Yeast diversity and persistence in botrytis-affected wine fermentations

Culture-dependent and -independent methods were used to examine the yeast diversity present in botrytis-affected ("botrytized") wine fermentations carried out at high ( approximately 30 degrees C) and ambient ( approximately 20 degrees C) temperatures. Fermentations at both temperatures possessed similar populations of Saccharomyces, Hanseniaspora, Pichia, Metschnikowia, Kluyveromyces, and Candida species. However, higher populations of non-Saccharomyces yeasts persisted in ambient-temperature fermentations, with Candida and, to a lesser extent, Kluyveromyces species remaining long after the fermentation was dominated by Saccharomyces. In general, denaturing gradient gel electrophoresis profiles of yeast ribosomal DNA or rRNA amplified from the fermentation samples correlated well with the plating data. The direct molecular methods also revealed a Hanseniaspora osmophila population not identified in the plating analysis. rRNA analysis also indicated a large population (>10(6) cells per ml) of a nonculturable Candida strain in the high-temperature fermentation. Monoculture analysis of the Candida isolate indicated an extreme fructophilic phenotype and correlated with an increased glucose/fructose ratio in fermentations containing higher populations of Candida. Analysis of wine fermentation microbial ecology by using both culture-dependent and -independent methods reveals the complexity of yeast interactions enriched during spontaneous fermentations.

Typing of non-Saccharomyces yeasts with enzymatic activities of interest in wine-making

Enzymatic activity of potential interest in wine-making was studied for 182 non-Saccharomyces yeasts isolated from musts before and at the onset of fermentation at wine cellars operating under the La Mancha Appellation of Origin in Spain. Tests were carried out on plates containing differential substrates appropriate for each case (casein, gelatin, polygalacturonic acid, and arbutin) to determine whether each of the isolates exhibited proteolytic, polygalacturonase, and beta-glucosidase activities. Nearly 80% of the wild yeasts possessed one or more enzymes of biotechnological interest. Once the enzymatic activities of the isolates had been established, 69 of the isolates that exhibited pronounced enzymatic activity and 11 randomly selected isolates that were devoid of any activity were typed using PCR/RFLP, which gave 13 different molecular profiles. The isolates for each of the profiles were then identified by classical methods. The enzyme beta-glucosidase was linked to the species Metschnikowia pulcherrima, and polygalacturonase activity was common in most of the species identified. Proteolytic activity was observed in Pichia membranifaciens and in Metschnikowia pulcherrima. Typing revealed the possibility of intraspecific differences in Pichia membranifaciens, because six different molecular profiles with one or more shared restriction bands were recorded for that species.