Aspectos da permeabilidade celular envolvidos na tolerancia a conservantes em leveduras de alteracao alimentar

Abstract

The effect of eight organic acids and of ethanol was evaluated on growth of the spoilage yeasts Saccharomyces cerevisiae, Zygosaccharomyces bailii, Pichia sp and Debaryomyces hansenii, by using an automatic system to record optical density. Exponential inhibition constants and inhibitory concentrations that reduce growth by 50% were calculated. Passive proton influx into the yeasts above mentioned was affected only by high concentrations of ethanol. Under these conditions the cells became suddenly very permeable. The results were not significantly affected by previous conditions of adaptation. Loss of intracellular content induced by ethanol only became apparent in non-viable cells. Linear kinetics indicative of simple diffusion were obtained for the initial uptake of benzoic acid into mutants of Saccharomyces cerevisiae in genes related with resistance to weak acids; adaptation to benzoic acid resulted, in general, in decreased permeability with the exception of one of the strains tested. The gene product Pdr12 was important in the extrusion of benzoic acid. Results suggest that other genes may be involved in the extrusion of this preservative. Results obtained by flow cytometry, although not conclusive, suggest that fluorescein was extruded, not exclusively, by the same transporter as benzoate in Zygosaccharomyces bailiiAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga