Enology Note #91 July 6, 2004
To: Regional Wine Producers
From: Bruce Zoecklein, Head, Wine/Enology-Grape Chemistry Group
Lysozyme. Lysozyme is a natural bacteriolytic enzyme that has useful application in juice and wines, by inhibiting certain bacteria or delaying the onset of malolactic fermentation. It is a low molecular weight protein (single peptide consisting of 129 amino acids,) which is effective against prokaryotic cells (bacteria), but not eukaroyotic cells such as yeast (Mckenzie and Whilte, 1991). It causes the lysis of gram-positive bacterial cell walls by cleaving the β(1-4) glycosidic linkages. Thus, lysozyme is active against Lactobacillus, Pediococcus, and Oenococcus spp. in grape juice and wine, but not against acetic acid bacteria (Acetobacter) or yeasts, including Saccharomyces and Brettanomyces spp.
Over the last decade, there has been interest in lysozyme as a supplement to sulfur dioxide for bacterial inhibition. The effectiveness of sulfur dioxide as a microbial inhibitor is dependent upon pH. The inhibitor form of sulfur dioxide (molecular sulfur dioxide) loses its effectiveness as the pH rises. Elevated pHs are generally favorable for the growth of bacteria, including lactic acid bacteria, in wine. Lysozyme has a high isoelectric point (pH 10.5), and is stable at wine pH ranges of 3-4. Unlike sulfur dioxide, lysozyme activity is greater at elevated pH ranges. Sulfur dioxide acts as a microbial inhibitor, an enzyme inhibitor, and an anti-oxidizing agent, while lysozyme acts only as an antimicrobial agent, and only on certain classes of microbes. The ability of this protein to inhibit LAB is not influenced by sugar or alcohol concentration, and it may be effective against large populations (106 cfu) (Bartowsky et al., 2004).
Commercial lysozyme is a finely granulated, microcrystalline power prepared from hen egg whites. It is easily re-suspended in water, and is usually added to juice or wines at a rate of 100-500 mg/L or 10-50 g/hL. Lysozyme has been added to grape juice that has a significant potential for developing high levels of Lactobacillus populations and, thus, an increased risk of volatile acidity formation. It can also be used to delay the onset of MLF.
The macromolecular structure of red wines can create instability with the addition of this protein. Additionally, in white wines, lysozyme may contribute to protein instability which is not easily corrected by bentonite. Bentonite will bind with a portion of the lysozyme added, and may reduce its concentration below that which is needed for bacterial control. Several researchers have demonstrated variability in effectiveness of lysozyme on different LAB genera and species, and the activity may be transitory. Bartowsky et al. (2004) demonstrated that lysozyme retained a 75-80% activity in Riesling wine after six months. However, they also observed no detectable activity in Cabernet Sauvignon and Shiraz wines two days post-addition.
While the addition of lysozyme does not directly impact wine aroma and flavor, there may be some secondary impacts. Because lysozyme is a protein, it has the ability to bind with phenolic compounds. Its addition to red wines may result in a perceptible reduction in wine tannins and color. Bartowsky et al. (2004) noted a 17% reduction in 520 nm OD (red wine anthocyanin absorption maximum) for Cabernet Sauvignon and Shiraz.
Lysozyme may be added to juices, wines, and sparking wine cuvées in which MLF is to be controlled. Such additions have not demonstrated a detrimental impact on aroma or sparkling wine mousseux characteristics.
Lysozyme is approved by the OIV and European Commission for use in winemaking, but not by the TTB. In the USA, lysozyme use is granted on an experimental basis, and permission from TTB in advance of use is required.
American Society for Enology and Viticulture Annual Meeting and Symposium. July 13-16, 2004, Hotel Roanoke, Roanoke, VA. The underlying goal of the symposium is to explore how soils, climate (particularly temperature), and cultural practices affect fruit and wine composition and quality. Presentation topics include the impact of viticultural practices on grape and wine quality (Kees van Leeuwen, Professor of Enology at Bordeaux Agricultural University, and viticulturist, Cheval Blanc; Andrew Reynolds, Professor of Viticulture at Brock University in Ontario; Phil Freese, viticultural consultant, WineGrow), climate indices used to predict grape and wine quality as a function of grape variety and environmental interaction (Erland Happ, Happs, Pty. Ltd., Western Australia; Zelma Long, Zelma Long Wines; Greg Jones, Professor of Geography, Southern Oregon University), and to explore the role of soil physical properties on grape and wine quality (Kees van Leeuwen). Symposium conveners are Professors Tony Wolf and Bruce Zoecklein of Virginia Tech. See you there!
Norton Roundtable Meeting. We will conduct a Norton Roundtable meeting July 26, 2004 at Chrysalis Vineyards at 1:30 PM. If you are interested in attending, RSVP to by July 22. For further details, see Enology Notes #90.
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Professor and Enology Specialist Head Enology-Grape Chemistry Group
Department of Food Science and Technology, Virginia Tech
Blacksburg VA 24061
Enology-Grape Chemistry Group Web address: http://www.vtwines.info/
Phone: (540) 231-5325
Fax: (540) 231-9293