Integración de enzimas lacasas en el proceso de producción de etanol de lignocelulosa: efecto sobre la hidrólisis enzimática y la fermentación

Los objetivos prioritarios de las políticas energéticas de los Estados miembros de la Unión Europea se dirigen a aumentar la seguridad del abastecimiento energético, garantizar la competitividad de la economía, la disponibilidad de una energía asequible, promover la sostenibilidad ambiental y luchar contra el cambio climático. Para ello, el Parlamento Europeo ha aprobado compromisos de reducción, respecto a 1990, del 20% mínimo de las emisiones de CO2, una participación del 20% mínimo de renovables en el total del consumo de energía en la U.E. y una participación del 10% mínimo de biocombustibles en el transporte por carretera. Entre las alternativas disponibles, el bioetanol lignocelulósico representa una de las opciones más atractivas para alcanzar los objetivos propuestos en el sector transporte. De entre los materiales lignocelulósicos disponibles, la paja de trigo es uno de los sustratos más interesantes por su abundancia, su distribución a nivel mundial y por tratarse de un residuo agrícola que evita interferencias con otros mercados como el de la alimentación humana. Por estos motivos se ha elegido como materia prima para la realización de esta Tesis Doctoral. Debido a la naturaleza recalcitrante de la biomasa lignocelulósica, la conversión eficiente de los carbohidratos que contienen estos sustratos en etanol resulta un proceso complejo en el que se requieren varias etapas. Estas son: (1) el pretratamiento que altere la estructura recalcitrante de la lignocelulosa facilitando el acceso de las enzimas hidrolíticas a la celulosa; (2) la hidrólisis enzimática de los carbohidratos (celulosa y hemicelulosas) hasta azúcares fermentables y (3) la fermentación de los azúcares simples a etanol mediante un microorganismo fermentador..

Hot compressed water pretreatment and surfactant effect on enzymatic hydrolysis using agave bagasse

Agave bagasse is a residual biomass in the production of the alcoholic beverage tequila, and therefore, it is a promising raw material in the development of biorefineries using hot compressed water pretreatment (hydrothermal processing). Surfactants application has been frequently reported as an alternative to enhance monomeric sugars production efficiency and as a possibility to reduce the enzyme loading required. Nevertheless, the surfactants action mechanisms in the enzymatic hydrolysis is still not elucidated. In this work, hot compressed water pretreatment was applied on agave bagasse for biomass fractionation at 194 °C in isothermal regime for 30 min, and the effect of non-ionic surfactants (Tween 20, Tween 80, Span 80, and Polyethylene glycol (PEG 400)) was studied as a potential enhancer of enzymatic saccharification of hydrothermally pretreated solids of agave bagasse (AGB). It was found that non-ionic surfactants show an improvement in the conversion yield of cellulose to glucose (100%) and production of glucose (79.76 g/L) at 15 FPU/g glucan, the highest enhancement obtained being 7% regarding the control (no surfactant addition), using PEG 400 as an additive. The use of surfactants allows improving the production of fermentable sugars for the development of second-generation biorefineries.This project was funded by the Secretary of Public Education of Mexico—Mexican Science and Technology Council (SEP-CONACYT) with the Basic Science Project-2015-01 (Ref. 254808). Marcela Sofía Pino also thanks the National Council for Science and Technology (CONACYT, Mexico) for her Master Fellowship support (grant number: 611312/452636).info:eu-repo/semantics/publishedVersio

Solid-state fermentation of oil palm frond petiole for lignin peroxidase and xylanase-rich cocktail production

In current practice, oil palm frond leaflets and stems are re-used for soil nutrient recycling, while the petioles are typically burned. Frond petioles have high commercialization value, attributed to high lignocellulose fiber content and abundant of juice containing free reducing sugars. Pressed petiole fiber is the subject of interest in this study for the production of lignocellulolytic enzyme. The initial characterization showed the combination of 0.125 mm frond particle size and 60% moisture content provided a surface area of 42.3 m2/g, porosity of 12.8%, and density of 1.2 g/cm3, which facilitated fungal solid-state fermentation. Among the several species of Aspergillus and Trichoderma tested, Aspergillus awamori MMS4 yielded the highest xylanase (109 IU/g) and cellulase (12 IU/g), while Trichoderma virens UKM1 yielded the highest lignin peroxidase (222 IU/g). Crude enzyme cocktail also contained various sugar residues, mainly glucose and xylose (0.1–0.4 g/L), from the hydrolysis of cellulose and hemicellulose. FT-IR analysis of the fermented petioles observed reduction in cellulose crystallinity (I900/1098), cellulose–lignin (I900/1511), and lignin–hemicellulose (I1511/1738) linkages. The study demonstrated successful bioconversion of chemically untreated frond petioles into lignin peroxidase and xylanase-rich enzyme cocktail under SSF condition

