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Gluconic acid's potential as a wheat straw pretreatment agent was studied at different concentrations (0.125–1 M) and temperatures (160–190 °C) for 30 min, followed by enzymatic hydrolysis. 0.125 M gluconic acid, 170 °C, yielded the highest xylose output, while 0.5 M gluconic acid at 190 °C yielded the best glucose yield. A fraction of gluconic acid decomposed during pretreatment. Detoxified hemicellulose hydrolysate from 0.125 M gluconate at 170 °C for 60 min showed promise for ethanol production. The gluconate contained in the detoxified hemicellulose hydrolysate can be fermented to ethanol along with other hemicellulose sugars present by Escherichia coli SL100. The ethanol yield from gluconate and sugars was about 90.4 ± 1.8%. The pretreated solids can be effectively converted to ethanol by Saccharomyces cerevisiae D5A via simultaneous saccharification and fermentation with the cellulase and β-glucosidase addition. The ethanol yield achieved was 92.8 ± 2.0% of the theoretical maximum. The cellulose conversion was about 70.8 ± 0.8%. [ABSTRACT FROM AUTHOR]

Biological synthesis of high added-value compounds like adipic acid (AA), levulinic acid (LA), or polyhydroxybutyrate (PHB) using pure culture has been separately reported. However, pure culture requires sterile conditions and the use of specific carbon sources resulting in high operating costs. Different alternatives based on the use of mixed microbial cultures (MMC) have been explored to resolve this problem. MMC have been widely reported for the production of PHB, but scarcely reported for LA production and never for AA synthesis. This work presents a novel strategy for the co-production of AA LA, and PHB using MMC. The strategy consists in selecting an MMC producer of AA, LA and PHB from an inoculum obtained from a wastewater treatment plant, which is then subjected to the feast and famine culture strategy in a sequential batch reactor, coupled with a batch reactor step to enhance the accumulation of AA and LA. The results showed that the MMC could produce a 16 ± 2, 23 ± 1 and 5 ± %1 (g compound/g volatile solids) of AA, LA and PHB, respectively, using a non-fermented residual biomass rich in pentose, namely synthetic hemicellulose hydrolysate (SHH) as the carbon source. These results contribute to generating future research to better understand and optimise the biosynthesis of these compounds by MMC. [ABSTRACT FROM AUTHOR]

Biological synthesis of high added-value compounds like adipic acid (AA), levulinic acid (LA), or polyhydroxybutyrate (PHB) using pure culture has been separately reported. However, pure culture requires sterile conditions and the use of specific carbon sources resulting in high operating costs. Different alternatives based on the use of mixed microbial cultures (MMC) have been explored to resolve this problem. MMC have been widely reported for the production of PHB, but scarcely reported for LA production and never for AA synthesis. This work presents a novel strategy for the co-production of AA LA, and PHB using MMC. The strategy consists in selecting an MMC producer of AA, LA and PHB from an inoculum obtained from a wastewater treatment plant, which is then subjected to the feast and famine culture strategy in a sequential batch reactor, coupled with a batch reactor step to enhance the accumulation of AA and LA. The results showed that the MMC could produce a 16 ± 2, 23 ± 1 and 5 ± %1 (g compound/g volatile solids) of AA, LA and PHB, respectively, using a non-fermented residual biomass rich in pentose, namely synthetic hemicellulose hydrolysate (SHH) as the carbon source. These results contribute to generating future research to better understand and optimise the biosynthesis of these compounds by MMC.

Nanocellulose, owing to its environmentally friendly and unique attributes, is gaining traction in various industries. However, commercialization of nanocellulose faces challenges due to structural alterations during drying process, leading to irreversible aggregation. This study, inspired by wood's natural structure, introduces a cellulose nanofibril (CNF) drying system using hemicellulose hydrolysate (HH) as a capping agent. The addition of only 1 wt% of HH to the CNF suspension not only prevents aggregation among CNFs during dehydration and drying but also dramatically enhances the redispersion rate and dispersion stability of the dried CNFs. The redispersed CNF/HH suspension exhibits physicochemical properties comparable to the original CNF suspension before drying. This confirms that HH inhibits irreversible hydrogen bonding among CNFs, leading to the restoration of the nanostructure during redispersion. Moreover, HH in the CNF suspension after redispersion can be easily removed through a simple water rinsing process, highlighting HH as a highly suitable candidate for preventing aggregation of CNFs. [Display omitted] • Hemicellulose hydrolysate (HH) was used as an anti-aggregation agent for CNF drying. • The addition of HH effectively prevented the aggregation of CNFs during the drying. • The added HH dramatically improved the redispersion rate and stability of dried CNFs. • HH was easily removed by washing process with water from the redispersed CNFs. [ABSTRACT FROM AUTHOR]

