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• W91068339 abstract "Grappa is an alcoholic beverage obtained from the distillation of grape pomace derived from grapes produced exclusively in Italy. The process of production of Grappa starts in the winery where winemaking takes place: after harvesting and grape crushing, the must is separated from grape marcs mainly composed by grape skins and seeds, with or without rasp. In the case of red winemaking, separation of marcs takes place after maceration when fermentation has already started, so that they contain alcohol and a low quantity of sugar. On the contrary, marcs obtained from white winemaking contain sugars not yet fermented. For this reason in this second case the raw vegetable material conferred to the distillery is stored for a variable period to allow alcohol production to occur. Marcs can be conserved in different manners, using silos or smaller containers such as plastic tunnels, for period lasting from few days to several weeks. During this period, the main chemical process is sugar degradation and alcohol production, carried out by yeasts, although a large number of other molecules with positive (aromatic substances) or negative (off-flavours and toxic compounds) effect can rise from the activity of the indigenous microflora. Among the technological supports (pH improvement, temperature control, anaerobic environment) developed by modern distilleries to avoid spoiling of the raw material due to unsuitable storing conditions the management of microbial populations by means of selected yeast introduction is pursued. Concerning the case of grappa, international studies are almost absent, as its production is limited by the legislation to our national territory.This study is part of a wider project, supported by Regione Veneto, concerning the selection of an yeast to be inoculated in grape marcs destined to the production of grappa. The first objective to be achieved was about the study of the composition and population dynamics of the yeast microflora of grape marcs using conventional and molecular methods present in literature or studied by the Microbiology Unit working at the Department of Agricultural Biotechnology. Two white grape varieties, namely Moscato and Prosecco, from two distinct areas of the Veneto Region, were used. Yeast counts were made at the beginning, after 4 and after 15 days of marc storage under anaerobic conditions. Seventy isolates from each sampling time were identified to species by RAPD-PCR analysis and subsequent ITS region sequencing. A good biodiversity of yeasts occurred in both marcs at the beginning of fermentation, with high presence of Hanseniaspora opuntiae, but without detectable presence of Saccharomyces strains, which instead became the dominant yeast after just 4 days of fermentation, remaining at that level until the end of fermentation. Colonization of Moscato marc by S. cerevisiae resulted better, in relation to its higher sugar content. Characterization of S. cerevisiae isolates by mitochondrial DNA restriction analysis revealed the presence of 66 different strains in the marc from the Moscato grapes, without the occurrence of a clearly dominant strain, while in the marc from the Prosecco grapes only 23 different profiles were scored, with a dominant strain that accounted for 62.7% of the Saccharomyces population after 4 days of fermentation.Subsequentely, the effects of refrigeration and acidification treatments of grape pomace on dynamics of yeast populations during the storage period have been studied. A total of 200 isolates were collected from Prosecco grape marcs acidified and non acidified, after 4 and 15 days from the beginning of storage. Identification of enological yeasts belonging to Saccharomyces sensu stricto group was performed by means of a multiplex PCR, and their characterization at strain level was achieved by mitochondrial DNA restriction analysis. Genetic analyses evidenced the development of different microbial strains in the acidified environment and in the non-acidified control. Acidification treatment, applied to inhibit bacterial microflora, disclosed to be able to influence yeast population from a qualitative rather than quantitative point of view. pH decreasing caused a great effect of selection, indeed only 18 out of 121 identified strains were found in both conditions. A total of 104 isolates identified as belonging to Saccharomyces cerevisiae group were chosen from a pool of about 1000 yeasts collected in various experimentations, from marcs of different origin or submitted to technological treatments during the ensilage period. Such isolates were grown in a synthetic must formulation in order to investigate their fermentation performances. Yeast strains isolated from Moscato grape marcs showed the best features in terms of vigour, expressed as sugar consumption after 2 and 7 days of fermentation. The level of foam production was also investigated and a sensory evaluation was conducted at the end of fermentation, mainly to evaluate possible off-flavour production. Other technological traits such as the level of resistance to the antioxidant sulphur dioxide and the hydrogen sulphide production were tested. Considering SO2 resistance all isolates are able to tolerate the concentration of 50 mg/l, commonly used in the winery. At the intermediate dose of 100 mg/l the most resistant strains come from non acidified Prosecco marc. Moreover, it is stated that microbial glycosidase activity contributes to wines and distillates aroma through the hydrolysis of non-volatile flavourless glycoconjugate precursors, which releases free terpenols and other aromatic compounds. Glycosides, composed of a terpenic hydrocarbon (aglycon) and a carbohydrate moiety, are concentrated in grape berries hence contribution of glycosidase activity is determinant for the expression of Grappa aroma. So, from all these isolates ?-glucosidase activity was rapidly screened both by using a newly developed fluorimetric method and by growing the cells in a minimal medium containing the disaccharide cellobiose as the only carbon source. Both the technological and quality traits found for all the isolates were submitted to a statistical analysis in order to detect yeast strains with the best overall characteristics, to be used as starter for distillate production. Recently the ?-glucosidase activity was suggested to be related to the major exo- ?-1,3-glucanase EXG1 of Saccharomyces cerevisiae, which is involved in processes like growth, budding and mating. For this reasons the molecular approach based on construction of mutant strains in exoglucanases genes was recently considered. In particular two deletion mutant for EXG1 and EXG2 genes respectively has been constructed, following a protocol essentially based on homology recombination. The effect of gene knock-out on ?-glucosidase activity was ascertained through fluorimetric assays, showing a little reduction in exg1 null mutant. Growth in Prosecco must was also performed, in 1L bioreactors, but fermentation curves did not reveal significative differences among strains, showing that probably deletion of exoglucanase genes do not influence yeast growth.All the showed results indicate that grape marcs of different origins or submitted tocdifferent technological treatments are a variable source of yeasts that can be selected to be inoculated as starter for grappa production." @default.
• W91068339 created "2016-06-24" @default.
• W91068339 creator A5056407429 @default.
• W91068339 date "2009-01-03" @default.
• W91068339 modified "2023-09-27" @default.
• W91068339 title "Selezione e caratterizzazione di microrganismi destinati alla produzione di distillati" @default.
• W91068339 hasPublicationYear "2009" @default.
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