Residues For Ethanol Production Research Articles

Screening of Novel Basidiomycetes for the Production of Lignocellulolytic Enzymes During Fermentation of Food Wastes

Nine species of white-rot basidiomycetes isolated from the forests of Georgia have been screened for the endoglucanase, xylanase, laccase, and manganese peroxidase production in both glycerol-containing synthetic medium and mandarin peels-based medium. Irpex lacteus and Trametes ochracea expressed the highest hydrolases activity in submerged and solid-state fermentation (SSF), respectively, of ethanol production residue (EPR). Lenzites betulina appeared to be very promising producer of laccase in both synthetic (52.5 U ml -1 ) and complex (76.7 U ml -1 ) media. The tested white-rot fungi exhibited quite different responses to growth substrates used. Mandarin peelings, ethanol production residue, and wheat bran appeared to be excellent growth substrates for the production of complex preparations of hydrolases and oxidases. The same substrates as well as walnut pericarp enhanced laccase and MnP secretion. In addition, the ratio of individual enzymes in final preparations signifi cantly depended on growth substrate. Thus, the laccase/MnP ratio changed from 3 to 548 with substitution of EPR by walnut pericarp in submerged fermentation by L. betulina. Usually, the submerged fermentation of lignocellulosic materials was preferable for the target enzyme secretion. However, the SSF of wheat bran was essential for the CMCase production by I. lacteus, L. betulina, and S. hirsutum. The SSF of EPR was preferable for the laccase production by G. resinaceum, L. betulina, and T. ochracea while the SSF of wheat bran favored MnP accumulation as compared to submerged cultivation.

Lignocellulolytic Enzyme Activity of New Corticoid and Poroid Basidiomycetes Isolated from Latvian Cultural Monuments

Eleven corticoid and three poroid fungi have been isolated from Latvian cultural monuments and evaluated for their potential to produce wood-degrading enzymes. In submerged fermentation of mandarin peels, notable intergeneric and intrageneric differences were revealed with regard to the extent of hydrolase and oxidase activity. The xylanase activity of the tested basidiomycetes varied from 0.1 to 2.4 U/mL depending on the fungus species, while that among the strains of Athelia neuhoffii varied from 0.1 to 1.3 U/mL. Five strains of white-rot fungi produced neither laccase nor manganese peroxidases. Cellulase and xylanase of Hyphoderma praetermissum and Tubulicrinis glebulosus appeared to be inducible enzymes. Lignocellulosic substrates strongly affected the enzyme production, because the laccase of H. praetermissum and T. glebulosus was secreted only in the submerged fermentation on mandarin peels and wheat bran, whereas the production of manganese peroxidase by Hypochnicium punctulatum and Phellinus chrisoloma was observed only in the solid-state fermentation of wheat bran and ethanol production residue.

Effect of aromatic compounds on the production of laccase and manganese peroxidase by white-rot basidiomycetes

Three white-rot fungi displayed a wide diversity in their response to supplemented aromatic compounds. Pyrogallol stimulated Cerrena unicolor laccase and manganese peroxidase (MnP) synthesis in synthetic medium 2.5- and 2-fold, respectively, whereas 2,4,6-trinitrotoluene (TNT) brought about a 2.8-fold increase in laccase yield by Trametes versicolor in submerged fermentation of ethanol production residue. No effect of the tested aromatic compounds on enzyme secretion by Ganoderma lucidum in mannitol-containing medium was detected. Nevertheless, G. lucidum is a potent producer of laccase in submerged fermentation of wheat bran and enzyme synthesis can be further increased by supplementation of medium with an appropriate inducer. The structure and the concentration of aromatic compounds play an important role in the regulation of enzyme synthesis. The supplementation of synthetic medium with 0.03-0.3mM TNT or hydroquinone increased the differential rate of laccase synthesis by C. unicolor from 1,267 to 3,125-8,630 U mg biomass(-1) day(-1). Moreover, the same aromatic compound may function as either an inducer or a repressor, depending on the fungus and enzyme studied. Thus, hydroquinone increased 3-fold T. versicolor laccase activity decreasing 2- and 8-fold the yields of MnP and endoglucanase, respectively.

Quantifying Straw Removal through Baling and Measuring the Long‐Term Impact on Soil Quality and Wheat Production

Crop residues are considered the feedstock of choice for the production of ethanol, but removing crop residues may negatively impact soil productivity. The objectives were to quantify the proportion of total aboveground crop residues removed through baling and to evaluate the effects of 50 yr of straw removal with baling on soil quality and wheat (Triticum aestivum L.) production. The first study evaluated three harvesting systems and their impact on straw removal with baling. The second study measured straw removal after 50 yr on soil quality and wheat production using a fallow‐spring wheat‐spring wheat rotation (F‐W‐W) with three different treatments imposed. One treatment was not fertilized with straw retained, and the other two were fertilized with N and P but one treatment retained the straw while the other had the straw baled every year during the cropping years. The proportion of total aboveground residues other than grain removed with baling ranged from 22 to 35% or 26 to 40% depending on the method of calculation based on the first study. Measurements of soil organic carbon (SOC) and nitrogen (SON) showed no differences after 50 yr of straw removal, and spring wheat grain yields and grain protein concentration were also not affected based on the second study. The potential therefore exists to use crop residues for ethanol production or other industrial purposes without adversely affecting the long‐term productivity of medium‐ to heavy‐textured soils providing that <40% of the total aboveground residues other than grain are removed and the frequency of removal is no more than 2 yr out of three.

