Effect of external pH on ethanol oxidation by Candida utilis

External conditions influencing ethanol oxidation by resting cells of Candida utilis

Effects of ethanol inhibition, initial pH and buffering capacity of media on the catabolic activity of nongrowing cells of Candida utilis were studied. Effects of external conditions on the kinetic of ethanol oxidation and cell respiration are described by mathematical models. The results revealed a significant influence of both the external pH and the buffering capacity of the medium on the kinetic parameters of catabolic activity. The inhibitory effect results in the bottleneck of one of the reaction of the citrate cycle, glyoxylate cycle or electron transfer in a respiratory chain although the total rate of ethanol dissimilation increases under these conditions.

Effect of external pH on acidification and excretion of ethanol intermediates by Candida utilis

External pH affects the acidification induced by ethanol. The apparent specific rate of acidification depends on the dissociation properties and production of carbon dioxide, acetic and lactic acid which are intermediates of ethanol oxidation. The organic acids are transported by Nernst-Einstein diffusion. We designed and identified a new and simple mathematical model that allows us to describe the effect of external pH on nonstationary transport of dissociated intermediates of ethanol oxidation.