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Acid stress and cellular heterogeneity during successive cycles of ethanol production in the presence of lactic acid

Grant number: 05/03681-2
Support type:Scholarships in Brazil - Doctorate
Effective date (Start): January 01, 2006
Effective date (End): August 31, 2008
Field of knowledge:Agronomical Sciences - Food Science and Technology - Food Science
Principal researcher:Cecilia Laluce
Grantee:Karen Fernanda de Oliveira
Home Institution: Instituto de Química (IQ). Universidade Estadual Paulista (UNESP). Campus de Araraquara. Araraquara , SP, Brazil


The lactic acid is a weak organic acid produced by contaminant strains of lactic acid bacteria that usually compete with the yeast-cell population for nutrients, in a no-sterilize fed-bath process for fuel-ethanol production. The presence of lactic acid bacteria leads to decreases in the growth of the yeast population followed by a lowering in ethanol yields of a fed-bath process, reducing the profits of the alcohol industries. The present work proposes an evaluate of the physiological and phenotypic alterations occurring in the starter-yeast population of Saccharomyces cerevisiae during the fed-bath process with cells recycling in presence of added-lactic acid. The optimal concentrations of the lactic acid added initially to the process, inoculum size, initial sugar concentration and fermentation time will be determined based on factorial planning. Physiology parameters of the yeast cells (total protein, trehalose, lactate desidrogenase indicating the intracellular accumulation of lactic acid, intracellular glycerol and NADP-glutamate dehydrogenase indicating nitrogen or carbon starvation and stress level) will be determined. A second stage of the present work will be performed to select the stress-resistant cells and ‘petite’ mutants formed during the fed-bath process by plating. In order to confirm genetic alterations occurred in cells of the starter strain remaining into the cell recycling process, molecular analysis will be carried out using PCR and CHEF techniques. The results obtained will be submitted to variance analysis. The molecular characteristics (PCR and CHEF profiles) of clones of resistant cells to the successive fermentation cycles will be compared to the similarity coefficients. The variations in physiological parameters observed during successive fermentation cycles in the presence of lactic acid will be also compared to dissimilarity coefficients. (AU)

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Academic Publications
(References retrieved automatically from State of São Paulo Research Institutions)
OLIVEIRA, Karen Fernanda de. Effects of the lactic acid added on ethanol production on fermentations with cell reuse at 34ºC.. 2008. Doctoral Thesis - Universidade de São Paulo (USP). Instituto de Ciências Biomédicas (ICB/SDI) São Paulo.

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