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Fermentation, Volume 3, Issue 2 (June 2017)

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Cover Story In the modern biorefinery concept, laccases constitute a potential tool for the complete [...] Read more.
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Research

Jump to: Review

Open AccessFeature PaperArticle Purification of Polymer-Grade Fumaric Acid from Fermented Spent Sulfite Liquor
Fermentation 2017, 3(2), 13; doi:10.3390/fermentation3020013
Received: 28 February 2017 / Revised: 29 March 2017 / Accepted: 30 March 2017 / Published: 1 April 2017
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Abstract
Fumaric acid is a chemical building block with many applications, namely in the polymer industry. The fermentative production of fumaric acid from renewable feedstock is a promising and sustainable alternative to petroleum-based chemical synthesis. The use of existing industrial side-streams as raw-materials within
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Fumaric acid is a chemical building block with many applications, namely in the polymer industry. The fermentative production of fumaric acid from renewable feedstock is a promising and sustainable alternative to petroleum-based chemical synthesis. The use of existing industrial side-streams as raw-materials within biorefineries potentially enables production costs competitive against current chemical processes, while preventing the use of refined sugars competing with food and feed uses and avoiding purposely grown crops requiring large areas of arable land. However, most industrial side streams contain a diversity of molecules that will add complexity to the purification of fumaric acid from the fermentation broth. A process for the recovery and purification of fumaric acid from a complex fermentation medium containing spent sulfite liquor (SSL) as a carbon source was developed and is herein described. A simple two-stage precipitation procedure, involving separation unit operations, pH and temperature manipulation and polishing through the removal of contaminants with activated carbon, allowed for the recovery of fumaric acid with 68.3% recovery yield with specifications meeting the requirements of the polymer industry. Further, process integration opportunities were implemented that allowed minimizing the generation of waste streams containing fumaric acid, which enabled increasing the yield to 81.4% while keeping the product specifications. Full article
(This article belongs to the Special Issue Carboxylic Acid Production)
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Open AccessFeature PaperArticle A Sequential Steam Explosion and Reactive Extrusion Pretreatment for Lignocellulosic Biomass Conversion within a Fermentation-Based Biorefinery Perspective
Fermentation 2017, 3(2), 15; doi:10.3390/fermentation3020015
Received: 16 March 2017 / Revised: 12 April 2017 / Accepted: 14 April 2017 / Published: 20 April 2017
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Abstract
The present work evaluates a two-step pretreatment process based on steam explosion and extrusion technologies for the optimal fractionation of lignocellulosic biomass. Two-step pretreatment of barley straw resulted in overall glucan, hemicellulose and lignin recovery yields of 84%, 91% and 87%, respectively. Precipitation
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The present work evaluates a two-step pretreatment process based on steam explosion and extrusion technologies for the optimal fractionation of lignocellulosic biomass. Two-step pretreatment of barley straw resulted in overall glucan, hemicellulose and lignin recovery yields of 84%, 91% and 87%, respectively. Precipitation of the collected lignin-rich liquid fraction yielded a solid residue with high lignin content, offering possibilities for subsequent applications. Moreover, hydrolysability tests showed almost complete saccharification of the pretreated solid residue, which when combined with the low concentration of the generated inhibitory compounds, is representative of a good pretreatment approach. Scheffersomyces stipitis was capable of fermenting all of the glucose and xylose from the non-diluted hemicellulose fraction, resulting in an ethanol concentration of 17.5 g/L with 0.34 g/g yields. Similarly, Saccharomyces cerevisiae produced about 4% (v/v) ethanol concentration with 0.40 g/g yields, during simultaneous saccharification and fermentation (SSF) of the two-step pretreated solid residue at 10% (w/w) consistency. These results increased the overall conversion yields from a one-step steam explosion pretreatment by 1.4-fold, showing the effectiveness of including an extrusion step to enhance overall biomass fractionation and carbohydrates conversion via microbial fermentation processes. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production)
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Open AccessArticle Production and Quality Analysis of Wine from Honey and Coconut Milk Blend Using Saccharomyces cerevisiae
Fermentation 2017, 3(2), 16; doi:10.3390/fermentation3020016
Received: 6 February 2017 / Revised: 14 April 2017 / Accepted: 20 April 2017 / Published: 26 April 2017
