Abstract
The efficiency and efficacy of alcoholic fermentation by yeast is crucial for the winemaking process. Sluggish or arrested fermentations can negatively impact winery operations and wine quality. Here we present a novel mechanism by which problem fermentations can arise. Yeast can induce a prion known as [GAR+] that allows the cell to circumvent glucose repression of alternative carbon substrates. We have confirmed that strain UCD932 can spontaneously generate the [GAR+] phenotype, and that this phenotype exhibits the genetic traits of a prion. Differences were observed in the fermentative behavior of UCD932 wild-type [gar−] vs. [GAR+] yeasts in laboratory scale model juice fermentations. To further understand these differences, fermentations were performed in Chardonnay juice to study the interaction of the [GAR+] prion and presence of SO2 on fermentation kinetics, bacterial community composition, and volatile compound production. Cells harboring the [GAR+] prion displayed reduced fermentation capacity, which was especially evident in the absence of SO2. Presence of SO2 and time in fermentation had the most significant effect on the types of bacteria present. However [GAR+] yeasts without added SO2 were especially sensitive to bacterial competition. This difference was also reflected in the bacterial and volatile profiles of the finished wine. We hypothesize that the bacterial induction of the [GAR+] prion by yeast during fermentation is another possible mechanism by which stuck/sluggish fermentations may become established.
- Saccharomyces
- sulfur dioxide (SO2)
- [GAR+] prion
- lactic Acid Bacteria (LABs)
- glycerol glucosamine media (GGM)
- minimal must media (MMM)
- ©2016 by the American Society for Enology and Viticulture
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