RESUMO
Xylitol was produced by Candida guilliermondii by fermentation of sugarcane bagasse hemicellulosic hydrolysate. Undesirable impurities were extracted from the broth using either ethyl acetate, chloroform or dichloromethane. The best results on clarification of the broth without xylitol loss were obtained with ethyl acetate. When ethanol, acetone or tetrahydrofuran were used for precipitation of impurities, only tetrahydrofuran clarified the fermented broth, but a high xylitol loss (approximately 30%) was observed.
Assuntos
Bioquímica/métodos , Biotecnologia/métodos , Polissacarídeos/química , Xilitol/química , Xilitol/isolamento & purificação , Acetatos/química , Acetona/farmacologia , Precipitação Química , Clorofórmio/química , Cromatografia Líquida de Alta Pressão , Fermentação , Furanos/química , Hidrólise , Cloreto de Metileno/química , Xilose/químicaRESUMO
Rice straw was hydrolyzed into a mixture of sugars using diluted H(2)SO(4). During hydrolysis, a variety of inhibitors was also produced, including acetic acid, furfural, hydroxymethylfurfural, and lignin degradation products (several aromatic and phenolic compounds). To reduce the toxic compounds concentration in the hydrolyzate and to improve the xylitol yield and volumetric productivity, rice straw hemicellulosic hydrolyzate was treated with activated charcoal under different pH values, stirring rates, contact times, and temperatures, employing a 2(4) full-factorial design. Fermentative assays were conducted with treated hydrolyzates containing 90 g/L xylose. The results indicated that temperature, pH, and stirring rate strongly influenced the hydrolyzate treatment, temperature and pH interfering with all of the responses analyzed (removal of color and lignin degradation products, xylitol yield factor, and volumetric productivity). The combination of pH 2.0, 150 rpm, 45 degrees C, and 60 min was considered an optimal condition, providing significant removal rates of color (48.9%) and lignin degradation products (25.8%), as well as a xylitol production of 66 g/L, a volumetric productivity of 0.57 g/L.h, and a yield factor of 0.72 g/g.
Assuntos
Algoritmos , Candida/metabolismo , Carvão Vegetal/química , Oryza/microbiologia , Polissacarídeos/química , Polissacarídeos/metabolismo , Xilitol/biossíntese , Adsorção , Reatores Biológicos/microbiologia , Biotransformação , Técnicas de Química Combinatória , Análise Fatorial , Hidrólise , Modelos Biológicos , Oryza/química , Oryza/metabolismo , Polissacarídeos/isolamento & purificação , Controle de Qualidade , Eliminação de Resíduos/métodos , Xilitol/isolamento & purificaçãoRESUMO
Batch fermentation of sugarcane bagasse hemicellulosic hydrolyzate by the yeast Candida guilliermondii FTI 20037 was performed using controlled pH values (3.5, 5.5, 7.5). The maximum values of xylitol volumetric productivity ( Q(p)=0.76 g/l h) and xylose volumetric consumption ( Q(s)=1.19 g/l h) were attained at pH 5.5. At pH 3.5 and 7.5 the Q(p) value decreased by 66 and 72%, respectively. Independently of the pH value, Y(x/s) decreased with the increase in Y(p/s) suggesting that the xylitol bioconversion improves when the cellular growth is limited. At the highest pH value (7.5), the maximum specific xylitol production value was the lowest ( q(pmax)=0.085 g/l h.), indicating that the xylose metabolism of the yeast was diverted from xylitol formation to cell growth.
Assuntos
Reatores Biológicos/microbiologia , Candida/metabolismo , Técnicas de Cultura de Células/métodos , Celulose/metabolismo , Polissacarídeos/metabolismo , Saccharum/metabolismo , Xilitol/biossíntese , Candida/citologia , Candida/crescimento & desenvolvimento , Divisão Celular , Celulose/química , Meios de Cultura/metabolismo , Concentração de Íons de Hidrogênio , Hidrólise , Polissacarídeos/química , Xilitol/isolamento & purificação , Xilose/metabolismoRESUMO
Xylitol, a sweetener comparable to sucrose, is anticariogenic and can be consumed by diabetics. This sugar has been employed successfully in many foods and pharmaceutical products. The discovery of microorganisms capable of converting xylose present in lignocellulosic biomass into xylitol offers the opportunity of producing this poliol in a simple way. Xylitol production by biotechnological means using sugar cane bagasse is under study in our laboratories, and fermentation parameters have already been established. However, the downstream processing for xylitol recovery is still a bottleneck on which there is only a few data available in the literature. The present study deals with xylitol recovery from fermented sugar cane bagasse hydrolysate using 5.2 g/l of aluminium polychloride associated with activated charcoal. The experiments were performed at pH 9, 50 degrees C for 50 min. The results showed that aluminium polychloride and activated charcoal promoted a 93.5% reduction in phenolic compounds and a 9.7% loss of xylitol from the fermented medium, which became more discoloured, facilitating the xylitol separation.