Chemical evaluation and sensory relevance of thiols in South African wine: Chenin blanc and selected red cultivars

Project Number
WW ASB 15-01

Project title
Chemical evaluation and sensory relevance of thiols in South African wine: Chenin blanc and selected red cultivars

Project leader
Buica, A

Institution
Stellenbosch University. Department of Viticulture and Oenology

Team members
Buica, A
Du Toit, W
Stander, M
Mokwena, L
Brand, J
Panzeri, V

Project description
Thiols, 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) are important components of wine, as they have strong aromas associated with their presence even at ultra-trace level (ng/l). Correlations between chemical composition and perception attributes can lead to a better understanding of wine aroma from a consumer’s and expert’s point of view. In order to achieve this, both chemical analysis methods and sensory methods have to be well-established and robust.

Additionally, it is known that the level of aroma compounds present in wine can influence their perception (i.e. different attributes for different levels of the same compound) and studying this aspect of wine composition can bring additional relevant knowledge.

For thiols, their low concentration in wine, combined with their labile nature and the complexity of the wine matrix, makes their chemical analysis challenging, but nonetheless of extreme relevance, especially when combined with sensory characterization of wines.

Methods for the chemical analysis of thiols have been proposed for a number of years. They are usually complex and labour intensive, and either not very robust or require equipment that is not standard. We have recently established a robust method for analyzing thiols in white wine that has already made a positive impact on the quality of the results delivered by various projects that made use of it. The challenge now is to develop a similar method for the analysis of thiols in red wines. There are existing methods that can determine thiols in red wine, but they make use of dangerous chemicals (mercury-derived compounds) and equipment that is not readily available.

Chenin blanc is an extremely important wine cultivar in South Africa. Typical sensory attributes often include tropical fruits such as grapefruit, guava and passion fruit, which have been already associated in Sauvignon blanc with thiol compounds. Thiols has not been investigated in Chenin blanc. These aromas also form part of the fruit aromas of other white varieties such as Riesling, Pinot gris and Gewurztraminer.

Thiols are known to occur in of Cabernet Sauvignon, Merlot, Shiraz, Grenache and Malbec. Recent reports indicated the presence of thiols in Bordeaux blends and their correlation with blackcurrant attributes. Clear statistical correlation between chemical composition and sensory attributes has not been established though in single cultivar wines.

The objectives of the research are: Chemical characterization of South African Chenin blanc and selected red wine cultivars (thiol content) and correlation with typical thiol sensory attributes (grapefruit, guava, passion fruit, blackcurrant, etc.). Evaluation of the extent of the influence of thiols present in wine (nature of compound and level) on the sensory attributes (nature and intensity of attributes).

Poster(s)
Wilson, C, Brand, J and Buica, A. 2016. Holistic approach to the characterization of three South African Chenin blanc wine using polarized projective mapping. Poster presented at 1st AfroSense Conference 2015. 23-26 November 2015, Stellenbosch, South Africa.

Buica, A, Brand, J, J, Wilson, C and Stander, M. 2016. Evaluating South African Chenin blanc wine styles using an LC-MS screening method. Paper presented at Macrowine 2016: Macromolecules and Secondary Metabolites of Grapevine and Wine. 27-30 June 20, Changins (Nyons), Geneva, Switzerland.

Buica, A, Brand, J, J and Wilson, C. 2016. Evaluation of polarized projective mapping as a possible tool for attributing South African Chenin blanc dry wine styles. Paper presented at Macrowine 2016: Macromolecules and Secondary Metabolites of Grapevine and Wine. 27-30 June 20, Changins (Nyons), Geneva, Switzerland.

Wilson, C L, Brand, J, Du Toit, W J and Buica, A. 2016. Thiol levels in commercial dry South African Chenin blanc wines. Paper presented at the South African Society of Enology and Viticulture Conference. 23-25 August, Somerset West, South Africa.

Panzeri, V and Buica, A. 2016. Thiol levels in young 2016 fresh and fruity Chenin blanc wines. Poster presented at Focus on Chenin blanc. Oct 2016

Wilson, C, Brand, J, Du Toit, W J and Buica, A. 2017. Interaction of 3MH, ethyl hexanoate, and linalool in dearomatized Chenin blanc by descriptive analysis. Poster presented at Wine Active Compounds. March 2017, Beaune, France. March 2017

Buica, A, Wilson, C, Du Toit, W J and Brand, J. 2017. Thiol interaction in different Chenin Blanc matrices by Projective Mapping (PM) with intensity: Matrix effect. Poster presented at Wine Active Compounds. March 2017, Beaune, France.

Buica, A and Panzeri, V 2017. Thiol levels in young South African Chenin blanc wine and their impact on sensory perception. Poster present at Wine Active Compounds. March 2017 Beaune, France.

Presentation(s)
Brand, J, Wilson, C and Buica, A. 2015. Holistic approach to the characterization of three South African Chenin blanc wine styles: Comprehensive chemical volatile composition and sensory evaluation using polarized projective mapping method. Paper presented at Oeno 2015. 29 June – 1 July 2015, Bordeaux, France.

Panzeri, V and Buica, A. 2016. Thiol levels in young 2016 fresh and fruity Chenin blanc wines. Paper presented at Focus on Chenin blanc, Oct 2016

Brand, J, Wilson, C and Buica, A. 2017. South African Chenin blanc styles description as perceived by local experts. Presented at Wine Active Compounds. March 2017 Beaune, France.

Buica, A and Tredoux, A. 2017. Wine style investigation using untargeted chromatographic approaches and chemometrics. Paper presented at In Vino Analytica Scientia. July 2017, Salamanca, Spain.

Coetzee, C, Du Toit, W J and Buica, A. 2017. Thiol levels in young commercial South African Sauvignon blanc and Chenin banc wines using propiolate derivatization.

Article
Buica, A, Brand, J, Wilson, C, Stander, M. 2017. Evaluating South African Chenin blanc wine styles using an LC-MS screening method, Studia Universitatis Babes-Bolyai Chemia, Mnth June v. 62 (2) (p. 113-123)
10.24193/subbchem.2017.2.09

Thesis
Wilson, C L. 2017. Chemical evaluation and sensory relevance of thiols in South African Chenin blanc wines, Mnth Mar
Wilson_chemical_2017.pdf sequence=1&isAllowed=y

 

 

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