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- Hydrothermal processing of hardwoods and agro-industrial residues :evaluation of xylo-oligosaccharides productionPublication . Carvalheiro, Florbela; Fernandes, Talita Silva; Duarte, Luís C.; Lopes, Sónia; Moura, Patrícia; Pereira, Helena; Gírio, FranciscoAutohydrolysis was used as a pre-treatment method for the selective hydrolysis of hemicelluloses of four lignocellulosic materials: eucalypt wood chips (EWC), corn cobs (CC), wheat straw (WS) and brewery’s spent grain (BSG), and the process was optimized towards the production of xylo-oligosaccharides (XOS). The effects of temperature, both at isothermal (150-190ºC), and non-isothermal (up to 240ºC) conditions, and liquid-to-solid ratio (LSR), 8 or 10 g/g, on the composition of both the liquid and solid phases were studied. The operational conditions leading to the maximal recovery of XOS for each raw material were established and discussed based on the severity factor (log R0). The higher yields obtained were in the range of 43–65% of the feedstock (arabino)xylan, with the highest value attained for CC for log R0 =3.75. Under the optimised conditions for XOS production, glucan was only slightly solubilised, enabling an enrichment of the solid phase (up to 67% of glucan for EWC). Delignification was also not extensive reaching utmost 18%, in the case of CC. cosmetic industries.
- Hydrothermal processing of corn residues:process optimisation and products characterisationPublication . Moniz, Patricia; Gírio, Francisco; Carvalheiro, Florbela; Pereira, HelenaHydrothermal processing was used as pre-treatment method for the selective solubilisation of hemicellulose from corn residues (leaves and stalks). The raw material was treated at a liquidto- solid ratio of 10 g/g, under non-isothermal conditions (150-240ºC) and the effect of treatment on the composition of both liquid and solid phases was evaluated. The yields of solid residue and soluble products, e.g., oligosaccharides, monosaccharides, acetic acid and degradation compounds, such as furfural, hydroxymethylfurfural are presented and interpreted using the severity factor (log R0). The operational conditions leading to the maximum recovery of XOS (53% of initial (arabino)xylan) and for highest glucan content of the solid residue (64%) were established for log R0 of 3.75 and 4.21, respectively. Under the severest condition 95% of xylan was selectively solubilised and 90% of initial glucan was recovered on the solid residue, making it very attractive for further processing in a biorefinery framework.
- The pros and cons of the dedicated upgrade of the hemicellulosic sugar stream in a biorefinery frameworkPublication . Duarte, Luís C.; Carvalheiro, Florbela; Fernandes, Talita Silva; Gírio, FranciscoThe challenge of the future integrated biorefineries is the full economically utilization of all biomass components with the simultaneously production of fuels and chemicals, preferably of added-value. This can only be achieved by the selective fractionation of the lignocellulosic biomass into its polymeric components, thus increasing their individual upgradeability to enhance the process economics. To reach this goal, the fractionation methods used are of crucial importance. Yet, many of the most widely accepted biochemical biorefineries potential lay-outs, are mainly concerned with cellulose hydrolysis and fermentation and the hemicellulosic fractions are, at best, clamped with cellulose, averting its differential upgrade. Therefore, a change in perspective by which the fractionation processes, as well as the overall biorefinery lay-out, are thought and evaluated is needed. The objective of this work is to review, compare and discuss the main advantages and bottlenecks of the currently available biomass pre-treatment technologies, particularly those leading to the selective fractionation of hemicelluloses. The advantages and disadvantages of the methods will be analysed foreseeing the added-value products possible to obtain from the hemicellulose path, and the most relevant factors which influence both product yield and consistency. Actually, the chemical composition and structural diversity of hemicelluloses constitutes an opportunity for the production of many chemicals, which has not yet been fully exploited. The integration of potential added-value products, e.g. oligosaccharides, polyols, and enzymes in a biorefinery framework will also be presented and discussed based on data for the upgrade of agro-food industrial residues and by-products. Examples will compare the use of mild processes for the selective recovery of hemicelluloses such autohydrolysis and dilute acid hydrolysis of brewery's spent grain, wheat straw, and eucalypt wood and the biotechnological processing of the hydrolysates. It is foreseen that hemicellulose-derived chemicals will become an ever more relevant category of products, as they hold a promise of economic benefit for the biorefineries.