• An innovative co-culture fermentation strategy for bioethanol production was developed. • A mixed sugar composition (C5 and C6) from sugarcane bagasse diluted with molasses was evaluated. • Hexose and xylose-fermenting yeast were cultivated together in a single batch fermentation. • Co-culture strategy was related to upper xylose consumption and bioethanol productivity. • Maximum productivity was achieved during co-culture with S. cerevisiae and S. passalidarum. Mixed sugar co-fermentation represents an interesting fermentation strategy to improve bioethanol production from low-cost raw materials, such as sugarcane bagasse. The aim of this study was to evaluate a mixture of sugars (hexoses and pentoses) from sugarcane bagasse hemicellulosic hydrolysate diluted with sugarcane molasses as substrate to be converted either in monoculture or co-culture fermentations. A co-culture fermentation technique using hexoses-fermenting yeasts (Saccharomyces cerevisiae: from Santa Adélia Mill, an industrial strain (SA) and a respiratory-deficient mutant strain (ScP)) together with xylose-fermenting yeasts (Scheffersomyces stipitis (SS) and Spathaspora passalidarum (SP)) was carried out to enhance bioethanol production. Co-culture fermentation in a medium with a high mixed sugar concentration (100 g.L−1) resulted in a complete sugar consumption, ethanol titer of 30.2 g.L−1 and increased ethanol productivity (Q p =4.44 g.L−1. h−1) using wild type strains (SP + SA). In contrast, the maximum ethanol titer (49.2 g.L−1) was reached during co-culture performed with S. stipitis and the respiratory-deficient mutant strain of S. cerevisiae , however ethanol productivity (Q p =0.60 g.L−1. h−1) decreased due to the poor fermentation performance of the mutant strain. This work suggests that improved efficiency and good scalability of the mixed sugar fermentation process makes an important basis for the economic viability of bioethanol production from lignocelluloses. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is the most abundant bioresource on earth containing polymers mainly consisting of d‐glucose, d‐xylose, l‐arabinose, and further sugars. In order to establish this alternative feedstock apart from applications in food, we engineered Pseudomonas putida KT2440 as microbial biocatalyst for the utilization of xylose and arabinose in addition to glucose as sole carbon sources. The d‐xylose‐metabolizing strain P. putida KT2440_xylAB and l‐arabinose‐metabolizing strain P. putida KT2440_araBAD were constructed by introducing respective operons from Escherichia coli. Surprisingly, we found out that both recombinant strains were able to grow on xylose as well as arabinose with high cell densities and growth rates comparable to glucose. In addition, the growth characteristics on various mixtures of glucose, xylose, and arabinose were investigated, which demonstrated the efficient co‐utilization of hexose and pentose sugars. Finally, the possibility of using lignocellulose hydrolysate as substrate for the two recombinant strains was verified. The recombinant P. putida KT2440 strains presented here as flexible microbial biocatalysts to convert lignocellulosic sugars will undoubtedly contribute to the economic feasibility of the production of valuable compounds derived from renewable feedstock. Lignocellulosic biomass is the most abundant bioresource on earth containing polymers mainly consisting of d‐glucose, d‐xylose, l‐arabinose, and further sugars. In order to establish this alternative feedstock apart from applications in food, we engineered Pseudomonas putida KT2440 as microbial biocatalyst for the utilization of xylose and arabinose in addition to glucose as sole carbon sources. The growth characteristics on various mixtures of these sugars and the possibility of using lignocellulosic hydrolysate as substrate for the recombinant strains were investigated. [ABSTRACT FROM AUTHOR]

Furfural is one of the typical inhibitors present in hemicellulose hydrolysate. Furfural is harmful to cell growth and biofuel production in microbes. As one of the microbes that could use xylose in hemicellulose hydrolysate, Candia. tropicalis shows a promising potential for metabolic engineering to produce biofuels and value-added chemicals. In this study, we found that the rate of furfural degradation and half maximal inhibitory concentration for furfural of C. tropicalis in xylose medium increased 1.68-fold and 1.19-fold, respectively, compared with those in glucose medium, indicating that C. tropicalis obtained better furfural tolerance in xylose medium. The dehydrogenation of xylitol, which produces coenzyme NADH, promotes the recycle of NAD + and facilitates the reduction of furfural. This study provides important information for metabolic regulation and metabolic engineering of efficient lignocellulose fermentation strains. [ABSTRACT FROM AUTHOR]

Production of ethanol from concentrated D-xylose solutions and hemicellulose hydrolysate of sweet sorghum bagasse was achieved by using Pichia stipitis NCIM 3497 and an isolated yeast Debaryomyces hansenii sp. These yeasts were capable of producing ethanol from solutions containing 800 g/L D-xylose, and the optimum sugar concentration was found to be 150 g/L at pH 4, 30oC, with a production time of 72 hours. These yeasts were capable of utilizing multiple sugars. Hemicellulose hydrolysates of sweet sorghum bagasse were obtained by dilute acid hydrolysis and autohydrolysis including steam explosion treatment. The hydrolysate was treated by an over-liming process for detoxification and pH adjustment. Ethanol yield from hemicellulose hydrolysate was found to be higher than that of synthetic medium containing D-xylose. These yeasts can be used in production of ethanol from concentrated hemicellulose hydrolysates containing high pentose sugars obtained while treating lignocellulosic biomass at high substrate concentrations.

