Herbst, M - [email protected]

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Role of Antioxidants and Polyphenols in the
Stability of Sauvignon Blanc Aromas
1Department
M.
1
Herbst ,
1
Kilmartin
P.A.
and L.
1
Nicolau
of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand
[[email protected]]
1. Introduction
2. Experimental Design
The volatile thiols 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexan-1-ol
acetate (3MHA) contribute to the fruity aroma of Vitis vinifera L. var. Sauvignon
blanc wines (fig. 1), and improving their stability is seen as key to retaining fresh,
fruity characters in these wines for a longer period of
time.
Assaying volatile thiols by GC/MS
The extent of 3MH and 3MHA loss in a model wine
solution (ultrapure water [MilliQ]/EtOH [88:12 v/v];
5g/L tartaric acid; pH 3.5) after four weeks was
monitored by GC/MS1.
3-Mercaptohexan-1-ol
(Grapefruit)
Analysis of polyphenols and glutathione by RP-HPLC
A reversed phase-HPLC method allowed the separation
of polyphenols and glutathione present in Sauvignon Blanc
wines by direct injection of the sample using a gradient
elution with a ternary solvent mixture and a diode array
detector and electrochemical detector to identify and
quantify the polyphenols and glutathione, respectively2,3.
3-Mercaptohexan-1-ol acetate
(Passion fruit)
Fig. 1: Volatile thiols involved in Sauvignon blanc aroma
The loss of 3MH and 3MHA has been linked to polyphenol oxidation involving the
hydroxycinnamic acids in white wines, a process which is inhibited by the
presence of antioxidants such as glutathione and sulfur dioxide.
In order to understand the flavour change 31 New Zealand (18 months old)
and
21
overseas wines (12 to 24 months old) were screened for glutathione
and
polyphenol levels.
The influence of varying levels of the polyphenol caffeic acid, dissolved oxygen, and
the antioxidants sulfur dioxide and glutathione were tested in
a model wine medium to determine the extent of 3MH and 3MHA loss.
References:
Tominaga,T., Murat, M.L., Dubourdieu, D. (1998). J. Agric. Food Chem. 46: 1044-1048.
2 Kilmartin, P.A., Zou, H., Waterhouse, A.L. (2002). Am. J. Enol. Vitic. 53: 294-302.
3 Smith, N.C., Dunnett, M., Mills, P.C. (1995). J. Chromatogr. B. 673: 35-41.
1
3. Results
Fig. 3: Survey of glutathione levels in Sauvignon blanc
wines from 6 different countries
Fig 2: HPLC of Sauvignon blanc
Tab. 1: Evolution of 3MH and 3MHA in model
wine after 28 days storage at 20ºC4
4.5
Electrode at 0.75 V
Juice (42 mg/l)
% 3MHA
GSH [mg/L]
% 3MH
4.0
Change
levels
ChangeininGlutathione
glutathione
levels
1
Sample
5.0
Wine at Bottling (29 mg/l)
Day 0
Wine at 3 months (4 mg/l)
3.5
3.0
2.5
2.0
1.5
Control
56
41
Control + SO2
68
65
5
10
15
20
67
30
5.0
Electrode at 0.75 V
5.5
Fig. 4: Total hydroxycinnamates in Sauvignon blanc
wines from 6 different countries
6.0
1
320 nm - Hydroxycinnamates
61
3
Control + SO2 + GSH
67
Control + caffeic acid
65
4
6
7
8
Control + caffeic acid + O2
4
5
60
63
48
43
The values shown in tab. 1 are means of triplicates of each
treatment.
SO2 (30 mg/L), GSH (10 mg/L), caffeic acid (100 mg/L),
O2 (> 8 ppm)
0.0
Compounds in an 18 month old wine
2
Control + GSH
25
0
10
20
30
40
9
50
Time (minutes)
1 = glutathione; 2 = caftaric acid; 3 = GRP; 4 = t-coutaric
acid; 5 = fertaric acid; 6 = caffeic acid; 7 = p-coumaric
acid; 8 = ferulic acid; 9 = t-resveratrol
Total hydroxycinnamates [mg/L]
Day 28
0.5
GSH
100
100
(3000 ng/L) (700 ng/L)
HPLC response
Control
GSH
1.0
70
60
Hawkes Bay Wairarapa
Marlborough
50
40
30
20
10
0
4. Conclusions
 The low glutathione levels (~ 0.8 mg/L or less in 18 month old New Zealand Sauvignon blanc wines) might be a reason for the instability of
the volatile thiols 3MH and 3MHA in bottled wines. The level of hydroxycinnamates, the initial substrate of wine oxidation, was similar across
New Zealand regions and compared to overseas wines.
 The addition of sulfur dioxide and glutathione lessened the decrease in 3MH and 3MHA over a four week period, whereas in the presence of oxygen and
caffeic acid 3MH and 3MHA declined by 37 % and 57 %, respectively. 3MHA was a little less stable than 3MH in this study.
Acknowledgements
wine
science
This research is supported by the New Zealand Foundation for Research, Science and Technology.
The author acknowledges the support of the Wine Science group at the University of Auckland.
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