This research was concerned with testing a hypothesis that brewer’s yeast cells, which were physiologically “preconditioned” with Mg ions, had improved fermentative output and stress tolerance. Ale and lager yeast cells preconditioned in the presence of elevated levels of Mg-actate, yielded highest cellular Mg contents in malt extract broth and dilute brewer’s wort media. Mg-acetate preconditioned lager yeast cells exhibited higher fermentative activities than non-preconditioned yeasts, resulting in higher yields of ethanol. The specific activity of the alcohologenic enzyme pyruvate decarboxylase was stimulated by Mg enrichment and a correlation between cellular Mg and PDC activity exists. This was especially evident in Mg acetate preconditioned cells. Mg ion homeostasis in Mg non-and preconditioned yeast cells was altered by temperature shock (both cold shock at 4°C and heat shock at 40°C) and toxic ethanol shock (at 10-20%). This resulted in significant cellular losses of Mg, which indicated that some of the extra Mg present in these cells was in a free (releasable) form rather than being tightly bound. Stress tolerance was found to be strain specific with lager yeast cells found to be more tolerant to low temperature stress (4°C) and ale yeast cells more tolerant to high temperature stress (40°C). The results of this study showed that intracellular Mg is beneficial to brewing yeasts at two levels: at the biochemical level to stimulate fermentative enzymes; and at the biophysical level to protect the structural integrity of the plasma membrane in stressed cells. This study has highlighted gaining a fundamental insight into aspects of yeast physiology may prove of direct practical value to industries concerned with production of ethyl alcohol by fermentation.
|Date of Award||Nov 2001|
|Supervisor||Graeme Walker (Supervisor)|