Use of Glutathione in White Winemaking – Friend or Foe?
Pascal Wegmann-Herr,* Sebastian Ullrich, and Dominik Durner
*Institute for Viticulture and Enology (DLR-Rheinpfalz), Breitenweg 71, Neustadt, 67435, Germany (firstname.lastname@example.org)
Recently two OIV resolutions (OENO 445-2015 and OENO 446-2015) were adopted, defining the use of glutathione (GSH) up to a maximum concentration of 20 mg/L in must and wine. Studies have shown the benefits of GSH addition, especially in Sauvignon blanc wines. We evaluated the impact of added GSH on oxidation product formation in model wines, which was compared to ascorbic acid and sulfur dioxide additions. The analysis of oxidation products formation focused on determining yellowish-colored xanthylium compounds by LC-ESI-ToFMS and acetaldehyde by HS-GC-FID. The results showed that, under certain conditions, GSH did not inhibit carboxymethine-bridged (+)-catechine dimer formation and subsequent xanthylium cation pigment generation, unlike ascorbic acid or sulfur dioxide, both of which provided a good protection against oxidative color changes. In systems containing 0.08 to 0.32 mmol/L GSH without any further addition of SO2 or ascorbic acid, increased acetaldehyde concentrations were observed. Next, we investigated the effect of GSH addition to white wine with respect to color development, sensory expression, and sulfide off-flavor formation. Riesling, Sauvignon blanc, and Chardonnay grapes were processed under different conditions and musts were obtained with different phenolic concentrations. The addition of GSH as a pure substance or the use of GSH-rich inactivated yeast preparations (IDY), either prior to or after fermentation, resulted in wines with varying GSH concentrations. GSH treatment yielded lighter-colored musts, but there were no differences in the yellow color of the bottled wines. GSH and IDY addition prior to fermentation increased 3-mercaptohexanol concentrations in Sauvignon blanc wines. Excess GSH treatment of musts and wines before bottling led to increased formation of off-flavored sulfur volatiles (e.g., H2S, dimethyl sulfide), determined using a novel HS-SPME-GC method followed by SIDA quantification, negatively influencing the wines’ sensory quality.
Funding Support: This IGF Project (AIF 28645N) of the FEI is supported via AiF within the program for promoting the Industrial Collective Research (IGF) of the German Ministry of Economics and Energy (BMWi)