This study aimed at optimizing the net energy recovery from hydrogen and methane production through anaerobic digestion of the hemicellulose hydrolysate (HH) obtained by desirable conditions (DC) of autohydrolysis pretreatment (AH) of sugarcane bagasse (SB). Anaerobic digestion was carried out in a two-stage (acidogenic-methanogenic) batch system where the acidogenic phase worked as a hydrolysis and biodetoxification step. This allowed the utilization of more severe AH pretreatment conditions, i.e. T = 178.6 °C and t = 55 min (DC3) and T = 182.9 °C and t = 40.71 min (DC4). Such severe conditions resulted in higher extraction of hemicelluloses from SB (DC1 = 68.07%, DC2 = 48.99%, DC3 = 77.40% and DC4 = 73.90%), which consequently improved the net energy balance of the proposed process. The estimated energy from the combustion of both biogases (H 2 and CH 4 ) accumulated during the two-stage anaerobic digestion of HH generated by DC4 condition was capable of producing a net energy of 3.15 MJ·kg SB −1 dry weight . [ABSTRACT FROM AUTHOR]

During xylitol fermentation, Candida tropicalis is often inhibited by inhibitors in hemicellulose hydrolysate. The mechanisms involved in the metabolic responses to inhibitor stress and the resistances to inhibitors are still not clear. To understand the inhibition mechanisms and the metabolic responses to inhibitors, a GC/MS-based metabolomics approach was performed on C. tropicalis treated with and without complex inhibitors (CI, including furfural, phenol and acetic acid). Partial least squares discriminant analysis was used to determine the metabolic variability between CI-treated groups and control groups, and 25 metabolites were identified as possible entities responsible for the discrimination caused by inhibitors. We found that xylose uptake rate and xylitol oxidation rate were promoted by CI treatment. Metabolomics analysis showed that the flux from xylulose to pentose phosphate pathway increased, and tricarboxylic acid cycle was disturbed by CI. Moreover, the changes in levels of 1,3-propanediol, trehalose, saturated fatty acids and amino acids showed different mechanisms involved in metabolic responses to inhibitor stress. The increase of 1,3-propanediol was considered to be correlated with regulating redox balance and osmoregulation. The increase of trehalose might play a role in protein stabilization and cellular membranes protection. Saturated fatty acids could cause the decrease of membrane fluidity and make the plasma membrane rigid to maintain the integrity of plasma membrane. The deeper understanding of the inhibition mechanisms and the metabolic responses to inhibitors will provide us with more information on the metabolism regulation during xylitol bioconversion and the construction of industrial strains with inhibitor tolerance for better utilization of bioresource. [ABSTRACT FROM AUTHOR]

Remaining cells of Candida guilliermondii cultivated in hemicellulose-based fermentation medium were used as intracellular protein source. Recovery of glucose-6-phosphate dehydrogenase (G6PD) was attained in conventional aqueous two-phase systems (ATPS) was compared with integrated process involving mechanical disruption of cells followed by ATPS. Influences of polyethylene glycol molar mass ( M) and tie line lengths (TLL) on purification factor (PF), yields in top ( Y) and bottom ( Y) phases and partition coefficient ( K) were evaluated. First scheme resulted in 65.9 % enzyme yield and PF of 2.16 in salt-enriched phase with clarified homogenate ( M 1500 g mol, TLL 40 %); Y of 75.2 % and PF of 2.9 with unclarified homogenate ( M 1000 g mol, TLL 35 %). The highest PF value of integrated process was 2.26 in bottom phase ( M 1500 g mol, TLL 40 %). In order to optimize this response, a quadratic model was predicted for the response PF for process integration. Maximum response achieved was PF = 3.3 ( M 1500 g mol, TLL 40 %). Enzyme characterization showed G6P Michaelis-Menten constant ( K) equal 0.07-0.05, NADP K 0.02-1.98 and optimum temperature 70 °C, before and after recovery. Overall, our data confirmed feasibility of disruption/extraction integration for single-step purification of intracellular proteins from remaining yeast cells. [ABSTRACT FROM AUTHOR]

Validamycin A (VAL-A) is an important agricultural antibiotic produced by Streptomyces hygroscopicus 5008, which uses starch as carbon source occupying about 20% of total production cost. To reduce the medium cost, corncob hydrolysate – a hemicellulose hydrolysate was applied as a low-cost substrate to VAL-A fermentation. It was found that three major sugars in corncob hydrolysate including d -glucose, d -xylose and l -arabinose could all be utilized by S. hygroscopicus 5008 to produce VAL-A while d -xylose was the main contributor. A higher VAL-A production titer from d -xylose was achieved by using a genetically engineered strain TC03 derived from S. hygroscopicus 5008, which resulted in 1.27-fold improvement of VAL-A production from the medium containing 13% (v/v) corncob hydrolysate compared to that by its original strain. A medium cost analysis was done and compared with previous reports. This work indicates a great potential of the hemicellulose hydrolysate as substrate for antibiotic fermentation. [ABSTRACT FROM AUTHOR]

