Utilize este identificador para referenciar este registo: http://hdl.handle.net/10400.14/16239
Título: Characterization of phenolic acid reductase and decarboxylase activities of lactic acid bateria
Autor: Soares, Ana de Seabra Leão Ferreira
Orientador: Campos, Francisco
Couto, José António
Data de Defesa: 28-Jan-2014
Resumo: Hydroxycinnamic acids are natural constituents of grape juice and wine, and are precursors of volatile phenols produced by yeasts and lactic acid bacteria (LAB). The organoleptic defects due to the presence of this volatile phenols are usually associated with “animal”, “horsey”, “leather”, “phenolic” or “spicy” aromatic notes. The most common pathway for the degradation of hydroxycinnamic acids involves two enzymes. In first place, it occurs a decarboxylation by the phenolic acid decarboxylase (PAD), and secondly a reduction of the intermediate metabolite carried out by the vinylphenol reductase (VPR). Some LAB strains seem to be able to metabolise hydroxycinnamic acids through an alternative route, involving a reduction step by a phenolic acid reductase (PAR) followed by a decarboxylation reaction. In order to characterize PAR and PAD/VPR activities, six different LAB strains were tested for the production of volatile phenols and non-volatile metabolites. The main objective of this work was to study the influence of certain factors/growth conditions on the extent of these activities. In the first part of this study, we evaluated the influence of the concentration of p-coumaric acid (1.0, 5.0 and 50 mg/L) as precursor for the production of volatile phenols. In the second part, the effect of the presence of L-malic acid and fructose on PAR and PAD/VPR activities with regard to the metabolism of p-coumaric acid was studied. The results show that all of the LAB strains tested have the ability to produce volatile phenols, however, strain-dependent patterns were observed. Four of the strains were also found to produce phloretic acid from 50 mg/l of p-coumaric acid using the alternative metabolic route mentioned above, thus indicating PAR activity. L-malic acid and fructose seemed to stimulate VPR activity, while no alteration was observed on the PAR activity. Moreover, the initial concentration of p-coumaric acid used seems to play an important role on volatile phenols production.
URI: http://hdl.handle.net/10400.14/16239
Aparece nas colecções:ESB - Dissertações de Mestrado / Master Dissertations
R - Dissertações de Mestrado / Master Dissertations

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