Abstract
Most yeast and bacteria in wine are able to metabolize hydroxycinnamic acids into volatile phenols via enzyme-mediated decarboxylation. Our trials performed in wine and model systems suggest that lysozyme addition prior to fermentation affects both bacterial activity and the release of hydroxycinnamic acids from their tartrate esters. This increases the potential for volatile phenol formation, as microorganisms can only metabolize free hydroxycinnamates. Wines with delayed malolactic fermentation due to lysozyme addition contained significantly higher concentrations of free hydroxycinnamic acids and elevated levels of volatile phenols in some cases. The reason for this is likely related to the side activity of lysozyme in combination with a detoxification mechanism that only occurs under stressful conditions for the yeast. Experiments in model systems indicate that lysozyme can affect the yeast at a pH higher than usually found in wine by attacking chitin in the bud scars of the cell walls and therefore weakening the cell structure. Free hydroxycinnamates can also affect yeast viability, making an increased release during fermentation problematic for a successful fermentation.
Highlights
Fresh and acid-driven white wines are commonly produced without intentional bacterial activity.Traditional ways to prevent bacterial growth are stabilization with sulfur dioxide (SO2 ), pasteurization at 60 ◦ C for two minutes [1], or lysozyme addition
Previous studies suggest that a delay in malolactic fermentation can lead to elevated levels of volatile phenols [27]; the reason for that phenomenon is currently unknown
The malic acid degradation in Chardonnay and Pinot blanc shown in Figure 1 confirms that lysozyme can delay but not inhibit Malo-lactic fermentation (MLF) if it is added in concentrations below the legal limit
Summary
Fresh and acid-driven white wines are commonly produced without intentional bacterial activity. Traditional ways to prevent bacterial growth are stabilization with sulfur dioxide (SO2 ), pasteurization at 60 ◦ C for two minutes [1], or lysozyme addition. Commercial lysozyme is a white slightly sweet powder that is purified from egg-white and was approved for wine treatment by the International Organisation of. In contrast to sulfur dioxide, the efficiency of lysozyme increases with increasing pH [5], with an effective pH range from 3.5 to. Malo-lactic fermentation (MLF) can be delayed by the addition of 250 mg/L and a treatment with 500 mg/L generally prevents any bacterial activity. The inhibiting effect of 500 mg/L lysozyme is comparable to the addition of 40 mg/L SO2 [5]
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