http://hdl.handle.net/10362/3606 Wed, 19 Jun 2013 13:05:50 GMT 2013-06-19T13:05:50Z http://hdl.handle.net/10362/8554 Title: Biogenic amines in wine: gene transcription as a tool for selection of Oenococcus oeni starter strains Authors: Marques, Ana Paula Gomes Abstract: Wine is a complex environment where the microbial flora can have both a positive (e.g. malolactic fermentation) and a negative (e.g. production of biogenic amines) impact on the quality of wine. Biogenic amines are nitrogenous compounds of low molecular weight that can be found in fermented food and beverages, including wine. Biogenic amines are formed primarily by decarboxylation of the corresponding amino acids by microorganisms through substrate-specific decarboxylases. Some authors consider the presence of biogenic amines to be a fundamental parameter for detriment of alcoholic beverages. These compounds can have adverse health effects on sensitive individuals at high concentrations. The role of microorganisms in wine involves two important fermentation processes, the alcoholic fermentation conducted by yeasts and the malolactic fermentation conducted by lactic acid bacteria. The malolactic fermentation refers to the conversion of L-malic acid into L-lactic acid and CO2, catalysed by the malolactic enzyme. This mechanism contributes for deacidification, bacterial stability and flavour changes in wine. Oenococcus oeni is the leading lactic acid bacteria responsible for malolactic fermentation, mainly due to its adaptability to such a chemically harsh wine environmental (low pH and high ethanol concentrations). The two main goals of this PhD thesis were to contribute to the: (1) increase of knowledge of biogenic amines occurrence in wine; (2) oenological characterization and selection of Portuguese autochthonous O. oeni strains, isolated from different winemaking regions, to be used as malolactic starters on the wine industry.(...) Description: Dissertation presented to obtain the Ph.D degree in Biology Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10362/8554 2012-01-01T00:00:00Z http://hdl.handle.net/10362/6860 Title: Dynamics of cork mycobiota throughout stopper manufacturing process: from diversity to metabolite Authors: Barreto, Maria do Carmo Abstract: Cork, the continuous layer of outer bark of the Quercus suber L. tree, has physical and chemical properties that are unique. Portugal possesses 33 % of the world’s cork oak forests and accounts for approximately half of total global cork production. The manufacture of cork discs (or stoppers) comprises several stages, including two boiling stages, during which slabs of cork are steeped in boiling water. In days following the boiling the humidity of the slabs decreases and they become completely covered in a white mycelium of Chrysonilia sitophila until the cork achieves a certain water activity level (ca 0.9 aw). Below this level other fungal species (e.g. Penicillium, Aspergillus or Trichoderma) can germinate and shift the fungal colonization of the cork slabs. The two main objectives of the research described in the presented PhD thesis are (1) a taxonomic identification of the mycobiota present in cork slabs throughout the manufacture of cork discs, and (2) an investigation into the chemical compounds, which can give unfavourable properties to the cork, produced by these fungi.(...) Description: Dissertation presented to obtain the Ph.D degree in Biology Thu, 01 Dec 2011 00:00:00 GMT http://hdl.handle.net/10362/6860 2011-12-01T00:00:00Z