The replicative lifespan of an individual cell of the yeast Saccharomyces cerevisiae is finite. As many other cells, yeast cells age and undergo modifications in terms of physiology, morphology, and gene expression during that process. These changes on the single-cell level influence sugar uptake, alcohol and flavour production, and the flocculation properties of the cell.
The cell age also affect the fermentative activity, which defines the production of CO2 per cell. Together with other yeast metabolites, CO2 influences dough rheology, brad texture, volume, and taste and is thus of critical importance for the final bread quality. In addition, industrial baker’s yeast strains suffer from a variety of different stressors throughout the dough fermentation process (e.g. osmotic stress, cold shock, nutrient starvation,…). Undergoing the process of aging, the stress tolerance of yeast cells changes severely.
Furthermore, yeasts are facultative anaerobes, and can grow in a respiratory or fermentative mode. However, the yield of biomass is increased under respiratory conditions, as no carbon is lost on the production of by-products like glycerol or ethanol. The respiratory activity is dependent on the activity and number of mitochondria, which changes as cells undergo the process of aging. On the other side, the high respiratory activity causes oxidative damage on the cellular level.
All the above mentioned make the aging properties an important parameter for strain development and zoptimization in the areas of the brewing (e.g. beer and wine), dough fermentation, and food-grade production of yeast (e.g. yeast extract as a natural flavour enhancer).
While the optimization parameter “age” is being used in classical breeding for centuries, etc. to breed cattle with the highest productivity for a particular and maximal timespan.
Using the HAPPY chip, the RLS can be used as an optimization parameter during strain development for the first time. Comparing the RLS of different potential production strains provides e.g. a tool to normalize the production yields. RLS determination also allows a differentiation between product formation by young (even virgin) cells compared to mature cells, or even cells that are not dividing anymore. Thus, a rational strain development towards shorter or longer living cells will be possible.