| Yeasts isolated from must before and during fermentation at a wine cellar were characterised using PCR/RFLP and PCR/TTGE. S. cerevisiae strains were differentiated using mtDNA restriction analysis. Direct PCR-TTGE was also used to study biodiversity during wine fermentation, and revealed the variations in the population. It was observed that isolation by conventional plating may afford a skewed view of the strains taking part in wine fermentation.; Polygalacturonase activity in S. cerevisiae wine yeast strains was also studied. In the 61 assayed strains, was a great variability of results, for it a simple and repetitive quantification was completed method of using polygalacturonic acid as substrate. On the other hand it was analyzed by PCR and Southern the presence of the PGU1 gene, encoding polygalacturonase activity, showing that some strains had it and they did not express this activity and others in which it was not amplified and that did not have activity, reason why the presence of the gene could be used like a genetic marker.; A pectynolytic industrial yeast strain of S. cerevisiae containing the S. cerevisiae PGU1 endopolygalacturonase gene constitutively expressed under the PGK1 promoter was generated. The new strain contains DNA derived exclusively from yeast and expresses a high polygalacturonic acid hydrolyzing activity. Microvinifications on white and red must were made, being that the extraction of the color and the must yield were significantly higher whereas the content in ethanol and the volatile ones analyzed were not modified.; beta-glucosidasic activity was also assayed in S. cerevisiae strains, finding that some of them could break the glycosidic bonds of some of the synthetic substrates depending on the conditions of growth. On the other hand, the hydrolysis of glycosides of moscatel must by different Saccharomyces and non Saccharomyces strains was analyzed. Of all the tried strains, Hanseniaspora uvarum, was the one that released a range of volatile analyzed by CG-MS. Finally, the glycosidic aromatic precursors of white grapes of neutral varieties by means of their chemical and enzymatic hydrolysis, and the effect of a S. cerevisiae wine strain were studied. |
