| 1. |
- Bonturi, Nemailla, et al.
(author)
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Single Cell Oil Producing Yeasts Lipomyces starkeyi and Rhodosporidium toruloides : Selection of Extraction Strategies and Biodiesel Property Prediction
- 2015
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In: Energies. - : MDPI AG. - 1996-1073. ; 8:6, s. 5040-5052
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Journal article (peer-reviewed)abstract
- Single cell oils (SCOs) are considered potential raw material for the production of biodiesel. Rhodosporidium sp. and Lipomyces sp. are good candidates for SCO production. Lipid extractability differs according to yeast species and literature on the most suitable method for each oleaginous yeast species is scarce. This work aimed to investigate the efficiency of the most cited strategies for extracting lipids from intact and pretreated cells of Rhodosporidium toruloides and Lipomyces starkeyi. Lipid extractions were conducted using hexane or combinations of chloroform and methanol. The Folch method resulted in the highest lipid yields for both yeasts (42% for R. toruloides and 48% for L. starkeyi). Also, this method eliminates the cell pretreatment step. The Bligh and Dyer method underestimated the lipid content in the tested strains (25% for R. toruloides and 34% for L. starkeyi). Lipid extractability increased after acid pretreatment for the Pedersen, hexane, and Bligh and Dyer methods. For R. toruloides unexpected fatty acid methyl esters (FAME) composition were found for some lipid extraction strategies tested. Therefore, this work provides useful information for analytical and process development aiming at biodiesel production from the SCO of these two yeast species.
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| 2. |
- Charisteidis, Ioannis, et al.
(author)
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Catalytic Fast Pyrolysis of Lignin Isolated by Hybrid Organosolv—Steam Explosion Pretreatment of Hardwood and Softwood Biomass for the Production of Phenolics and Aromatics
- 2019
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In: Catalysts. - : MDPI. - 2073-4344. ; 9:11
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Journal article (peer-reviewed)abstract
- Lignin, one of the three main structural biopolymers of lignocellulosic biomass, is the most abundant natural source of aromatics with a great valorization potential towards the production of fuels, chemicals, and polymers. Although kraft lignin and lignosulphonates, as byproducts of the pulp/paper industry, are available in vast amounts, other types of lignins, such as the organosolv or the hydrolysis lignin, are becoming increasingly important, as they are side-streams of new biorefinery processes aiming at the (bio)catalytic valorization of biomass sugars. Within this context, in this work, we studied the thermal (non-catalytic) and catalytic fast pyrolysis of softwood (spruce) and hardwood (birch) lignins, isolated by a hybrid organosolv–steam explosion biomass pretreatment method in order to investigate the effect of lignin origin/composition on product yields and lignin bio-oil composition. The catalysts studied were conventional microporous ZSM-5 (Zeolite Socony Mobil–5) zeolites and hierarchical ZSM-5 zeolites with intracrystal mesopores (i.e., 9 and 45 nm) or nano-sized ZSM-5 with a high external surface. All ZSM-5 zeolites were active in converting the initially produced via thermal pyrolysis alkoxy-phenols (i.e., of guaiacyl and syringyl/guaiacyl type for spruce and birch lignin, respectively) towards BTX (benzene, toluene, xylene) aromatics, alkyl-phenols and polycyclic aromatic hydrocarbons (PAHs, mainly naphthalenes), with the mesoporous ZSM-5 exhibiting higher dealkoxylation reactivity and being significantly more selective towards mono-aromatics compared to the conventional ZSM-5, for both spruce and birch lignin.
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| 3. |
- Kalogiannis, Konstantinos G, et al.