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Abstract
Honey is a high-sugar jelly-like substance produced by bees from flower nectar, and coconut milk is the creamy (rich in fat and minerals) extract of coconut meat (endosperm). Studies on honey-fruit wines are scant, and mostly documented in unpublished or personal blogs. This
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Honey is a high-sugar jelly-like substance produced by bees from flower nectar, and coconut milk is the creamy (rich in fat and minerals) extract of coconut meat (endosperm). Studies on honey-fruit wines are scant, and mostly documented in unpublished or personal blogs. This study produced honey–coconut wine using Saccharomyces cerevisiae. Honey slurry (HS, a 100% diluted honey) was mixed with undiluted coconut milk (CM) at varying ratios to obtain six wine (W) versions (HS:CM) designated as WA (1:1), WB (1:2), WC (2:1), WD (3:1), WE (1:3), and control was coded as CTRL (1:0). Each version (1800 mL) was inoculated with 200 mL (~6.0 log10 cfu/mL) of S. cerevisiae, fermented (25 ± 2 °C) for 60 days, degassed and agitated every 2 days, pasteurized to stop fermentation, and clarified by siphoning the supernatant. Irrespective of the wine version, the optimum range of microbial growth and duration for HS-CM wines were 8.1–8.2 log10 cfu/mL and 25–30 days respectively. Most enological (pH, total acidity, and free SO2) and physicochemical (temperature and fermentation velocity) parameters were relatively stable across all wine versions. However, fermentative capacity and degree, and alcoholic and caloric contents were proportional to the quantity of HS. Sensory rating of wines by 50 assessors were in the decreasing order of CTRL > WC > WD > WA > WE > WB. Conclusively, honey–coconut wines are acidic wines and could be dry or semi-sweet wines, low to high alcoholic wines, or very low to moderate caloric wines, depending on the quantity of honey added. This study observed a correlation of more than 95% precision between wine compositions (HS:CM) and wine qualities (alcoholic and caloric contents). Thus, models of enological parameters would enhance HS-CM winemaking process. Full article
(This article belongs to the Special Issue Microbiology and Food Hygiene)
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Open AccessFeature PaperArticle Process Development for Enhanced 2,3-Butanediol Production by Paenibacillus polymyxa DSM 365
Fermentation 2017, 3(2), 18; doi:10.3390/fermentation3020018
Received: 9 March 2017 / Revised: 21 April 2017 / Accepted: 2 May 2017 / Published: 7 May 2017
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Abstract
While chiral 2,3-Butanediol (2,3-BD) is currently receiving remarkable attention because of its numerous industrial applications in the synthetic rubber, bioplastics, cosmetics, and flavor industries, 2,3-BD-mediated feedback inhibition of Paenibacillus polymyxa DSM 365 limits the accumulation of higher concentrations of 2,3-BD in the bioreactor
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While chiral 2,3-Butanediol (2,3-BD) is currently receiving remarkable attention because of its numerous industrial applications in the synthetic rubber, bioplastics, cosmetics, and flavor industries, 2,3-BD-mediated feedback inhibition of Paenibacillus polymyxa DSM 365 limits the accumulation of higher concentrations of 2,3-BD in the bioreactor during fermentation. The Box-Behnken design, Plackett-Burman design (PBD), and response surface methodology were employed to evaluate the impacts of seven factors including tryptone, yeast extract, ammonium acetate, ammonium sulfate, glycerol concentrations, temperature, and inoculum size on 2,3-butanediol (2,3-BD) production by Paenibacillus polymyxa DSM 365. Results showed that three factors; tryptone, temperature, and inoculum size significantly influence 2,3-BD production (p < 0.05) by P. polymyxa. The optimal levels of tryptone, inoculum size, and temperature as determined by the Box-Behnken design and response surface methodology were 3.5 g/L, 9.5%, and 35 °C, respectively. The optimized process was validated in batch and fed-batch fermentations in a 5-L Bioflo 3000 Bioreactor, and 51.10 and 68.54 g/L 2,3-BD were obtained, respectively. Interestingly, the production of exopolysaccharides (EPS), an undesirable co-product, was reduced by 19% when compared to the control. These results underscore an interplay between medium components and fermentation conditions, leading to increased 2,3-BD production and decreased EPS production by P. polymyxa. Collectively, our findings demonstrate both increased 2,3-BD titer, a fundamental prerequisite to the potential commercialization of fermentative 2,3-BD production using renewable feedstocks, and reduced flux of carbons towards undesirable EPS production. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production)
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Open AccessArticle Kinetics of Bioethanol Production from Waste Sorghum Leaves Using Saccharomyces cerevisiae BY4743
Fermentation 2017, 3(2), 19; doi:10.3390/fermentation3020019
Received: 16 January 2017 / Revised: 28 April 2017 / Accepted: 2 May 2017 / Published: 8 May 2017
