Hydroxycinnamic acid decarboxylase activity of Brettanomyces bruxellensis involved in volatile phenol production: Relationship with cell viability

Brettanomyces bruxellensis populations have been correlated with an increase in phenolic off-flavors in wine. The volatile phenols causing the olfactory defect result from the successive decarboxylation and reduction of hydroxycinnamic acids that are normal components of red wines. The growth of B. bruxellensis is preventable by adding sulfur dioxide (SO2), with variable effectiveness. Moreover, it was hypothesized that SO2 was responsible for the entry of B. bruxellensis into a viable but non-culturable (VBNC) state. The aim of this project was to investigate the effects of SO2 on the remaining enzyme activities of B. bruxellensis populations according to their viability and cultivability, focusing on the hydroxycinnamate decarboxylase enzyme, the first enzyme needed, rather than the metabolites produced. Enzyme activity was determined both in cell-free extracts and resting cells after various SO2 treatments in synthetic media. After slight sulfiting (around 50 mg/L total SO2), the yeasts had lost part of their enzyme activity but not their cultivability. At higher doses (at least 75 mg/L total SO2) the majority of yeasts had lost their cultivability but still retained part of their enzyme activity. These results suggested that non culturable cells retained some enzyme activity. ► Effects of SO2 on enzyme activity of Brettanomyces bruxellensis. ► Relationship between viability, cultivability, and enzyme activity. ► Low dose of SO2 leads to a small loss of activity but not cultivability. ► High dose of SO2 leads to a loss of cultivability but not a total loss of activity. ► Cells in a non-culturable state may exhibit enzyme activity.