate up to 1.5 g L^?1 2-furaldehyde with a growth and ethanol production inhibition of 23 and 22 %, respectively. The use of respiratory deficient yeast phenotype is a strategy for ethanol production improvement in a medium with toxic compounds such as hydrolysed sugarcane bagasse amongst others.     

Improving the production yield and productivity of 1,3-dihydroxyacetone from glycerol fermentation using <Emphasis Type="Italic">Gluconobacter oxydans</Emphasis> NL71 in a compressed oxygen supply-sealed and stirred tank reactor (COS-SSTR)

In this study, a compressed oxygen gas supply was connected to a sealed aerated stirred tank reactor (COS-SSTR) bio-system, leading to a high-oxygen pressure bioreactor used to improve the bio-transformative performance in the production of 1,3-dihydroxyacetone (DHA) from glycerol using Gluconobacter oxydans NL71. A concentration of 301.2 ± 8.2 g L^?1 DHA was obtained from glycerol after 32 h of fed-batch fermentation in the COS-SSTR system. The volumetric productivity for this process was 9.41 ± 0.23 g L^?1 h^?1, which is presently the highest obtained level of glycerol bioconversion into DHA. These results show that the application of this bioreactor would enable microbial production of DHA from glycerol at the industrial scale.     

Ethanol production by immobilized whole cells ofZymomonas mobilis in a continuous flow expanded bed bioreactor and a continuous flow stirred tank bioreactor

Continuous ethanol fermentation by immobilized whole cells ofZymomonas mobilis was investigated in an expanded bed bioreactor and in a continuous stirred tank reactor at glucose concentrations of 100, 150 and 200 g L^–1. The effect of different dilution rates on ethanol production by immobilized whole cells ofZymomonas mobilis was studied in both reactors. The maximum ethanol productivity attained was 21 g L^–1 h^–1 at a dilution rate of 0.36 h^–1 with 150 g glucose L^–1 in the continuous expanded bed bioreactor. The conversion of glucose to ethanol was independent of the glucose concentration in both reactors.     

Kinsenoside and polysaccharide production by rhizome culture of <Emphasis Type="Italic">Anoectochilus roxburghii</Emphasis> in continuous immersion bioreactor systems

Anoectochilus roxburghii (Wall) Lindl. (Orchidaceae) is a precious raw material for medicine. However, the wild resource of A. roxburghii has been endangered, and artificial cultivation results in low yields. To provide rhizomes of A. roxburghii as alternative plant materials, the present study used continuous immersion bioreactor systems to investigate several factors affecting rhizome biomass and bioactive compound accumulation. The bioreactor with a net at the bottom of the sphere in the bioreactor was suitable for production of rhizomes. The rhizome biomass and kinsenoside and polysaccharide accumulation peaked at 30 days of the bioreactor culture. Thus, 30 days was the appropriate culture period. Maximum rhizome biomass and kinsenoside and polysaccharide accumulation were determined when a bioreactor was inoculated with 12.5 g L^??1 (fresh weight) of rhizomes, aerated at 500 mL min^??1, and maintained under 45 µmol m^??2 s^??1 light intensity. This process resulted in the production of 2980.5 mg L^??1 of kinsenoside and 5672.9 mg L^?1 of polysaccharides.     

Optimization of culture conditions for the production of polysaccharides and kinsenoside from the rhizome cultures of <Emphasis Type="Italic">Anoectochilus roxburghii</Emphasis> (Wall.) Lindl.

The present study designed two sets of experiments by using the uniform design method and investigated the effects of medium components on the accumulation of bioactive compounds (polysaccharide and kinsenoside) in rhizomes, in order to select a suitable culture medium for the rhizome suspension culture of Anoectochilus roxburghii (Wall.) Lindl. Among the combinations of Murashige and Skoog (MS) medium strengths and plant growth regulator (benzylaminopurine, BA; kinetin, KT; and α-naphthaleneacetic acid, NAA) concentrations, and the combinations of nitrogen, phosphorus, and sucrose concentrations, the maximum yield of polysaccharides and kinsenoside was achieved with 0.75 × MS?+?2.0 mg L^?1 BA?+?0.2 mg L^?1 KT?+?0.5 mg L^?1 NAA and 45 mM nitrogen?+?0.93 mM phosphorus?+?35 g L^?1 sucrose, respectively. Therefore, the optimal rhizome suspension culture medium was 0.75 × MS medium supplemented with 2.0 mg L^?1 BA, 0.2 mg L^?1 KT, 0.5 mg L^?1 NAA, and 35 g L^?1 sucrose. Yeast extract (YE) enhanced bioactive compound accumulation in rhizomes. The polysaccharide and kinsenoside production was significantly improved when 75 mg L^?1 YE was added to the culture medium after 30 d of rhizome suspension culture; 8.3 g L^?1 of polysaccharide and 6.1 g L^?1 of kinsenoside were obtained after 4 d of YE treatment. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of YE-treated rhizomes was higher than that of YE-untreated rhizomes, demonstrating enhanced antioxidant activity of the treated bioreactor-cultured rhizomes.     