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Abstract
Kinetic models for bioethanol production from waste sorghum leaves by Saccharomyces cerevisiae BY4743 are presented. Fermentation processes were carried out at varied initial glucose concentrations (12.5–30.0 g/L). Experimental data on cell growth and substrate utilisation fit the Monod kinetic model with a coefficient
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Kinetic models for bioethanol production from waste sorghum leaves by Saccharomyces cerevisiae BY4743 are presented. Fermentation processes were carried out at varied initial glucose concentrations (12.5–30.0 g/L). Experimental data on cell growth and substrate utilisation fit the Monod kinetic model with a coefficient of determination (R2) of 0.95. A maximum specific growth rate (μmax) and Monod constant (KS) of 0.176 h−1 and 10.11 g/L, respectively, were obtained. The bioethanol production data fit the modified Gompertz model with an R2 value of 0.98. A maximum bioethanol production rate (rp,m) of 0.52 g/L/h, maximum potential bioethanol concentration (Pm) of 17.15 g/L, and a bioethanol production lag time (tL) of 6.31 h were observed. The obtained Monod and modified Gompertz coefficients indicated that waste sorghum leaves can serve as an efficient substrate for bioethanol production. These models with high accuracy are suitable for the scale-up development of bioethanol production from lignocellulosic feedstocks such as sorghum leaves. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production)
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Open AccessArticle Valorization of a Pulp Industry By-Product through the Production of Short-Chain Organic Acids
Fermentation 2017, 3(2), 20; doi:10.3390/fermentation3020020
Received: 8 February 2017 / Revised: 2 May 2017 / Accepted: 8 May 2017 / Published: 12 May 2017
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Abstract
In this work, hardwood sulfite spent liquor (HSSL)—a by-product from a pulp and paper industry—was used as substrate to produce short-chain organic acids (SCOAs) through acidogenic fermentation. SCOAs have a broad range of applications, including the production of biopolymers, bioenergy, and biological removal
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In this work, hardwood sulfite spent liquor (HSSL)—a by-product from a pulp and paper industry—was used as substrate to produce short-chain organic acids (SCOAs) through acidogenic fermentation. SCOAs have a broad range of applications, including the production of biopolymers, bioenergy, and biological removal of nutrients from wastewaters. A continuous stirred tank reactor (CSTR) configuration was chosen to impose selective pressure conditions. The CSTR was operated for 88 days at 30 °C, without pH control, and 1.76 days of hydraulic and sludge retention times were imposed. The culture required 46 days to adapt to the conditions imposed, reaching a pseudo-steady state after this period. The maximum concentration of SCOAs produced occurred on day 71—7.0 g carbon oxygen demand (COD)/L that corresponded to a degree of acidification of 36%. Acetate, propionate, butyrate, valerate, and lactate were the SCOAs produced throughout the 88 days, with an average proportion of 59:17:19:1.0:4.0%, respectively. Full article
(This article belongs to the Special Issue Carboxylic Acid Production)
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Open AccessArticle Continuous Ethanol Production from Synthesis Gas by Clostridium ragsdalei in a Trickle-Bed Reactor
Fermentation 2017, 3(2), 23; doi:10.3390/fermentation3020023
Received: 27 March 2017 / Revised: 7 May 2017 / Accepted: 18 May 2017 / Published: 24 May 2017
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Abstract
A trickle-bed reactor (TBR) when operated in a trickle flow regime reduces liquid resistance to mass transfer because a very thin liquid film is in contact with the gas phase and results in improved gas–liquid mass transfer compared to continuous stirred tank reactors
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A trickle-bed reactor (TBR) when operated in a trickle flow regime reduces liquid resistance to mass transfer because a very thin liquid film is in contact with the gas phase and results in improved gas–liquid mass transfer compared to continuous stirred tank reactors (CSTRs). In the present study, continuous syngas fermentation was performed in a 1-L TBR for ethanol production by Clostridium ragsdalei. The effects of dilution and gas flow rates on product formation, productivity, gas uptakes and conversion efficiencies were examined. Results showed that CO and H2 conversion efficiencies reached over 90% when the gas flow rate was maintained between 1.5 and 2.8 standard cubic centimeters per minute (sccm) at a dilution rate of 0.009 h−1. A 4:1 molar ratio of ethanol to acetic acid was achieved in co-current continuous mode with both gas and liquid entered the TBR at the top and exited from the bottom at dilution rates of 0.009 and 0.012 h−1, and gas flow rates from 10.1 to 12.2 sccm and 15.9 to 18.9 sccm, respectively. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production)
