Article by Wineland Magazine

Introduction

It has been known for the past 30 years that glutathione can play a role in the anti-oxidant capacity of wine, but new interest has been sparked in this molecule. This article will focus mainly on the latest findings on the role of GSH in wine, as well as recent research conducted at the Department of Viticulture and Oenology, Stellenbosch University.

Molecule

Glutathione is a tri-peptide consisting of three amino-acids glutamate, cysteine and glycine. Glutathione in wine grapes mainly exist in either the reduced form (GSH, Figure 1), the oxidised form (GSSG) or as the grape reaction product (GRP). Some other intermediates can also exist at very low levels in wine, but the three major forms will be discussed in this article. As can be seen from Figure 1, GSH has a free sulfhydral moiety on the cysteine residue, lending it specific anti-oxidant properties. GSSG forms on the oxidation of GSH and does not have anti-oxidant properties.

GSH in grapes

GSH is formed during ripening on the vine and is thought to be produced in the leaves and transported to the berries. GSH levels have been found to increase significantly after veraison, with some authors finding levels to stabilise after 16°B, while others reported that it increases until commercially harvest in Sauvignon blanc grapes.

Other factors such as vintage, location and certain viticultural practices may all influence GSH levels in grapes. Grapes harvested from nitrogen deficient vines that were exposed to nitrogen fertilization after bloom had significantly higher GSH levels compared to those that did not receive fertilisation. However, it is unknown whether these tendencies will occur in vines with high nitrogen availability. GSH levels in grapes at harvest can range from 10 to 80 mg/L.

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