Influence of Medium Buffering Capacity on Inhibition ofSaccharomyces cerevisiaeGrowth by Acetic and Lactic Acids

Abstract

Acetic acid (167 mM) and lactic acid (548 mM) completely inhibited growth of Saccharomyces cerevisiae both in minimal medium and in media which contained supplements, such as yeast extract, corn steep powder, or a mixture of amino acids. However, the yeast grew when the pH of the medium containing acetic acid or lactic acid was adjusted to 4.5, even though the medium still contained the undissociated form of either acid at a concentration of 102 mM. The results indicated that the buffer pair formed when the pH was adjusted to 4.5 stabilized the pH of the medium by sequestering protons and by lessening the negative impact of the pH drop on yeast growth, and it also decreased the difference between the extracellular and intracellular pH values (⌬pH), the driving force for the intracellular accumulation of acid. Increasing the undissociated acetic acid concentration at pH 4.5 to 163 mM by raising the concentration of the total acid to 267 mM did not increase inhibition. It is suggested that this may be the direct result of decreased acidification of the cytosol because of the intracellular buffering by the buffer pair formed from the acid already accumulated. At a concentration of 102 mM undissociated acetic acid, the yeast grew to higher cell density at pH 3.0 than at pH 4.5, suggesting that it is the total concentration of acetic acid (104 mM at pH 3.0 and 167 mM at pH 4.5) that determines the extent of growth inhibition, not the concentration of undissociated acid alone.The yeast Saccharomyces cerevisiae under aerobic conditions can use short-chain organic acids, such as acetic acid and lactic acid, as carbon sources. The process involves induction of certain anabolic pathways, enzymes, and specific transport mechanisms (2,4,5,6,17). If glucose is available in the growth medium, these pathways and permeases are repressed. Glucose-repressed yeast cells are unable to take up the anions of these acids (6), but the undissociated acids diffuse freely into the cells. Once inside, these acids dissociate because of the higher intracellular pH and cause acidification of the cytoplasm. Generally, eucaryotic cells maintain their intracellular pH within a narrow range despite wide variations that may occur in the extracellular pH (7). Under fermentation conditions, the intracellular pH of S. cerevisiae is usually maintained between 5.5 and 5.75 when the external pH is 3.0 (9) or between 5.9 and 6.75 when the external pH is varied between 6.0 and 10.0 (8). To maintain the intracellular pH within a physiological range optimum for metabolism, the cells pump out protons at the expense of metabolic energy (ATP). Increased diversion of energy (ATP) to pump out protons results in decreased molar growth yield with respect to glucose (Y glucose ) (19,24). It has also been reported that the Y ATP (grams of biomass produced per mole of ATP generated) decreased from 14 to 4 when the concentration of acetic acid was increased from 0 to 170 mM (19). As the gap between the extracellular pH and the intracellular pH widens, greater stress i...

Acetate but not propionate induces oxidative stress in bakers’ yeastSaccharomyces cerevisiae

“…At рН 3.0-4.5, YPD medium has been shown to act as a buffer system and recommended to be used for yeast incubation under WOA-induced stress. 29,30 To study pre-adaptation effect on cell survival under weak organic stress, aliquots of experimental culture were pre-incubated with 0.05, 0.10, and 0.25 mM H 2 O 2 at pH 6.75 for 30 minutes, followed by incubation with 200 mM AA at pH 3.0 for 120 minutes.…”

Composition and biochemical properties of l‐carnitine fortified Makgeolli brewed by using fermented buckwheat

“…The amino acid contents of Makgeolli were shown to be associated with the raw material (Kang et al., 2014). As a result, the increased pH in 25% buckwheat Makgeolli or fermented buckwheat Makgeolli may be due to increased amino acid contents and their buffering capacity (Thomas, Hynes, & Ingledew, 2002). …”

Growth in brine, at low temperature and different organic acids, of yeasts from table olives

“…El comportamiento del láctico en estos experimentos se debe sin duda a que los niveles alcanzados fueron en todo momento relativamente bajos. En efecto, se ha demostrado que las concentraciones mínimas inhibidoras de los ácidos acético y láctico en un medio mínimo eran del 0,6% (100 mM) y 2,5% (278 mM) respectivamente (Narendrananrh et al, 2001a), habiéndose demostrado recientemente que ese poder inhibidor no depende del porcentaje de ácido sin disociar sino que es más bien consecuencia de las concentraciones totales de los mismos (Thomas et al, 2002) así como que los mecanismos a través de los que actúan ambos ácidos son diferentes (Narendrananth et al, 2001b). La presencia de ácido acético apenas altera el pH interior de Sacch.…”

“…cerevisiae (Thomas et al, 2002;Narendranath et al, 2001a y b), otras levaduras que pueden producir alteraciones de los alimentos (Loureiro, 2000), así como patógenos (Samelis et al, 2001;Tienungoon et al, 2000).…”