Fungal metabolism of fermentation inhibitors present in corn stover dilute acid hydrolysate

Use of agricultural residues for ethanol production requires pretreatment of the material to facilitate release of sugars. Physical–chemical pretreatment of lignocellulosic biomass can, however, give rise to side-products that may be toxic to fermenting microorganisms and hinder utilization of sugars obtained from biomass. Potentially problematic compounds include furan aldehydes formed by degradation of sugars, organic acids released from hemicellulose side-groups, and aldehydes and phenolics released from lignin. A fungal isolate, Coniochaeta ligniaria NRRL30616, metabolizes furfural and 5-hydroxymethylfurfural (HMF) as well as aromatic and aliphatic acids and aldehydes. NRRL30616 grew in corn stover dilute-acid hydrolysate, and converted furfural to both furfuryl alcohol and furoic acid. Hydrolysate was inoculated with NRRL30616, and the fate of pretreatment side-products was followed in a time-course study. A number of aromatic and aliphatic acids, aldehydes, and phenolic compounds were quantitated by analytical extraction of corn stover hydrolysate, followed by HPLC–UV–MS/MS analysis. Compounds representing all of the classes of inhibitory side-products were removed during the course of fungal growth. Biological abatement of hydrolysates using C. ligniaria improved xylose utilization in subsequent ethanol fermentations.

Effect of the Carbon Source and Inoculum Preparation Method on Laccase and Manganese Peroxidase Production in Submerged Cultivation by the Medicinal Mushroom Ganoderma lucidum (W. Curt.: Fr.) P. Karst. (Aphyllophoromycetideae)

The genus Ganoderma includes medicinal species that belong to the group of white rot fungi due to their ability to produce extracellular ligninolytic enzymes: laccase and manganese peroxidase (MnP). The aim of this study was to evaluate the significance of various carbon and inoculum preparation methods for oxidative enzyme production by the medicinal mushroom G. lucidum. Mushroom growth, as well as the production of laccase and MnP, significantly depends on the inoculum age and cultivation method. Synthetic medium experiments have shown that xylose ensured the highest laccase activity of G. lucidum 447 accumulating 116 U L -1 after 12 days of submerged mushroom cultivation. In all lignocellulosic substrate experiment variants, laccase activity reached maximum after 8 days of mushroom cultivation. Analogical regularities were detected when the MnP activity was measured in submerged fermentation of ethanol production residue by G. lucidum 447. A more interesting finding is the fact that mycelium grown on solid agar medium and used as inoculum not only provided a 3-fold increase in laccase yield in submerged fermentation of both lignocellulosic substrates but also stimulated MnP accumulation by G. lucidum 447.

Ethanol production from crop residues and soil organic carbon

In decision making about the use of residues from annual crops for ethanol production, alternative applications of these residues should be considered. Especially important is the use of such residues for stabilizing and increasing levels of soil organic carbon. Such alternative use leads to a limited scope for residue removal from the field. Scope for removal of residues from annual crops can however, ceteris paribus, be increased when such crops generate relatively large amounts of biomass. Also selecting residues that contain relatively high levels of available cellulose and hemicellulose for removal or returning suitable ‘waste’ from processing crop residues that is rich in refractory compounds such as lignin to the field may increase scope for removal of crop residues for ethanol production.

Dilute sulfuric acid pretreatment of agricultural and agro-industrial residues for ethanol production

The potential of dilute-acid prehydrolysis as a pretreatment method for sugarcane bagasse, rice hulls, peanut shells, and cassava stalks was investigated. The prehydrolysis was performed at 122 degrees C during 20, 40, or 60 min using 2% H(2)SO(4) at a solid-to-liquid ratio of 1:10. Sugar formation increased with increasing reaction time. Xylose, glucose, arabinose, and galactose were detected in all of the prehydrolysates, whereas mannose was found only in the prehydrolysates of peanut shells and cassava stalks. The hemicelluloses of bagasse were hydrolyzed to a high-extent yielding concentrations of xylose and arabinose of 19.1 and 2.2 g/L, respectively, and a xylan conversion of more than 80%. High-glucose concentrations (26-33.5 g/L) were found in the prehydrolysates of rice hulls, probably because of hydrolysis of starch of grain remains in the hulls. Peanut shells and cassava stalks rendered low amounts of sugars on prehydrolysis, indicating that the conditions were not severe enough to hydrolyze the hemicelluloses in these materials quantitatively. All prehydrolysates were readily fermentable by Saccharomyces cerevisiae. The dilute-acid prehydrolysis resulted in a 2.7- to 3.7-fold increase of the enzymatic convertibility of bagasse, but was not efficient for improving the enzymatic hydrolysis of peanut shells, cassava stalks, or rice hulls.