Evolving biocatalysis to meet bioeconomy challenges and opportunities

4siThe unique selectivity of enzymes, along with their remarkable catalytic activity, constitute powerful tools for transforming renewable feedstock and also for adding value to an array of building blocks and monomers produced by the emerging bio-based chemistry sector. Although some relevant biotransformations run at the ton scale demonstrate the success of biocatalysis in industry, there is still a huge untapped potential of catalytic activities available for targeted valorization of new raw materials, such as waste streams and CO2. For decades, the needs of the pharmaceutical and fine chemistry sectors have driven scientific research in the field of biocatalysis. Nowadays, such consolidated advances have the potential to translate into effective innovation for the benefit of bio-based chemistry. However, the new scenario of bioeconomy requires a stringent integration between scientific advances and economics, and environmental as well as technological constraints. Computational methods and tools for effective big-data analysis are expected to boost the use of enzymes for the transformation of a new array of renewable feedstock and, ultimately, to enlarge the scope of biocatalysis.partially_openopenPellis, Alessandro; Cantone, Sara; Ebert, Cynthia; Gardossi, LuciaPellis, Alessandro; Cantone, Sara; Ebert, Cynthia; Gardossi, Luci

Effects of Biosurfactants on Enzymatic Saccharification and Fermentation of Pretreated Softwood

The enzymatic hydrolysis of cellulose is inhibited by non-productive adsorption of cellulases to lignin, and that is particularly problematic with lignin-rich materials such as softwood. Although conventional surfactants alleviate non-productive adsorption, using biosurfactants in softwood hydrolysis has not been reported. In this study, the effects of four biosurfactants, namely horse-chestnut escin, Pseudomonas aeruginosa rhamnolipid, and saponins from red and white quinoa varieties, on the enzymatic saccharification of steam-pretreated spruce were investigated. The used biosurfactants improved hydrolysis, and the best-performing one was escin, which led to cellulose conversions above 90%, decreased by around two-thirds lignin inhibition of Avicel hydrolysis, and improved hydrolysis of pretreated spruce by 24%. Red quinoa saponins (RQS) addition resulted in cellulose conversions above 80%, which was around 16% higher than without biosurfactants, and it was more effective than adding rhamnolipid or white quinoa saponins. Cellulose conversion improved with the increase in RQS addition up to 6 g/100 g biomass, but no significant changes were observed above that dosage. Although saponins are known to inhibit yeast growth, no inhibition of Saccharomyces cerevisiae fermentation of hydrolysates produced with RQS addition was detected. This study shows the potential of biosurfactants for enhancing the enzymatic hydrolysis of steam-pretreated softwood

Unraveling the effects of laccase treatment on enzymatic hydrolysis of steam-exploded wheat straw

Laccase enzymes are promising detoxifying agents during lignocellulosic bioethanol production from wheat straw. However, they affect the enzymatic hydrolysis of this material by lowering the glucose recovery yields. This work aimed at explaining the negative effects of laccase on enzymatic hydrolysis.Relative glucose recovery in presence of laccase (10. IU/g substrate) with model cellulosic substrate (Sigmacell) at 10% (w/v) was almost 10% points lower (P<. 0.01) than in the absence of laccase. This fact could be due to an increase in the competition of cellulose binding sites between the enzymes and a slight inhibition of β-glucosidase activity. However, enzymatic hydrolysis and infrared spectra of laccase-treated and untreated wheat straw filtered pretreated residue (WS-FPR), revealed that a grafting process of phenoxy radicals onto the lignin fiber could be the cause of diminished accessibility of cellulases to cellulose in pretreated wheat straw. © 2014 Elsevier Ltd

Heads and tails of laccases in bioethanol production

In a lignocellulosic biorefinery, the sugar platform could lead to bioethanol production through biochemical routes. The bioethanol production process is, however, hindered by the recalcitrant structure of lignocellulose and a pretreatment is needed to increase biomass digestibility. Current pretreatment technologies generate inhibitory compounds that hamper the sugar conversion to ethanol by the fermenting microorganism.High ethanol titers are necessary to make the process economically-viable. This could be reached by using high substrate loadings, which implies high inhibitor concentration in the broth. Laccases are powerful biocatalysts to overcome the effect of inhibitory compounds. Laccases are multicopper oxidases that catalyze the oxidation of substituted phenols, anilines and aromatic thiols to their corresponding radicals. This capacity allows laccases to act specifically on phenolic compounds present in pretreated materials.In our studies, the potential of laccases as detoxification agents has been demonstrated by removing 70 to 100% of total phenols. Laccases trigger the fermentation of slurries non-fermentable without laccase treatment by increasing dramatically the ethanol yield (from 0.1 g/g to 0.36 g/g). The implementation of the laccase detoxification step boosts ethanol production at substrate loadings as high as 25% (w/w) reaching 58.6 g/L ethanol concentration for a cost-effective industrial ethanol production.Despite the great phenolic reduction, sugar recovery is reduced after laccase addition. Our results suggest that laccase-derived products exert a negative effect on enzymatic hydrolysis. An increase in Klason lignin together with changes observed in the ATR–FTIR spectra supported a grafting process that would limit the accessibility of cellulolytic enzymes to cellulose