Resistance to oxidation of white wines: Relationship between potentiometric measurements, sensorial analysis and some substances responsible for aroma degradation of white wines

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Relationship between potentiometric measurements and substances responsible for aroma degradation.

Evaluation the Oxidation “status” of a white wine and in what extent

this measure could be related with the typical aroma of “Oxidative

Spoiled” character :

Index of degradation (ID) measured by sensorial analysis.

Levels of substances responsible for “off-flavors” in white wines.

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Redox Sequential Titration : Species captured by PIP

-400 -300 -200 -100 100 200 300 400

Volume (reducer / oxidant) added (ml)

0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 1 st -Reduction [TiCl₃] E(mV) Wine Potential E = - 400(mV)

Reduction titration Oxidation titration

Redox Sequential Titration : Species captured by PIP

-400 -300 -200 -100 100 200 300 400

0 _2.5 _5.0 _7.5 _10.0 _12.5 _15.0 _17.5 _20.0 E = - 400(mV) 2 nd - Oxidation Dichlorophenol- -indophenol Coumaric acid Vanillic acid Resveretrol Malvidins Ferrulic acid Rutin Cafeic acid Gallic acid Epicatechin Quercetin Delphinidin Myricetin Ascorbic acid Catechin 800 750 650 470 300 210 360 Potential E (mV) E = 400(mV) E(mV) Wine Potential

•  PIP : Selectively pick out wine fraction more readily oxidized by dissolved oxygen ( - 400 mV < E < 400 mV) !!!

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Redox Sequential Titration : Species captured by PIP

-400 -300 -200 -100 100 200 300 400

0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 E = - 400(mV) Coumaric acid Vanillic acid Resveretrol Malvidins Ferrulic acid Rutin Cafeic acid Gallic acid Epicatechin Quercetin Delphinidin Myricetin Ascorbic acid Catechin 800 750 650 470 300 210 360 Potential E (mV) E = 400(mV) E(mV) Wine Potential

Reduction titration Oxidation titration •  PIP : Selectively pick out wine fraction more readily oxidized by dissolved oxygen ( - 400 mV < E < 400 mV) !!!

2 nd - Oxidation Dichlorophenol- -indophenol

ROX-value

= _{mmol [Dichlorophenolindophenol, PIP] (OXIDANT)}mmol [Trichlorotitanium, TiCl3] (REDUCER)

Veq RED Veq OXI

Oliveira, C.M, A.C. Silva Ferreira, P. Guedes de Pinho and T. Hogg. J. of Agric. Food Chem., 2002, 50 (7), 2121-2124.

Similarity “Oxidative Spoiled ”

OSW

“normal white wine” nW O OH O H₃C H3C [1] [3] [2] nW OSW nW + [1] nW + [2] nW + [3] nW + [1] + [3] nW + [1] + [2] nW + [2] + [3] nW + [1] + [2] + [3] S = 5.4 S = 3.2

•  The highest value from the similarity tests was founded when the three compounds were added simultaneously SV=5.4 !

methional Phenylacetaldehyde

sotolon

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Treatment IV pH = 4.2 Treatment II SO2 (free) = 50 mg/L Treatment I pH = 3.2 Treatment III O2 dissolved = 6.5 mg/l Stored at T = 20 ºC // 40 ºC // 60ºC White Wine - Group I - pH= 3.2 ; [SO2 ]free =12 mg/L ; [O2 ]= 1.0 mg/L

Forced Aging protocol

Normal Aged white wines : •  Different Vintages (n=24) Age 1-20 years Old _{- Group II -} •  Same Vintage (n=35) Age 2-3 years Old

- Group III -

Sensorial Degradation

•  Samples saturated with oxygen suffers

faster aroma degradation !

0 2 4 6 8 10 12 14 16 18 20 Control Treatments 0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 Abs 420 (nm) ROX-value

"Index of Degradation" (ID)

T = 20 ºC pH3 pH4 O2 SO2 ROX-value & “Index Degradation”(ID) Abs 420 (nm) T = 40 ºC pH3 pH4 O2 SO2 T = 60 ºC pH3 pH4 O2 SO2

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ROX-value : Relation with Sensorial Data

Sensorial Degradation

•  Aromatic degradation occurs before

chromatic degradation which is in agreement with published data !

