Uptake of Linoleic Acid by Cropped Brewer's Yeast and its Incorporation in Cellular Lipid Fractions

Previous results have indicated that supplementation of stationary-phase cropped brewer's yeast with the unsaturated fatty acid linoleic acid is a good alternative to wort aeration with respect to its fermentation performance in a subsequent fermentation cycle. The experiments were carried out with a well-defined fermentation medium. Here, we show that, also with beer wort, the cropped yeast that was suspended in fermented wort and under nongrowing conditions rapidly incorporated the exogenous y acid. Linoleic acid is also taken up by spheroplasts, which excludes the possibility that it is adsorbed onto the cell walls. The intracellular localization of linoleic acid was studied. It was rapidly recovered from the free fatty acids pool, diglycerides, triglycerides, and phospholipids. The highest amounts were recovered from the neutral lipids and the free fatty acids fractions. The results obtained with yeast first grown under stirred conditions were the same as those obtained with yeast grown under nonstirred conditions. The results with the stationary-phase cells are discussed with respect to results obtained with cropped yeast suspended in fresh wort under growing conditions. Some differences in uptake were also found when the cropped yeast was suspended and supplemented in water rather than in fermented wort. Further studies are required to investigate the fermentation performance of the supplemented yeast in a subsequent fermentation cycle.