Effect of sugar concentration on ginsenoside biosynthesis in hairy root cultures of Panax quinquefolium cultivated in shake flasks and nutrient sprinkle bioreactor

The study assessed the influence of sugar concentration (10, 20, 30, 50, 70, 100, 120 g l^?1) on growth and ginsenoside biosynthesis in Panax quinquefolium hairy roots cultivated in shake flasks and a nutrient sprinkle bioreactor. The highest growth rate was achieved in medium containing 3–5 % sucrose. More than 70 g l^?1 or less than 20 g l^?1 sugar content in the medium induces significant inhibition of root growth when cultivated in shake flasks. The saponin content was determined using HPLC. The maximum yield (above 9 mg g^?1 d.w.) of the sum of six examined ginsenosides (Rb₁, Rb₂, Rc, Rd, Re and Rg₁) in hairy roots cultivated in shake flasks was obtained with 30 g l^?1 sucrose in the medium. The sucrose concentration in the medium was found to correlate with saponin content in bioreactor-cultured specimens. A higher level of protopanaxadiol derivatives was found for lower (20 and 30 g l^?1) sucrose concentrations; higher sucrose concentrations (50 and 70 g l^?1) in the medium stimulated a higher level of Rg group saponins.     

Process Engineering for High-Cell-Density Cultivation of Lipid Rich Microalgal Biomass of <Emphasis Type="Italic">Chlorella</Emphasis> sp. FC2 IITG

In the present study, process engineering strategy was applied to achieve lipid-rich biomass with high density of Chlorella sp. FC2 IITG under photoautotrophic condition. The strategy involved medium optimization, intermittent feeding of limiting nutrients, dynamic change in light intensity, and decoupling growth and lipid induction phases. Medium optimization was performed using combinations of artificial neural network or response surface methodology with genetic algorithm (ANN-GA and RSM-GA). Further, a fed-batch operation was employed to achieve high cell density with intermittent feeding of nitrate and phosphate along with stepwise increase in light intensity. Finally, mutually exclusive biomass and lipid production phases were decoupled into two-stage cultivation process: biomass generation in first stage under nutrient sufficient condition followed by lipid enrichment through nitrogen starvation. The key findings were as follows: (i) ANN-GA resulted in an increase in biomass titer of 157 % (0.95 g L^?1) in shake flask and 42.8 % (1.0 g L^?1) in bioreactor against unoptimized medium at light intensity of 20 μE m^?2 s^?1; (ii) further optimization of light intensity in bioreactor gave significantly improved biomass titer of 5.6 g L^?1 at light intensity of 250 μE m^?2 s^?1; (iii) high cell density of 13.5 g L^?1 with biomass productivity of 675 mg L^?1 day^?1 was achieved with dynamic increase in light intensity and intermittent feeding of limiting nutrients; (iv) finally, two-phase cultivation resulted in biomass titer of 17.7 g L^?1 and total lipid productivity of 313 mg L^?1 day^?1 which was highest among Chlorella sp. under photoautotrophic condition.     

Bioprospecting of thermo- and osmo-tolerant fungi from mango pulp–peel compost for bioethanol production

