Constraints and advances in high-solids enzymatic hydrolysis of lignocellulosic biomass : a critical review

The industrial production of sugar syrups from lignocellulosic materials requires the conduction of the enzymatic hydrolysis step at high-solids loadings (i.e., with over 15% solids [w/w] in the reaction mixture). Such conditions result in sugar syrups with increased concentrations and in improvements in both capital and operational costs, making the process more economically feasible. However, this approach still poses several technical hindrances that impact the process efficiency, known as the "high-solids effect" (i.e., the decrease in glucan conversion yields as solids load increases). The purpose of this review was to present the findings on the main limitations and advances in high-solids enzymatic hydrolysis in an updated and comprehensive manner. The causes for the rheological limitations at the onset of the high-solids operation as well as those influencing the "high-solids effect" will be discussed. The subject of water constraint, which results in a highly viscous system and impairs mixing, and by extension, mass and heat transfer, will be analyzed under the perspective of the limitations imposed to the action of the cellulolytic enzymes. The "high-solids effect" will be further discussed vis-a-vis enzymes end-product inhibition and the inhibitory effect of compounds formed during the biomass pretreatment as well as the enzymes' unproductive adsorption to lignin. This review also presents the scientific and technological advances being introduced to lessen high-solids hydrolysis hindrances, such as the development of more efficient enzyme formulations, biomass and enzyme feeding strategies, reactor and impeller designs as well as process strategies to alleviate the end-product inhibition. We surveyed the academic literature in the form of scientific papers as well as patents to showcase the efforts on technological development and industrial implementation of the use of lignocellulosic materials as renewable feedstocks. Using a critical approach, we expect that this review will aid in the identification of areas with higher demand for scientific and technological efforts

Optimized atrazine degradation by Pleurotus ostreatus INCQS 40310: an alternative for impact reduction of herbicides used in sugarcane crops

Submitted by Alexandre Sousa ([email protected]) on 2016-08-02T17:44:51Z No. of bitstreams: 1 J_Microb_Biochem_Technol_S12-006.pdf: 1943299 bytes, checksum: a00c7d9cf985dde3762ab7b885ab8ef0 (MD5)Approved for entry into archive by Alexandre Sousa ([email protected]) on 2016-08-02T18:01:36Z (GMT) No. of bitstreams: 1 J_Microb_Biochem_Technol_S12-006.pdf: 1943299 bytes, checksum: a00c7d9cf985dde3762ab7b885ab8ef0 (MD5)Made available in DSpace on 2016-08-02T18:01:36Z (GMT). No. of bitstreams: 1 J_Microb_Biochem_Technol_S12-006.pdf: 1943299 bytes, checksum: a00c7d9cf985dde3762ab7b885ab8ef0 (MD5) Previous issue date: 2013Instituto Nacional de Tecnologia. Rio de Janeiro, RJ, Brasil.Universidade Federal do Rio de Janeiro. Instituto de Química. Rio de Janeiro, RJ, Brasil.Universidade Federal de Juiz de Fora. Departamento de Química. Rio de Janeiro, RJ, Brasil.Fundação Oswaldo Cruz. Instituto Nacional de Controle de Qualidade em Saúde. Programa de Pós-Graduação em Vigilância Sanitária. Rio de Janeiro, RJ, Brasil.Instituto Nacional de Tecnologia. Rio de Janeiro, RJ, Brasil.The herbicide atrazine (2-chloro-4-ethylamine-6-isopropylamine-s-triazine) is extensively used for weed control in sugarcane crops. The application of fungi for the biodegradation of xenobiotics has been studied with promising results. Therefore, atrazine degradation mediated by Pleurotus ostreatusINCQS 40310 was evaluated, and the involvement of ligninolytic enzymes along with the degradation process was also investigated. To promote high degradation percentages and rates, a fractional factorial experimental design was first used to determine the most significant medium components for atrazine degradation. This strategy improved atrazine degradation from 39.0% to 71.0% after 15 days, with the formation of different metabolites. Afterward, a 32 full factorial design was performed using the variables selected in the first part of this study. The salts FeSO4and MnSO4showed significant influence in the percentages and the rates of atrazine degradation. The medium optimization resulted in 90.3% and 94.5% of atrazine degradation after 10 days and 15 days, respectively. Although laccase activity was measured during the degradation process, it was not possible to correlate laccase activity with atrazine degradation. The results demonstrated the efficiency of P. Ostreatus INCQS 40310 for atrazine degradation, thus demonstrating the potential of this fungus as a bioremediation agent

Efficient production of lignocellulolytic enzymes xylanase, β-xylosidase, ferulic acid esterase and β-glucosidase by the mutant strain Aspergillus awamori 2B.361 U2/1

The production of xylanase, β-xylosidase, ferulic acid esterase and β-glucosidase by Aspergillus awamori 2B.361 U2/1, a hyper producer of glucoamylase and pectinase, was evaluated using selected conditions regarding nitrogen nutrition. Submerged cultivations were carried out at 30 ºC and 200 rpm in growth media containing 30 g wheat bran/L as main carbon source and either yeast extract, ammonium sulfate, sodium nitrate or urea, as nitrogen sources; in all cases it was used a fixed molar carbon to molar nitrogen concentration of 10.3. The use of poor nitrogen sources favored the accumulation of xylanase, β-xylosidase and ferulic acid esterase to a peak concentrations of 44,880; 640 and 118 U/L, respectively, for sodium nitrate and of 34,580, 685 and 170 U/L, respectively, for urea. However, the highest β-glucosidase accumulation of 10,470 U/L was observed when the rich organic nitrogen source yeast extract was used. The maxima accumulation of filter paper activity, xylanase, β-xylosidase, ferulic acid esterase and β-glucosidase by A. awamori 2B.361 U2/1 was compared to that produced by Trichoderma reesei Rut-C30. The level of β-glucosidase was over 17-fold higher for the Aspergillus strain, whereas the levels of xylanase and β-xylosidase were over 2-fold higher. This strain also produced ferulic acid esterase (170 U/L), which was not detected in the T. reesei culture

Aspergillus awamori endoglucanase-rich supernatant enhances lignocellulosic biomass liquefaction in high-solids enzymatic hydrolysis

Endoglucanases are particularly important in high-solids enzymatic hydrolysis of lignocellulosic biomass due to the operational need to decrease the medium viscosity via liquefaction, alleviating one of the processes' significant hindrances. This study evaluated an endoglucanase-rich supernatant produced by a particular strain of Aspergillus awamori to speed up biomass liquefaction in reactions with 30% solids. Supplementing commercial enzymes with the crude supernatant of A. awamori (Aa) comparatively decreased the media viscosity 10-fold and improved glucose release by 20% after 24 h hydrolysis. The A. awamori supernatant was fractionated by sizeexclusion chromatography, and an endoglucanase-rich fraction was identified by liquid chromatography-mass spectrometry. The endoglucanase fraction and the crude Aa supplementations, under comparative conditions to a highly efficient commercial enzyme, resulted in equivalent improvements in medium viscosity and glucose release, indicating that A. awamori endoglucanases are particularly efficient for biomass liquefaction in conditions of high-solids hydrolysis