FACTORS AFFECTING CULTURABILITY, VIABILITY, AND FILTERABILITY OF DEKKERA BRUXELLENSIS IN RED WINE

Nicole Lynn Umiker

<italic>Dekkera bruxellensis</italic> tolerance to enological conditions makes growth in wine and influence on wine character difficult to manage. The objective of this work was to define <italic>D. bruxellensis</italic> characteristics regarding culturability, viability, and filterability in wine. Forty–eight commercial Washington state red wines suspected of <italic>D. bruxellensis</italic> contamination, determined by winemakers, were donated for this work. Nine strains of <italic>D. bruxellensis</italic>, confirmed by PCR analysis and DNA sequencing, were isolated from eight wines. All isolated yeast strains had infinite inhibition concentrations (IIC) of >0.40 mg/L molecular sulfur dioxide (mSO2) in Yeast/Mold medium. Strains B1b (IIC = 1.09 mg/L mSO2) and F3 (IIC = 0.56 mg/L mSO2), the most mSO2 resistant strains, were further tested in a simulated winemaking setting; regarding detection, culturability, viability, mSO2 addition, filtration, and 4–ethylphenol (4EP) production. Following &sim;0.3, 0.5, and 0.8 mg/L mSO2 addition to wine (after allowing 12 days of growth), strain B1b entered a ‘viable but non–culturable’ (VBNC) state by Day 14. These VBNC cells lacked culturability on non–selective media while esterase activity, membranes, and target DNA sequences were detected. VBNC was determined by quantitative PCR and epifluorescence microscopy. Viable B1b cell size decreased following mSO2 exposure observed by epifluorescence microscopy. Resurgence of culturable strains F3 and B1b populations in all three levels of mSO2 treated wines were detected on non–selective media. Wines (without and with mSO2 additions) filtered through 1.2 μm pore size membranes removed strain B1b from a ‘Syrah’ wine, but failed to remove strain F3 from a blended wine. A membrane with a 0.8 μm pore size successfully removed strain F3 from the blended wine. A simplified 4EP quantification method for wines (50 mL) by liquid–liquid extraction (ethyl acetate:wine = 4:25) and gas chromatography–mass spectrometry (GC–MS) set for selected ion monitoring at <italic>m/z</italic> 107 was optimized. Results from this method were linear, accurate, and reproducible between 50 to 3,200 μg/L 4EP. Strains F3 and B1b growth in ‘Syrah’ wine with differing levels of mSO2 addition were monitored for <40 days regarding culturability and 4EP production. Culturable populations persisted in mSO2 treated wines, without detectable increase in 4EP concentrations.

FACTORS AFFECTING CULTURABILITY, VIABILITY, AND FILTERABILITY OF DEKKERA BRUXELLENSIS IN RED WINE

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