If you could add glutathione, would you?
A research project getting under way on Adelaide’s Waite Campus is designed to find out more about glutathione, for better or worse.
It could reveal the potential value of using this naturally-occurring product more widely in winemaking or highlight potential reasons for caution – or it might land somewhere in the middle.
The aim is to ‘stay ahead of the curve’, according to Dr Simon Schmidt, a Senior Research Scientist at the AWRI, who is collaborating on the four-year project with the University of Adelaide’s Dr David Jeffery and Dr Gabriel Perrone from University of Western Sydney.
Glutathione, or GSH, is a tripeptide found in wine grapes and other living systems including yeast. In humans, it is increasingly being touted as an antioxidant supplement.
The concentration of GSH in grape juice or wine can be manipulated as part of the winemaking process, and it can even be included as an additive, but currently that can only happen indirectly (GSH is a component of commercial inactive dry yeast preparations, for example). However, there are rumblings from Europe about making it a permitted additive in its own right.
The motivation for these rumblings isn’t clear, though Dr Schmidt suspects it may at least in part be a feeling that what GSH can achieve indirectly could more easily be achieved directly, so why not cut out the middle man (or inactive dry yeast in this case). Either way, it helps to understand the implications of such a regulatory change and the potential for Australian winemakers if that happens.
Most GSH research to date has focused on two areas. The first is its role as an antioxidant that protects aromas and prevents browning and therefore its potential to complement or even replace sulfur dioxide as a post-ferment additive for preserving wine quality.
The second is its role as a precursor for varietal thiols and other sulfur compounds, which impact on the aroma of finished wine. As varietal thiols are particularly dominant in Sauvignon Blanc, it’s not surprising that most of this research has been carried out in New Zealand, South Africa and France. However, that is about to change.
‘We are really well placed to take a broad look at GSH and its impact’, Dr Jeffery said. ‘Simon has been working on yeast nutrient demands and the impacts of juice composition on yeast strain performance, we’ve been working on its impact on varietal thiols, and others in the AWRI have been looking at GSH and metals and the post-bottling effects of closures and wine pH.
‘And the phenolics team has been looking at some things that might link GSH to textural and taste properties through a compound known as grape reaction product.’
There are a lot of questions to be answered. We know a lot about how GSH impacts on Sauvignon Blanc, for example, but would that naturally translate to other white wine varieties? Is there a risk that adding GSH might alter some wine styles? As GSH is a natural component of precursors to varietal thiols, could choosing to add more GSH – for whatever reason – lead to an increase in thiols as well?
‘Thiols are important in other varieties as well; they just don’t lead to quite such a dominant aromatic profile as in Sauvignon Blanc’, Dr Schmidt said. ‘It might be subtler in some types of wine; but they are still important components of the aroma profile of the wine. So what would be the potential benefits or risks for the winemaker increasing the GSH content in Chardonnay or Riesling?’
We hope to know more in four years from now.