Intracellular ethanol accumulation in yeast cells during aerobic fermentation: a Raman spectroscopic exploration

AIMS: To investigate the intracellular ethanol accumulation in yeast cells by using laser tweezers Raman spectroscopy (LTRS). METHODS AND RESULTS: Ethanol accumulation in individual yeast cells during aerobic fermentation triggered by excess glucose was studied using LTRS. Its amount was obtained by comparing intracellular and extracellular ethanol concentrations during initial process of ethanol production. We found that (i) yeasts start to produce ethanol within 3 min after triggering aerobic fermentation, (ii) average ratio of intracellular to extracellular ethanol is 1.54 ± 0.17 during the initial 3 h after addition of 10% (w/v) excess glucose and (iii) the accumulated intracellular ethanol is released when aerobic fermentation is stimulated with decreasing glucose concentration. CONCLUSIONS: Intracellular ethanol accumulation occurs in initial stage of a rapid aerobic fermentation and high glucose concentration may attribute to this accumulation process. SIGNIFICANCE AND IMPACT OF THE STUDY: This work demonstrates LTRS is a real-time, reagent-free, in situ technique and a powerful tool to study kinetic process of ethanol fermentation. This work also provides further information on the intracellular ethanol accumulation in yeast cells.