introduction to oxidation in wine andrew l. waterhouse department of viticulture & enology...
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Introduction to Oxidation in Wine
Andrew L. WaterhouseDepartment of Viticulture & EnologyUniversity of California, Davis
Oxidation Avoidance
Traditional limit to wine preservation Current technology can exclude oxygen Wine oxidation - a fault?
Manage Wine Oxidation
At crush / press– Anaerobic press to hyperoxidation
Fermentation– Add oxygen for yeast, reductive aromas
Post fermentation/s– Micro-ox, barrels, racking
In bottle– Affects flavor development
Oxygen Measurement
Standard meter – Limit of Detection ~0.5 ppm
Orbisphere or other Clark electrode – LOD ~2 ppb
Nomasense, Mocon, others– Oxydots, fiber optic measure-contact not
needed! 10 ppb – Temperature sensitive!
Antioxidants
SO2
Ascorbic acid Glutathione
Wine Oxidation Chemistry
OH
OH
O
O
O2 + H2O2+EtOH
Step 2Step 1
Acetaldehyde
Oxygen reacts with phenols to yield quinone and hydrogen peroxide
Hydrogen peroxide oxidizes ethanol to acetaldehyde
Known Oxidation Products
Quinones– Thiol adducts– Coupling Products
Aldehydes– Acetaldehyde– Glyoxylic Acid
• (Tartaric Acid product)
– Flavonoid coupling
O
O
OH
Oxidative Changes in Wine Formation of quinones from catechols
– React with thiols, SO2, ascorbate, phenolics
Fenton oxidation of alcohols– Formation of aldehydes– Reactions of all other substances
Oxygen Pathway in Wine
O2
Fe+2 Fe+3
Fe+2
Fe+3
Fe+3
(Semiquinone radical) (Hydrogen peroxide)
(Hydroxyl radical)
(Quinone)
(Hydroperoxylradical)
1
2
3
4
RCHOHRC=O
RC=O
5
O2
RCOH
H+
OHOH
OHO · O ·H
O
OH OH
O·OH
OO
OOH
OH
OH–
H+
O·H OH2
C·R
+
++
+
Sulfur Dioxide and Oxygen
Sulfite is the sink for oxidation
O2 + 2 SO2 2 SO3
1 mg of O2 will consume 4 mg SO2
SO3 + H2O H2SO4
Polyphenols are Pro-oxidants
OHOH
OH OH
O OH
OO
O2
H+
Fe+2
+
+
Generation of quinone and hydrogen peroxide from dioxygen
Nikolantonaki , ACA 660: 102 (10) Blanchard, AJEV 55:115 (04)
Catechin + 3-Mercaptohexanol
OOH
OH
O
O
OH
OOH
OH
OH
OH
OH
OH
S
OH
SH+
Catechin dimer in model juice
Poupard, J Chrom A, 1179: 161 (08)
Quinone Options
OH
OH
S R
O
O
OHOH
OH
OH
OH
OH
OH
OH
OH
(Quinone)
RSH
Phenolic Coupling(polymerization)
Mercaptan Trapping
Phloroglucinol
AA's, StreckerDegradation
Aldehydes ?
SO2
Ascorbate
?
Oxygen Pathway in Wine
O2
Fe+2 Fe+3
Fe+2
Fe+3
Fe+3
(Semiquinone radical) (Hydrogen peroxide)
(Hydroxyl radical)
(Quinone)
(Hydroperoxylradical)
1
2
3
4
RCHOHRC=O
RC=O
5
O2
RCOH
H+
OHOH
OHO · O ·H
O
OH OH
O·OH
OO
OOH
OH
OH–
H+
O·H OH2
C·R
+
++
+
Peroxide Competition
H2O2
EtOH
Fe+2
SO2
·OH
H2O
Fe+3 CH3CHO
+
+
+
Wine Minor ComponentsRed Wine Composition, Minor Components
Sorbitol & Mannitol
Sulfites
Amino acids
Esters
Higher Alcohols
Phenols
Acid
Volatile Acidity
Sugar
Glycerol
Minerals *
Acetaldehyde
Oxidation of Wine Acids (Alcohols) to Carbonyls
O OH
OH
CH3
O OH
O
CH3
H2O2
Fe+2
Lactic Acid(or Malic)
Pyruvic Acid
Pyruvic– Observed in wine– Reacts with
anthocyanins to make wine pigments
Glyoxylic– Observed in wine– Condenses with
flavan-3-ols
O OH
OH
OH
O OH
O OH
O OH
OHCH
O OH
O
H2O2
Fe+2
Tartaric AcidHydroxymalonic Glyoxylic Acid
Aldehyde Pigment Reactions
O+
OH
OH
R1
OH
R2
O
GluOH
O
O
O+
OH
O
R1
OH
R2
O
Glu
R
H
O
O OH
or
R = H,
“D-ring” formation by acetaldehyde and pyruvate
Alcohol Oxidations with ∙OH
Aldehydes known oxidation products
OH
OH
O H
O H
S
O
H
O
S H
O
H
O
H
Wine Oxidation
Aroma and color changes Can be managed
– A few key steps need better understanding Many current investigations State of the art and practice today