Rapid assessment of Oenococcus oeni activity by measuring intracellular pH and membrane potential by flow cytometry, and its application to the more effective control of malolactic fermentation

pHin measurement throughout the entire growth shows that the pH was equal to the pH of the culture medium during the early stage, increased to pH 6 in the exponential phase, and then decreased to equilibrate with the pH of the medium in the late stationary phase. Membrane potential increased in early MLF and then decreased. The decrease in pHin and membrane potential occurred when all of the malic acid was consumed. Finally, we showed that the higher the ΔpH (pHin − pHex) in O. oeni cells was, the shorter the lag phase of the MLF was. To better manage the initiation of MLF in wines, the physiological state of O. oeni cells must be taken into account. These results allow us to understand the sometimes random initiation of MLF in wines inoculated with O. oeni and to suggest ways to improve this control.