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- Problems in the use of benzoic acid for estimating the internal pH of yeastsPublication . Henriques, M.; Quintas, Célia; Loureiro-Dias, M. C.Some yeasts have the peculiar ability to grow in the presence of weak acids at rather low pH. These conditions are predominant in preserved foods and beverages such as fruit concentrates, juices, wine, where these yeasts are responsible for spoilage. The main preservatives currently utilized by food industries are sorbic, propionic, benzoic acids and SO2. It is usually assumed that weak acids diffuse through the plasma membrane in the undissociated form. In the cytoplasm, where the pH is higher, dissociation occurs resulting in accumulation of the lipid-insoluble anion and internal acidification. This is probably a very general mechanism of preventing microbial growth in foods.
- Extrusion of benzoic acid in Saccharomyces cerevisiae by an energy-dependent mechanismPublication . Henriques, M.; Quintas, Célia; Loureiro-Dias, M. C.When grown in the presence of benzoic acid, Saccharomyces cerevisiae was able to extrude [C-14]benzoic acid when a pulse of glucose was given to preloaded cells. While octanoic, sorbic, hexanoic, salicylic, butyric and propionic acids were also inducers, ethanol and acetic acid were not. The mechanism of extrusion required energy and prior growth in the presence of the inducers. Diethylstilbestrol, an inhibitor of ATPases, prevented benzoic acid extrusion. Propionic acid was not actively extruded in cells adapted to either benzoic or propionic acid, behaving as an appropriate probe to measure intracellular ph. Even though the extrusion mechanism was active, benzoic acid entered the cells by a simple diffusion mechanism.