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Title: Avaliação da tolerância ao selénio de diferentes espécies de leveduras em ensaios de fermentação
Author: Assunção, Mónica Alexandra da Silva
Advisor: Couto, Maria Margarida dos Santos
Martins, Maria Luísa Louro
Keywords: yeast
oxidative stress
Defense Date: 2011
Publisher: ISA/UTL
Citation: Assunção, Mónica Alexandra da Silva - Avaliação da tolerância ao selénio de diferentes espécies de leveduras em ensaios de fermentação. Lisboa, ISA, 2011
Abstract: Selenium is an essential trace element that has raised great interest because of its antioxidant and anti-carcinogenic properties. The development of nutritional supplements fortified with selenium is a way to increase intake. Some of these supplements contain inorganic selenium, mainly sodium selenate. There are also some supplements of selenium preparations made from the yeast Saccharomyces cerevisiae enriched with selenium. The yeast Saccharomyces cerevisiae has the ability to transform inorganic selenium into organic compounds and, depending on growing conditions, can accumulate high amounts of selenium (up to 3 000 mg kg-1) and turn it into selenomethionine. This work aimed to study the tolerance of different strains of yeast to selenium and evaluate the possibility of producing selenium-enriched wine yeasts cells. In this study, tests of cell viability in the presence of increasing concentrations of Se (0 μg mL-1, 5 μg mL-1, 100 μg mL-1 ) using strains of six different species of yeast, namely, C. zemplinina EVN 1154, H. guilliermondii EVN 390, H. uvarum EVN1117, L. thermotolerans EVN 372, S. cerevisiae EVN 166 and T. delbrueckii EVN 1141 were performed. These trials showed that the most tolerant yeast to selenium levels of 100 μg mL-1 was the Torulaspora delbrueckii EVN 1141. The yeast strain H. uvarum EVN1117 proved to be the most sensitive to Se. The determination of protein and antioxidant enzyme activities showed that the response to the toxic effect of selenium varies among species and according to the concentration of selenium applied. Yeasts that showed better response were the S. cerevisiae EVN 166 and H. guilliermondii EVN 390, for concentrations of 250 μg mL-1 and 100 μg mL-1, respectively. The fermentations were performed in the grape must from Seara Nova Portuguese variety with the yeast species S. cerevisiae and T. delbrueckii in two modalities, without selenium and selenium-enriched cells (grown in medium with 5 μg mL-1 selenium). Fermentations were performed using T. delbrueckii and S. cerevisiae without selenium and selenium-enriched cells during 25 days. In order to assess the evolution of fermentation, samples were taken after 25 days of fermentation for determination of sugars (g L-1), alcohol by volume (% v / v), pH, total acidity (g tartaric acid L -1) and volatile acidity (acetic acid g dm-3). The fermentations with the yeast T. delbrueckii was slower compared to the fermentation using the S. cerevisiae yeast. The fermentation with the selenium-enriched cells presented, at the end of fermentation, higher concentration values of sugars and lower alcohol levels compared to the fermentation using yeast cells without selenium, indicating a negative effect of selenium in the fermentation process. V The concentration of total sugars and the levels of ethanol reached at the end fermentation lead to the conclusion that only the yeast S. cerevisiae had a more complete fermentation. The fermented with the yeast S. cerevisiae and T. delbrueckii with and without selenium-enrichment cells is reported to have identical pH and total acidity, which indicated that selenium did not interfered with these parameters. On the contrary, fermentation with selenium-enrichment T. delbrueckii increased significantly the volatile acidity of the fermented must. The fermented must obtained selenium-enriched S. cerevisiae yeast reached the highest concentration of selenium, after 25 days of fermentation. Having reached values of selenium of about 84,01 μg L-1 which may be related to the fact that the fermentation was more complete, with values of total sugars of 15,75 g L-1 while the fermentation with the yeast T. delbrueckii showed a total sugar content of 89,31 g L-1 at the end of fermentation. The results are preliminary, but allowed to evaluate the possibility of using selenium-enriched cells to produce wine, and will allow future studies on full-scale vinification processes for potential industrial use.
Description: Mestrado em Engenharia Alimentar - Instituto Superior de Agronomia
Appears in Collections:BISA - Dissertações de Mestrado / Master Thesis

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