Statistical approach to optimization of ethanol fermentation by saccharomyces cerevisiae in the presence of valforspi® 100 zeolite NaA

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.