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Open AccessArticle Production of Bioethanol from Agricultural Wastes Using Residual Thermal Energy of a Cogeneration Plant in the Distillation Phase
Fermentation 2017, 3(2), 24; doi:10.3390/fermentation3020024
Received: 27 March 2017 / Revised: 19 May 2017 / Accepted: 21 May 2017 / Published: 25 May 2017
Cited by 1 | PDF Full-text (381 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Alcoholic fermentations were performed, adapting the technology to exploit the residual thermal energy (hot water at 83–85 °C) of a cogeneration plant and to valorize agricultural wastes. Substrates were apple, kiwifruit, and peaches wastes; and corn threshing residue (CTR). Saccharomyces bayanus was chosen
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Alcoholic fermentations were performed, adapting the technology to exploit the residual thermal energy (hot water at 83–85 °C) of a cogeneration plant and to valorize agricultural wastes. Substrates were apple, kiwifruit, and peaches wastes; and corn threshing residue (CTR). Saccharomyces bayanus was chosen as starter yeast. The fruits, fresh or blanched, were mashed; CTR was gelatinized and liquefied by adding Liquozyme® SC DS (Novozymes, Dittingen, Switzerland); saccharification simultaneous to fermentation was carried out using the enzyme Spirizyme® Ultra (Novozymes, Dittingen, Switzerland). Lab-scale static fermentations were carried out at 28 °C and 35 °C, using raw fruits, blanched fruits and CTR, monitoring the ethanol production. The highest ethanol production was reached with CTR (10.22% (v/v) and among fruits with apple (8.71% (v/v)). Distillations at low temperatures and under vacuum, to exploit warm water from a cogeneration plant, were tested. Vacuum simple batch distillation by rotary evaporation at lab scale at 80 °C (heating bath) and 200 mbar or 400 mbar allowed to recover 93.35% (v/v) and 89.59% (v/v) of ethanol, respectively. These results support a fermentation process coupled to a cogeneration plant, fed with apple wastes and with CTR when apple wastes are not available, where hot water from cogeneration plant is used in blanching and distillation phases. The scale up in a pilot plant was also carried out. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production)
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Open AccessArticle Amylase Production from Thermophilic Bacillus sp. BCC 021-50 Isolated from a Marine Environment
Fermentation 2017, 3(2), 25; doi:10.3390/fermentation3020025
Received: 27 March 2017 / Revised: 18 May 2017 / Accepted: 26 May 2017 / Published: 1 June 2017
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Abstract
The high cost of fermentation media is one of the technical barriers in amylase production from microbial sources. Amylase is used in several industrial processes or industries, for example, in the food industry, the saccharification of starchy materials, and in the detergent and
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The high cost of fermentation media is one of the technical barriers in amylase production from microbial sources. Amylase is used in several industrial processes or industries, for example, in the food industry, the saccharification of starchy materials, and in the detergent and textile industry. In this study, marine microorganisms were isolated to identify unique amylase-producing microbes in starch agar medium. More than 50 bacterial strains with positive amylase activity, isolated from marine water and soil, were screened for amylase production in starch agar medium. Bacillus sp. BCC 021-50 was found to be the best amylase-producing strain in starch agar medium and under submerged fermentation conditions. Next, fermentation conditions were optimized for bacterial growth and enzyme production. The highest amylase concentration of 5211 U/mL was obtained after 36 h of incubation at 50 °C, pH 8.0, using 20 g/L molasses as an energy source and 10 g/L peptone as a nitrogen source. From an application perspective, crude amylase was characterized in terms of temperature and pH. Maximum amylase activity was noted at 70 °C and pH 7.50. However, our results show clear advantages for enzyme stability in alkaline pH, high-temperature, and stability in the presence of surfactant, oxidizing, and bleaching agents. This research contributes towards the development of an economical amylase production process using agro-industrial residues. Full article
(This article belongs to the Special Issue Fermentation and Bioactive Metabolites)
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Open AccessFeature PaperArticle Reappraising a Controversy: Formation and Role of the Azodication (ABTS2+) in the Laccase-ABTS Catalyzed Breakdown of Lignin
Fermentation 2017, 3(2), 27; doi:10.3390/fermentation3020027
Received: 11 May 2017 / Revised: 1 June 2017 / Accepted: 8 June 2017 / Published: 15 June 2017
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Abstract
In fermentations of lignocelluloses, redox potentials (If not indicated otherwise, redox potentials in Volt are taken versus Normal Hydrogen Reference Electrodes (NHE).) E0 of laccases/plant peroxidases by 0.79/0.95 V enable oxidations of phenolic substrates and transformations of synthetic and substrate-derived compounds to
