The importance of stress tolerance to baker's yeast

Baker's yeasts are mostly strains of Saccharomyces cerevisiae. They are able to reproduce rapidly by aerobic metabolism, which is important to their economic efficiency for producers. They are also capable of vigorous fermentation (ie., carbon dioxide and ethanol production via glycolytic catabolism of sugars) in a variety of doughs and bread manufacturing processes, which is essential for their usefulness in the baking industry. In reality, baker's yeast never see ideal physiological conditions and are subjected to numerous stresses including, nutritional starvation, osmotic pressure, oxidation, temperature abuse, and in some cases dehydration/rehydration or freezing and thawing. Nevertheless, in order for a yeast strain to be of industrial use it must be able to adapt to unfavourable environments and to produce the necessary growth and fermentation rates. The baker's yeast industry is very competitive and the production of new strains better able to cope with the varieties of stresses encountered during growth and application is of paramount importance to manufacturers. The ease of genetic manipulation of yeast (both by classical and recombinant means) and our knowledge of the DNA sequence of S. cerevisiae, would suggest that it is easy to generate new strains with markedly improved economic perfromance. However, such improvements remain limited by our understanding of key physiological processes that determine commercially relevant traits. Thus there is a need for continued effort in fundamental research into key biological causes and effects of economically relevant traits. Indeed an improved understanding of the biological consequences of stresses and of the nature of stress response in yeast is an essential prerequisite to enhancing strains for the baking industry, and is arguably rate limiting in producing major advances in strain improvement.