Authors
Advisor(s)
Abstract(s)
A acumulação de fenóis voláteis em vinhos tem causado grande preocupação na
enologia moderna, sendo considerado, nos dias de hoje, um ponto-chave no controlo da
qualidade dos vinhos. Os vinilfenóis (4-vinilfenol e 4-vinilguaiacol) e etilfenóis (4-
etilfenol e 4-etilguaiacol) podem ser produzidos nos vinhos na sequência de atividade
microbiana dando origem a odores e sabores indesejados geralmente descritos como
“couro”, “suor de cavalo”, “animal” e “medicinal”. A origem exata dos fenóis voláteis
tem sido pesquisada em diferentes estudos de diferentes autores. A produção destes
compostos tem sido reconhecida como uma característica importante das leveduras
Brettanomyces/Dekkera.
O objetivo deste trabalho é a caracterização da conversão metabólica da levedura
Brettanomyces/Dekkera, nomeadamente no que respeita à atividade das enzimas
hidroxicinamato descarboxilase e vinilfenol reductase usando diferentes precursores
para a produção de 4-etilfenol.
Foi observado que os ácidos p-cumárico e ácido florético não têm influência
significativa no crescimento de D. bruxellensis e D. anomala nas concentrações testadas
(até 500 mg L-1) A enzima hidroxicinamato descarboxilase mostrou ter afinidade para
substratos contendo a ligação dupla no grupo carboxílico (para os ácidos
hidroxicinâmicos). A posição do grupo –OH também demonstrou ter influencia no
funcionamento da enzima e consequente produção de 4-etilfenol. O ácido florético não
foi transformado em 4-etilfenol por Dekkera/Brettanomyces. Todas as estirpes
metabolizaram (totalmente ou parcialmente) os precursores, ácido p-cumárico e 4-
vinilfenol a 4-etilfenol.
The accumulation of volatile phenols in wine has been a cause of great concern in modern enology, being considered, nowadays, a key point in the control of wine quality. Vinylphenols (4-vinylphenol and 4 vinylguaiacol) and ethylphenols (4- ethylphenol and 4-ehtylguaiacol) may be produced in wine, in a sequence pathway, due to microbial activity, imparting undesirable odours and flavours commonly described as “leather”, “horse sweat”, “animal” and “medicinal”. The precise origin(s) of volatile phenols has been under discussion for some time. The production of these compounds has been recognised as an important characteristic of the yeast Brettanomyces/Dekkera. It is aimed in this work to characterize growth and metabolic activity of Brettanomyces/Dekkera in particular as regards the activity of the enzymes hidroxicinamato decarboxylase and vinylphenol reductase using different precursors for the production of 4-ethylphenol. It was identified that the p-coumaric acid and phloretic acid have no significant influence on the growth of D. bruxellensis and D. anomala. The enzyme hidroxicinamate decarboxylase showed specificity towards precursors with a double bond at the carboxylic group (hydroxycinnamic acids). The position of the substituent - OH group also shown to have influence on the functioning of the enzyme and subsequent production of 4-ethylphenol. Phloretic acid was metabolized but not in 4- ethylphenol. All tested strains converted p-coumaric acid and vinylphenol to 4- ethylphenol, although to different extents.
The accumulation of volatile phenols in wine has been a cause of great concern in modern enology, being considered, nowadays, a key point in the control of wine quality. Vinylphenols (4-vinylphenol and 4 vinylguaiacol) and ethylphenols (4- ethylphenol and 4-ehtylguaiacol) may be produced in wine, in a sequence pathway, due to microbial activity, imparting undesirable odours and flavours commonly described as “leather”, “horse sweat”, “animal” and “medicinal”. The precise origin(s) of volatile phenols has been under discussion for some time. The production of these compounds has been recognised as an important characteristic of the yeast Brettanomyces/Dekkera. It is aimed in this work to characterize growth and metabolic activity of Brettanomyces/Dekkera in particular as regards the activity of the enzymes hidroxicinamato decarboxylase and vinylphenol reductase using different precursors for the production of 4-ethylphenol. It was identified that the p-coumaric acid and phloretic acid have no significant influence on the growth of D. bruxellensis and D. anomala. The enzyme hidroxicinamate decarboxylase showed specificity towards precursors with a double bond at the carboxylic group (hydroxycinnamic acids). The position of the substituent - OH group also shown to have influence on the functioning of the enzyme and subsequent production of 4-ethylphenol. Phloretic acid was metabolized but not in 4- ethylphenol. All tested strains converted p-coumaric acid and vinylphenol to 4- ethylphenol, although to different extents.