Optimização da hidrólise com ácido diluído para o fraccionamento selectivo das hemiceluloses de palha de sorgo: estudo da bioconversão dos hidrolisados para produção de xilitol

O sorgo é uma potencial cultura energética com especial interesse para os climas mediterrânicos. Quer o seu suco quer a sua fracção lenhocelulósica podem ser utilizados no âmbito das biorrefinarias. O objectivo deste trabalho consistiu na optimização da hidrólise com ácido diluído da hemicelulose do sorgo e sua posterior bioconversão a xilitol. Dada a dificuldade de trabalhar o sorgo verde e a quantidade potencial de açúcares ainda presentes no sorgo seco foi feita uma pré-extracção aquosa (PEA) do sorgo biomassa, cujas condições foram optimizadas (100ºC, 45 min, razão líquido/sólido 7 g/g). Para além disso, foram também caracterizados três tipos de sorgo verde (doce, forrageiro e biomassa) relativamente ao teor e tipo de açúcares presentes no suco e licor da PEA, anteriormente optimizada. O material seco pré-tratado foi submetido a uma hidrólise com ácido diluído, tendo-se estudado a influência do tempo de operação e concentração de catalisador (H2SO4) na hidrólise da hemicelulose, a 130ºC. Os resultados foram interpretados através do factor de severidade combinado (CS), num intervalo entre 1,17-2,31. As condições óptimas correspondem a um CS de 1,98, (1,4% H2SO4 e 75 min), tendo-se recuperado na fase líquida 80% da hemiceluloses sob a forma de pentoses livres, juntamente com baixas concentrações de inibidores. O hidrolisado obtido nas condições optimizadas foi utilizado como meio de crescimento e, após concentração, como meio de cultura para a produção de xilitol pela levedura Debaryomyces hansenii CCMI 941. Como meios de inóculo foram testados o hidrolisado ácido e o licor da PEA, ambos suplementados. O último permitiu o crescimento mais rápido da levedura e a obtenção de concentrações celulares adequadas. No entanto, dado que a fase de latência no meio de produção de xilitol foi superior e, consequentemente a produtividade em xilitol inferior, optou-se pelo crescimento do inóculo em meio contendo hidrolisado. A remoção de compostos inibidores foi avaliada através da destoxificação do hidrolisado com carvão activado que permitiu uma remoção significativa de furfural, compostos fenólicos e ácido acético. No entanto, os melhores resultados da produção de xilitol foram obtidos em hidrolisado não-destoxificado e correspondem a um rendimento em xilitol e produtividade volumétrica de 0,64 g.g-1 e 0,56 g.L-1.h-1, respectivamente. Estes resultados encontram-se entre os melhores descritos na literatura para hidrolisados nãodestoxificados, mostrando assim as potencialidades deste material, da levedura e do processo desenvolvido

Microwave-assisted hydrothermal processing of pine nut shells for oligosaccharide production

ABSTRACT: Pine nut shells, a biomass residue from the Mediterranean Pinus pinea pine nut industrial processing, were treated by microwave-assisted autohydrolysis to produce xylo-oligosaccharides. Microwave-assisted processes provide alternative heating that may reduce energy input and increase overall process efficiency. The autohydrolysis treatments were performed under isothermal and non-isothermal operations within a wide range of operational conditions (temperature/reaction times) covering several severity regimes (as measured by the log R-0 severity factor). The composition of the autohydrolysis liquors was determined in terms of oligo- and monosaccharides, aliphatic acids and degradation compounds. The process was highly selective towards hemicelluloses hydrolysis and liquid streams containing a mixture of oligomeric compounds (mainly xylo-oligosaccharides) could be obtained under relatively mild operation conditions (190 degrees C, 30 min) with a maximal oligosaccharides' concentration of 18.48 g/L. The average polymerization degree of the obtained oligosaccharides was characterised by HPLC, showing that for the optimal conditions a mixture of oligomers with DPs from 2 to 6.info:eu-repo/semantics/publishedVersio

Bioethanol production from globe artichoke residues: From the field to the fermenter

The suitability of globe artichoke crop residues to be transformed into bioethanol was assessed in this paper from the field to the fermenter. A 2-year field trial on “Opera F1” (OF1), a hybrid variety of globe artichoke, resulted in an average annual production of residues of 14 t/ha. The residual biomass of OF1 is made up of 24% glucan and 17% hemicelluloses and is rich in soluble sugars. Water extraction (WE) (100 °C, 15 min) was initially applied to remove simple sugars that can be transformed into saccharification and fermentation inhibitors during the pretreatments. Subsequent dilute acid hydrolysis (DAH) (H2SO4 2%, 121 °C, 1 h) produced a slurry with 17.7, 4.2, and 0.5% (dry matter: DM) of soluble sugars, acetic acid, and total furanic compounds, respectively, and a solid fraction with 52% glucan and 14% xylan, with practically 100% digestibility. Slurry enzymatic hydrolysis (45 FPU/g DM, 7 CBU/g DM, 24 h) had a 69% glucan yield, showing an inhibition of the saccharification process due to the presence of simple sugars and inhibitors. Co-fermentation of the enzymatic slurry with Escherichia coli MS04 produced 12.5 g/L ethanol with a volumetric productivity of 0.52 g/L/h and 76.0% fermentation efficiency after 24 h of fermentation. Considering all sugars generated during DAH, the applied strategy allowed a production of 283 kg/t DM and 2399 kg/ha of bioethanol, against the theoretical value of 2806 kg/ha

