engleski

Changes in phospholipid composition and fatty acid profile during low temperature storage of baker's yeast

Baker's yeast is widely used nowadays, not only for daily fresh bakery products, but also in the production of frozen doughs. That demands the usage of freezing/thawing resistant strains, the strains which can adapt to stress evoked by low temperature and preserve fermentative performance. In order to determine the effect of low temperature on the lipids of baker’ s yeast during storage, we analysed commercial baker’ s yeast of S. cerevisiae strain, fresh (before cold storage), maintained at 4°C (7 and 14 days) and -20°C (7, 14 and 120 days). Lipid extraction was performed by Folch method. Phospholipids were quantified spectrophotometricaly after the separation by two-dimensional TLC and fatty acids by GC. In comparison to the fresh yeast, significant differences were determined in the composition of phospholipids and fatty acids of the samples maintained both at 4 and -20°C. The major changes were observed after 14 days of exposure to -20°C. In the phospholipid composition of all analysed groups the most abundant was phosphatidylcholine accounting for 42-56 mass % of total phospholipids, while phosphatidylinositol was the second one (21-28%). Phosphatidylcholine to phosphatidylethanolamine ratio, one of the parameters of adaptation capability to extracellular changes in general, varied between 2.4 and 3.3. Oleic and palmitoleic acids were by far the most abundant fatty acids in all groups (39-48% and 33-38% cell fatty acids, respectively), showing significant decrease after 14 days of exposure to -20°C. The obtained results suggest that the analysed baker's yeast has a high capability of adapting to low temperatures by changing the lipid composition, which among other makes it a freeze-tolerant strain and therefore suitable for the production of frozen doughs. Short exposure of the yeast to 4°C prior to exposure to -20°C resulted in less expressed changes in the lipid composition which could be regarded as a positive effect and potentially used as a pre-treatment method.

baker’ s yeast ; low temperature ; storage ; phospholipids ; fatty acids

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