WINETECH Technical Yearbook 2020

REFERENCES Kinzurik, M.I., Herbst-Johnstone, M., Gardner, R.C. & Fedrizzi, B., 2015. Evo- lution of volatile sulfur compounds during wine fermentation. Journal of Agricultural and Food Chemistry 63(36): 8017-8024. Nguyen, D., Nicolau, L. & Kilmartin, P.A., 2007. Application of an automated headspace solid phase micro-extraction for the GC-MS detection and quantification of reductive sulfur compounds in wines. Gas Chromatography in Plant Science, Wine Technology, Toxicology and Some Specific Applications. Butzke, C.E. & Park, S.K., 2011. Impact of fermentation rate changes on potential hydrogen sulphide concentrations in wine. Journal of Microbiology and Biotechnology 21(5): 519-524.

By combining the two methods, a wide range of compounds can be measured and thus increase our knowledge regarding the RSC in wine. These methods also open the possibility for new projects and experiments that evaluate the impact that various winemaking techniques and products have on the final composition of wines. They can be applied further to a variety of projects that cover fundamental knowledge, such as the elucidation of pathways related to microorganisms and their metabolites in wine, which will translate into applied knowledge. SUMMARY Organic sulphur (S) compounds play a con- siderable role in the sensory characteristics of a wine, as they are frequently present among the character impact compounds. The presence of reductive sulphur com­ pounds (RSC) in wines can affect quality and typical off-flavours resemble onions, garlic, cooked cabbage, rubber and putre­ faction. The difficulties to overcome when

measuring these compounds are related to the required sensitivity of the analytical technique and to the instability, reactivity and differences in volatility of reductive S compounds. The need for reliable data can be addressed by developing new analysis methods that make use of available technology. Some methods are easy to implement because they make use of low- tech equipment, while others are highly specialised and require state-of-the-art instrumentation. In this study the determination of RSC was divided into two measurement types: • Measurement of H 2 S using a colorimet- ric reaction and • determination of other RSC by GC-MS/ MS. The two methods were proven to give reproducible results and were implemented at the Department of Viticulture and Oenology, in collaboration with the Central Analytical Facility.

Volatility and contamination issues can be encountered in the measurement of RSC by GC-MS/MS if adequate care is not taken. Nevertheless, the developed method has shown to be linear, sensitive and reproducible in the conditions tested. The measurement of H 2 S using the tubes is easy to implement and does not require any high-tech setup. It can easily be transferred to the industry for the producers to measure H 2 S in situ if necessary, while taking into account the restrictions on the measuring conditions to ensure accuracy. The sensitivity can be adapted based on the sample and on the type of tube chosen. At the other end of the technology spectrum, the RSC method requires state-of-the-art equipment. The method is already added to the portfolio of analyses to be performed on commercial and experimental wines. The method is set up at the Chemical Analytical Lab of the Department of Viticulture and Oenology (DVO), in collaboration with the Central Analytical Facility.

For more information, contact Astrid Buica at abuica@sun.ac.za.

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