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In fermentations of lignocelluloses, redox potentials (If not indicated otherwise, redox potentials in Volt are taken versus Normal Hydrogen Reference Electrodes (NHE).) E0 of laccases/plant peroxidases by 0.79/0.95 V enable oxidations of phenolic substrates and transformations of synthetic and substrate-derived compounds to radicals that mediate attacks on non-phenolic lignin (models) by 1.5 V. In consecutive one-electron abstractions, the redox mediator 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) is oxidized by electro- or wet-chemistry to the green cation radical (ABTS•+, 0.68 V) and the red dication (ABTS2+, 1.09 V). The enzyme/ABTS couple generates the stable ABTS•+ whose low E0 cannot explain the couple’s contemporary attack on non-phenolic lignins. This paradoxon indicates the non-confirmed production of the ligninolytic ABTS2+ by the enzymes. During incubations of live sapwood chips in ABTS/H2O2 to prove their constitutive peroxidase, the enzyme catalyzed the formation of the expected green-colored ABTS•+ solution that gradually turned red. Its spectrophotometric absorbance peaks at λ = 515–573 nm resembled those of ABTS2+ at 518–520 nm. It is shown that portions of an ABTS•+ preparation with inactivated enzyme are reduced to ABTS during their abiotic oxidation of low-MW extractives from lignocelluloses to redox mediating radicals. The radicals, in turn, apparently transform the remaining ABTS•+ to red derivatives in the absence of functional oxidoreductases. Ultrafiltration and Liquid-Chromatography suggest the presence of a stable ABTS2+ compound absorbing at 515 nm, red protein/ABTS adducts, and further ABTS moieties. Therefore, ABTS mediated lignin degradations could result from chain reactions of ABTS•+-activated lignocellulose extractives and fissured rather than complete ABTS2+ molecules. Full article
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Review

Jump to: Research

Open AccessFeature PaperReview Microbial Production of Malic Acid from Biofuel-Related Coproducts and Biomass
Fermentation 2017, 3(2), 14; doi:10.3390/fermentation3020014
Received: 24 February 2017 / Revised: 5 April 2017 / Accepted: 6 April 2017 / Published: 10 April 2017
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Abstract
The dicarboxylic acid malic acid synthesized as part of the tricarboxylic acid cycle can be produced in excess by certain microorganisms. Although malic acid is produced industrially to a lesser extent than citric acid, malic acid has industrial applications in foods and pharmaceuticals
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The dicarboxylic acid malic acid synthesized as part of the tricarboxylic acid cycle can be produced in excess by certain microorganisms. Although malic acid is produced industrially to a lesser extent than citric acid, malic acid has industrial applications in foods and pharmaceuticals as an acidulant among other uses. Only recently has the production of this organic acid from coproducts of industrial bioprocessing been investigated. It has been shown that malic acid can be synthesized by microbes from coproducts generated during biofuel production. More specifically, malic acid has been shown to be synthesized by species of the fungus Aspergillus on thin stillage, a coproduct from corn-based ethanol production, and on crude glycerol, a coproduct from biodiesel production. In addition, the fungus Ustilago trichophora has also been shown to produce malic acid from crude glycerol. With respect to bacteria, a strain of the thermophilic actinobacterium Thermobifida fusca has been shown to produce malic acid from cellulose and treated lignocellulosic biomass. An alternate method of producing malic acid is to use agricultural biomass converted to syngas or biooil as a substrate for fungal bioconversion. Production of poly(β-l-malic acid) by strains of Aureobasidium pullulans from agricultural biomass has been reported where the polymalic acid is subsequently hydrolyzed to malic acid. This review examines applications of malic acid, metabolic pathways that synthesize malic acid and microbial malic acid production from biofuel-related coproducts, lignocellulosic biomass and poly(β-l-malic acid). Full article
(This article belongs to the Special Issue Carboxylic Acid Production)
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Open AccessFeature PaperReview Laccases as a Potential Tool for the Efficient Conversion of Lignocellulosic Biomass: A Review
Fermentation 2017, 3(2), 17; doi:10.3390/fermentation3020017
Received: 26 March 2017 / Revised: 20 April 2017 / Accepted: 26 April 2017 / Published: 2 May 2017
Cited by 2 | PDF Full-text (864 KB) | HTML Full-text | XML Full-text
Abstract
The continuous increase in the world energy and chemicals demand requires the development of sustainable alternatives to non-renewable sources of energy. Biomass facilities and biorefineries represent interesting options to gradually replace the present industry based on fossil fuels. Lignocellulose is the most promising
[...] Read more.
