Moynihan, E. A.1, Smart, K. A.2, James, S. M.2 and Powell, C.3, (1)University Of Nottingham, Nottingham, UNITED KINGDOM, (2)SABMiller Plc, Woking, UNITED KINGDOM, (3)University Of Nottingham, Loughborough, UNITED KINGDOM
Technical Session 4: Yeast
Monday, June 05, 2017
3:30–4:45 p.m.
Camellia AB
Yeast quality is integral to ensuring consistency during fermentation and has a significant and direct impact on the final product. While yeast quality is often defined by the physiological characteristics or microbiological purity of a culture, the terminology also incorporates a variety of additional metrics, including the capacity of cells to function to their maximum capacity. One of the major factors that can cause populations to ferment poorly is the accumulation of mutants, arguably the most frequent of which is the “petite” mutation. Petite mutants are caused by damage to mitochondrial DNA (mtDNA) and can be found in two forms: where mtDNA is present but exists as a series of non-coding regions (ρ–), and where mitochondria are completely lacking from the cell (ρ0). These can be observed in most brewing yeast cultures at approximately 1–3% of the total cell count. However, in certain circumstances the number of petites can exceed 10–20%, at which point they begin to have a major negative impact on both the fermentation process and the final product. Fermentations conducted using cultures with an abnormal number of petite cells are typically slow with a less efficient conversion of sugar to alcohol, and produce beer with a range of flavor defects. The underlying causes behind the development of the petite mutation in brewing yeast are currently poorly understood. In this study we aim to elucidate the relationship between yeast handling practices and the development of the petite mutation, using a number of both lager and ale production strains. Specifically, we investigate conditions associated with propagation, fermentation and yeast storage and determine the impact of these on the number of mitochondria per cell, mitochondrial development and inheritance, and overall mtDNA integrity. The data presented will demonstrate the changes that occur to mitochondria during active growth and fermentation, and the precise impact of process stage on mitochondria number. We also show how mitochondria morphology changes during fermentation in response to stress factors associated with industrial processes. Finally, we determine why some industrial strains have a higher propensity to form petite mutants than others, and reveal which brewery yeast handling practices have the greatest influence on promoting mtDNA damage. It is anticipated that this data will further our understanding of the petite mutation and it is hoped that in the future it will be possible to remove or mitigate their occurrence and impact during brewery fermentations.
Eoin Moynihan is an SABMiller-funded Ph.D. student at the International Centre for Brewing Science at the University of Nottingham, U.K. Eoin holds a B.S. (honors) degree in plant biotechnology (2009) and an M.S. degree in applied biotechnology (2013), both obtained at University College of Cork, Ireland. During his M.S. degree studies, he focused on yeast diversity throughout spontaneous cider production and now is examining the role of mtDNA in brewing yeast.
