Statistical approach to optimization of ethanol fermentation by Saccharomyces cerevisiae in the presence of Valfor® 100 zeolite NaA
Optimización estadística de fermentación etanólica de Saccharomyces cerevisiae en presencia de zeolita Valfor® NaA
G. Inei–Shizukawa, H. A. Velasco–Bedrán, G. F. Gutiérrez–López and H. Hernández–Sánchez*
Departamento de Ingeniería Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Carpió y Plan de Ayala, CP. 11340, México, DF, México. * Corresponding author. E–mail: hhernan1955@yahoo.com
]]> Received 15 of June 2009
Abstract
The technologies for ethanol production from sugars, starch and lignocellulosic materials for food and biofuel applications are being constantly improved. A number of modifications to increase the production and yield of ethanol have been implemented such as immobilization of cells, genetic modification and use of mixed cultures. In this work, the addition of zeolites to increase the alcohol production of the yeast Saccharomyces cerevisiae was studied. The experiments were designed with seven factors for ethanol yield (carbon and nitrogen source, Mg2+ and zeolite concentration, temperature, pH and inoculum size) at two levels with an orthogonal array layout of L8 (27) designed to keep the number of experiments to a minimum. Addition of 0.2 g L–1 of Valfor® 100 zeolite NaA resulted in important increases in ethanol production (20%) and yield (25%). An adsorption phenomenon could be observed by SEM between the zeolite particles and the yeast cells. This and the well known effects of toxic cation concentration decrease, pH regulation and ethanol and carbon dioxide adsorption could have caused the improvement in the ethanol production and yield. The optimization study indicated that zeolite concentration was the most significant factor in this increase even though it was used at lower levels compared with other studies, indicating the importance of the optimization studies in bioprocesses.
Keywords: zeolite, ethanol, Taguchi optimization, Saccharomyces cerevisiae.
Resumen
En la actualidad existe gran interés en mejorar las tecnologías para producir etanol a partir de azúcares, almidón y materiales lignocelulósicos para aplicaciones en alimentos y como biocombustibles. Se han introducido varias modificaciones para incrementar la producción y el rendimiento de etanol como son la inmovilización de células, la modificación genética y el uso de cultivos mixtos. En este trabajo se estudió la adición de zeolitas para incrementar la producción de etanol de la levadura Saccharomyces cerevisiae. El diseño experimental se planeó con siete factores importantes para la producción de etanol (concentración de las fuentes de carbono y nitrógeno, Mg+2 y zeolita, temperatura, pH y tamaño de inóculo) a dos niveles con una matriz de diseño ortogonal L8 (27) diseñada para un número mínimo de experimentos. La adición de 0.2 g L–1 de la zeolita Valfor® 100 resultó en incrementos importantes en la producción (20%) y rendimiento (25%) de etanol. Se pudo observar el fenómeno de adsorción entre las partículas de zeolita y las células de levadura por microscopía electrónica de barrido. Esto y los efectos conocidos de adsorción de cationes tóxicos, regulación de pH y adsorción de etanol y CO2 podrían ser responsables de la mejora en la producción y rendimiento de alcohol. El estudio de optimización indicó que la concentración de zeolita fue el factor más importante para este aumento, sobretodo porque se usaron niveles más bajos que en otros estudios, indicando la importancia de los estudios de optimización en bioprocesos.
Palabras clave: zeolita, etanol, optimización de Taguchi, Saccharomyces cerevisiae.
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