One other interesting result was that l-cysteine, while present at even high concentrations than ammonium ion,urea and l-leucine, was used in small amounts by the yeasts during wine ageing and subsequently by the acetification bacteria, possibly because it plays some protective role – it is a precursor of glutathione, which is a powerful agent against oxidative stress in cells (Jamieson, 1998). Therefore, l-cysteine may form a pool for immediate use if needed. Likewise, l-proline has been reported to possess cell protective properties(Takagi, 2008).