No abstract
In this work the potential of thermotolerant strains of Kluyveromyces marxianus to produce xylitol from rice straw hemicellulosic hydrolyzed was evaluated. In addition, were also established conditions of diluted alkaline treatment (deacetylation) previously to the process of rice straw acid hydrolysis, aiming to decrease the toxicity of the hydrolysate. Initially, four yeast strains of K.marxianus (Y-6860, Y-6373, Y-2265 e Y-8287) were evaluated regarding to the xylitol production in a semi-defined medium, varying the temperature from 30 to 40 ºC. From these results, the strain Y-6373 was selected, due to high values of xylose conversion into xylitol (YP/S = 0.70 g/g) and volumetric productivity (QP = 0.60 g/L.h) at 40ºC. This strain was thus used in the fermentative tests employing the hemicellulosic hydrolysate obtained. The hemicellulosic hydrolysate of rice straw was prepared in two steps; firstly the rice straw was submitted to the alkaline treatment, which was carried out in Erlenmeyer flasks scale. In these experiments, the effects of temperature from 50 to 70 °C and NaOH load from 20 to 80 mg/g biomass on the removal of acetyl groups were evaluated. According to the model obtained, the maximum acetyl removal (97.2 ±3.4%) could be achieved by employing 70 ºC; 80 mg of NaOH/g of straw during 45 minutes. Under these conditions, the model predicted lignin and ashes removals of 41.3±4.3 and 62.3±5.3%, respectively, without significant loss of sugars. On a large scale (reactor of 50L), the alkaline treatment showed outcomes of acetyl removal near the ones predicted by the model. After, the deacetylating straw was submitted to acid hydrolysis process, varying the H2SO4 concentration from 0.5 to 1.5% w/v, and the residence time from 30 to 90 minutes, aiming to stablish the conditions that maximize the efficiency of hemicellulose hydrolysis (EHH). Under optimized conditions, (H2SO4 1.0% w/v and 85 minutes) 75% EHH was achieved in Erlenmeyers flasks and 76% in reactor. As regarding the hydrolysate fermentability employing K. marxinuas Y-6373, the results showed that, regardless of the nutritional supplementation, the conversion of xylose into xylitol was high ~ 0.87 g/g and superior in relation to the one obtained at a semidefined medium containing only xylose as a carbon source. Nevertheless, the values ofvolumetric productivity were approximately 6.5 times inferior ~ 0.13 g/L.h, due to the lowefficiency of xylose consumption (XC) ~ 20%, after 72h of cultivation. The hydrolysate fermentability was improved after detoxification and the results varied with the method employed. The best results were obtained on hydrolysate treated with CaO (YP/S= 0.74 g/g; QP = 0.32 g/L.h and XC = 92%). The glucose effect was further examined in semi-defined medium. The results showed that xylose assimilation and xylitol production by K. marxianus was repressed by glucose, since in a semi-defined media simulating the concentrations of xylose/glucose found in the hydrolyzed, the values of XC e YP/S were reduced in approximately 40%. ...
RESUMO -A produção de etanol a partir de resíduos de oleaginosas figura uma estratégia que pode complementar ou até suprir a demanda de álcool em reações de transesterificação nas indústrias de biodiesel. O presente estudo teve por objetivo avaliar a composição química e o potencial das tortas de algodão, girassol, pinhãomanso, mamona, tremoço, macaúba, corda-de-viola, pequi, dendê, crambe e nabo forrageiro para produção de etanol. A estimativa de produção por tonelada das tortas referidas variou de 100 L/ton a 395 L/ton. As projeções feitas a partir das biomassas supracitadas, com exceção da torta de mamona e de nabo forrageiro, demonstraram atender a demanda de álcool para produção de biodiesel. Observou-se grande potencial estimado de produtividade de etanol paras as tortas de algodão, dendê e macaúba, com valores de 520, 900 e 1000 L/ha, respectivamente. Assim, a produção de etanol a partir de tortas pode ser promissora para atender à cadeia produtiva do biodiesel. INTRODUÇÃOA matriz atual do consumo global de energia é dominada por combustíveis fósseis (petróleo, gás, carvão), fontes não-renováveis, cuja queima vem acompanhada das conhecidas consequências ambientais, sobretudo em razão das emissões de gases poluentes, como COx, SOx e NOx, para a atmosfera (Misra, 2013). Neste panorama, tem-se observado o crescimento de pesquisas voltadas para o desenvolvimento de energias alternativas. O biodiesel, em particular, teve crescimento significativo nos últimos oito anos (Brasil, 2013). Concomitante com o aumento da produção de biodiesel cresce também a geração de resíduos oriundos da sua cadeia produtiva, tais como a glicerina e as tortas, tornando necessário um enfoque especial na destinação destes subprodutos. A torta ou farelo, gerada na extração do óleo, possui potencial para agregar valor ao biodiesel, mas, para isso, suas potencialidades nutricionais e econômicas devem ser explanadas. Atualmente, os principais empregos das tortas são na adubação orgânica, alimentação animal e geração de energia por queima direta.Em nível mundial, as indústrias de biodiesel são responsáveis por captar 10,2% da produção de óleo vegetais anualmente (BiodieselBr.com). Algumas oleaginosas já são consolidadas na produção de matéria-prima para esse setor e outras estão sendo pesquisadas como produtoras em potencial de óleos. Dentre as oleaginosas já consolidadas, pode-se citar: o dendezeiro (Elaeis guineensis), algodoeiro (Gossypium ssp) e o girassol (Helianthus annuus). Já dentre as oleaginosas que estão sendo alvos de pesquisa, destaca-se a mamona (Ricinus communis L.), pinhão-manso (Jatropha curcas L.), pequi (Caryocar brasiliense Área temática: Processos Biotecnológicos 1
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