- Hemicellulose biorefineries: a review on biomass pretreatmentsPublication . Carvalheiro, Florbela; Duarte, Luís C.; Gírio, FranciscoBiomass pretreatment (BP) plays a crucial role in a lignocellulose feedstock-based biorefinery (LCFBR) for processing of three major output streams (cellulose, hemicelluloses and lignin) into chemicals and biofuels. BP includes processing of lignocellulosic material (LCM) under aqueous, dilute acid or alkaline media to obtain a cellulosic fraction, which is then fermented to produce bioethanol. Hemicellulose is usually treated as a secondary stream due to lack of efficient fermentation of hemicellulosic sugars to ethanol. This review provides BPs assuming that hemicellulose stream should be integrated in LCFBR as a primary fraction for converting into value-added compounds other than bioethanol. Different LCM treatments are analyzed foreseeing bio-based products possible to obtain from hemicellulose path.
- Simplex optimization and mathematical modeling of wheat straw dilute acid hydrolysisandPublication . Fernandes, T.; Duarte, Luís C.; Carvalheiro, Florbela; Gírio, FranciscoWheat straw is an interesting biorefinery raw material, due to its abundance, chemical composition, and cost. Among the different pretreatments suitable for its processing, dilute acid hydrolysis still presents some benefits due to its simplicity. Nevertheless, it requires a careful optimization to avoid excessive by-products formation and catalyst spending. An attractive and simple optimization approach is the Sequential Simplex Method, an iterative procedure that enables to rapidly screen a large area ofoperational conditions and effectively encircle the optimal. In this work, dilute acid hydrolysis of wheat straw was optimized to selectively hydrolyze the hemicellulose fraction and obtain a pentose-rich fermentable hydrolyzate. The influence oftime (up to 180 min), and sulfuric acid concentration (up to 4%, w/w) were studied. The hydrolyzates obtained in the optimized conditions mainly contain free sugars (total content higher than 46 giL). The main potential microbial inhibitors found were acetic acid, furfural, and HMF, in concentrations lower than 4.8,1.7 and 0.3 giL, respectively. Empirical models describing the influence ofthe studied variables on sugars and by-products formation were validated for the entire domain. Sulfuric acid concentration was found to be the most influential variable, although both variables are statistically significant for xylose recovery. Interaction effects play a significant (negative) role. Data was also modeled based on the combined severity parameter (CS) and the results of these two approaches are compared and discussed. These hydrolyzates were easily utilized by Debaryomyces hansenii, a natural pentose assimilating yeast.
- Os subprodutos agro-industriais de natureza lenhocelulósica:caracterização da situação portuguesa.Publication . Duarte, Luís C.; Esteves, M. P.; Carvalheiro, Florbela; Vicente, Paula; Gírio, FranciscoOs materiais provenientes do processamento de matérias-primas nas agro-indústrias são usualmente considerados como não perigosos, abundantes, facilmente biodegradáveis, baratos e potencialmente valorizáveis. No entanto, devido às grandes quantidades processadas, podem constituir um problema ambiental, impondo assim um encargo económico significativo neste sector. A viabilidade económica da sua transformação/valorização depende de vários factores, como a quantidade disponível, os custos do material e transporte, as utilizações já existentes e eventuais restrições político-económicas regionais. Para o desenvolvimento de programas de valorização que potenciem a cadeia de valor do sector agro- -industrial, é necessário deter uma caracterização qualitativa e quantitativa destes materiais. Com este propósito, foi desenvolvido um inquérito postal junto das empresas agro-industriais portuguesas que processam materiais de natureza lenhocelulósica. A amostra apresenta uma boa cobertura geográfica e uma adequada representação dos diferentes subsectores agro-industriais, tendo a taxa de resposta obtida sido de 17%. O inquérito permitiu a caracterização, ao nível dos subsectores, em termos da sua composição e distribuição regional, bem como identificar os diferentes materiais produzidos, respectivas quantidades, destinos e valores económicos actuais, o que permitiu definir os principais subsectores/ materiais que mais poderão beneficiar com o investimento em actividades de I&D. Os principais subprodutos identificados foram os seguintes: dreche cervejeira, bagaço de uva sem álcool, polpa de alfarroba, casca de arroz, repiso de tomate, bagaço de azeitona extractado, casca de frutos rijos, engaço, borra de vinho sem álcool e grainha de uva. Por fim, apresentam-se e discutem-se as principais oportunidades e restrições para a valorização destes subprodutos utilizando tecnologias biológicas.
