Sunday, May 4, 2008
2-46

Semi-continuous xylitol production from sugarcane bagasse hemicellulose by Ca-alginate entrapped yeast cells in a bench-scale stirred tank reactor

Walter Carvalho1, Larissa Canilha1, and Silvio S. Silva2. (1) Departamento de Biotecnologia, Escola de Engenharia de Lorena, Universidade de São Paulo, Estrada Municipal do Campinho, s/n, Lorena, 12602810, Brazil, (2) Department of Biotechnology, Escola de Engenharia de Lorena, Universidade de São Paulo, Estrada Municipal do Campinho, s/n, Lorena, 12602-810, Brazil

In Brazil, much more ethanol would be obtained from the same amount of sugarcane if the sugar-alcohol mills used not only the sugarcane juice but also the sugarcane bagasse as a source of carbohydrates. Together with the conversion of hexose sugars into ethanol, the conversion of pentose sugars into value-added products could benefit the economics of using lignocellulosic sugars as raw-materials. For instance, xylitol, a specialty sweetener widely used by food and pharmaceutical industries, could be produced from xylose, the major pentose sugar found in sugarcane bagasse hemicellulose. This sweetener is non and anticariogenic, can be consumed by diabetics and can replace antibiotics in the treatment of otitis, among other applications. In the present study, we report the operational stability of the semi-continuous xylitol production from sugarcane bagasse hemicellulosic hydrolysate by Ca-alginate entrapped Candida guilliermondii cells during five successive fermentation batches carried out in a stirred tank reactor. The average volume of the Ca-alginate beads was reduced by about 30 % after the 600 h taken to perform the five bioconversion cycles, thus demonstrating physical instability under the conditions prevailing in the vessel. In spite of this, almost steady bioconversion rates and yields were observed along the repeated batches. In average, a production of 51.6 gl-1, a productivity of 0.43 gl-1h-1 and a yield of 0.71 gg-1 were attained in each batch, variation coefficients being smaller than 10 %.
Acknowledgements: Fapesp and CNPq

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