The plasma membrane and mitochondria of bottom fermenting brewer's yeast obtained as a by-product of industrial beer production were isolated and the lipid fraction was analyzed. The phospholipid content accounted for 78 mg/g protein in the plasma membrane and 59 mg/g protein in the mitochondria. Major phospholipids in both preparations were phosphatidylinositol, phosphatidylcholine and phosphatidylethanolamine but their proportions differed significantly. In the plasma membrane phosphatidylinositol, and in the mitochondria phosphatidylcholine were present in the highest concentration (37 and 30%, respectively). The main classes of neutral lipids (triacylglycerols, ergosterol, squalene and steryl esters) were twice more abundant in the plasma membrane than in the mitochondria (61 and 33 mg/g protein, respectively). A characteristic of the neutral lipid composition of both organelles was the low content of ergosterol (12 and 7 mg/g protein, respectively) and a high content of squalene (25 and 22 mg/g protein). The main feature of the fatty acid composition of both organelles was the preponderance of saturated fatty acids (78 and 79%, respectively), among which palmitic acid was the principal one. The most expressed characteristics of lipid fractions of the analyzed plasma membranes and mitochondria, high concentration of squalene and preponderance of saturated fatty acids are the consequences of anaerobic growth conditions. The lack of oxygen had possibly the strongest effect on the lipid composition of the plasma membranes and mitochondria of bottom fermenting brewer's yeast.

The neutral lipid fraction of the aerobically grown starter yeast culture of a Saccharomyces cerevisiae brewing strain, and three-first recycled yeast generations exposed to multiple stress factors during beer fermentation was studied. No pronounced changes in the cellular neutral lipid content between the non-stressed starter and stressed recycled cells were found. However, it was found that recycled yeast generations modulate their neutral lipid composition during fermentation. The ergosterol content was increased at the expense of steryl esters (SEs) and squalene, which resulted in a higher ergosterol/SEs molar ratio and a slightly higher ergosterol/squalene molar ratio. In addition, the proportion of unsaturated fatty acids, mainly palmitoleic acid increased in the neutral lipid fraction of the stressed recycled yeast generations. These results suggest that some specific neutral lipid species and fatty acids stored in the neutral lipid fraction are involved in the adaptive response of the brewer's yeast to stressful fermentation conditions. The striking finding was a high squalene content in the neutral lipid fraction of both the starter yeast culture and recycled yeast generations (22.4 vs. 19-20%, respectively), implying a possible biotechnological exploitation of this biologically active molecule from the yeast biomass.

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Yarrowia lipolytica yeast was grown batchwise on n-hexadecane as the carbon and energy source. Two cerebroside species were quantitatively isolated from sphingolipid fractions of total lipids by a combination of column chromatography and preparative high-performance thin-layer chromatography. The cerebroside content accounted for 1.3% of the total cell lipids. Glucose was detected as the sole sugar constituent in cerebrosides. The fatty acid composition of cerebrosides was characterized by a high proportion of hydroxylated long-chain saturated fatty acids. The major fatty acids were h16:0 and 16:0. The long-chain bases composition shows a preponderance of trihydroxy bases and a small amount of dihydroxy bases. The striking finding was a high proportion of 19-phytosphingosine.

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