Xylose, the second most abundant sugar in lignocellulosic materials, is not efficiently utilized in current lignocellulose biotransformation processes, such as cellulosic ethanol production. The bioconversion of xylose to value-added products, such as pullulan, is an alternative strategy for efficient lignocellulose biotransformation. This paper reports the production of pullulan from xylose and hemicellulose hydrolysate by Aureobasidium pullulans AY82. The effects of DL-dithiothreitol (DTT) and pH on pullulan production from xylose were also intensively investigated. A maximal increase of 17.55% of pullulan production was observed in flasks added with 1.0 mM DTT. Batch fermentations with controlled pH were also conducted, and the optimal pH for cell growth and pullulan synthesis was 3.0 and 5.0, respectively. Based on these findings, two-stage pH control fermentations were performed, in which the pH of the medium was first adjusted to 3.0 for cell growth, and then changed to 5.0 for pullulan synthesis. However, the earlier the pH was changed to 5.0, the more pullulan was produced. Fermentation with controlled pH of 5.0 acquired the highest pullulan production. Under the optimized conditions (with the addition of 1.0 mM DTT and controlled pH of 5.0), the maximal pullulan production obtained from xylose was 17.63 g/L. A. pullulans AY82 also readily fermented hemicellulose hydrolysate under these optimized conditions, but with lower pullulan production (12.65 g/L). Fourier transform infrared spectroscopy and high-performance liquid chromatography showed that the structure of the pullulan obtained in this study was identical to that of the pullulan standard. [ABSTRACT FROM AUTHOR]

A sugar solution containing 31 g l-1 xylose was prepared from the culm of Sasa kurilensis by hydrolysis with 2% sulfuric acid with a liquor-to-solid ratio of 6 (g g-1) at 121°C for 1 h. During acid hydrolysis, also some byproducts were generated, such as acetic acid, furfural, 5-hydroxymethylfurfral, and low molecular weight phenolics, which inhibit bioconversion of xylose to xylitol. Except for acetic acid, these inhibitors were successfully removed from the hydrolysate by contacting with a steam-activated charcoal (15 g l-1 dose) for 24 h. Bioconversion of the detoxified hydrolysate to xylitol by the yeast, Candida magnoliae, was investigated under various microaerobic conditions. The oxygen transfer rate (OTR) varied from 8.4 to 27.6 mmol-O2 l-1 h-1. The maximum xylitol yield (0.62 g-xylitol g-xylose-1) was attained at the OTR of 1.2 mmol-O2 l-1 h-1. An additional increase in the OTR brought about cell growth, which consumed xylose. A proper control of the oxygen supply is necessary to produce efficiently xylitol from the culm hydrolysate. [ABSTRACT FROM AUTHOR]

• Aqueous phase reforming of real hemicellulose hydrolysates was performed. • The best results were obtain with a tailored bimetallic Pd-Pt/sibunit catalyst. • Complete conversion was achieved for C5 and C6 sugars and formic acid. The current work focuses on studying the aqueous phase reforming (APR) of pine and birch hydrolysate obtained from waste wood by using organic acids available from biorefineries. Processing of representative synthetic mixtures was utilized in the work in order to support data interpretation related to the influence of different chemical compound and processing parameters on the APR of the actual hydrolysates. It was shown, that hydrogenation of the hydrolysates prior to APR was not feasible in the presence of formic acid, which ruled out one potential processing route. However, it was successfully demonstrated that birch and pine hydrolysates could be directly processed obtaining close to full conversion. The best results were obtained with tailored bimetallic Pd-Pt/sibunit catalyst in a trickle bed reactor system in the temperature range 175 °C–225 °C. [ABSTRACT FROM AUTHOR]

Bioconversion of hemicellulosic hydrolysates into ethanol with the desired yields plays a pivotal role for the overall success of biorefineries. This paper aims to evaluate the ethanol production potential of four native strains of Scheffersomyces shehatae (syn. Candida shehatae) viz. S. shehatae BR6-2AI, CG8-8BY, PT1-1BASP and BR6-2AY, isolated from Brazilian forests. These strains were grown in commercial d-xylose-supplemented synthetic medium and sugarcane bagasse hemicellulose hydrolysate. S. shehatae BR6-2AY showed maximum ethanol production [0.48 ± 0.019 g g, 95 ± 3.78 % fermentation efficiency (FE)] followed by S. shehatae CG8-8BY (0.47 ± 0.016 g g, 93 ± 3.12 % FE), S. shehatae BR6-2AI (0.45 ± 0.01 g g, 89 ± 1.71 % FE) and S. shehatae PT1-1BASP (0.44 ± 0.02 g g, 86 ± 3.37 % FE) when grown in synthetic medium. During the fermentation of hemicellulose hydrolysates, S. shehatae CG8-8BY and S. shehatae BR6-2AY showed ethanol production (0.30 ± 0.05 g g, 58 ± 0.02 % FE) and (0.21 ± 0.01 g g, 40 ± 1.93 % FE), respectively. [ABSTRACT FROM AUTHOR]

Abstract: The present study validated a bioconversion technology for the production of 2,3-butanediol (2,3-BD) using sugars, glycerol and lignocellulosic material by three newly isolated strains—two Klebsiella sp. and one Serratia sp. One Klebsiella sp. afforded a high diol production yield (0.45g/g) using the less common sugar arabinose and Serratia sp. was used for the first time to convert glycerol to 2,3-BD and afforded a yield of 0.43g/g. Furthermore, acid-pretreated rice straw hydrolysate was used to determine the feasibility of its conversion to 2,3-BD. Both cellulose and hemicellulose hydrolysate were successfully fermented to 2,3-BD and acetoin by the isolates with yields for the diol between 0.39 and 0.44g/g (equivalent to 78–88% of the maximum yield). These results demonstrate that 2,3-butanediol can be considered as the main product or a value-added byproduct of biofuel production and then potentially improve the economy of lignocellulosic biorefinery. [Copyright &y& Elsevier]

