|1691-1||Saccharomyces cerevisiae STRAINS FOR HIGH ETHANOL FERMENTATION WITH CELL REUSE|
|Autores:||Renata Maria Christofoleti Furlan (ESALQ/USP - Escola Superior de Agricultura Luiz de Queiroz - USP) ; Natália Alexandrino (ESALQ/USP - Escola Superior de Agricultura Luiz de Queiroz - USP) ; Stefania Vital (ESALQ/USP - Escola Superior de Agricultura Luiz de Queiroz - USP) ; Camila de Souza Varize (ESALQ/USP - Escola Superior de Agricultura Luiz de Queiroz - USP) ; Elisangela de Souza Miranda (ESALQ/USP - Escola Superior de Agricultura Luiz de Queiroz - USP) ; Elisa de Almeida Lucatti (ESALQ/USP - Escola Superior de Agricultura Luiz de Queiroz - USP) ; Luiz Carlos Basso (ESALQ/USP - Escola Superior de Agricultura Luiz de Queiroz - USP) |
Huge demand is expected for bioethanol. Then Brazil should produce more ethanol and at a lower cost to maintain competitiveness in relation to fossil fuels. One of the technological approaches which emerges is the high ethanol content fermentation. Great economical and environmental advantages arose from this fermentation: lesser stillage volume, reduced water usage and energy consumption during distillation, suggesting an increased energy balance of the produced ethanol. However one of the limiting factors for that is the absence of proper strains to face the very harsh fermentation condition, where several stresses are simultaneously imposed to the fermenting yeast. In the present work, Saccharomyces strains were searched for high ethanol fermentation with cell reuse. Yeast isolates (290) from several Brazilian distilleries (20), assigned as Saccharomyces sp by means of electrophoretic karyotyping, were evaluated for 24 h biomass formation (OD570nm) at 30oC in 25% (w/v) total sugar industrial substrate (cane juice and molasses), using 96 well plate reader. Cultures (200) presenting higher biomass formation were re-selected, by means of the same procedure, using a more stressful medium (15% total sugar, 7% ethanol, 660 mg/L acetic acid, 3,000 mg/L lactic acid and pH 3.5), and 15 strains arouse with better parameters when compared with S. cerevisiae PE-2, the reference strain. One of these strains (ST-207) was compared with PE-2 in fermentation trials simulating the industrial process with cell reuse in condition of high ethanol fermentation. The first 3 cycles were performed at 32,5 oC with increasing supply of sugar resulting in more than 14% (v/v) ethanol at the third fermentation. During this very stressful condition, biomass gain was higher for ST-207 strain, simultaneously with a sharp drop in PE-2 cell viability. For the following fermentation cycles (30oC), ethanol titers were around 13-14%, with little differences between strains. But the biomass recovery was higher for ST-207 strain, also presenting higher cell viabilities. Higher glycerol formation is known to be a yeast response to several stressors, mainly osmotic stress. It was observed lower levels of glycerol during ST-207 strain fermentation, which suggests its higher tolerance when compared with PE-2. Accordingly, cellular storage carbohydrates levels (trehalose and glycogen), which enable yeast to become more tolerant to stress conditions, were higher for the ST-207 strain at the end of the fermentation. The ST-207 strain can better stand the stressing conditions of a high ethanol fermentation, when osmotic, ethanolic, acidic and others stressors are simultaneously imposed. Strains with multitolerance can be obtained from the natural biodiversity found in Brazilian distilleries.
Palavras-chave: Brazilian distilleries, Cell reuse, High ethanol fermentation, Saccharomyces cerevisiae, Stress