Boscaino, Floriana (2015) SELECTION AND USE OF YEAST STRAINS ISOLATED FROM AUTOCHTHONOUS SOUTHERN ITALY GRAPEWINE CULTIVARS AND IMPACT ON AROMA PROFILE OF PRODUCED WINES. [Tesi di dottorato]

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Abstract

Today, the use of selected commercial yeasts (LSA) from Saccharomyces species "sensu stricto" is widespread, because it allows to minimize risks in the production process, to standardize the winemaking procedure and ensure the quality of the final product. On the other hand, the widespread use of starter cultures in the wine industry has resulted in a loss of wine sensory characteristics and in a flattening of those differences crucial to distinguish wines of different cultivars. For this reason, the research is focused on studying new selected yeast cultures that can give a final product enrich of those aromatic compounds which enhance the character of the wine. It is known that the production of many of this aromatic molecules occurs due to the presence of non-Saccharomyces yeasts, found on the grapes and must. These non-Saccharomyces yeast strains predominate in the first phase of the alcoholic fermentation, are able to release metabolites and enzymes, responsible of the aromatic complexity of the wine. Indeed, experimental tests have shown the positive role of non-Saccharomyces yeasts in the fermentation, improving the behavior of the starter and increasing the complexity of the composition of the wine, in particular, the chemical and sensory properties. The biochemical transformation of flavour-inactive grape juice constituents into aromatic components has emerged, as an important, additional mechanism whereby yeasts substantially impact on wine aroma and flavour and facilitate greater expression of grape varietal character. In addition to ethanol, produced of the primary alcoholic fermentation, there are numerous compounds such as esters, higher alcohols, aldehydes, acids, terpenes, ketones, that determine the final quality of the product. The yeasts have the ability to produce these compounds, but it is the quantitative level that determines the difference between the different species and then, within the same species, between different biotypes. The wine yeasts for starter culture development have been sourced from grapes, winery environment or old cellars and spontaneous fermentations that have given wines of acceptable or unique quality. They are selected based on characteristics such as vigor fermentative, alcoholigenous power and they should be tolerant to the antioxidant and antimicrobial compounds, produce minimal foam, as well as produce a balanced array of flavour metabolites, without undesirable excess of volatile compounds and produce enzymes that transform the neutral compounds in flavor active component. Glycosidases and esterases are some of the enzymes produced by yeasts that can make a significant contribution to the aroma of the wine. In particular, the non-Saccharomyces yeasts have more enzymatic activities respect to yeasts S. cerevisiae. The aim of this work was the selection and use of autochthonous yeast strains isolated from cultivars of "Vitis Vinifera" of southern Italy and their impact on aroma profile of wines. We have tested different combination of autochthonous yeasts (S. cerevisiae and non-Saccharomyces) to improve the quality and organoleptic characteristics of the final product but also to emphasize its link with the territory and the ancient wine cultivars. In order to evaluated the aromatic profile, the different wine samples were characterized by Solid Phase Micro Extraction-Gas Crhomatography/Mass Spectrometry (SPME-GC/MS technique).

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