AN OPTIMIZATION OF ETHANOL PRODUCTION IN MOLASSES USING A NEW YEASY STRAIN

Leonardo de Almeida Ferreira E Silva (UNESP); Meline Rezende Morais (UNESP); Reinaldo Marchetto (UNESP); Cecília Laluce (UNESP)

The performance of a fermentation process depends on improvements in growth, specific ethanol production rate and the concentration of viable cells in response to the nutrients available as required by the starter yeast, temperature, concentration of the fermentable sugars and other factors. The toxicity of the ethanol increases with the temperature of the process while the must composition is not stable due to the usual oscillations in the composition of the harvested sugar cane. Although belonging to the same genera and species, strains of Saccharomyces cerevisiae produce ethanol but show distinct physiological responses (ethanol produced, by-products, viability to the variations in the medium composition, stress resistance to ethanol, sugar concentration and temperature). The enrichment of the must with the nitrogen source can be obtained by adding diamonium hydrogen phosphate (DAP) as reported in literature. The addition of zinc has been reported to prevent cell death, while the addition of magnesium increases the rate of sugar consumption and increases the resistance against the ethanol stress. In the present work, a strain constructed in our laboratory was assayed in sugar-cane molasses. The fermentation experiments were carried out in mini-reactors operating in a discontinuous fed-batch process of variable volume due to a constant substrate feed. Amounts of 56.82% sucrose, 2.63% free glucose, 3.5% free fructose were present in concentrated molasses (64.80%, ART). In the present study, experiments were carried out in order to optimize the concentration of the total sugar in the molasses medium, along with DAP supplementation, zinc sulfate, and magnesium sulfate, which were also determined for fermentations with the yeast strain 63M. Optimization of the amount of yeast biomass added to the reactors and the best feeding rate were also determined. The diluted molasses used to feed the reactors was deficient in magnesium and DAP as shown by the improvements in the rate of biomass accumulation and sugar consumption. Concerning ethanol production, supplementation with DAP, zinc sulfate and magnesium sulfate improved rates of ethanol production, biomass accumulation and also leads to reductions in the final residual sugar. Increases of around 1.3 times in the final biomass in relation to the initial biomass were obtained in experiments carried out at 37°C.