Bioprodução semi-contínua de xilitol em hidrolisado de bagaço de cana: efeito da suplementação nutricional

Xylose-to-xylitol bioconversion by Ca-alginate entrapped Candida guilliermondii cells in sugarcane bagasse hemicellulosic hydrolysate was carried out in erlenmeyer flasks using the repeated-batch mode of fermentation. The hydrolysate was supplemented or not with ammonium sulfate and/or rice bran extract at the beginning of each repeated batch. Altogether, six sets of three repeated-batches were carried out, the immobilized cells being reused at the end of each batch. The best results were achieved when the hydrolysate was supplemented with both nutrients in all the three repeated batches, which provided xylitol productions of 25.9, 46.8, 48.7 gL-1, productivities of 0.27, 0.49, 0.51 gL-1h-1, and yields of 0.45, 0.58, 0.55 gg-1, respectively. In the absence of nutrients, the xylitol production, productivity and yield did not exceed 12.1 gL-1, 0.13 gL-1h-1 and 0.30 gg-1, respectively.A bioconversão de xilose em xilitol por células de Candida guilliermondii imobilizadas em alginato de cálcio, em hidrolisado hemicelulósico de bagaço de cana-de-açúcar, foi realizada em frascos erlenmeyer no modo bateladas repetidas de fermentação. O hidrolisado foi suplementado ou não com sulfato de amônio e/ou extrato de farelo de arroz no início de cada batelada repetida. No total, seis experimentos com três bateladas repetidas cada um foram realizados, sendo as células imobilizadas reutilizadas ao final de cada batelada. Os melhores resultados foram alcançados quando o hidrolisado foi suplementado com ambos nutrientes em todas as três bateladas repetidas, resultando em concentrações de xilitol iguais a 25,9, 46,8 e 48,7 gL-1, produtividades de 0,27, 0,49 e 0,51 gL-1h-1, e rendimentos de 0,45, 0,58 e 0,55 gg-1, respectivamente. Na ausência de nutrientes, a concentração de xilitol, a produtividade e o rendimento não ultrapassaram 12,1 gL-1, 0,13 gL-1h-1 e 0.30 gg-1, respectivamente

As chuvas e sua interferência na paisagem urbana de Pelotas-RS: um relato da oficina itinerante do Pibid Geografia

Contexto: A oficina itinerante teve como foco central realizar uma abordagem sobre a relação entre as chuvas e as interferências na paisagem urbana na cidade de Pelotas/RS. A cidade é caracterizada por uma baixa declividade, cercada por corpos d’água e canais fluviais que podem implicar em alagamentos e inundações em diversos locais. Metodologia: A atividade foi desenvolvida com alunos do 6o ano do ensino fundamental de uma escola pública de Pelotas. A metodologia utilizada foi baseada no método freiriano, que permitiu a união de prática, teoria e reflexão. Os conteúdos abordados foram relacionados ao cotidiano dos alunos, visando a compreensão da importância da relação entre a paisagem urbana e a gestão de águas pluviais. Considerações: Durante o desenvolvimento da oficina, observou-se um avanço significativo no conhecimento dos alunos. No início das intervenções, o conhecimento sobre o tema era raso, mas ao final, os alunos demonstraram embasamento teórico e maior aprofundamento. Eles foram capazes de estabelecer relações consistentes entre a realidade local e contextos mais complexos em outras escalas

Uma visão sobre a estrutura, composição e biodegradação da madeira A vision of wood structure, composition and biodegradation

<abstract language="eng">Wood is the main raw material used in the pulp and paper industry. It is a material that presents heterogeneous structure and complex composition, which results in a relatively resistant material to the biodegradation process. In the present review, we attempted to summarize the structural characteristics of wood and describe the chemical nature of its major components to, afterwards, comment about its biodegradation. The role of the enzyme manganese peroxidase in the lignin degradation by a selective white-rot fungus, Ceriporiopsis subvermispora, was highlighted

Clarification of a wheat straw-derived medium with ion-exchange resins for xylitol crystallization

BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion-exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum-concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion-exchange resins (A-860S and A-500PS) promoted considerable reductions in the content of soluble by-products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark-colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion-exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose-derived fermentation media. (c) 2008 Society of Chemical Industry

Ethanol Production from Sugarcane Bagasse Hydrolysate Using Pichia stipitis

The objective of this study was to evaluate the ethanol production from the sugars contained in the sugarcane bagasse hemicellulosic hydrolysate with the yeast Pichia stipitis DSM 3651. The fermentations were carried out in 250-mL Erlenmeyers with 100 mL of medium incubated at 200 rpm and 30 A degrees C for 120 h. The medium was composed by raw (non-detoxified) hydrolysate or by hydrolysates detoxified by pH alteration followed by active charcoal adsorption or by adsorption into ion-exchange resins, all of them supplemented with yeast extract (3 g/L), malt extract (3 g/L), and peptone (5 g/L). The initial concentration of cells was 3 g/L. According to the results, the detoxification procedures removed inhibitory compounds from the hemicellulosic hydrolysate and, thus, improved the bioconversion of the sugars into ethanol. The fermentation using the non-detoxified hydrolysate led to 4.9 g/L ethanol in 120 h, with a yield of 0.20 g/g and a productivity of 0.04 g L(-1) h(-1). The detoxification by pH alteration and active charcoal adsorption led to 6.1 g/L ethanol in 48 h, with a yield of 0.30 g/g and a productivity of 0.13 g L(-1) h(-1). The detoxification by adsorption into ion-exchange resins, in turn, provided 7.5 g/L ethanol in 48 h, with a yield of 0.30 g/g and a productivity of 0.16 g L(-1) h(-1).FAPESPCNP

A study on the pretreatment of a sugarcane bagasse sample with dilute sulfuric acid

Experiments based on a 2(3) central composite full factorial design were carried out in 200-ml stainless-steel containers to study the pretreatment, with dilute sulfuric acid, of a sugarcane bagasse sample obtained from a local sugar-alcohol mill. The independent variables selected for study were temperature, varied from 112.5A degrees C to 157.5A degrees C, residence time, varied from 5.0 to 35.0 min, and sulfuric acid concentration, varied from 0.0% to 3.0% (w/v). Bagasse loading of 15% (w/w) was used in all experiments. Statistical analysis of the experimental results showed that all three independent variables significantly influenced the response variables, namely the bagasse solubilization, efficiency of xylose recovery in the hemicellulosic hydrolysate, efficiency of cellulose enzymatic saccharification, and percentages of cellulose, hemicellulose, and lignin in the pretreated solids. Temperature was the factor that influenced the response variables the most, followed by acid concentration and residence time, in that order. Although harsher pretreatment conditions promoted almost complete removal of the hemicellulosic fraction, the amount of xylose recovered in the hemicellulosic hydrolysate did not exceed 61.8% of the maximum theoretical value. Cellulose enzymatic saccharification was favored by more efficient removal of hemicellulose during the pretreatment. However, detoxification of the hemicellulosic hydrolysate was necessary for better bioconversion of the sugars to ethanol.FAPESP Fundacao de Amparo a Pesquisa do Estado de Sao PauloCNPq Conselho Nacional de Desenvolvimento Cientifico e Tecnologic