•  The ROX-Values curve closely follows the “Index of degradation” curve ! R = 0,8869 •  Samples saturated with oxygen suffers

faster aroma degradation !

0 2 4 6 8 10 12 14 16 18 20 Control Treatments 0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 Abs 420 (nm) ROX-value

"Index of Degradation" (ID)

T = 20 ºC pH3 pH4 O2 SO2 ROX-value & “Index Degradation”(ID) Abs 420 (nm) T = 40 ºC pH3 pH4 O2 SO2 T = 60 ºC pH3 pH4 O2 SO2

0 10 20 30 40 50 60 70 0 10 15 ROX 25 M eth ion al (u g/ L) methional 5 Oxygen pH3 pH4 SO2 Free 0 40 80 120 160 200 0 5 10 15 25 P h en yl eth an al (u g/ L) ROX Oxygen pH3 pH4 SO2 Free phenylacetaldehyde

ROX-value : Relation with Key-Odorants

•  Levels of methional and phenylacethaldehyde are highly dependent on temperature and oxygen regimes :

Useful indicators of “aroma spoilage” !

•  ROX-values, are highly correlated with methional and phenylacethaldehyde, respectively r = 0.8430 and

r = 0.8476 !

r = 0.8430 r = 0.8476

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ROX > 10 Concentrations are above the odor threshold !

ROX

Chemical analysis : Samples from Group I

ROX-value : Relation with Key-Odorants

•  Levels of methional and phenylacethaldehyde are highly dependent on temperature and oxygen regimes :

Useful indicators of “aroma spoilage” !

•  ROX-values, are highly correlated with methional and phenylacethaldehyde, respectively r = 0.8430 and

r = 0.8476 ! 0 10 20 30 40 50 60 70 0 10 15 ROX 25 M eth ion al (u g/ L) methional 5 Oxygen pH3 pH4 SO2 Free 0 40 80 120 160 200 0 5 10 15 25 P h en yl eth an al (u g/ L) ROX Oxygen pH3 pH4 SO2 Free phenylacetaldehyde T= 0.5 ug/L T = 25 ug/L r = 0.8430 r = 0.8476

ROX-value : application to normal aged wines

Methional (ug/L) 4.1 13.0 0.9 1.4 14.5 2.5 1.7 0.8 7.4 n.d. 2.4 n.d. 4.7 n.d. 1.7 n.d. n.d. n.d. n.d. n.d. n.d. Phenylacetaldehyde (ug/L) 5.9 16.6 2.8 7.0 33.3 6.7 4.6 3.4 10.9 3.9 4.3 1.8 13.8 4.2 4.1 0.9 0.9 0.9 n.d. 2.9 1.0 TDN (nor area) 4.2 8.2 5.3 3.3 5.6 6.8 4.0 5.9 7.0 4.4 4.8 4.0 9.4 8.5 6.2 3.2 2.6 4.2 1.6 6.9 3.5 Abs 420 (nm) 0.495 0.292 0.180 0.322 0.433 0.307 0.252 0.171 0.135 0.218 0.314 0.126 0.231 0.215 0.175 0.167 0.128 0.147 0.122 0.226 0.254 18 9 7 20 17 14 17 4 7 9 19 5 8 6 7 10 4 6 3 8 4 Age 13 12 11 11 10 9 9 9 8 8 8 7 7 5 5 3 3 3 2 2 2 ROX 17 15 15 15 17 17 16 12 12 12 14 7 15 12 13 9 7 7 2 6 7 Index Degradation

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ROX-value : application to normal aged wines

