Oxidative/Reductive Taints

1. Oxidative/Reductive Taints Linda F. Bisson Department of Viticulture and Enology University of California, Davis

2. Oxidative Taints • Off-colors: • pink • brown • Off-flavors: • aldehyde (nutty) • rancid • “hamster fur”/ animal characters • chemical notes

3. Reductive Taints • Sulfur Compounds • Sun dried characters • Wood characters

4. Oxidative/Reductive Reactions in Wine • Enzymatic (biological) Oxidation • Polyphenol Oxidase (PPO;Tyrosinase) (plant) • Laccase (Botrytis & molds) • Chemical Oxidation/Reduction • Cascade initiated by molecular oxygen • Electron rearrangements in absence of oxygen

5. Oxidative Taints • Function of oxygen exposure and wine’s ability to consume oxygen • Related to phenolic content • Impacted by other factors such as pH • Some oxidation reactions are desired; not all lead to defects = a delicate balance!

6. PPO versus Laccase • PPO = tyrosinase/catecholase • Laccase = p-phenoloxidase/diphenol oxidase • Some overlap of substrates • PPO mostly associated with off-colors; Laccase can give both off-colors and off-odors

7. Polyphenol Oxidase/Laccase OH O R OH R O O2 H2O R

8. Laccase O- OH e- O2 OH OH

9. PPO versus Laccase • PPO is inhibited by sulfite • PPO is inactivated by ethanol • Laccase has a broader range of substrates than PPO • Broader range of off-color compounds formed • Can oxidize phenol-glutathione complexes • Laccase is still active in wine post-fermentation

10. Laccase Substrates:

11. Control of Enzymatic Oxidation • Use of sulfite to inhibit PPO (grape) • Use of yeast to consume oxygen until ethanol inactivates PPO • Laccase: Control mold in vineyard • Laccase: use of HTST (high temperature short time) treatment to inactivate enzyme • Bentonite fining of juice to remove enzymes

12. Control of Laccase • Sulfite sensitivity: 150 ppm shows only 20% inhibition • Ascorbic acid is a substrate of laccase • More sensitive to heat than PPO

13. Is My Problem Laccase? • Does it continue in presence of 50-75 ppm SO2? (wine in glass for 12-24 hours) • If wine is heated to inactivate enzymes (50°C+), does oxidation continue (is it chemical versus enzymatic?) • Is syringaldazine oxidized? (need to remove other phenolics first with PVPP) • Are there laccase-characteristic odor taints?

14. Chemical Oxidation/Reduction

15. Redox Chemistry: Introduction • Transfer of electrons: reactions in which a transfer of electrons occurs are known as oxidation-reduction (redox) reactions • Oxidation involves the loss of electrons • Reduction is the gain of electrons • Redox potential refers to the tendency to gain or yield electrons of a specific atom, molecule or solution

16. Redox Chemistry of Wine • Wine contains both oxidizing and reducing reagents • Molecular oxygen is a good oxidizing agent (possessing an affinity for electrons) O2e O2-e O22- e OH e OH- OH- + H+ H2O

17. Redox Chemistry of Wine • Phenolic compounds can be oxidized in the presence of oxygen • Oxygen has limited reactivity towards phenolic compounds in its normal O2 form • Oxygen is “activated” by metal ion catalysts in the wine such as iron (Fe) • Oxidation in wine is caused by the formation of reactive oxygen species (ROS) • The hydroxyl radical ( OH) is the reactive agent

18. Redox Potential of Wine Dependent upon: • Oxygen concentration • Metals availability • Ethanol • Phenolic composition • Type of container • Stirring/agitation • pH (increasing pH decreases redox potential; oxidative reactions occur more readily)

19. Formation of Acetaldehyde Danilewicz 2007 Waterhouse and Laurie 2006 Waterhouse and Laurie 2006

20. Chemical Bridging by Oxidized Compounds 1 2 3 4 5

21. Controlling Wine Oxidation • Minimize oxygen exposure • Use of antioxidant: SO2 or ascorbate • Monitor aldehyde levels

22. Oxygen in Wine • From any transfer operation • Pumping over or cap irrigation • Centrifugation • Filtration • Mixing • From headspace, penetrates only the first 10 to 20 cm of wine: stratification effects are observed • Singleton: white wine 10 saturations; red wine 30 saturations

23. When Is Wine Damaged by Oxidation? • Oxidation reactions can be positive: • Stabilization of color • Loss of tannins due to polymerization • Loss of compounds that are perceived as negative when reduced • Negative effects arise when: • Acetaldehyde or glyoxylic acid start to accumulate • Higher aldehydes start to accumulate • Loss of varietal character occurs

24. Factors Affecting Oxidation • pH: hydrogen ions with a positive charge can quench oxidation cascades in the formation of water; oxidation 9 times faster at pH 4.0 than at pH 3.0 • Amount of exposure to oxygen • Type of closure: current practices optimized for natural cork? • Antioxidants and Redox buffering capacity • Time!

25. Predicting Oxygen Impact • Termination of aging • Closure decision • Market shelf-life assessment

26. Predicting Oxygen Impact • Exposure to air: hard to separate microbial and chemical effects • Spiking with H2O2 • Dose relationship to normal aging? • Dependent upon wine composition

27. Oxidized Character Observations with Hydrogen Peroxide Spiking: • Acetaldehyde: chemical taint (rotten apple) • Higher aldehydes • Nutty (sherry) • Rancid • Mustiness • Fur (hamster not mousy)

28. Oxidative Taints Tasting • Glass 1: Control (French Colombard) • Glass 2: French Colombard H2O2: 10ppm • Glass 3: French Colombard H2O2: 25ppm • Glass 4: Chardonnay with Laccase • Glass 5: Chardonnay with Laccase H2O2: 50 ppm • Glass 6: Commercial Wine