engleski

Alterations in the lipid composition of the mitochondria of the bottom-fermenting brewer’s yeast caused by unfavourable growth conditions

Strains of Saccharomyces cerevisiae yeast are by far the most used ones in the brewing industry, in which the recycling of one culture through a series of fermentations is a common process. In the industrial process of beer production, yeast undergoes propagation, fermentation and storage, during which it is exposed to various types of stress. Stress in general, especially anaerobic conditions and ethanol toxicity in the case of the bottom fermenting brewer’s yeast, cause many changes in the cells, including the changes in the content and composition of lipids. An important role in brewing yeast physiology and fermentation performance play mitochondria and it is well established that ethanol tolerance is closely related to their lipid composition. The aim of this study was to determine the composition of the mitochondrial lipids of the bottom fermenting brewer's yeast of the zeroth generation (pure culture) and of the 1st and the 4th recycled generation. Mitochondria were isolated from the yeast cells after enzymatic disruption of the cell wall. Proteins were determined by the method of Lowry. Lipids were extracted by the method of Folch et al. Neutral lipids were separated from total lipids by two-step thin-layer chromatography and quantified by densitometry. It was found that only ergosterol and squalene were present in significant amounts. The concentration of ergosterol was the highest in the zeroth generation (9.7 µg/mg proteins), while it was significantly lower (7.0 and 6.4 µg/mg proteins) in the 1st and the 4th generation. The mitochondria of all of the analysed generations contained substantial amounts of squalene (7.1, 4.0, 5.4 µg/mg), which is known to accumulate in the cells during anaerobic conditions. Another interesting finding was that the mitochondria of the zeroth generation, grown in the aerobic conditions, contained a significant amount of squalene. We assume that the accumulation of squalene in the mitochondrial membranes, as well as in other cell membranes, is not only the way of storing the squalene, but also has a certain function, which is the result of a millennium-long adaptation of the bottom fermenting yeast.

lipids; mitochondria; brewer's yeast; growth conditions

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