Production of Oligosaccharides from Pine Nut Shells by Autohydrolysis

ABSTRACT: Pinus pinea nuts are commercial relevant Mediterranean edible forest nuts, with an increasing production and market value, whose industrial processing yields a lignocellulosic by-product, the pine nut shells, currently only used for combustion. Little research has been done on pine nut shells that could support a value-added application for this residue. This work studies for the first time the production of oligosaccharides by autohydrosis, and aims at an integrated upgrade within the biorefinery framework. Autohydrolysis was explored in the temperature range between 150 and 230 degrees C (corresponding to severity factors 2.13-4.63). Oligosaccharides, mainly xylo-oligosaccharides (95% of the total), were the key soluble products, reaching 28.7 g/100 g of xylan of the feedstock at the optimal conditions (log R-0 4.01). Other products were monosaccharides and phenolic compounds that reached 7.8 and 4.7 g/L, respectively, under the most severe conditions. The stability of the oligosaccharides at different temperatures (room, 37 degrees C and 100 degrees C) and pH (between 1 and 11) grant them significant market potential in the food and pharma sectors. The pre-treated pine nut shells by autohydrolysis presented an improved, although low, enzymatic digestibility (14%), and an improved high-heating value, therefore advising their further valorization by thermochemical pathways.info:eu-repo/semantics/publishedVersio

Xylitol Production by Debaryomyces hansenii in Extracted Olive Pomace Dilute-Acid Hydrolysate

ABSTRACT: The extracted olive pomace (EOP) is an industrial lignocellulosic by-product of olive pomace oil extraction, currently mainly used for energy production through combustion. In this work, the hemicellulosic fraction of EOP was selectively hydrolyzed by diluted acid hydrolysis to obtain pentose-rich hydrolysates that can potentially be upgraded by Debaryomyces hansenii, targeting xylitol production. The monosaccharides and degradation by-products released along the pre-treatment were quantified and several detoxification methods for the removal of potentially toxic compounds were evaluated, including pH adjustment to 5.5, the use of anion-exchange resins, adsorption into activated charcoal, concentration by evaporation, and membrane techniques, i.e., nanofiltration. The latter approach was shown to be the best method allowing the full removal of furfural, 41% of 5-hydroxymethylfurfural, 54% of acetic acid, and 67% of the phenolic compounds present in the hydrolysate. The effects of the supplementation of both non-detoxified and detoxified hydrolysates were also assessed. The non-detoxified hydrolysate, under aerobic conditions, supported the yeast growth and xylitol production at low levels. Supplementation with the low-cost corn steep liquor of the nanofiltration detoxified hydrolysate showed a higher xylitol yield (0.57 g/g) compared to the non-detoxified hydrolysate. The highest xylitol productivity was found in hydrolysate detoxified with anionic resins (0.30 g/L-h), which was 80% higher than in the non-detoxified culture medium. Overall, the results showed that EOP dilute acid hydrolysates can efficiently be used for xylitol production by D. hansenii if detoxification, and supplementation, even with low-cost supplements, are performed.info:eu-repo/semantics/publishedVersio

Novel processes and products from Mediterranean Biomass within the biorefinery framework

Doutoramento em Engenharia Florestal e dos Recursos Naturais / Instituto Superior de Agronomia. Universidade de LisboaIn the present context of environmental threats and the desired adoption of bioeconony, full resource use and sustainability principles, the valorisation of residual biomass to obtain value-added products within the biorefinery framework is showing has shown a great potential. In this work, a valorisation strategy centred on hemicellulosic oligosaccharides (OS) was developed using several forest, agricultural and agro-industrial residual materials relevant in the Mediterranean region, and in particular in the montado ecosystem, namely pine nut shells, almond shells, corncobs and extracted olive pomace. Autohydrolysis, microwave-assisted autohydrolysis and propylene glycol organosolv (PG-organosolv) processes were used for OS production with different process severity factors and the hydrolysate liquors were analysed for OS, monosaccharides, acids and furans. Comparing with PG-organosolv, autohydrolysis allowed a more selective removal of hemicelluloses. Overall, all the materials tested allowed the production of OS and optimal conditions with low monosaccharides and furan content could be selected. Microwave assisted autohydrolysis had a 15% better results for OS concentration and yield. The produced OS showed temperature (37 ºC / 100 ºC) and pH (1 and 11) stability and have therefore commercial potential. Different microwave heating conditions were tested, and the production of OS was favoured by slow heating, when the process is carried out under industrially relevant conditions (non-isothermal). Autohydrolysis liquors from corncobs with a high xylo-oligosaccharides (XOS) content were produced and used as growth media for Lactobacilli. Strain screening was carried out and six strains were selected that effectively assimilated XOS, thus being potentially considered probiotic strains. The best performing strains were inoculated in autohydrolysis OS-rich liquors from coffee grounds to obtain a symbiotic coffee-flavoured beverage.N/