•  Samples from Group II : Ranked by ROX-value Methional (ug/L) 4.1 13.0 0.9 1.4 14.5 2.5 1.7 7.4 n.d. 2.4 n.d. 4.7 n.d. 1.7 n.d. n.d. n.d. n.d. n.d. n.d. n.d. Phenylacetaldehyde (ug/L) 5.9 16.6 2.8 7.0 33.3 6.7 4.6 10.9 3.9 4.3 1.8 13.8 4.2 4.1 0.9 0.9 0.9 n.d. 1.0 3.6 2.8 TDN (nor area) 4.2 8.2 5.3 3.3 5.6 6.8 4.0 7.0 4.4 4.8 4.0 9.4 8.5 6.2 3.2 2.6 4.2 1.6 3.5 1.2 0.1 Abs 420 (nm) 0.495 0.292 0.180 0.322 0.433 0.307 0.252 0.135 0.218 0.314 0.126 0.231 0.215 0.175 0.167 0.128 0.147 0.122 0.254 0.080 0.054 18 9 7 20 17 14 17 7 9 19 5 8 6 7 10 4 6 3 4 2 1 Age 13 12 11 11 10 9 9 8 8 8 7 7 5 5 3 3 3 2 2 1 1 ROX 17 15 15 15 17 17 16 12 12 14 7 15 12 13 9 7 7 2 7 4 2 Index Degradation n.d. n.d. 5.4 0.194 9 1 9 0.8 3.4 5.9 0.171 4 9 12 n.d. 2.9 6.9 0.226 8 2 6 0 5 10 15 20 0.0 5.0 10.0 ROX15.0 Methional 70 140 210 Linalool

•  Samples from Group II : Ranked by ROX-value

ROX-value : application to normal aged wines

• f (ROX) : r = 0.8725 • f (AGE) : r = 0.7491 • f (Abs 420 nm) : r = 0.6966 ID ROX close 10 Methional (ug/L) 4.1 13.0 0.9 1.4 14.5 2.5 1.7 7.4 n.d. 2.4 n.d. 4.7 n.d. 1.7 n.d. n.d. n.d. n.d. n.d. Phenylacetaldehyde (ug/L) 5.9 16.6 2.8 7.0 33.3 6.7 4.6 10.9 3.9 4.3 1.8 13.8 4.2 4.1 0.9 0.9 0.9 n.d. 1.0 TDN (nor area) 4.2 8.2 5.3 3.3 5.6 6.8 4.0 7.0 4.4 4.8 4.0 9.4 8.5 6.2 3.2 2.6 4.2 1.6 3.5 Abs 420 (nm) 0.495 0.292 0.180 0.322 0.433 0.307 0.252 0.135 0.218 0.314 0.126 0.231 0.215 0.175 0.167 0.128 0.147 0.122 0.254 18 9 7 20 17 14 17 7 9 19 5 8 6 7 10 4 6 3 4 Age 13 12 11 11 10 9 9 8 8 8 7 7 5 5 3 3 3 2 2 ROX 17 15 15 15 17 17 16 12 12 14 7 15 12 13 9 7 7 2 7 Index Degradation 0.8 3.4 5.9 0.171 4 9 12 n.d. 2.9 6.9 0.226 8 2 6

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ROX-value : Relation with Oxygen consumption

•  A positive impact of Oxygen consumption on ROX was observed : r = 0.7176 ! •  The ROX-value for samples (n=35) same Vintage ranged from 0.4 to 4.4.

•  Seven samples From Group III analyzed after one year. •  Samples from Group III :

•  Five samples from Group III - supplemented with O2,

Stored at 30 ºC (10 days). 0.0 1.0 2.0 3.0 4.0 5.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 ROX_increment O xyge n c on su mp ti on (mg/ L) r = 0.7176

Normal aging Oxygen Saturated

A potentiometric method based upon a sequence of redox titrations in order to quantify the “first line of defense” of white wine, against “aroma spoilage” is proposed.

“Resistance to Oxidation” were strongly correlated with the “Index of Degradation” rated by the sensorial panel, both in normal aged wines and in “forced aged” experiments, respectively r = 0.8725 and r = 0.8869.

ROX-values higher than 10 the concentration of methional and phenylacetaldehyde were respectively above odor threshold.

Finally, it was observed a positive relationship between consumed oxygen and the respective ROX. These last results needed to be further complemented in order to