Results

Conclusions

Results

Future Study

• More varietal thiols were formed in the wines when more glutathione or glutathione-ascorbic acid pair were added, in addition to a sub-optimal sulfite application.

• A positive benefit is demonstrated to the formation of polyfunctional mercaptans with passionfruit/ tropical aromas, from additions of glutathione and ascorbic acid at harvest.

• The oxygen or nitrogen applied during fermentation did notresult in the removal of undesirable reductive aromacompounds.

• Juice Analysis: Total soluble solids (Brix), pH, titratable acidity, Yeast Assimilable Nitrogen, free SO2 and 420 nm absorbance.

• Wine Analysis: C6 alcohols and varietal thiols measured using solid phase extraction followed by a GC-MS method [4], while polyphenols and glutathione were quantified by HPLC [2].

• Two gas sparging regimes (oxygen and nitrogen), applying during fermentation, on the removal of reductive sulfur aromas in Sauvignon Blanc wines.

• Further trials are needed to examine increased oxygen as well as nitrogen dosages during fermentation, and their effects on reductive compounds.

1

The Effects of Antioxidants and Gas Sparging on New Zealand White WinesXiaotong Lyu1, Leandro Dias Araujo1, Siew-Young Quek 1, Wessel Du Toit2, Paul A. Kilmartin1

1School of Chemical Sciences, University of Auckland, Auckland, New Zealand2Stellenbosch University, Stellenbosch, South Africa

Introduction

A large number of studies have been carried investigating the drivers behind quality Sauvignon Blanc wines in terms of varietal thiol content, namely 3-mercaptohexanol (3MH) and its acetate ester (3MHA). In this report different levels of the antioxidants glutathione and ascorbic acid were added to grapes at harvest. The effects on the chemical composition and sensory profile of New Zealand Sauvignon Blanc were examined. Elemental sulfur is a common fungicide applied in vineyards before harvest, and has been found to increase the production of desirable polyfunctional mercaptans, but also H2S and unwanted reductive sulfur aroma compounds. This report also investigated the effectiveness of oxygen and nitrogen sparging, applying during fermentation, on the removal of volatile sulfur compounds in New Zealand Sauvignon Blanc wines.

References

1. O. Makhotkina and P.A. Kilmartin, (2009) J. Electroanal. Chem., 633, 165-174.2. O. Makhotkina, L.D. Araujo, K. Olejar, M. Herbst-Johnstone, B. Fedrizzi, and P.A.

Kilmartin, (2104), Am.J.Enol.Vitic., 65, 388-393.3. L. Dias Araujo, S. Vannevel, A. Buica, S. Callerot, B. Fedrizzi, P.A. Kilmartin and W. J. Du

Toit, (2017) Food Res. Int., 98 , 79-86.4. M. Herbst-Johnstone, F. Piano, N. Duhamel, D. Barker, and B. Fedrizzi, (2013) J. Chromatogr. A, 1312, 104-110.

AcknowledgementsI would like to express my deep gratitude to my supervisor Professor Paul Kilmartin, Dr. Leandro D. Araujo,Dr. Mandy Herbst-Johnstone, Ute Herold and Jose Munoz for their precious advices and supports on myresearch. I also want to thank Dr. Frank Benkwitz and Joanne Brady from Constellation Brands New ZealandLtd, for their assistance and guidance with the sample taking in Blenheim. I am very grateful for ChineseScholarship Council for funding my scholarship.

Results

Methodology

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0 GSH 20 GSH 100 GSH 100AA+20GSH 0 GSH 20 GSH 100 GSH 100AA+20GSH 0 GSH 20 GSH 100 GSH 100AA+20GSH

SAUVIGNON BLANC 20173MHA ng/L 3MH ng/L

Site 1 Site 2 Site 3

Additives

Glutathione is an efficient preservative, and is recently being

considered for use during winemaking, as it can scavenge oxidized phenolic compounds to protect wines from oxidation [1,2]. Nevertheless, the amount of the glutathione that can be added prior to alcoholic fermentation is limited (20 mg/kg) by current regulation of International Organisation of Vine and Wine.

Ascorbic acid is another complementary antioxidant to sulfur

dioxide that has a long history of use in winemaking. However, ascorbic acid can have mixed effects in regard to wine oxidation, and cannot be used alone as a substitute for SO2.

Elemental Sulfur is added to grapes as a fungicide to protect

against powdery mildew. Resides of elemental sulfur can act as a source of H2S and markedly increase varietal thiol formation [3].

0 GSH: SO2 20 ppm 20 GSH: SO2 20 ppm + GSH 20 ppm100 GSH: SO2 20 ppm + GSH 100 ppm 100 AA+20 GSH: SO2 20 ppm + GSH 20 ppm + Ascorbic Acid 100 ppmGSH = Glutathione AA = Ascorbic Acid

• Additions of glutathione to the grape juices increased the levels of

polyfunctional mercaptans in the finished wines.

• The lowest levels of polyfunctional mercaptan compounds were

found in the wines with little supplementary antioxidants added.

• A high level of the joint combination of ascorbic acid and

glutathione provided the wines with even higher production of

polyfunctional mercaptans.

• Increasing the amount of elemental sulfur addition to the grape

must before pressing led to an increase in the formation of several

thiol compounds, including some unwanted reductive compounds.

• Few changes were observed in the concentrations of aroma

compounds when the juices were sparged with nitrogen during

fermentation.

• Additions of oxygen during fermentation led to some decrease in

the concentration of polyfunctional mercaptans for the 10 mg/L

sulfur additions, but did not significantly remove reductive aroma

compounds.