The persistent edaphic stress on microbial succession due to dynamic changes during composting was explored for selection of multi-stress tolerant microbe(s) desirable for ethanol production. A total of 23 strains were isolated from mango compost using four successive enrichments in YP broth (g l^?1): glucose, 100; 150; 250 with ethanol (40) and cycloheximide (0.4) at 40 °C, pH 6.0. Based on multi-gene ribotyping, 14 yeasts (61 %) of Saccharomycetaceae, 2 filamentous fungi (8.6 %) and 7 bacteria (30.4 %) were obtained. Phenetic and phylogenetic analysis of the 14 yeasts revealed 64.3 % tolerant to 500 g l^?1 glucose, growth at 45 °C and resemblance to Candida sp. (14.3 %), Kluyveromyces marxianus (35.7 %), Pichia kudriavzevii (21.4 %) and Saccharomyces cerevisiae (28.6 %). Assessment of the 14 yeasts in glucose fermentation medium (pH 4.5 at 40 °C) showed ethanol productivity of ≥92 % by 12 yeasts with theoretical yields of 90–97 %. Fermentation of molasses (150 g l^?1 glucose equivalent) by P. kudriavzevii D1C at 40 °C resulted in 73.70 ± 0.02 g l^?1 ethanol and productivity of 4.91 ± 0.01 g l^?1 h^?1. Assessment of P. kudriavzevii D1C revealed multi-stress tolerance towards 5-hydroxymethyl furfural, ethanol (20 %, v/v), high gravity and H₂O₂ (0.3 M) indicating suitability for ethanol production using high gravity molasses and pre-treated lignocellulosic biomass fermentation.     

Evaluation of ethanol production by a new isolate of yeast during fermentation in synthetic medium and sugarcane bagasse hemicellulosic hydrolysate

A new xylose fermenting yeast was isolated from over-ripe banana by enrichment in xylose-containing medium. The phylogenetic analysis of ITS1-5.8S-ITS2 region sequences of ribosomal RNA of isolate BY2 revealed that it shows affiliation to genus Pichia and clades with Pichia caribbica. In batch fermentation, Pichia strain BY2 fermented xylose, producing 15 g l^?1 ethanol from 30 g l^?1 xylose under shaking conditions at 28°C, with ethanol yield of 0.5 g g^?1 and volumetric productivity of 0.31 g l^?1 h^?1. The optimum pH range for ethanol production from xylose by Pichia strain BY2 was 5–7. Pichia strain BY2 also produced 6.08 g l^?1 ethanol from 30 g l^?1 arabinose. Pichia strain BY2 can utilize sugarcane bagasse hemicellulose acid hydrolysate for alcohol production, efficiency of fermentation was improved by neutralization, and sequential use of activated charcoal adsorption method. Percent total sugar utilized and ethanol yield for the untreated hydrolysate was 17.14% w/v and 0.33 g g^?1, respectively, compared with 66.79% w/v and 0.45 g g^?1, respectively, for treated hemicellulose acid hydrolysate. This new yeast isolate showed ethanol yield of 0.45 g g^?1 and volumetric productivity of 0.33 g l^?1 h^?1 from sugarcane bagasse hemicellulose hydrolysate detoxified by neutralization and activated charcoal treatment, and has potential application in practical process of ethanol production from lignocellulosic hydrolysate.     

Co-generation of ethanol and <Emphasis Type="SmallCaps">l</Emphasis>-lactic acid from corn stalk under a hybrid process

Background

Corn stover, as one important lignocellulosic material, has characteristics of low price, abundant output and easy availability. Using corn stover as carbon source in the fermentation of valuable organic chemicals contributes to reducing the negative environmental problems and the cost of production. In ethanol fermentation based on the hydrolysate of corn stover, the conversion rate of fermentable sugars is at a low level because the native S. cerevisiae does not utilize xylose. In order to increase the conversion rate of fermentable sugars deriving from corn stover, an effective and energy saving biochemical process was developed in this study and the residual xylose after ethanol fermentation was further converted to l-lactic acid.

Results

In the hybrid process based on the hydrolysate of corn stover, the ethanol concentration and productivity reached 50.50 g L^?1 and 1.84 g L^?1 h^?1, respectively, and the yield of ethanol was 0.46 g g^?1. The following fermentation of l-lactic acid provided a product titer of 21.50 g L^?1 with a productivity of 2.08 g L^?1 h^?1, and the yield of l-lactic acid was 0.76 g g^?1. By adopting a blank aeration before the inoculation of B. coagulans LA1507 and reducing the final cell density, the l-lactic acid titer and yield reached 24.25 g L^?1 and 0.86 g g^?1, respectively, with a productivity of 1.96 g L^?1 h^?1.

Conclusions

In this work, the air pumped into the fermentor was used as both the carrier gas for single-pass gas stripping of ethanol and the oxygen provider for the aerobic growth of B. coagulans LA1507. Ethanol was effectively separated from the fermentation broth, while the residual medium containing xylose was reused for l-lactic acid production. As an energy-saving and environmental-friendly process, it introduced a potential way to produce bioproducts under the concept of biorefinery, while making full use of the hydrolysate of corn stover.