Discriminating wine yeast strains and their fermented wines : an integrated approach
Thesis (MSc (Wine Biotechnology))--University of Stellenbosch, 2007.
The discrimination between wine yeast strains as well as between their fermented wines has been investigated in this pilot study. The study was divided in two parts, the first to investigate the discrimination between wines fermented with five different Saccharomyces cerevisiae yeast strains, analysed by gas chromatography (GC) and Fourier transform infrared spectroscopy (FTIR) and the second part to investigate discrimination between wine yeast strains in different liquid media and in dried form using FTIR in transmission and attenuated total reflectance (ATR) modes. Wines from three cultivars (Clairette Blanche, Pinotage and Cabernet Sauvignon) that were fermented by five Saccharomyces cerevisiae yeast strains (VIN13, WE372, VIN13-EXS, VIN13-PPK and ML01) were analysed by GC and FTIR. This analysis was done on individual sample sets that consisted of the wines of each of the mentioned cultivars and also on samples drawn throughout the ageing process of these wines. The data obtained were analysed by PLS-Discrimination (PLS-discrim), a chemometric method. Using the data from both the analytical methods, discrimination was observed between wines fermented with different yeast strains in each of the two vintages (2005 and 2006) for all the cultivars. When combining the data from the two vintages no discrimination could be observed between the fermented wines. The discrimination of the fermented wines was found to be similar when using data from GC and FTIR, respectively. Since analysis with FTIR is considerably faster than analysis by GC, it would be recommended that FTIR is used for future studies of similar nature. Combining the samples into one set consisting of wines fermented with commercial wine yeast strains and wines fermented from closely related wine yeast strains (the parental strain and two genetically modified versions thereof (VIN13, VIN13-EXS and VIN13- PPK), those fermented with closely related stains did not show good discrimination from each other. Discrimination was found between wines fermented with genetically modified (GM) wine yeast strains and those fermented with non-GM wine yeast strains. This was done on a limited number of yeast strains and a larger study is needed to confirm these results. As this is the first study of this nature and differences seen could be as result of the different phenotypes. It was shown that it is possible to use both FTIR-transmission and FTIR-ATR (attenuated total reflectance) to discriminate between different wine yeast strain phenotypes. It was shown that when using FTIR-transmission there is discrimination between yeast samples suspended in yeast-peptone-dextrose (YPD) and in water. Dried yeast samples could be discriminated when the yeast samples were in a granular, powder form or in a pellet form, using FTIR-ATR. It was possible to discriminate between the closely related yeast strain phenotypes using FTIR-ATR. In this pilot study it was shown that there can be discriminated between different wine yeast strains and also between the wines fermented with different wine yeast strains. It is recommended that further studies be conducted to refine and expand the study.