(author)
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Acid Assisted Organosolv Delignification of Beechwood and Pulp Conversion towards High Concentrated Cellulosic Ethanol via High Gravity Enzymatic Hydrolysis and Fermentation
- 2018
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In: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 23:7
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Journal article (peer-reviewed)abstract
- Background: Future biorefineries will focus on converting low value waste streams to chemical products that are derived from petroleum or refined sugars. Feedstock pretreatment in a simple, cost effective, agnostic manner is a major challenge.Methods: In this work, beechwood sawdust was delignified via an organosolv process, assisted by homogeneous inorganic acid catalysis. Mixtures of water and several organic solvents were evaluated for their performance. Specifically, ethanol (EtOH), acetone (AC), and methyl- isobutyl- ketone (MIBK) were tested with or without the use of homogeneous acid catalysis employing sulfuric, phosphoric, and oxalic acids under relatively mild temperature of 175 °C for one hour.Results: Delignification degrees (DD) higher than 90% were achieved, where both AC and EtOH proved to be suitable solvents for this process. Both oxalic and especially phosphoric acid proved to be good alternative catalysts for replacing sulfuric acid. High gravity simultaneous saccharification and fermentation with an enzyme loading of 8.4 mg/gsolids at 20 wt.% initial solids content reached an ethanol yield of 8.0 w/v%.Conclusions: Efficient delignification combining common volatile solvents and mild acid catalysis allowed for the production of ethanol at high concentration in an efficient manner
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| 4. |
- Kalogiannis, Konstantinos G., et al.
(author)
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Aromatics from Beechwood Organosolv Lignin through Thermal and Catalytic Pyrolysis
- 2019
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In: Energies. - : MDPI. - 1996-1073. ; 12:9
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Journal article (peer-reviewed)abstract
- Biomass fractionation, as an alternative to biomass pretreatment, has gained increasing research attention over the past few years as it provides separate streams of cellulose, hemicellulose, and lignin. These streams can be used separately and can provide a solution for improving the economics of emerging biorefinery technologies. The sugar streams are commonly used in microbial conversions, whereas during recent years lignin has been recognized as a valuable compound as it is the only renewable and abundant source of aromatic chemicals. Successfully converting lignin into valuable chemicals and products is key in achieving both environmental and economic sustainability of future biorefineries. In this work, lignin retrieved from beechwood sawdust delignification pretreatment via an organosolv process was depolymerized with thermal and catalytic pyrolysis. ZSM-5 commercial catalyst was used in situ to upgrade the lignin bio-oil vapors. Lignins retrieved from different modes of organosolv pretreatment were tested in order to evaluate the effect that upstream pretreatment has on the lignin fraction. Both thermal and catalytic pyrolysis yielded oils rich in phenols and aromatic hydrocarbons. Use of ZSM-5 catalyst assisted in overall deoxygenation of the bio-oils and enhanced aromatic hydrocarbons production. The oxygen content of the bio-oils was reduced at the expense of their yield. Organosolv lignins were successfully depolymerized towards phenols and aromatic hydrocarbons via thermal and catalytic pyrolysis. Hence, lignin pyrolysis can be an effective manner for lignin upgrading towards high added value products
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| 5. |
- Karnaouri, Anthi C, et al.
(author)
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Fine-tuned enzymatic hydrolysis of organosolv pretreated forest materials for the efficient production of cellobiose
- 2018
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In: Frontiers in Chemistry. - : Frontiers Media S.A.. - 2296-2646. ; 6
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Journal article (peer-reviewed)abstract
- Non-digestible oligosaccharides (NDOs) are likely prebiotic candidates that have been related to the prevention of intestinal infections and other disorders for both humans and animals. Lignocellulosic biomass is the largest carbon source in the biosphere, therefore cello-oligosacharides (COS), especially cellobiose, are potentially the most widely available choice of NDOs. Production of COS and cellobiose with enzymes offers numerous benefits over acid-catalyzed processes, as it is milder, environmentally friendly and produces fewer by-products. Cellobiohydrolases (CBHs) and a class of endoglucanases (EGs), namely processive EGs, are key enzymes for the production of COS, as they have higher preference toward glycosidic bonds near the end of cellulose chains and are able to release soluble products. In this work, we describe the heterologous expression and characterization of two CBHs from the filamentous fungus Thermothelomyces thermophila, as well as their synergism with proccessive EGs for cellobiose release from organosolv pretreated spruce and birch. The properties, inhibition kinetics and substrate specific activities for each enzyme are described in detail. The results show that a combination of EGs belonging to Glycosyl hydrolase families 5, 6 and 9, with a CBHI and CBHII in appropriate proportions, can enhance the production of COS from forest materials, underpinning the potential of these biocatalysts in the production of NDOs.