The continuous increase in the world energy and chemicals demand requires the development of sustainable alternatives to non-renewable sources of energy. Biomass facilities and biorefineries represent interesting options to gradually replace the present industry based on fossil fuels. Lignocellulose is the most promising feedstock to be used in biorefineries. From a sugar platform perspective, a wide range of fuels and chemicals can be obtained via microbial fermentation processes, being ethanol the most significant lignocellulose-derived fuel. Before fermentation, lignocellulose must be pretreated to overcome its inherent recalcitrant structure and obtain the fermentable sugars. Usually, harsh conditions are required for pretreatment of lignocellulose, producing biomass degradation and releasing different compounds that are inhibitors of the hydrolytic enzymes and fermenting microorganisms. Moreover, the lignin polymer that remains in pretreated materials also affects biomass conversion by limiting the enzymatic hydrolysis. The use of laccases has been considered as a very powerful tool for delignification and detoxification of pretreated lignocellulosic materials, boosting subsequent saccharification and fermentation processes. This review compiles the latest studies about the application of laccases as useful and environmentally friendly delignification and detoxification technology, highlighting the main challenges and possible ways to make possible the integration of these enzymes in future lignocellulose-based industries. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production)
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Open AccessFeature PaperReview Microbial Propionic Acid Production
Fermentation 2017, 3(2), 21; doi:10.3390/fermentation3020021
Received: 27 March 2017 / Revised: 3 May 2017 / Accepted: 7 May 2017 / Published: 15 May 2017
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Abstract
Propionic acid (propionate) is a commercially valuable carboxylic acid produced through microbial fermentation. Propionic acid is mainly used in the food industry but has recently found applications in the cosmetic, plastics and pharmaceutical industries. Propionate can be produced via various metabolic pathways, which
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Propionic acid (propionate) is a commercially valuable carboxylic acid produced through microbial fermentation. Propionic acid is mainly used in the food industry but has recently found applications in the cosmetic, plastics and pharmaceutical industries. Propionate can be produced via various metabolic pathways, which can be classified into three major groups: fermentative pathways, biosynthetic pathways, and amino acid catabolic pathways. The current review provides an in-depth description of the major metabolic routes for propionate production from an energy optimization perspective. Biological propionate production is limited by high downstream purification costs which can be addressed if the target yield, productivity and titre can be achieved. Genome shuffling combined with high throughput omics and metabolic engineering is providing new opportunities, and biological propionate production is likely to enter the market in the not so distant future. In order to realise the full potential of metabolic engineering and heterologous expression, however, a greater understanding of metabolic capabilities of the native producers, the fittest producers, is required. Full article
(This article belongs to the Special Issue Carboxylic Acid Production)
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Open AccessFeature PaperReview Biochemical Production and Separation of Carboxylic Acids for Biorefinery Applications
Fermentation 2017, 3(2), 22; doi:10.3390/fermentation3020022
Received: 25 April 2017 / Revised: 12 May 2017 / Accepted: 16 May 2017 / Published: 19 May 2017
Cited by 2 | PDF Full-text (1179 KB) | HTML Full-text | XML Full-text
Abstract
Carboxylic acids are traditionally produced from fossil fuels and have significant applications in the chemical, pharmaceutical, food, and fuel industries. Significant progress has been made in replacing such fossil fuel sources used for production of carboxylic acids with sustainable and renewable biomass resources.
