Developing a Novel Method of Analysis for Thiols in Sauvignon blanc

Abstract

New Zealand wine had an export value of $1.21 billion in 2013. Of the total 170million litres of wine exported thatyear, Sauvignon blanc madeup 84.5%. Sauvignon blanc wines have specific flavours and aromas that consumers detect and enjoy including grapefruit, passion fruit,and citrus characters that are due to the presence of sulfur containing thiols. Unfortunately, thiols are also responsible for aromas such as cat’s urine, grass, and gasoline, which taint the flavour of a wine. Careful analysis of these compounds could lead to wines tailored to specific palates and a reduction of taint aromas and flavours, therefore further increasing the market potential for New Zealand Sauvignon blanc. The aim of this project was to further develop an SPME-based technique for thiol analysis of wine that is more reproducible, more accessible, and less toxic than the current method that concentrates the thiols using organomercury columns. To do this, gold nanoparticles were synthesised and coated onto SPME fibres in an attempt to selectively extract thiols from wine samples. Initial results showed an inconsistency between analyses and led to the need for a more comprehensive analysis ofthe gold surface,the gold-sulfur bond, and its RED-OX chemistry. Techniques employed for analysis of the gold surface included scanning electron microscopy, transmission electron microscopy,zeta-sizing and UV-VisSpectrophotometry. To examine the interactions between gold and sulfur, Surface-Enhanced Raman Spectroscopy and computational chemistry were used. The RED-OX chemistry was initially assessed in terms of the carrier gas in the gas chromatographs but was later changed to reductive and oxidative dips. It was found that an H2O2 dip in between samples oxidised the bound thiolates to a series of dimers that were easier to remove from the gold. While not yet completely resolving the hysteresis observed in previous attempts, this method of cleaning the fibres will lead to future experimentation and development in this area.