Produção de compostos de enxofre por bactérias láticas do vinho durante a fermentação malolática

Abstract

Although several references on the effect of malolactic fermentation (MLF) on wine composition can be found on the scientific literature, very little information is available about the metabolism of sulfur compounds by lactic acid bacteria (LAB) in wine. The main objective of this work was the study of the impact of MLF in the volatile composition of wine, in particular on the sulfur compounds. Special attention was paid to the catabolism of sulfur containing amino acids as potential precursors for the production of sulfur compounds. Red wines (Touriga Franca and Tinta Roriz grape varieties) as well as defined synthetic wines and synthetic fermented musts were inoculated with different strains of Oenococcus oeni. Different concentrations of methionine, cysteine, ammonium sulfate and ammonium phosphate were used to assess the influence on the production of sulfur compounds. In all fermentations, the bacterial growth, the degradation of L-malic acid and the production of L-latic acid were followed. At the end of fermentation, the sulfur compounds were analysed by GC-FDP. The results obtained in the synthetic wines demonstrated the importance of the methionine as principal precursor of methionol, which was the sulfur compound produced in greater quantity. It has been found quite clearly that the higher the concentration of methionine in the medium the higher the concentration of methionol produced. The addition of methionine let to the production of other compounds in addition to methionol as thioesters (S-ethylthio acetate). The results indicate that cysteine, in the presence of other amino acids, can also lead to the synthesis of methionol. No sulfur compound were detected when ammonium sulfate or ammonium phosphate were used as sole nitrogen sources. The alcoholic fermentation and its interaction with MLF seem to be crucial for the final profile of sulfur compounds. MLF affected the concentration of several sulfur compounds obtained from the alcoholic fermentation. The bacterial activity lowered the concentration of some of these compounds (S-Methyl thioacetate, S-ethyl thioacetate, 3 - (Ethylthio)-1-propanol, 4-(Methylthio)-1-butanol and 3-Methylthiopropionic acid), which can be interpreted as a positive since these can be harmful to the wine quality.

Date of Award	2012
Original language	Portuguese
Awarding Institution	Universidade Católica Portuguesa
Supervisor	José António Couto (Supervisor) & Nathalie Moreira (Co-Supervisor)