DETERMINATION OF OXYGEN UTILIZATION PATHWAYS IN AN INDUSTRIAL STRAIN OF SACCHAROMYCES-CEREVISIAE DURING ENOLOGICAL FERMENTATION

It is generally admitted that, due to the low levels Of respiratory en zymes and mitochondrial cytochromes, classical oxidative phosphorylati on does not occur to any significant extent under alcoholic fermentati on conditions. Under anaerobiosis, yeast growth normally requires oxyg en in order to favour the synthesis of sterols and unsaturated fatty a cids. However, in such conditions, superfluous oxygen consumption by y east cells is observed. In this study, the potential relationship betw een this oxygen consumption and the known respiratory pathways of S. c erevisiae was investigated during enological fermentation. Partial and limited synthesis of mitochondrial cytochromes was observed during th e growth phase. The superfluous oxygen consumed by the yeast cells app eared not to be related to classical respiration, but mainly to the op eration of several mitochondrial alternative respiration pathways, whi ch were linked to the cell cytochrome contents. It was further found t hat oxygen-dependent ergosterol biosynthesis accounted for less than 1 5% of the total oxygen consumption at the beginning of stationary phas e in the absence of anaerobic growth factors. No significant oxygen co nsumption could be clearly attributed to fatty acids desaturation in t he yeast cells.