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Yeast: Difference between revisions
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Kerr et al. (2018), used SWATH-MS to understand the causes of the flocculation behavior of yeast and to identify differences between brewing strains. Flocculation is important at the end of fermentation, in which yeast cells adhere together to form large flocs. This phenotype is highly desired after fermentation, as it allows easy removal of yeast cells from the beer (Govender et al., 2011; Verstrepen et al., 2003). Differences in Flo10 and Flo1/5 proteins responsible for flocculation behaviors were found in the cell walls of industrially relevant yeast (Kerr et al., 2018). This study also identified YIQ9, a homolog to Cfg1 (Carlsbergensis foaming gene) (Blasco et al., 2012; Kerr et al., 2018), in brewing yeasts, which was absent in the laboratory strain BY4743. Further, large differences were found between strains at the level of the global whole cell proteome (Kerr et al., 2018).<ref name=kerr>Kerr ED, Fox GP, Schulz BL. [https://www.sciencedirect.com/science/article/pii/B9780081005965228692 Grass to glass: Better beer through proteomics.] In: Cifuentes A, ed. ''Comprehensive Foodomics.'' Elsevier; 2020:407–416.</ref> | Kerr et al. (2018), used SWATH-MS to understand the causes of the flocculation behavior of yeast and to identify differences between brewing strains. Flocculation is important at the end of fermentation, in which yeast cells adhere together to form large flocs. This phenotype is highly desired after fermentation, as it allows easy removal of yeast cells from the beer (Govender et al., 2011; Verstrepen et al., 2003). Differences in Flo10 and Flo1/5 proteins responsible for flocculation behaviors were found in the cell walls of industrially relevant yeast (Kerr et al., 2018). This study also identified YIQ9, a homolog to Cfg1 (Carlsbergensis foaming gene) (Blasco et al., 2012; Kerr et al., 2018), in brewing yeasts, which was absent in the laboratory strain BY4743. Further, large differences were found between strains at the level of the global whole cell proteome (Kerr et al., 2018).<ref name=kerr>Kerr ED, Fox GP, Schulz BL. [https://www.sciencedirect.com/science/article/pii/B9780081005965228692 Grass to glass: Better beer through proteomics.] In: Cifuentes A, ed. ''Comprehensive Foodomics.'' Elsevier; 2020:407–416.</ref> | ||
Protein thiols are effective against inhibition of yeast growth in the presence of reactive oxygen species.<ref>Wu MJ, Rogers PJ, Clarke FM. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.17 125<sup>th</sup> anniversary review: The role of proteins in beer redox stability.] ''J Inst Brew.'' 2012;118(1):1–11.</ref> | Protein thiols are effective against inhibition of yeast growth in the presence of reactive oxygen species.<ref>Wu MJ, Rogers PJ, Clarke FM. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.17 125<sup>th</sup> anniversary review: The role of proteins in beer redox stability.] ''J Inst Brew.'' 2012;118(1):1–11.</ref> Yeast thioredoxin (TRX) is another thiol-rich candidate ripe for consideration as a functional element of anti-ROS cascades. At one time we anticipated that TRX, which is secreted by yeast during fermentation, could be linked to beer stability. That was in fact the start of our move into beer proteomics. Yeast cells protect themselves against oxidative stress with interlinking processes that can transfer electrons within cells to where they are needed to quench reactive oxygen species. More contentiously, they can transfer reducing equivalents to outside the cell, where presumably they may carry out different or perhaps the same defence strategies. The trouble with this view, at least on face value, is that, outside the cell, the rest of the machinery for recycling oxidized TRX is just not present. Yet it might be possible — if yeast happens to secrete small thiols like cysteine as some mammalian cells do — this might be how LTP is reduced during fermentation after probably being oxidized in the wort and in the kettle. Taking together the data of beer proteomics and thiol proteins, we propose that there could be a thiol-based cycle operating in beer that involves oxidized thiols and reversible reduction after peroxide destruction using sulfite or some reductant molecules.<ref name=wu/> | ||