Aims: To examine the potential use of hemicellulose hydrolysate (HH) for the production of chitosan by Rhizopus oryzae and investigate the influence of contents in HH on mycelia growth and chitosan synthesis. Methods and Results: Compared to xylose medium, HH enhanced mycelia growth, chitosan content and production of R. oryzae by 10·2, 64·5 and 82·1%, respectively. During sulfuric acid hydrolysis of corn straw, sugars (glucose, galactose, etc) and inhibitors (formic acid, acetic acid and furfural) were generated. Acetic acid (2·14 g l−1) and formic acid (0·83 g l−1) were stimulative, while furfural (0·55 g l−1) was inhibitory. Inhibitors, at different concentrations, increased the mycelia growth and chitosan production by 24·5–37·8 and 60·1–207·1%. Conclusions: HH of corn straw is a good source for chitosan production. Inhibitors in HH, at proper concentrations, can enhance chitosan production greatly. Significance and Impact of the Study: This work for the first time reported chitosan production from HH. Chitosan production can be greatly enhanced by cheap chemicals such as inhibitors in HH. [ABSTRACT FROM AUTHOR]

Abstract: Saccharum (Saccharum spontaneum L. ssp. aegyptiacum (Willd.) Hack.), is a rapidly growing, wide ranging high-yield perennial, suitable for second generation bioethanol production. This study evaluated oxalic acid as a pretreatment for bioconversion. Overall sugar yields, sugar degradation products, enzymatic glucan hydrolysis and ethanol production were studied as effects of temperature (150–190°C), reaction time (10–40min) and oxalic acid concentration 2–8% (w/w). Time and temperature were combined into a single parameter, Severity Factor (SF) [Log(R 0)], and related to oxalic acid using a response surface methodology. Maximum total sugar yield was attained at a SF of 2.93 and 6.79% (w/w) oxalic acid, while maximum formation of sugar degradation products was observed at the highest SF (4.05) and 5% (w/w) oxalic acid. These were also the conditions for maximum simultaneous saccharification and fermentation (SSF) of the residual solids. Commercial cellulases and Saccharomyces cerevisiae attained 89.9% glucan conversion and 17.8g/l ethanol. Pichia stipitis CBS 6054 fermented hemicellulosic hydrolysates from less severe conditions to ethanol with a yield of 0.35 (g e/g s). Maximal product yields were 69% of theoretical value and 90% of the SSF conversion efficiency for hydrolysate fermentation and SSF, respectively. [Copyright &y& Elsevier]

In the dilute acid pretreatment of lignocellulose, xylose substituted with α-1,2-methylglucuronate is released as methylglucuronoxylose (MeGAX), which cannot be fermented by biocatalysts currently used to produce biofuels and chemicals. Enterobacter asburiae JDR-1, isolated from colonized wood, efficiently fermented both MeGAX and xylose in acid hydrolysates of sweetgum xylan. Deletion of pflB and als genes in this bacterium modified the native mixed acid fermentation pathways to one for homolactate production. The resulting strain, Enterobacter asburiae L1, completely utilized both xylose and MeGAX in a dilute acid hydrolysate of sweetgum xylan and produced lactate approximating 100% of the theoretical maximum yield. Enterobacter asburiae JDR-1 offers a platform to develop efficient biocatalysts for production of fuels and chemicals from hemicellulose hydrolysates of hardwood and agricultural residues. [ABSTRACT FROM AUTHOR]

Abstract: Lignocellulosic biomass, if properly hydrolyzed, can be an ideal feedstock for fermentative hydrogen production. This work considered the pretreatment of corn stover (CS) using a dilute acid hydrolysis process and studied its fermentability for hydrogen production by the strain Thermoanaerobacterium thermosaccharolyticum W16. The effects of sulfuric acid concentration and reaction time in the hydrolysis stage of the process were determined based on a 22 central composite experimental design with respect to maximum hydrogen productivity. The optimal hydrolysis conditions to yield the maximum quantity of hydrogen by W16 were 1.69% sulfuric acid and 117min reaction time. At these conditions, the hydrogen yield was shown to be 3305mlH2 L−1 medium, which corresponds to 2.24molH2 mol−1 sugar. The present results indicate the potential of using T. thermosaccharolyticum W16 for high-yield conversion of CS hemicellulose into bio-H2 integrated with acid hydrolysis. [Copyright &y& Elsevier]

Environmental concerns and unease with U.S. dependence on foreign oil have renewed interest in converting biomass into fuel ethanol. The volume of plant matter available makes lignocellulose conversion to ethanol desirable, although no one isolated organism has been shown to break bonds in lignocellulose and efficiently metabolize resulting sugars into one product. This work reviews directed engineering coupled with metabolic evolution resulting in microbial biocatalysts that produce up to 45 g L−1 ethanol in 48 hours in a simple mineral salts medium and that convert various compounds of lignocellulosic materials to ethanol. Mutations contributing to ethanologenesis are discussed along with adding enzymatic capabilities to existing biocatalysts in order to decrease the commercial enzymes required to reduce plant matter into fermentable sugars. [ABSTRACT FROM AUTHOR]

