WW WDT 15-02
Establishing advanced chromatographic tannin analysis techniques for assessing the influence of different winemaking procedures on red wine tannins
Du Toit, W. J.
De Villiers, A. J.
University of Stellenbosch. Faculty of Science. Department of Chemistry and Polymer Sciences
Du Toit, W J
De Villiers, A
Objectives & Rationale
The main objectives of this project were to develop state-of-the-art chromatographic techniques suitable for quantitative in-depth tannin analysis, and to use these methods to assess the effect of different winemaking and viticultural treatments on tannins and other phenolics in SA red wines. As a parallel objective during this project the relationship between factors affecting tannins and other phenolics in red wine was also assessed.
Several prepared or purchased proanthocyanins were first used to systematically study the fluorescence (FL), ultraviolet (UV) and mass spectrometry (MS) properties of different classes of tannins as a function of concentrations and mobile phase/solvents. Subsequently, reversed-phase liquid chromatography (RPLC) and hydrophilic interaction chromatography (HILIC) methods were developed for grape and wine tannins, and calibration was performed using fluorescence (FL), ultraviolet (UV) and mass spectrometry (MS) detection. These were subsequently used to quantify tannins in grapes and wine, and the relative merits of each mode of detection compared. Powerful comprehensive two-dimensional HILIC×RP-LC methods were also developed for the detailed analysis of proanthocyanidins (PACs) in grape seed and anthocyanin and pigmented tannins in red wine. The suitability of UVVis and Infrared techniques for individual phenolic analyses in wines were also assessed. The tannin and phenolic content of different Shiraz clones, and Shiraz grapes harvested from different ripeness levels were determined. The phenolic evolution during wine fermentation and ageing of these wines were assessed using spectrophotometric and HPLC based phenolic methods. We also followed the evolution of different anthocyanin to tannin ratios in a model wine system.
RRF for different classes of tannins were determined for UV, FL and MS detection. RP-LC-DAD-FLD-MS and HILIC-DAD-FLD-MS were developed and used to quantify tannins in commercial and experimental wine samples and grape seed samples. Detailed quantitative information on the tannin content at molecular level were obtained for these samples. Furthermore, powerful LC×LC-MS methods were developed for the detailed qualitative analysis of wine and grape tannin composition, which provided the tools for the further in-depth study of these compound classes. Ripening influenced the amounts of tannins and their extraction during alcoholic fermentation in Shiraz. Phenolic evolution during wine ageing showed differences over time, but the same sensorial trends due to increased phenolics in wine made from riper grapes was still found over time. Different ratios of tannins to anthocyanins also evolved differently in a model wine over time, which was confirmed with the novel HILIC method.
Results obtained to date show promise for the development of accurate quantitative HPLC-FL-MS methods for tannin analysis. HILIC proved to be more sensitive than RPLC and gives sufficient separation of isomers, and is thus the preferred method. LC×LC provides a powerful method for the detailed qualitative analysis of wine tannins. New easy to perform spectrophotometric analyses for individual phenolic compounds seems like a good alternative for wine producers to follow the evolution of these compounds in red wines. Phenolic differences in terms of Shiraz clones will probably be reflected in the wines. Ripening seems to lead to the increased extraction of tannins in Shiraz during fermentation, which is probably linked to the polysaccharide composition of the grape cell walls. Such higher extraction will probably be maintained in a wine over time and lead to higher astringency. The above-mentioned HILIC method also seems like a good option to study tannin development further in wine.
Terblanche, E. 2016. Development of hydrophilic interaction chromatography(HILIC) and reversed phase LC (RP-LC) methods hyphenated to UV, fluorescence and high-resolution mass spectrometry for the accurate quantification of grape and wine tannins. Paper presented at the 38th South African Society of Enology and Viticulture Conference. 23-25 August, Somerset West, South Africa.
Terblanche, E. 2016. Development of hydrophilic interaction chromatography(HILIC) and reversed phase LC (RP-LC) methods hyphenated to UV, fluorescence and high-resolution mass spectrometry for the accurate quantification of grape and wine tannins. Paper presented at the ChromSAAMS 2016 Conference. 11-14 September, Vanderbijlpark, South Africa.
Garrido-Bañuelos, G, Buica, A, Moore, J P and Du Toit, W J. 2016.Understanding the relationship between phenolic extractability during fermentation and compositional changes of the grape skins cell walls of Vitis vinifera L. Shiraz grapes harvested at different ripening stages. Paper presented at the 38th South African Society of Enology and Viticulture Conference. 23-25 August, Somerset West, South Africa.
Garrido-Bañuelos, G, Buica, A and Du Toit, W J. 2016. Chemical and sensory evaluation over time of Vitis vinifera L. Shiraz wines made from four different ripening stages. Paper presented at the 38th South African Society of Enology and Viticulture Conference. 23-25 August, Somerset West, South Africa.