engleski

The ratio and fatty acid composition of brewer’ s yeast phospholipids change with recycling

Normal practice in beer production is yeast recycling. It is theoretically unlimited, but usually reduced to only few cycles because stress factors impair yeast growth and fermentative performance. Beside the toxic effect of ethanol, oxygen depletion is of special importance for bottom-fermenting brewer’ s yeast. A common response of the yeast cells exposed to ethanol is the change of phospholipid (PL) composition and increased unsaturation of their fatty acids (FA). On the other hand, biosynthesis of unsaturated FAs under anaerobic conditions is limited. The aim of this study was to investigate the changes of content and composition of PL species of the whole cells and plasma membrane of brewer’ s yeast which occur with recycling. Pure culture and three recycled generations of bottom-fermenting brewer’ s yeast of Saccharomyces cerevisiae strain were analysed. Cell content of PI was significantly increased in recycled yeast generations, while the content of PS did not show significant changes. In the plasma membrane the content of PI decreased with recycling, while the content of PS after decrease in the 1st generation increased, and became almost equal to PI in the 3rd generation. The ratio of PI/PS in the whole cells and plasma membrane as well, showed similar pattern: the increase in the 1st and then decrease to the 3rd generation, which was more expressed in the plasma membrane. Characteristic of FA composition of PI and PS of the whole cells was significant prevalence of C16-FAs. Palmitic acid was the main one accounting for more than 35% in all generations. While in PI saturated FAs prevailed significantly, in PS unsaturated FAs prevailed in all recycled generations. In conclusion we may say that the ratio of PI/PS, as well as their FA composition varied with recycling. The PI/PS profile, similar for some other parameters, may be attributed to stress response in the 1st and gradual adaptation of the yeast cells to unfavourable conditions in the later generations.

fatty acids; phospholipids; brewer’ s yeast

nije evidentirano