engleski

The Influence of unfavourable conditions on the composition of yeast lipids

The main lipids of the yeast membranes are phospholipids, ergosterol, and sphingolipids. Their composition is rigidly maintained during exponential growth under favourable conditions ; however, it alters markedly in response to extracellular changes. For that reason interest in yeasts has been renewed for their potential application in the production of highly specific fats. Until now it has been shown that the brewery liquid waste is a good substrate for producing biomass, vitamins and enzymes. For economical, as well as ecological reasons, it would be useful to find some additional applications for surplus/waste brewer's yeast. Therefore, for better evaluation of nutritive and potentially pharmacological properties a detailed analysis of its lipid fraction was performed. Besides, to get insight how yeasts adjust the composition of their membranes to unfavourable conditions, the lipid fraction of the plasma membrane and mitochondria were analysed. Both, the phospholipid and fatty acid compositions had some interesting features, but more or less easy to explain regarding the growth phase and conditions. Regarding neutral lipids, squalene accounted for more than 30% of total cell lipids, which was three times more than ergosterol and may be explained as the consequence of anaerobic growth conditions. Although brewer's yeast does not belong to the so-called lipid yeasts, the high content of squalene, which is used in antitumor therapy and in cosmetics, gives reason for additional exploitation. The results of the analysis of neutral lipid composition of the plasma membrane and mitochondria were rather surprising. Ergosterol was present in very low concentrations in both organelles, as well (12 and 7 g/mg proteins, respectively), but squalene, which is present eventually only in trace amounts in the membranous systems, accounted for 25 and 22 g/mg proteins, respectively. Such finding led us to the conclusion that recycled brewer’s yeast grown in the anaerobic conditions, in the lack of ergosterol incorporates squalene in its membranes. However, it must be pointed out that this survival mechanism was developed by careful selection during more than two thousand years.

brewer's yeast; membrane lipids; growth conditions

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