Abstract: Acetic acid is a compound commonly found in hemicellulosic hydrolysates. This weak acid strongly influences the bioconversion of sugar containing hydrolysates. Previous investigators have used anion exchange resins for acetic acid removal from different hemicellulosic hydrolysates. In this study, the efficiency of an anion exchange membrane was compared to that of an anion exchange resin, for acetic acid removal from a DI water solution and an acidic hemicellulose hydrolysate pretreated using two different methods. Ion exchange membranes and resins have very different geometries. Here the performance of membranes and resins is compared using two dimensionless parameters, the relative mass throughput and chromatographic bed number. The relative mass throughput arises naturally from the Thomas solution for ion exchange. The results show that the membrane exhibit better performance in terms of capacity, and loss of the desired sugars. In addition acetic acid may be eluted at a higher concentration from the membrane thus leading to the possibility of recovery and re-use of the acetic acid. [Copyright &y& Elsevier]

Abstract: Adsorbing carriers for immobilisation of Candida guilliermondii cells to use for xylitol production from sugarcane bagasse hemicellulose hydrolysate were tested. Biomass was immobilised in situ by natural adsorption, i.e. through direct contact between cells for the inoculum and carrier particles at the beginning of fermentations. The carriers employed were: Syrane porous glass beads with 2.53mm diameter in average and pore diameter in the range 60–300μm, supplied by Bioengineering (Wald, Switzerland), and NaX zeolite UOP WE 894 purchased from Plury Química S.A. (Diadema, SP, Brazil). At the end of the run with free cells taken as a reference test, xylitol concentration (Pf) achieved 35.5g/l, corresponding to a xylose-to-xylitol yield factor (YP/S) of 0.72g/g and a volumetric productivity (QP) of 0.49g/lh, while final cell concentration (Xf) and productivity (Qx) were only 5.32g/l and 0.048g/lh, respectively. Both systems with immobilised cells exhibited lower xylitol productions (Pf=28.8–29.5g/l, YP/S=0.52–0.53g/g, QP=0.32–0.33g/lh) and higher cell growth, with particular concern to porous glass (Xf=10.5g/l, Qx=0.10g/lh). Electronic microscopy observations demonstrated that the excellent performance of porous glass as cell support was due to the development of a thick extracellular matrix either within the large pores or on the surface of this material. As a consequence, almost 50% of the cells resulted to be adsorbed to the carrier at the end of the run. This growth was also responsible for a decrease in the fraction of xylose available for xylitol production. Employing zeolite, a material with pore size smaller than cell size, immobilised cells represented only 30% of the final population and immobilisation was just observed on the carrier surface. The low cell attachment on this material can be explained by the stress exerted on the outer immobilised cells by the friction among beads. [Copyright &y& Elsevier]

Sugar cane bagasse hemicellulose, hydrolyzed by dilute H2SO4, supplemented with mineral salts and 0.5% corn steep liquor, was fermented to l(+)-lactic acid using a newly isolated strain of Bacillus sp. In batch fermentations at 50 °C and pH 5, over 5.5% (w/v) l(+)-lactic acid was produced (89% theoretical yield; 0.9 g lactate per g sugar) with an optical purity of 99.5%. [ABSTRACT FROM AUTHOR]

Sugar cane bagasse hemicellulosic fraction was hydrolysed by treatment with 70 mg of sulphuric acid per gram of dry mass at 125 °C for 2 h. The hydrolysate was used as the substrate to grow Candida langeronii RLJ Y-019 at 42 °C; initial pH 6.0; stirring at 700 rev/min and aeration at 1.0 and 2.0 v/v/min. The utilization of D-xylose, L-arabinose, and acetic acid were delayed due to the presence of D-glucose, but after D-glucose depletion the other carbon sources were utilized. The kinetic parameters calculated for both cultivations at 1.0 and 2.0 v/v/min included: maximum specific growth rate (μmax) of 0.29 ± 0.01 h−1 and 0.43 ± 0.016 h−1, yields ( Yx/s) of 0.36 ± 0.012 and 0.40 ± 0.012 gx/gs and productivity ( Qx) of 0.81 ± 0.016 and 0.97 ± 0.012 gx/l/h, respectively, and compared favourably with published results obtained with Candida utilis and Geotrichum candidum. Candida langeronii appeared superior to C. utilis for biomass production from hemicellulose hydrolysate, in that it utilized L-arabinose and was capable of growth at higher temperatures. The biomass contained 48.2, 1.4, 5.8 and 23.4% of total protein, DNA, RNA and carbohydrate, respectively and contained essential amino acids for animal feed. [ABSTRACT FROM AUTHOR]

