Oxidative/Reductive Taints

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Oxidative/Reductive Taints

• Linda F. Bisson
• Department of Viticulture and Enology
• University of California, Davis

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Oxidative Taints

• Off-colors
• pink
• brown
• Off-flavors
• aldehyde (nutty)
• rancid
• hamster fur/ animal characters
• chemical notes

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Reductive Taints

• Sulfur Compounds
• Sun dried characters
• Wood characters

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Oxidative/Reductive Reactions in Wine

• Enzymatic (biological) Oxidation
• Polyphenol Oxidase (PPOTyrosinase) (plant)
• Laccase (Botrytis molds)
• Chemical Oxidation/Reduction
• Cascade initiated by molecular oxygen
• Electron rearrangements in absence of oxygen

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Oxidative Taints

• Function of oxygen exposure and wines 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!

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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

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Polyphenol Oxidase/Laccase

• OH
  O
• R OH R
  O
• O2 H2O

R
8
Laccase
O-
OH
e-
O2
OH
OH
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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

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Laccase Substrates
Substrate Relative Activity ()
4-Methylcatechol 100
Catechol 104
Protocatechuic acid 119
Caffeic acid 132
() Catechin 100
Gallic acid 109
Phloroglucinol 143
p-Coumaric acid 90
Ferulic acid 109
Anthocyanins 97
Leucoanthocyanins 84
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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

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Control of Laccase

• Sulfite sensitivity 150 ppm shows only 20
  inhibition
• Ascorbic acid is a substrate of laccase
• More sensitive to heat than PPO

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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 (50C),
  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?

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Chemical Oxidation/Reduction
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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

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Redox Chemistry of Wine

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

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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

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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)

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Formation of Acetaldehyde
Danilewicz 2007
Waterhouse and Laurie 2006
Waterhouse and Laurie 2006
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Chemical Bridging by Oxidized Compounds
1 2 3 4
5
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Controlling Wine Oxidation

• Minimize oxygen exposure
• Use of antioxidant SO2 or ascorbate
• Monitor aldehyde levels

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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

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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

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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!

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Predicting Oxygen Impact

• Termination of aging
• Closure decision
• Market shelf-life assessment

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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

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Oxidized Character Observations with Hydrogen
Peroxide Spiking

• Acetaldehyde chemical taint (rotten apple)
• Higher aldehydes
• Nutty (sherry)
• Rancid
• Mustiness
• Fur (hamster not mousy)

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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