Detoxification of hemicellulosic hydrolysates from extracted olive pomace by diananofiltration

Xylitol can be obtained from the pentose-rich hemicellulosic fraction of agricultural residues, such as extracted olive pomace, by fermentation. Dilute acid hydrolysis of lignocellulosic materials, produces the release of potential inhibitory compounds mainly furan derivatives, aliphatic acids, and phenolic compounds. In order to study the potential on the increase of the hydrolysate fermentability, detoxification experiments based on diananofiltration membrane separation processes were made. Two membranes, NF270 and NF90, were firstly evaluated using hydrolysate model solutions under total recirculation mode, to identify the best membrane for the detoxification. NF270 was chosen to be used in the diananofiltration experiment as it showed the lowest rejection for toxic compounds and highest permeate flux. Diananofiltration experiments, for hydrolysate model solutions and hydrolysate liquor, showed that nanofiltration is able to deplete inhibitory compounds and to obtain solutions with higher xylose content. Conversely to non-detoxified hydrolysates, nanofiltration detoxified hydrolysates enabled yeast growth and xylitol production by the yeast Debaryomyces hansenii, clearly pointing out that detoxification is an absolute requirement for extracted olive pomace dilute acid hydrolysate bioconversion

Autohydrolysis of Annona cherimola Mill. seeds: optimization, modeling and products characterization

Annona cherimola Mill. seeds are a residue of the industrial processing of this fruit, for which, presently, there is no industrial application. They have a considerable amount of oil, which can be converted into biodiesel, but the remaining lignocellulosic fraction still needs relevant added-value valorization routes. In this work, the selective hemicelluloses removal by autohydrolysis was optimized aiming to maximize the yield of oligosaccharides with potential applications in food, pharmaceutical and cosmetic industries. A maximum of 10.4 g L-1 of oligosaccharides was obtained, for a severity factor of 3.6, where 74.5% of the original hemicellulose was solubilized. The process kinetics is presented, modeled (based on the Arrhenius equation) and its scale-up is discussed. The hydrolyzate shelf-life was evaluated and the produced oligosaccharides are stable at room temperature for, at least, 3 weeks. Furthermore, all oligosaccharides are also stable at 100 °C for 1 h, in pH values between 1 and 11, enabling their industrial processing, and at 37 °C for 3 h, in pH values between 1 and 3, thus indicating its potential classification as non-digestible oligosaccharides. The remaining cellulose enriched solids presented an increased enzymatic digestibility (as a function of the autohydrolysis severity) that assures its efficient use in subsequent processes (e.g., bioethanol production). The upgrade route developed in this work in combination to the previously reported use of A. cherimola seed oil for biodiesel production can lead to an integrated zero-waste valorization strategy within the biorefinery framework

Detoxification of hemicellulosic hydrolysates from extracted olive pomace by diananofiltration

Xylitol can be obtained from the pentose-rich hemicellulosic fraction of agricultural residues, such as extracted olive pomace, by fermentation. Dilute acid hydrolysis of lignocellulosic materials, produces the release of potential inhibitory compounds mainly furan derivatives, aliphatic acids, and phenolic compounds. In order to study the potential on the increase of the hydrolysate fermentability, detoxification experiments based on diananofiltration membrane separation processes were made. Two membranes, NF270 and NF90, were firstly evaluated using hydrolysate model solutions under total recirculation mode, to identify the best membrane for the detoxification. NF270 was chosen to be used in the diananofiltration experiment as it showed the lowest rejection for toxic compounds and highest permeate flux. Diananofiltration experiments, for hydrolysate model solutions and hydrolysate liquor, showed that nanofiltration is able to deplete inhibitory compounds and to obtain solutions with higher xylose content. Conversely to non-detoxified hydrolysates, nanofiltration detoxified hydrolysates enabled yeast growth and xylitol production by the yeast Debaryomyces hansenii, clearly pointing out that detoxification is an absolute requirement for extracted olive pomace dilute acid hydrolysate bioconversion. (C) 2013 Elsevier Ltd. All rights reserved