Ecología de levaduras: Selección y adaptación a fermentaciones vínicas
This thesis had two different parts: Yeast ecology and selection and adaptive mechanisms for fermentations at low temperatures.<br/>The aim of the first part was to study the yeast ecology of two Spanish wine regions (Terra Alta and Priorat). This study was used to select some yeasts for ferme...
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| Formato: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2002 |
| País: | España |
| Recursos: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/8643 |
| Acesso em linha: | http://www.tdx.cat/TDX-0621102-115207 http://hdl.handle.net/10803/8643 |
| Access Level: | acceso abierto |
| Palavra-chave: | fermentaciones vínicas levaduras 663/664 |
| Resumo: | This thesis had two different parts: Yeast ecology and selection and adaptive mechanisms for fermentations at low temperatures.<br/>The aim of the first part was to study the yeast ecology of two Spanish wine regions (Terra Alta and Priorat). This study was used to select some yeasts for fermentation starters.<br/>This study confirmed that non-Saccharomyces species were limited to early stages of the fermentation, being the main species Candida stellata, whilst Saccharomyces dominated towards the end of fermentation. This study presented a large variability of Saccharomyces strains (a total of 112, all of them identified as S. cerevisiae). A classic selection with this high number of strains would have been very time-consuming. Thus, we used two criteria: massive competence during fermentation, to analyse the imposition of a strain over similar ones, and fermentation temperature. The temperature clearly determines the fermentation kinetics, the development of the Saccharomyces strains and the characteristics of the final wine.<br/>The selected strains were tested in cellars of both wine regions and as consequence, strain RV1 was selected to be sold commercially for the elaboration of red wines with high ethanol content.<br/>The aim of the second part was to study the effect of low temperature (13C) on the cell membrane fatty acid composition, production of volatile compounds and intracellular evolution of some metabolites (sugars, organic acids.)<br/>The optimal membrane fluidity at low temperature was modulated by changes in the unsaturation degree in S. cerevisiae. In S. bayanus, however, the change in the unsaturated fatty acid percentage was not observed at different growth temperatures but the percentage of medium-chain fatty acids at low temperatures was higher. Anyway, more strains should be tested to make any conclusion.<br/>In the study of intracellular metabolites, we observed that citric acid was the main intracellular acid in the middle stages of fermentation. However, tartaric acid, which was practically undetectable until mid fermentation, was clearly accumulated in the latter stages of the process. This accumulation was unexpected because this acid was not metabolised by S. cerevisiae.<br/>Further studies about the effect of the organic acids on the alcoholic fermentation were done. The most important result was that in a defined medium with ammonium sulphate as nitrogen source, an organic acid was necessary in order to prevent stuck fermentations. The effect of these acids on the fermentation seems to be not only related to its buffering capacity, but to the role of these acids inside the cells that remains unclear yet. Also, it is not known how these acids cross the membrane, although our results suggested a regulated transport.<br/>If instead ammonium, amino acids are used as nitrogen source, the fermentation finished without problems in absence of organic acids and the acidification of the media was lower. This lower acidification by amino acids was caused by a different transport mechanism of these compounds inside the cells. The nitrogen source also influences the cell fatty acid composition and the production of volatile compounds. |
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