Investigating the impact of non-Saccharomyces yeast on wine composition – focus on extracellular enzymes of enological interest
University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology
Du Toit, M
Bauer, F F
Jolly, N P
Over the past two decades, research has shown that certain non-Saccharomyces yeasts can be co-inoculated with S. cerevisiae in order to enhance the aromatic complexity of wines. Part of the contribution these non-Saccharomyces yeasts has been attributed to the secretion of extracellular enzymes (e.g. pectinases, glycosydases and proteases) that could break down certain grape compounds such as pectin, glycosylated aroma compounds and haze-forming proteins, respectively. In this study, a large collection of non-Saccharomyces yeasts was screened for these enzyme activities. The results show that pectinase activity is only found in Kluyveromyces marxianus. β-glucosidase activity was much more common and protease activity was the strongest in Metschnikowia pulcherrima and Zygoascus meyerae. Large strain variation was identified. The identification of extracellular proteins at the end of fermentation revealed that the main oenologically relevant enzymes present were glucanases and β-glucosidases. Novel protease genes from M. pulcherrima and Z. meyerase were retrieved. Their expression and the impact of their corresponding enzymes are currently under investigation in a follow-up project (IWBT W14/01). In conclusion, this study confirmed that non-Saccharomyces yeasts secrete a range of extracellular enzymes that could be of oenological interest. We also retrieved novel genetic genes encoding these enzymes. However, the actual secretion of these enzymes could only be partially confirmed under fermentative conditions and the actual activity and impact of these enzymes was not investigated. In future projects, we therefore propose to perform fermentations with pure and mixed yeast cultures and monitor the secretion and extracellular enzyme activity on wine substrates in order to confirm the relevance of these enzymes from an oenological perspective. In particular, the oenological potential of K. marxianus, M. pulcherrima and Z. meyerae should be investigated.
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