- Prebiotic xylo-oligosaccharides as high-value co-products on an integrated biorefinery approach from lignocellulosic feedstockPublication . Moura, Patrícia; Carvalheiro, Florbela; Esteves, M. P.; Gírio, FranciscoThe present work proposes the production of prebiotic xylo-oligosaccharides (XOS) as high-value co-products of the Lignocellulose Feedstock Biorefinery concept, foreseeing potential applications on food, feed and nutraceutical industries. Autohydrolysis was used to selectively solubilise the hemicellulosic fraction of several xylan-rich, widely available, agricultural, agro-industrial and forestry by-products: corn cobs, brewery’s spent grain and Eucalyptus wood chips. The soluble hemicellulose-rich and the solid cellulose- and lignin-rich fractions were separated, and the crude XOS-rich hydrolysates were further purified by gel filtration chromatography. Selected fractions of purified XOS within the desired ranges of polymerization degree were characterised and their prebiotic potential was investigated in in vitro fermentations by bifidobacteria, lactobacilli and intestinal inocula. Parameters such as bacterial growth and XOS consumption were evaluated and compared with commercially available xylo-oligosaccharides. The differences observed were considered of relevance for the formulation of symbiotic preparations and the future design of targeted, tailor-made prebiotic xylo-oligosaccharides.
- Physicochemical characterization of psyllium fiberPublication . Temudo, M. Salomé; Nunes, M. Cristina; Batista, Ana Paula; Carvalheiro, Florbela; Esteves, M. P.; Raymundo, AnabelaPsyllium is the common name used for several members of the plant genus Plantago, whose seeds are commercially used for mucilage production. Owing to its considerable fiber amount it has been used as dietary fiber supplement. Psyllium has a strong gelling ability, even at low temperature, enabling its use as a gelling agent in the food industry. This work is part of a project to developing jellies enriched with fiber, honey and propolis, aiming to increase these products intake, with evident health benefits. The chemical characterization of psyllium was performed, with the following results (in dry matter): total ash 2.5%, fat content 3.4% and total protein 1.4%. After qualitative acid hydrolysis polymeric sugars were quantified (in dry matter): glucan 7.3%, xylan 61.1% and arabinan 22.9%. This means that total fiber content is about 90%, being soluble fiber predominant, and allows classifying psyllium hemicellulose as an arabinoxylan. Psyllium functional properties were evaluated by water-binding capacity and swelling determination: 27.1 g/g and 36.9 ml/g, respectively. These properties are important in the food industry, but under certain circumstances may limit the food type that can be enriched with this fiber. An important part of the research consisted on the characterization of gels viscoelastic behavior and texture, which were prepared with different psyllium particle dimension (raw and ground) and concentration (2.0%, 2.5% and 3.0%). The Response Surface Methodology was used to study the effect of process conditions (time and temperature) on texture and color characteristics of gels. Texture properties of gels were evaluated by Texture Profile Analysis. Gels dynamic behaviour was studied by a sequence of oscillatory measurements of temperature, time and frequency sweeps. Psyllium gelling properties were improved with the reduction of the fiber particle dimension. Gels revealed potential viscoelastic properties that might be interesting in the industrial purpose of honey jelly production.