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Carboxylic acids are traditionally produced from fossil fuels and have significant applications in the chemical, pharmaceutical, food, and fuel industries. Significant progress has been made in replacing such fossil fuel sources used for production of carboxylic acids with sustainable and renewable biomass resources. However, the merits and demerits of each carboxylic acid processing platform are dependent on the application of the final product in the industry. There are a number of studies that indicate that separation processes account for over 30% of the total processing costs in such processes. This review focuses on the sustainable processing of biomass resources to produce carboxylic acids. The primary focus of the review will be on a discussion of and comparison between existing biochemical processes for producing lower-chain fatty acids such as acetic-, propionic-, butyric-, and lactic acids. The significance of these acids stems from the recent progress in catalytic upgrading to produce biofuels apart from the current applications of the carboxylic acids in the food, pharmaceutical, and plastics sectors. A significant part of the review will discuss current state-of-art of techniques for separation and purification of these acids from fermentation broths for further downstream processing to produce high-value products. Full article
(This article belongs to the Special Issue Carboxylic Acid Production)
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Open AccessFeature PaperReview Succinic Acid: Technology Development and Commercialization
Fermentation 2017, 3(2), 26; doi:10.3390/fermentation3020026
Received: 31 March 2017 / Revised: 2 June 2017 / Accepted: 5 June 2017 / Published: 9 June 2017
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Abstract
Succinic acid is a precursor of many important, large-volume industrial chemicals and consumer products. It was once common knowledge that many ruminant microorganisms accumulated succinic acid under anaerobic conditions. However, it was not until the discovery of Anaerobiospirillum succiniciproducens at the Michigan Biotechnology
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Succinic acid is a precursor of many important, large-volume industrial chemicals and consumer products. It was once common knowledge that many ruminant microorganisms accumulated succinic acid under anaerobic conditions. However, it was not until the discovery of Anaerobiospirillum succiniciproducens at the Michigan Biotechnology Institute (MBI), which was capable of producing succinic acid up to about 50 g/L under optimum conditions, that the commercial feasibility of producing the compound by biological processes was realized. Other microbial strains capable of producing succinic acid to high final concentrations subsequently were isolated and engineered, followed by development of fermentation processes for their uses. Processes for recovery and purification of succinic acid from fermentation broths were simultaneously established along with new applications of succinic acid, e.g., production of biodegradable deicing compounds and solvents. Several technologies for the fermentation-based production of succinic acid and the subsequent conversion to useful products are currently commercialized. This review gives a summary of the development of microbial strains, their fermentation, and the importance of the down-stream recovery and purification efforts to suit various applications in the context of their current commercialization status for biologically derived succinic acid. Full article
(This article belongs to the Special Issue Carboxylic Acid Production)
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Open AccessFeature PaperReview Syngas Fermentation: A Microbial Conversion Process of Gaseous Substrates to Various Products
Fermentation 2017, 3(2), 28; doi:10.3390/fermentation3020028
Received: 27 April 2017 / Revised: 9 June 2017 / Accepted: 12 June 2017 / Published: 16 June 2017
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Abstract
Biomass and other carbonaceous materials can be gasified to produce syngas with high concentrations of CO and H2. Feedstock materials include wood, dedicated energy crops, grain wastes, manufacturing or municipal wastes, natural gas, petroleum and chemical wastes, lignin, coal and tires.
[...] Read more.
Biomass and other carbonaceous materials can be gasified to produce syngas with high concentrations of CO and H2. Feedstock materials include wood, dedicated energy crops, grain wastes, manufacturing or municipal wastes, natural gas, petroleum and chemical wastes, lignin, coal and tires. Syngas fermentation converts CO and H2 to alcohols and organic acids and uses concepts applicable in fermentation of gas phase substrates. The growth of chemoautotrophic microbes produces a wide range of chemicals from the enzyme platform of native organisms. In this review paper, the Wood–Ljungdahl biochemical pathway used by chemoautotrophs is described including balanced reactions, reaction sites physically located within the cell and cell mechanisms for energy conservation that govern production. Important concepts discussed include gas solubility, mass transfer, thermodynamics of enzyme-catalyzed reactions, electrochemistry and cellular electron carriers and fermentation kinetics. Potential applications of these concepts include acid and alcohol production, hydrogen generation and conversion of methane to liquids or hydrogen. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production)
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