Kelly J. Dussán

Diversity and physiological characterization of D-xylose-fermenting yeasts isolated from the Brazilian Amazonian Forest.

Background This study is the first to investigate the Brazilian Amazonian Forest to identify new D-xylose-fermenting yeasts that might potentially be used in the production of ethanol from sugarcane bagasse hemicellulosic hydrolysates. Methodology/Principal Findings A total of 224 yeast strains were isolated from rotting wood samples collected in two Amazonian forest reserve sites. These samples were cultured in yeast nitrogen base (YNB)-D-xylose or YNB-xylan media. Candida tropicalis, Asterotremella humicola, Candida boidinii and Debaryomyces hansenii were the most frequently isolated yeasts. Among D-xylose-fermenting yeasts, six strains of Spathaspora passalidarum, two of Scheffersomyces stipitis, and representatives of five new species were identified. The new species included Candida amazonensis of the Scheffersomyces clade and Spathaspora sp. 1, Spathaspora sp. 2, Spathaspora sp. 3, and Candida sp. 1 of the Spathaspora clade. In fermentation assays using D-xylose (50 g/L) culture medium, S. passalidarum strains showed the highest ethanol yields (0.31 g/g to 0.37 g/g) and productivities (0.62 g/L·h to 0.75 g/L·h). Candida amazonensis exhibited a virtually complete D-xylose consumption and the highest xylitol yields (0.55 g/g to 0.59 g/g), with concentrations up to 25.2 g/L. The new Spathaspora species produced ethanol and/or xylitol in different concentrations as the main fermentation products. In sugarcane bagasse hemicellulosic fermentation assays, S. stipitis UFMG-XMD-15.2 generated the highest ethanol yield (0.34 g/g) and productivity (0.2 g/L·h), while the new species Spathaspora sp. 1 UFMG-XMD-16.2 and Spathaspora sp. 2 UFMG-XMD-23.2 were very good xylitol producers. Conclusions/Significance This study demonstrates the promise of using new D-xylose-fermenting yeast strains from the Brazilian Amazonian Forest for ethanol or xylitol production from sugarcane bagasse hemicellulosic hydrolysates.

Production of bioethanol in sugarcane bagasse hemicellulosic hydrolysate by Scheffersomyces parashehatae, Scheffersomyces illinoinensis and Spathaspora arborariae isolated from Brazilian ecosystems

This study aimed to evaluate new d‐xylose‐fermenting yeasts from Brazilian ecosystems for the production of second‐generation ethanol.

Role of Nanoparticles in Enzymatic Hydrolysis of Lignocellulose in Ethanol

The depletion in the limited sources of fossil fuels has generated the problem of energy crisis all over the world. This hunt forces scientific community towards the search for cost-effective, environment-friendly, renewable alternative sources which can replace fossil fuels and fulfill the increasing demands of energy. In this context, the use of lignocellulosic material (plant residues) composed of cellulose, hemicellulose, and lignin becomes the first choice. In the process of ethanol production, first lignocellulosic material is broken down and hydrolyzed into simple sugars like cellulose, and then these sugars are fermented into biofuels such as ethanol in the presence of enzymes like cellulases. The use of cellulases makes the process expensive, and therefore, immobilization of these enzymes on solid supports like nanoparticles can help to recover the enzyme, which ultimately decreases the cost of process. Therefore, the use of nanotechnology and nanomaterials could be one possible avenue to improve biofuel production efficiency and reduction in the processing cost.

Biomass Pretreatment With Oxalic Acid for Value-Added Products

Monomeric sugars released from carbohydrate fractions of lignocellulosic materials can be substrates for industrial fermentative processes in order to obtain bioproducts with potential economic and social interest. When diluted acid solutions are used to pretreat biomass, the result is a solid fraction in which cellulose is more accessible to hydrolytic enzymes and a liquid fraction enriched in sugars (mainly pentoses) from hemicellulose. Pretreatment with dilute oxalic acid is a promising approach, resulting in high efficiency in hemicellulose hydrolysis, which generates a lower quantity of compounds toxic to microbial metabolism. In addition, once this acid is organic, it can be recovered by usual techniques and reused in a pretreatment step. Within this context, this chapter presents the use of oxalic acid pretreatment for different biomasses, including the structural changes that occur after using this method as well as applications of the obtained solid and liquid fraction in fermentative processes.