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| 6. |
- Karnaouri, Anthi C., et al.
(author)
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Tailoring Celluclast (R) Cocktail's Performance towards the Production of Prebiotic Cello-Oligosaccharides from Waste Forest Biomass
- 2019
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In: Catalysts. - : MDPI. - 2073-4344. ; 9:11
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Journal article (peer-reviewed)abstract
- The main objective of this study focused on the sustainable production of cellobiose and other cellulose-derived oligosaccharides from non-edible sources, more specifically, from forest residues. For this purpose, a fine-tuning of the performance of the commercially available enzyme mixture Celluclast® was conducted towards the optimization of cellobiose production. By enzyme reaction engineering (pH, multi-stage hydrolysis with buffer exchange, addition of β-glucosidase inhibitor), a cellobiose-rich product with a high cellobiose to glucose ratio (37.4) was achieved by utilizing organosolv-pretreated birch biomass. In this way, controlled enzymatic hydrolysis combined with efficient downstream processing, including product recovery and purification through ultrafiltration and nanofiltration, can potentially support the sustainable production of food-grade oligosaccharides from forest biomass. The potential of the hydrolysis product to support the growth of two Lactobacilli probiotic strains as a sole carbon source was also demonstrated
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| 7. |
- Karnaouri, Anthi C., et al.
(author)
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Valorization of waste forest biomass toward the production of cello-oligosaccharides with potential prebiotic activity by utilizing customized enzyme cocktails
- 2019
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In: Biotechnology for Biofuels. - : BioMed Central. - 1754-6834. ; 12:1
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Journal article (peer-reviewed)abstract
- BackgroundProduction of value-added materials from lignocellulosic biomass residues is an emerging sector that has attracted much attention as it offers numerous benefits from an environmental and economical point of view. Non-digestible oligosaccharides represent a group of carbohydrates that are resistant to gastrointestinal digestion, and therefore, they are considered as potential prebiotic candidates. Such oligosaccharides can derive from the biomass cellulose fraction through a controlled enzymatic hydrolysis that eliminates the yield of monomers.ResultsIn the present study, hydrolysis of organosolv-pretreated forest residues (birch and spruce) was tested in the presence of four cellulases (EG5, CBH7, CBH6, EG7) and one accessory enzyme (LPMO). The optimal enzyme combinations were comprised of 20% EG5, 43% CBH7, 22% TtLPMO, 10% PaCbh6a and 5% EG7 in the case of birch and 35% EG5, 45% CBH7, 10% TtLPMO, 10% PaCbh6a and 5% EG7 in the case of spruce, leading to 22.3% and 19.1 wt% cellulose conversion into cellobiose, respectively. Enzymatic hydrolysis was applied on scale-up reactions, and the produced oligosaccharides (consisted of > 90% cellobiose) were recovered and separated from glucose through nanofiltration at optimized temperature (50 °C) and pressure (10 bar) conditions, yielding a final product with cellobiose-to-glucose ratio of 21.1 (birch) and 20.2 (spruce). Cellobiose-rich hydrolysates were tested as fermentative substrates for different lactic acid bacteria. It was shown that they can efficiently stimulate the growth of two Lactobacilli strains.ConclusionsControlled enzymatic hydrolysis with processive cellulases, combined with product recovery and purification, as well as enzyme recycling can potentially support the sustainable production of food-grade oligosaccharides from forest biomass.
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| 8. |
- Karnaouri, Anthi, et al.
