engleski

The Effect of Environmental Stress Conditions on the Content and Composition of Phosphatidylcholine and Phosphatidylethanolamine of the Brewing Strain of Saccharomyces cerevisiae

During beer fermentation and serial recycling, bottom-fermenting brewer’ s yeast (S. cerevisiae) is exposed to different stress factors, among which the toxic effect of ethanol and oxygen-limited conditions are the most important. They can cause “ stress injuries” and activate response mechanisms that influence lipids, especially membrane lipids. In addition, recycling of the yeast biomass that is normal practice in brewing industry, implies adaptive capability of the yeast cells, which is partially enabled by adjustments in lipid composition. In order to determine the effect of unfavourable conditions during fermentation on the phospholipid (PL) composition, in particular phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn), two phospholipid species involved in stress response, their ratio and fatty acid (FA) composition, the analysis of pure non-stressed yeast culture and three recycled yeast generations (1st, 2nd and 3rd) was performed. Lipids were extracted by Folch method after the disruption of the cell wall by zymoliase. PLs were quantified spectrophotometrically after the separation by two-dimensional TLC. FAs were analysed by GC. Significant differences in the PL-composition, PtdCho/PtdEtn ratio and their FA composition found between the pure culture and recycled generations were the most expressed in the 1st generation. The concentration of PtdCho, which was the main PL in the pure culture, increased significantly in recycled generations at the expense of PtdEtn. PtdCho/PtdEtn ratio increased from 1.1 in the pure culture to 2.0 in the 2nd generation. The common characteristics of the FA- composition of PtdCho and PtdEtn were the significant prevalence of C16-fatty acids in all generations, the prevalence of saturated acids in the pure culture and unsaturated ones in recycled generations. It may be concluded that the brewer’ s yeasts adapts to stress conditions, among other by changing the ratio and unsaturation of PtdCho and PtdEtn species.

brewer’ s yeast; S. cerevisiae; phosphatidylcholine; phosphatidylethanolamine; fatty acids; ethanol; oxygen

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