Vendrame, Marco
Study of Oenococcus oeni to improve wine quality [Tesi di dottorato]
Università degli Studi di Udine, 2013-03-22

Lactic acid bacteria (LAB) are, besides yeasts, the best adapted microbial family to wine conditions. Many genera have been isolated both from grape must and wine, and they represent an important resource in winemaking since most of them are able to perform malolactic fermentation (MLF), the conversion of L-malic acid into L-lactic acid, which is often required to obtain wines with positive flavor and taste characteristics, but has to be avoided in some cases. Among LAB, Oenococcus oeni is without any doubt the best adapted species to the wine environment, and is often used as a starter to perform MLF. However, this step in winemaking is often difficult to induce and control. Moreover, this microorganism requires up to 10 days to grow and develop countable colonies on plate using classical microbiological methods to enumerate viable cells, and the control of the inoculation, as well as the evaluation of the presence or absence of O. oeni in a sample, requires usually a considerable amount of time. For these reasons one of the purposes of this research project was the development of a Propidium monoazide - quantitative PCR (PMA-qPCR) technique for the fast enumeration of O. oeni in must and wine, and the results obtained show how the developed technique is able to provide a detection limit (0.33 log CFU/mL in must and 0.69 log CFU/mL in wine) which is lower than all of the other molecular biology techniques developed until now. Furthermore, to better understand which conditions are the most favorable for a successful MLF, a Reverse Transcription – quantitative PCR (RT-qPCR) technique has been developed to study the gene expression levels of the mleA gene, encoding for the malolactic enzyme, in O. oeni. The results obtained show that co-inoculation with Saccharomyces cerevisiae and high concentrations of ethanol in the medium are the best conditions to ensure high levels of transcription of the mleA gene. Besides the capacity of performing MLF, LAB are capable to influence the aromatic complexity of wine thanks to the release of volatile compounds due to the activity of the ?-glucosidase enzyme, which has been isolated in various strains, including O. oeni. For this reason, the last purpose of this work has been the development of a RT-qPCR technique to find out which winemaking practice (sequential inoculation or co-inoculation) is the best to ensure high levels of transcription of the gene encoding for the ?-glucosidase enzyme. Results point out that during co-inoculation higher levels of expression are registered. Therefore, and although winemakers try often to avoid this practice, co-inoculation can be considered the best winemaking scenario to ensure both rapid completion of MLF and expression of ?-glucosidase encoding gene, which can lead to the release of positive aromatic volatile compounds in wine.

diritti: info:eu-repo/semantics/openAccess
In relazione con info:eu-repo/semantics/altIdentifier/hdl/11390/1132690
Vendrame, Marco
Settore AGR/16 - - Microbiologia Agraria

Tesi di dottorato. | Lingua: Inglese. | Paese: | BID: TD18003804