Browsing Masters Degrees (Institute for Wine Biotechnology) by Subject "Alcoholic fermentation"
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- ItemInvestigating the influence of a wine yeast consortium on population dynamics, alcoholic and malolactic fermentation(Stellenbosch : Stellenbosch University, 2018-12) Janse van Rensburg, Philippe Jacques; Setati, Mathabatha Evodia; Du Toit, Maret; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture & Oenology & Institute for Wine Biotechnology.ENGLISH ABSTRACT: Non-Saccharomyces (NS) starter cultures of species such as Metschnikowia pulcherrima, Torulaspora delbrueckii, Pichia kluyveri and Lachancea thermotolerans, have received attention for their desirable properties and contributions in winemaking. These include the production of volatile compounds or enzymes to modify organoleptic attributes. Most studies have focussed on the use of single NS at a time with Saccharomyces cerevisiae to study the above contributions and properties; including effects on malolactic fermentation (MLF). However, there is growing interest in using complex multi-starter cultures to enhance wine aroma. Indeed, commercial products such as Anchor Alchemy II (Anchor Yeast), which comprises of different strains of S. cerevisiae, and Melody™ (CHR Hansen), comprising of S. cerevisiae, L. thermotolerans and T. delbrueckii in different ratios, are available. To develop such products, the understanding of genetic and phenotypic characteristics of strains and interactions amongst the different organisms is important. Consequently, some studies have investigated yeast-yeast interactions and their mechanisms, such as antagonistic interactions mediated by direct cell contact or through growth inhibitory metabolites. This, results in a decline of certain non-Saccharomyces like Hanseniaspora and therefore effect the final aroma composition. Conversely, synergistic effects can be observed in which species may be promoted to persist longer and therefore they contribute more to aroma. However, knowledge on population dynamics in multi-species starter cultures and their influence on alcoholic fermentation (AF) and MLF remains limited. The current study investigated a multi-species yeast consortium during AF and its effects on Oenococcus oeni viability during MLF. The consortium comprised of M. pulcherrima, L. thermotolerans, T. delbrueckii and S. cerevisiae. Fermentations were conducted in Chenin blanc and Pinotage at 15°C and 25°C, respectively. In all trials M. pulcherrima declined rapidly, while L. thermotolerans persisted until mid-fermentation. The best growth was observed for T. delbrueckii and it was able to persist until late fermentation stages. Fermentations that contained L. thermotolerans produced L-lactic acid in the Pinotage, but not in the Chenin blanc. There were no negative impacts observed on O. oeni populations during MLF for Pinotage and Chenin blanc wines. MLF kinetics were similar in all the Pinotage wines. In the Chenin blanc, the fastest L- malic acid consumption was displayed in wines that were fermented by L. thermotolerans and T. delbrueckii co-inoculations with S. cerevisiae. Different chemical profiles were detected using attenuated total reflection infrared (ATR-IR) spectroscopy. Mostly Chenin blanc wines were found to be significantly different from S. cerevisiae controls. Using gas chromatography, fold changes were observed for many volatile compounds. In conclusion, it is possible to predict a consortium population dynamic based on individual yeast performances in mixed fermentations. The volatile profiles are not additive between treatments and will be unique for each inoculation scheme. MLF seems to not be detrimentally affected by a consortium so long as each strain is regarded as compatible with lactic acid bacteria. Future work should include the evaluation of more yeast species and at alternate inoculation levels. Additionally, the inclusion of Lactobacillus plantarum for MLF needs to be investigated and quantification of detected volatiles should be performed.
- ItemMultispecies interactions in a simplified wine yeast consortium(Stellenbosch : Stellenbosch University, 2018-03) Nutt, John; Bauer, Florian; Setati, Mathabatha Evodia; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: Over the last two decades various studies have evaluated the impact of non-Saccharomyces (NS) yeasts on alcoholic fermentation of wine, the chemical imprint they leave in the wine and how this affects wine quality. These NS yeasts are either present naturally in the grape must or inoculated together with Saccharomyces cerevisiae, but little is known about how these NS interact with each other and with S. cerevisiae and how these interactions might influence the presences of other yeast during fermentation and ultimately affect the contribution of each yeast to the wine. In recent years, several strains of the species, Torulaspora delbrueckii, Pichia kluyveri, Metschnikowia pulcherrima and Lachancea thermotolerans have been commercialized. The availability of such commercial preparations allows winemakers to perform mixed-culture fermentations through different inoculation strategies. Research has evaluated co-inoculations and sequential inoculations between NS and S. cerevisiae, but grape must is a complex ecosystem with a large variety of indigenous yeasts that partake during fermentation. Understanding how various yeasts interact within such a larger matrix is challenging, but will make an essential contribution to sound decision making in wineries. This study was designed to better understand how NS yeasts perform individually and how their behaviour might differ in the presence of one or more other yeasts and what effect this might have on the final wine. Three commercial NS yeasts strains and one S. cerevisiae yeast strain were used to determine how these yeasts interact and how these interactions might alter the chemical composition of wine. Fifteen inoculations scenarios, including mono-culture, co-culture and combinations of three and ultimately a consortium containing all four yeasts were performed. Fermentations were carried out in synthetic grape juice at both 15°C and 25°C. The data showed significant variations in the cell densities of all species through-out fermentation depending on the nature of the co-inoculated species and the environmental conditions. These changes in population dynamics also had a clear impact on the concentration of and types of aromatic compounds produced. Chenin blanc wines made with the consortium of all four yeasts, S. cerevisiae and spontaneous fermentations, showed distinct chemical profiles. However, no correlation was found, regarding population dynamics or aroma profiles of the wines, between the synthetic wine and the Chenin blanc wines both derived from the consortium inoculation. This study provides the foundation for future work on understanding how multiple species (more than two yeasts) interact within fermentations and how this will affect wine quality. It also provides a better understanding of how one yeast can suppress the presence of other yeasts and how different temperatures might affect the presence of each yeasts and how this might influence the interactions between the yeasts.