(author)
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Development of Thermophilic Tailor-Made Enzyme Mixtures for the Bioconversion of Agricultural and Forest Residues
- 2016
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In: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 7
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Journal article (peer-reviewed)abstract
- Even though the main components of all lignocellulosic feedstocks include cellulose, hemicellulose, as well as the protective lignin matrix, there are some differences in structure, such as in hardwoods and softwoods, which may influence the degradability of the materials. Under this view, various types of biomass might require a minimal set of enzymes that has to be tailor-made. Partially defined complex mixtures that are currently commercially used are not adapted to efficiently degrade different materials, so novel enzyme mixtures have to be customized. Development of these cocktails requires better knowledge about the specific activities involved, in order to optimize hydrolysis. The role of filamentous fungus Myceliophthora thermophila and its complete enzymatic repertoire for the bioconversion of complex carbohydrates has been widely proven. In this study, four core cellulases (MtCBH7, MtCBH6, MtEG5, and MtEG7), in the presence of other four “accessory” enzymes (mannanase, lytic polyssacharide monooxygenase MtGH61, xylanase, MtFae1a) and β-glucosidase MtBGL3, were tested as a nine-component cocktail against one model substrate (phosphoric acid swollen cellulose) and four hydrothermally pretreated natural substrates (wheat straw as an agricultural waste, birch, and spruce biomass, as forest residues). Synergistic interactions among different enzymes were determined using a suitable design of experiments methodology. The results suggest that for the hydrolysis of the pure substrate (PASC), high proportions of MtEG7 are needed for efficient yields. MtCBH7 and MtEG7 are enzymes of major importance during the hydrolysis of pretreated wheat straw, while MtCBH7 plays a crucial role in case of spruce. Cellobiohydrolases MtCBH6 and MtCBH7 act in combination and are key enzymes for the hydrolysis of the hardwood (birch). Optimum combinations were predicted from suitable statistical models which were able to further increase hydrolysis yields, suggesting that tailor-made enzyme mixtures targeted toward a particular residual biomass can help maximize hydrolysis yields. The present work demonstrates the change from “one cocktail for all” to “tailor-made cocktails” that are needed for the efficient saccharification of targeted feed stocks prior to the production of biobased products through the biorefinery concept.
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| 9. |
- Katsimpouras, Constantinos, et al.
(author)
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Sequential high gravity ethanol fermentation and anaerobic digestion of steam explosion and organosolv pretreated corn stover
- 2017
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In: Bioresource Technology. - : Elsevier. - 0960-8524 .- 1873-2976. ; 244:1, s. 1129-1136
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Journal article (peer-reviewed)abstract
- The present work investigates the suitability of pretreated corn stover (CS) to serve as feedstock for high gravity (HG) ethanol production at solids-content of 24 wt%. Steam explosion, with and without the addition of H2SO4, and organosolv pretreated CS samples underwent a liquefaction/saccharification step followed by simultaneous saccharification and fermentation (SSF). Maximum ethanol concentration of ca. 76 g/L (78.3% ethanol yield) was obtained from steam exploded CS (SECS) with 0.2% H2SO4. Organosolv pretreated CS (OCS) also resulted in high ethanol concentration of ca. 65 g/L (62.3% ethanol yield). Moreover, methane production through anaerobic digestion (AD) was conducted from fermentation residues and resulted in maximum methane yields of ca. 120 and 69 mL/g volatile solids (VS) for SECS and OCS samples, respectively. The results indicated that the implementation of a liquefaction/saccharification step before SSF employing a liquefaction reactor seemed to handle HG conditions adequately.
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| 10. |
- Kirtania, Kawnish, et al.
(author)
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Alkali catalyzed gasification of solid biomass : influence on fuel conversion and tar/soot reduction
- 2016
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In: Proceedings of the 24th European Biomass Conference and Exhibition. - Amsterdam : ETA Florence Renewable Energies. ; , s. 533-536
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Conference paper (peer-reviewed)abstract
- Based on char gasification experiments in an isothermal thermogravimetric analyzer, a suitable concentration of alkali salt (K2CO3) was chosen for impregnation due to almost five-fold increase in gasification reactivity and relatively low amount of carbon leaching during impregnation. Furthermore, an optimum method for wet alkali impregnation was proposed based on the several tests performed by varying temperature and time. To study the catalytic effect on tar and soot yield, untreated and impregnated woody biomass were gasified under entrained flow condition between 900 oC and 1200 oC. Impregnation leads to 70% lower tar yield from gasification around 1000 oC and 1100 oC. The lowest amount of soot was detected for the same temperature range whereas the soot yield was one order of magnitude higher for untreated biomass. For tar, this influence became insignificant at a higher temperature (1200 oC). This defines the suitable temperature range for alkali catalyzed gasification without the loss of catalytic activity.
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