The production of xylitol by the yeast Candida guilliermondii was investigated in batch fermentations with aspenwood hemicellulose hydrolysate and compared with results obtained in semi-defined media with a mixture of glucose and xylose. The hemicellulose hydrolysate had to be supplemented by yeast extract and the maximum xylitol yield (0.8 g g-1) and productivity (0.6 g l-1 h-1) were reached by controlling oxygen input. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pediococcus pentosaceus ET34 genome contains the complete pediocin PA-1 operon. • Pediocin PA-1 was produced in a medium enriched with sugarcane bagasse hydrolysate. • The hydrolysate up-regulated pediocin-related transcripts in growing cells. • Optimal conditions for PA-1 production were 36.8 °C and 20.6% hydrolysate. • ET34 cells used only glucose and arabinose from the hydrolysate as carbon sources. Listeria monocytogenes is one of the foodborne pathogens of most concern for food safety. To limit its presence in foods, bacteriocins have been proposed as natural bio-preservatives. Herein, a bacteriocin was produced on hemicellulose hydrolysate of sugarcane bagasse by Pediococcus pentosaceous ET34, whose genome sequencing revealed an operon with 100% similarity to that of pediocin PA-1. ET34 grown on hydrolysate-containing medium led to an increase in the expression of PA-1 genes and a non-optimized purification step sequence resulted in a yield of 0.8 mg·L-1 of pure pediocin (purity > 95%). Culture conditions were optimized according to a central composite design using temperature and hydrolysate % as independent variables and validated in 3-L Erlenmeyers. Finally, a process for scaled-up implementation by sugar-ethanol industry was proposed, considering green chemistry and biorefinery concepts. This work stands up as an approach addressing a future proper sugarcane bagasse valorisation for pediocin production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fixed-bed bioreactor stabilization through nutrient supplementation and washing steps. • Continuous ethanol production with high sugar conversion for 360 h. • Continuous fermentation using xylose-rich hydrolysate for 2 G ethanol production. • Inhibitors and ethanol effect proved to be intensified by synergism and exposure time. Development of a robust and competitive process for second generation (2G) ethanol production requires efficient fermentation of both glucose and xylose fractions generated after biomass pretreatment and saccharification, using industrial media containing high sugars concentration and inhibitors, under prolonged exposure to high ethanol titers. Thus, it is important to study the influence of these industrial operation conditions on yeast fermentation performance, which has been little addressed in the literature. In this work we evaluated the steady-state stability of continuous 2G ethanol production from xylose in a fixed bed reactor. The bioreactor was packed with recombinant, xylose-utilizing Saccharomyces cerevisiae cells entrapped in calcium alginate and it was operated with different inlet xylose concentrations and dilution rates. Medium supplementation with nutrients and scheduled washing steps were effective in maintaining high xylose conversion levels during continuous fermentation for more than 15 days with an ethanol productivity of 5.0 g/L.h. Effects of prolonged exposure to ethanol and inhibitors present in undetoxified hydrolysate were further investigated in repeated batches. Overall, the results show that improved ethanol tolerance in recombinant yeasts and innovative solutions to increase sugar concentration in the hydrolysates are the main challenges to achieve a feasible industrial process for 2 G ethanol production. [ABSTRACT FROM AUTHOR]

The growth characteristics of Candida blankii as a function of temperature and pH in a simulated bagasse hemicellulose hydrolysate were determined in chemostat culture. The highest maximum specific growth rate of 0.44h was reached at 38°C and at pH 5.5, with a sharp decrease in growth rate on either side of this temperature. Growth occurred at 46°C but not at 48°C. The protein and cell yields varied little below 40°C and the respective values were 0.22 and 0.5 g/g at 38°C. At the lower pH values, a severe linear decrease in cell and protein yields occurred, whereas a small increase in these yields at decreasing pH values was found when acetic acid was omitted from the medium. In the presence of acetic acid, a very sharp decrease in the growth rate at pH values below pH 4.5 was noted, despite the very low residual acetic acid concentrations, of less than 50 mg/l, in the culture. [ABSTRACT FROM AUTHOR]

The influence of aeration level, initial pH, initial cell concentration, and fermentation time on the xylitol production from rice straw hemicellulose hydrolysate by Candida mogii was studied. A multifactorial experimental design was adopted to evaluate this influence. A statistical analysis of the results showed that the aeration level and the initial pH had significant effects on yield factor, volumetric productivity, and xylose consumption. For the latter, fermentation time was also a significant variable. Based on the response surface methodology, models for the range investigated were proposed. The maximum values for the yield factor (Yp/s) and volumetric productivity (Qp) were, respectively, 0.71 g/g and 0.46 g(Lh). [ABSTRACT FROM AUTHOR]

