Fabian Weber,* Sabrina Zimdars, Rita Caspers-Weiffenbach, and Pascal Wegmann-Herr
*University of Bonn, Friedrich Hirzebruch Allee 7, Institut of Nutritional and Food Sciences, 53121 Bonn, Germany (Fabian.Weber@uni-bonn.de)

Malolactic fermentation (MLF) is an important step in red winemaking to improve wine quality by microbiological deacidification, to increase microbial stability, and to modify general wine flavor by increasing red fruit perception. The phenolic composition of the wine influences the growth and metabolism of lactic acid bacteria (LAB) used for MLF. Due to increased emergence of fungus-resistant grape varieties, the present study aimed to analyze the influence of stilbenes on MLF; these compounds play an important role as phytoalexins in plants to counteract fungal pathogens and are therefore believed to accumulate in fungus-resistant grape varieties. It was shown that the grapevine-shoot extract Vineatrol and the stilbenes ε-viniferin, ampelopsin A, r2-viniferin, r-viniferin, and mixtures of the five stilbenes all decelerated malic acid degradation. This can be attributed only partially to fewer viable cells, so the direct impact of stilbenes on the malolactic enzyme also has an effect. This was deduced from a constant viability of LAB while, at the same time, malic acid degradation was reduced. Red wines from fungus-resistant grapes were analyzed and fractionated to reveal the presence of stilbene. These results show that wines made from stilbene-rich grapes like fungus-resistant varieties are at higher risk for an inhibited or incomplete MLF.

Funding Support: This research project was financially supported by the German Ministry of Economics and Technology (via AiF) and the FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn). Project AiF 18645N.