The changes in intracellular redox activity or in mitochondrial electron transport could be taken as indications of the changes in the physiological state of living cells, based on which a mediated electrochemical method was purposed to evaluate the inhibitory effects of weak acids on Zygosaccharomyces bailii, a known food spoilage yeast. The dual mediator systems menadione/ferricyanide and 2,6-dichlorophenolindophenol/ferricyanide were employed as probes to detect the variance in intracellular redox activity and in mitochondrial electron flux, respectively. Measurements were made with a microelectrode voltammetric method to assay the ferrocyanide accumulations arising from menadione- or 2,6-dichlorophenolindophenol-mediated reduction of ferricyanide by Z. bailii suspensions by the presence or absence of increasing concentrations of weak acids. The results obtained from 2 h of incubation showed that the variance in electrochemical response revealed some physiological information underlying the inhibitory effects of weak acid on the yeast. For the first time, it was shown that the mediated electrochemical method provides an adjunct to the conventional method based on respiration inhibition for establishing levels for the utilization of preservatives in the food industry.