Oxidative/Reductive Taints

Linda F. Bisson

Department of Viticulture and Enology

University of California, Davis

Oxidative Taints

Off-colors: – pink

– brown Off-flavors:

– aldehyde (nutty)

– rancid

– “hamster fur”/ animal characters

– chemical notes

Reductive Taints

Sulfur Compounds Sun dried characters Wood characters

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

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!

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

Polyphenol Oxidase/Laccase

OH O

R OH R O

O2 H2OR

Laccase

OH

OH OH

O-

e-

O2

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

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

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

Control of Laccase

Sulfite sensitivity: 150 ppm shows only 20% inhibition

Ascorbic acid is a substrate of laccase More sensitive to heat than PPO

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?

Chemical Oxidation/Reduction

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

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 O2

2- e OH e OH-

OH- + H+ H2O

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

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)

Formation of Acetaldehyde

Danilewicz 2007

Waterhouse and Laurie 2006

Waterhouse and Laurie 2006

Chemical Bridging by Oxidized Compounds

1 2 3 4 5

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

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

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

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!

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

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

Oxidized Character Observations with Hydrogen Peroxide Spiking:

Acetaldehyde: chemical taint (rotten apple) Higher aldehydes

– Nutty (sherry)

– Rancid Mustiness Fur (hamster not mousy)

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