Repositori URV

Identifier: TDX:463

Handle: https://hdl.handle.net/20.500.11797/TDX463

Authors:
Romero Tissera, Silvana Verónica

Abstract:
Ethyl carbamate (EC) is a well-known animal carcinogen found in fermented foods and beverages. The major precursor involved in EC formation in wine is urea, produced by the metabolism of arginine by yeast. It's also know that lactic acid bacteria (LAB) may form precursors of EC in wine, citrulline and carbamyl-phosphate, from arginine metabolism, although it is not widely accepted the involvement of LAB and malolactic fermentation (MLF) on EC formation. The main objective of this thesis was to fully understand different factors that influence EC formation during MLF with the purpose of finding patterns that allow us to prevent EC formation in wines. We found that neither the execution of MLF on yeast lees or wine storage for 12 months affected EC levels of wines. The development of MLF and a longer exposure time with the skins during alcoholic fermentation (AF) did not affect EC levels in wine, but they caused an increase in potential EC. We also found that grape variety and the duration of MLF influence citrulline concentrations in wines. Malolactic starter used for induction of MLF in wine also influences potential EC levels because they show different capacity to degrade arginine. Arginine degradation favours the growth of Oenococcus oeni in some conditions. The good correlation obtained between citrulline and potential EC allows us to use the citrulline produced during the bacterial metabolism of arginine during MLF to predict the levels of potential EC at the end of L-malic acid degradation. In those cases in which L-malic acid was degraded completely, arginine degradation was delayed in comparison to L-malic acid degradation in all strains tested. This has oenological importance because it means that the winemaker can prevent arginine degradation by removing cells