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UBC Theses and Dissertations

The initiation of alcoholic and/or malolactic fermentations : their effect on microbes conducting Chardonnay wine fermentation and on the resulting sensorial wine profile Tantikachornkiat, Mansak


Alcoholic and malolactic fermentations are two important conversions that are involved in wine fermentation. Changes in wine microorganisms from these inoculations can modify the final wine characteristics, thus monitoring changes in microorganisms during these fermentations is necessary. Next-generation sequencing (NGS) is a technology that uses a culture independent technique to identify different species of fungi and bacteria from a sample. At present, when using this technique, it is difficult to distinguish between live and dead cells. The chemical, PMA, has been shown to bind DNA of dead cells, which prevents it from being amplified. In Chapter 2, the use of PMA were optimized, as a precursor to NGS, for accurate identification and quantification of yeast and bacterial species. In Chapter 3, the living microbial community were monitored in fermentations that differed in their yeast (S. cerevisiae) inoculation method (inoculated versus spontaneous) and their timing of bacterial (Oenococcus oeni) inoculation (inoculated during the same time of S. cerevisiae inoculation, post alcoholic fermentation, and uninoculated, which resulted in a spontaneous inoculation). Using this 2 x 3 factorial design, the effect of these factors on the strain and species relative abundance, diversity, and composition of yeast and bacteria were explored . A successful implantation (>80% relative abundance) of the S. cerevisiae inoculum were found, which resulted in changes in relative abundance for both yeast and bacterial populations and community composition as compared with spontaneous alcoholic fermentation (AF). The inoculation of the O. oeni MBR31 strain affected both bacterial communities and O. oeni strain composition with no apparent effect on yeast strain and species relative abundance, diversity and composition. An interactive effect was found, where the bacteria in spontaneous alcoholic fermentations (AF) as compared with those in inoculated AF were more easily influenced by O. oeni inoculations. Sensorial profiles indicated that inoculation of both O. oeni and S. cerevisiae changed final wine sensorial attributes. Different timing of O. oeni inoculation treatments resulted in a smaller change in the bacterial community and wine attributes compared with adding or not adding S. cerevisiae. Results suggest that fermentations without an addition of yeast inoculum had higher yeast species and strain diversity, which correlated with higher positive sensorial attributes of the wine, such as body, long finish, tropical fruit flavors as well as butter and vanilla aromas. Different timing of O. oeni inoculation affect O. oeni strain composition and bacterial species diversity and composition with no apparent correlation between microbial changes and the final wine sensorial profiles.

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