Oxidative/Reductive Taints
-
Upload
honorato-pearson -
Category
Documents
-
view
43 -
download
0
description
Transcript of Oxidative/Reductive Taints
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
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
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?
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)
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 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)