Efficient utilization of the pentosan fraction of hemicellulose from lignocellulosic feedstocks offers an opportunity to increase the yield and to reduce the cost of producing fuel ethanol. During prehydrolysis (acid hydrolysis or autohydrolysis of hemicellulose), acetic acid is formed as a consequence of the deacetylation of the acetylated moiety of hemicellulose. Recombinant Escherichia coli B (ATCC 11303), carrying the plasmid pLO1297 with pyruvate decarboxylase and alcohol dehydrogenase II genes from Zymomonas mobilis (CP4), converts xylose to ethanol with a product yield that approaches theoretical maximum. Although other pentose-utilizing microorganisms are inhibited by acetic acid, the recombinant E. coli displays a high tolerance for acetic acid. In xylose fermentations with a synthetic medium (Luria broth), where the pH was controlled at 7, neither yield nor productivity was affected by the addition of 10.7 g/L acetic acid. Nutrient-supplemented, hardwood (aspen) hemicellulose hydrolysate (40.7 g/L xylose) was completely fermented to ethanol (16.3 g/L) in 98 h. When the acetic acid concentration was reduced from 5.6 to 0.8 g/L, the fermentation time decreased to 58 h. Overliming, with Ca(OH) to pH 10, followed by neutralization to pH 7 with sulfuric acid and removal of insolubles, resulted in a twofold increase in volumetric productivity. The maximum productivity was 0.93 g/L/h. The xylose-to-ethanol conversion efficiency and productivity in Ca(OH)-treated hardwood prehydrolysate, fortified with only mineral salts, were 94% and 0.26 g/L/h, respectively. The recombinant E. coli exhibits a xylose-to-ethanol conversion efficiency that is superior to that of other pentose-utilizing yeasts currently being investigated for the production of fuel ethanol from lignocellulosic materials. [ABSTRACT FROM AUTHOR]

Ethanol production from natural complex media has been studied in this work. A new kinetic approach is presented for two-substrate media, such as hardwood hemicellulose hydrolysate, which predominantly consists of a mixture of xylose and glucose. It has been founded on the supposition that the whole ethanol production and biomass growth can be subdivided into two separated components imputable to glucose and xylose consumptions, respectively. A model describing the continuous fermentation in CSTR by Pachysolen tannophilus has been also presented, and experimentally verified; it takes into account the different substrate consumption rates of these sugars contained in both natural and synthetic complex media. [ABSTRACT FROM AUTHOR]

Xylitol production by the yeast Candida guilliermondii was evaluated in a rice straw hemicellulose hydrolysate under different conditions of initial pH and nitrogen source. Xylitol production was significantly affected ( p <0.05) by the nitrogen source, pH, and the interaction between these factors. The best yield and productivity were observed at initial pH of 5.3 in medium containing ammonium sulfate as nitrogen source. Under these conditions, the xylitol yield factor (Y) was 0.68 g/g and volumetric productivity (Q) was 0.51 g/L.h. [ABSTRACT FROM AUTHOR]

• Use of 3D-printed nylon and bagasse carriers to produce butanol was evaluated. • Sugarcane bagasse was a better cell carrier than a 3D-printed nylon carrier. • The xylose utilization was improved from 16% (nylon carrier) to 33% (bagasse). • The bagasse carrier allowed for 43% of the butanol to be biomass-derived. To enable the production of butanol with undiluted, non-detoxified sugarcane bagasse hemicellulose hydrolysates, this study developed a three-staged repeated-batch immobilized cell fermentation in which the efficiency of a 3D-printed nylon carrier to passively immobilize Clostridium saccharoperbutylacetonicum DSM 14923 was compared with sugarcane bagasse. The first stage consisted of sugarcane molasses fermentation, and in the second stage, non-detoxified sugarcane bagasse hemicellulose hydrolysates (SBHH) was pulse-fed to sugarcane molasses fermentation. In the next four batches, immobilized cells were fed with undiluted SBHH supplemented with molasses, and SBHH-derived xylose accounted for approximately 50% of the sugars. Bagasse was a superior carrier, and the average xylose utilization (33%) was significantly higher than the treatment with the 3D-printed carrier (16%). Notably, bagasse allowed for 43% of the butanol to be SBHH-derived. Overall, cell immobilization on lignocellulosic materials can be an efficient strategy to produce butanol from repeated-batch fermentation of non-detoxified hemicellulose hydrolysates. [ABSTRACT FROM AUTHOR]

• Fermentation was initiated with diluted sugarcane molasses (45 g/L sugars). • Crude sugarcane bagasse hemicellulose hydrolysate (23 g/L xylose) was fed at 24 h. • The diluted molasses-to-hydrolysate volume ratio was 3:1. • Sugars were consumed (84 %) without supplementation of nutrients. • Butanol yield (0.31) was remarkable. Butanol is a chemical and advanced biofuel whose fermentative production from hemicellulose hydrolysates is hindered by lignocellulose-derived microbial inhibitory compounds. In this work, Clostridium saccharoperbutylacetonicum DSM 14923 was not able to ferment a sugarcane hemicellulose hydrolysate supplemented with either laboratory-grade nutrients or sugarcane molasses. To circumvent this problem, the crude hemicellulose hydrolysate was fed, after 24 h, to a molasses fermentation containing 45 g/L total reducing sugars. Without the need of supplementing nutrients, the culture was able to co-ferment sucrose, glucose, fructose, and xylose (conversion of sucrose and xylose were 81 and 90 %, respectively) in a fermentation containing a diluted molasses-to-hydrolysate volume ratio of 3:1. Butanol yield (0.31 g/g) was remarkable, and butanol titer was 10.0 g/L after 72 h of fermentation. Therefore, this research demonstrated that sugarcane molasses ‒ a by-product of the sugar industry rich in sucrose and nutrients ‒ can be an efficient feedstock for enabling the production of butanol from sugarcane bagasse hemicellulose hydrolysate. [ABSTRACT FROM AUTHOR]