Recebido em 26/4/11; aceito em 11/11/11; publicado na web em 13/1/12 POTENTIAL OF SUGARCANE STRAW FOR ETHANOL PRODUCTION. Sugarcane straw biomass accounts for 1/3 of the energy potential of sugarcane and represents a rich source of sugars. Studies have been intensified for the use of this biomass along with bagasse for the production of cellulosic ethanol. Development of this technological path will allow for taking full advantage of sugarcane, increasing ethanol production without expanding the area cultivated. However, in order for this technology to be viable certain challenges must be overcome, including establishment of appropriate conditions of pretreatment and hydrolysis of these materials for release of fermentable sugars.Keywords: sugarcane straw; lignocelullosic biomass; ethanol. INTRODUÇÃOA iminente escassez das reservas de petróleo, principal fonte energética mundial, juntamente com as preocupações da sociedade com a preservação ambiental, são os principais motivos que levaram os governos a buscarem estratégias para uma maior produção e maior consumo de combustíveis que sejam renováveis e sustentáveis. 1,2 Um dos principais objetivos do uso dos biocombustíveis é a substituição de combustíveis fósseis, permitindo a diminuição da dependência por recursos não renováveis e a redução das emissões de gases de efeito estufa. A queima de combustíveis fósseis representa aproximadamente 82% das emissões dos gases causadores do efeito estufa. 3 Portanto, seja pela questão ambiental global, seja pela importância em reduzir a dependência externa de energia, o etanol de cana-de-açúcar, que já apresenta indicadores ambientais muito positivos quando comparado a outras opções, representa uma alternativa viável na substituição de combustíveis fósseis. 4 O etanol obtido do caldo de cana-de-açúcar (etanol de primeira geração) é, até o momento, o único combustível com capacidade de atender à crescente demanda mundial por energia renovável de baixo custo e de baixo poder poluente. Deve-se considerar que as emissões gasosas com a queima do etanol são da ordem de 60% menores se comparadas às emissões da queima da gasolina, sendo ainda que o do CO 2 emitido é reabsorvido pela própria cana. 5 Atualmente, o etanol é produzido praticamente a partir de matérias-primas sacarinas ou amiláceas, cana-de-açúcar e milho, respectivamente. Entretanto, há um grande esforço da comunidade científica para o desenvolvimento de novos processos economicamente viáveis para o aproveitamento da componente lignocelulósica da biomassa, caso dos resíduos agrícolas (palha e bagaço de cana-de--açúcar, palha de trigo e resíduos de milho) e resíduos florestais (pó e restos de madeira), assim como o capim elefante para produção de etanol combustível (etanol de segunda geração). 6,7 O mais abundante recurso biológico renovável da terra é a biomassa lignocelulósica. 8 Estima-se que somente os EUA têm potencial para produzir mais de 1,3 bilhões de toneladas (base seca) de biomassa por ano. 9 Segundo Zhang, 10 um bilhão de toneladas de biomassa seca produz e...

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Raffinose oligosaccharides (RO) are the factors primarily responsible for flatulence upon ingestion of soybean-derived products. ROs are hydrolyzed by alpha-galactosidases that cleave alpha-1,6-linkages of alpha-galactoside residues. The objectives of this study were the purification and characterization of extracellular alpha-galactosidase from Debaryomyces hansenii UFV-1. The enzyme purified by gel filtration and anion exchange chromatographies presented an Mr value of 60 kDa and the N-terminal amino acid sequence YENGLNLVPQMGWN. The Km values for hydrolysis of pNP alphaGal, melibiose, stachyose, and raffinose were 0.30, 2.01, 9.66, and 16 mM, respectively. The alpha-galactosidase presented absolute specificity for galactose in the alpha-position, hydrolyzing pNPGal, stachyose, raffinose, melibiose, and polymers. The enzyme was noncompetitively inhibited by galactose (Ki = 2.7 mM) and melibiose (Ki = 1.2 mM). Enzyme treatments of soy milk for 4 h at 60 degrees C reduced the amounts of stachyose and raffinose by 100%.

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An Aspergillus niger UFV-1 phytase was characterized and made available for industrial application. The enzyme was purified via ultrafiltration followed by acid precipitation, ion exchange and gel filtration chromatography. This protein exhibited a molecular mass of 161 kDa in gel filtration and 81 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), indicating that it may be a dimer. It presented an optimum temperature of 60 °C and optimum pH of 2.0. The K M for sodium phytate hydrolysis was 30.9 mM, while the k cat and k cat / K M were 1.46 ×10 5 s −1 and 4.7 × 10 6 s −1 .M −1 , respectively. The purified phytase exhibited broad specificity on a range of phosphorylated compounds, presenting activity on sodium phytate, p-NPP, 2- naphthylphosphate, 1- naphthylphosphate, ATP, phenyl-phosphate, glucose-6-phosphate, calcium phytate and other substrates. Enzymatic activity was slightly inhibited by Mg 2+ , Cd 2+ , K + and Ca 2+ , and it was drastically inhibited by F − . The enzyme displayed high thermostability, retaining more than 90% activity at 60 °C during 120 h and displayed a t 1/2 of 94.5 h and 6.2 h at 70 °C and 80 °C, respectively. The enzyme demonstrated strong resistance toward pepsin and trypsin, and it retained more than 90% residual activity for both enzymes after 1 h treatment. Additionally, the enzyme efficiently hydrolyzed phytate in livestock feed, liberating 15.3 μmol phosphate/mL after 2.5 h of treatment.

Blending of the enzyme extracts produced by different fungi can result in favorable synergetic enhancement of the enzyme blend with regards to the main cellulase activities, as well as the inclusion of accessory enzymes that may not be as abundant in enzyme extracts produced by predominantly cellulase producing fungi. The Chrysoporthe cubensis:Penicillium pinophilum 50:50 (v/v) blend produced herein presented good synergy, especially for FPase and endoglucanase activities which were 76% and 48% greater than theoretical, respectively. This enzyme blend was applied to sugarcane bagasse previously submitted to a simple alkali pretreatment. Glucan hydrolysis efficiency reached an excess of 60% and xylan conversion exceeded 90%. Increasing the hydrolysis temperature from 45 to 50°C also resulted in a 16-20% increase in conversion of both glucan and xylan fractions. The blended enzyme extract obtained therefore showed great potential for application in the lignocellulose hydrolysis process.

Biomass enzymatic hydrolysis depends on the pretreatment methods employed, the composition of initial feedstock and the enzyme cocktail used to release sugars for subsequent fermentation into ethanol. In this study, sugarcane bagasse was pretreated with 1% H2SO4 and 1% NaOH and the biomass saccharification was performed with 8% solids loading using 10 FPase units/g of bagasse of the enzymatic extract from Chrysoporthe cubensis and three commercial cocktails for a comparative study. Overall, the best glucose and xylose release was obtained from alkaline pretreated sugarcane bagasse. The C. cubensis extract promoted higher release of glucose (5.32 g/L) and xylose (9.00 g/L) than the commercial mixtures. Moreover, the C. cubensis extract presented high specific enzyme activities when compared to commercial cocktails mainly concerning to endoglucanase (331.84 U/mg of protein), β-glucosidase (29.48 U/mg of protein), β-xylosidase (2.95 U/mg of protein), pectinase (127.46 U/mg of protein) and laccase (2.49 U/mg of protein).