Unravelling regional typicality of Australian premium Shiraz through an untargeted metabolomics approach

Aims: The current study seeks to demonstrate that premium Shiraz wines from different Australian geographic indications (GI) can be distinguished by their volatile compound composition. 

Method and Results: Barossa, McLaren Vale, Hunter Valley, Canberra District, Heathcote and Yarra Valley were selected to represent a range of climatic conditions. In each region, three to four wines were chosen by a panel of local winemakers to represent the regional wine styles. Volatile fractions of all wines (n = 22) were extracted from 3 bottles, using a solid phase extraction protocol. The extracts were analysed in random order with GC-EI-QTOFMS. Features (a feature is an ion fragment with unique m/z, retention time and intensity) were extracted from the raw MS data and then grouped and deconvoluted, to give 321 ‘compound’ spectra. The feature with the highest intensity in each spectrum was taken to build a classification model using the random forests (RF) algorithm. This model was able to correctly classify all samples according to their GI. Features with lower contributions to the model were gradually eliminated, and 80 features were found to be sufficient to maintain the accuracy of classification. Of these 80 features, 45 were tentatively identified by comparing their mass spectra and Kovats retention indices with either an in-house library or the NIST 14 library. A range of these compounds, including terpenoids, benzenoids, esters, furan derivatives and aliphatic alcohols, have been associated with grape composition, wine making influences and the aging process.

Conclusion:

This study showed that Shiraz wines from different GIs have unique volatile ‘fingerprints’. These classifications may be associated with the unique terroir of the GI, which includes climatic and production differences. Well-designed processing tools for MS data and robust data mining algorithms served as a powerful combination of techniques to uncover the regional ‘fingerprints’.

Significance and Impact of the Study: This study realised the challenging assignment of separating commercial Shiraz wines from six GIs according to their volatile composition. Forming a part of a broader project that include sensory and climate data, it helps to benchmark regional styles of Australian Shiraz wine.