Most yeast and bacteria species in wine can metabolize hydroxycinnamic acids under winemaking conditions to form volatile phenols by decarboxylation. During fermentation, the release depends on yeast strain, the availability of free hydroxycinnamic acids, and the concentration of phenolic inhibitors. Our studies performed with Chardonnay and Pinot blanc fermentations from two vintages suggested that lysozyme addition to the juice prior to fermentation does not only affect bacterial activity, but also the release of hydroxycinnamic acids from their tartrate esters. This increases the theoretical potential for volatile phenol formation because microorganisms can only metabolize free hydroxycinnamates. The general performance and yield of alcoholic fermentation was not influenced by lysozyme. However, wines with delayed malolactic fermentation due to lysozyme addition contained significantly greater concentrations of free hydroxycinnamic acids but did not necessarily show elevated concentrations of volatile phenols. The reasons for this inconsistent behavior are yet unknown, but it is likely to be a side effect of lysozyme in combination with a detoxification mechanism that only occurred under specific circumstances. Additional experiments in model systems indicate that lysozyme can affect the yeast at higher pH by attacking chitin, which is incorporated in the bud scars of yeast cell walls and therefore weakens the structure of the cell. Thus, an attempt to detoxify the medium to secure cell survival could consequently cause a higher production of volatile phenols. The increased release of monomeric hydroxycinnamates in the presence of lysozyme only occurred after alcoholic and malolactic fermentation, indicating only passive involvement of the present organisms. While the influence of different concentrations of lysozyme on the concentration of free hydroxycinnamic acids could be shown in wine model systems, the exact mechanisms leading to higher concentrations of volatile phenols in only some wines remain to be clarified.

Funding Support: Partially funded by the German Ministry of Economics and Technology (via AiF) and the FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn), Proiect AiF 15833N