Inhibitory effect of ethanol, sulphur dioxide and proanthocyanidinic tannins on lysozyme antimicrobial activity in model wine

• All tested wine constituents appeared reversible inhibitors for lysozyme activity.
• Ethanol and free SO2 exerted a very slight inhibiting effect.
• The strongest inhibition was exerted by proanthocyanidinic tannins.

The antimicrobial activity of lysozyme from hen egg white (HEWL) was tested against Oenococcus Oeni cell as substrate in wine-like acidic medium, composed of tartaric acid buffer (pH 3.2) fortified with ethanol (EtOH), free sulphur dioxide (SO2), grape skin and seed tannins, within the average range of their concentration in wine in order to identify, for each compound, the nature, the mechanism and the extent of inhibition. All of the tested wine constituents were reversible inhibitors for HEWL activity, with a limited inhibiting effect observed for both EtOH and free SO2, which proved to be competitive and mixed-type inhibitors, respectively. Contrarily, proanthocyanidinic tannins had the strongest inhibiting effect, which affected muramidase activity in two different ways: grape skin tannins proved to be uncompetitive while seed tannins were mixed-type inhibitors.