Degradation of Phospholipids and Liquefaction of Pressed Bakers Yeast by Acetic Acid Vapour

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When pressed bakers yeast (Saccharomyces cerevisiae) was exposed to the vapour of acetic acid, autolysis of yeast cells was induced in 3 or 4hr. In order to elucidate the mechanism of the autolysis caused by the AcOH-treatment, we investigated variations in the lipid content of yeast cells during the treatment. The degradation of phospholipids and the accumulation of free fatty acids occurred within 3hr. Formic acid exerted a similar effect on the pressed yeast. The effect of propionic acid was not seen in 3hr but was after 18hr. When the homogenate of fresh yeast cells was incubated in the acidic region below pH 4.5 for 1hr, phospholipids were hydrolyzed and free fatty acids were accumulated. Such deacylation of phospholipids was observed even at pH 6 on incubation for 12hr, but not observed at pH 7 or above pH 9. At pH 8, although phospholipids were somewhat degraded, free fatty acids almost never accumulated but diacylglycerol did accumulate. Therefore, yeast cells have inherently phospholipid-acylhydrolases and, on AcOH-treatment, such enzymes may degrade membrane phospholipids to induce the autolysis of pressed yeast.
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