ARS | Publication request: Factors affecting culturability, viability, and filterability of Dekkera bruxellensis in red wine

Submitted to: Ph D Dissertation
Publication Type: Other
Publication Acceptance Date: April 14, 2011
Publication Date: August 1, 2011
Citation: Umiker, N., Lee, J., Ross, C., Unlu, G., Smith, D. 2011. Factors affecting culturability, viability, and filterability of Dekkera bruxellensis in red wine. Ph D Dissertation. Washington State University. 116 p.

Technical Abstract: Forty-eight commercial Washington red wines suspected of Dekkera bruxellensis contamination, determined by winemakers, were donated for this work. Only eight out of 48 wines were confirmed to contain D. bruxellensis by PCR analysis and DNA sequencing. Nine strains of D. bruxellensis, one Candida pararugosa, and one Pichia guilliermondii were isolated from ten wines. All isolated yeast strains had infinite inhibition concentrations of >0.29 mg/L mSO2 in Yeast/Mold media. Strains B1b and F3, the most mSO2 resistant strains at pHs 3.5 and 3.8, were further tested in a simulated winemaking setting; regarding detection, culturability, viability, mSO2 addition, filtration, and 4-ethylphenol (4EP) production. Following ~0.3, 0.5, and 0.8 mg/L mSO2 addition to wine (after allowing 12 days of growth), B1b entered a viable but non-culturable state (VBNC) on Day 14: lack of culturability on non-selective media while esterase activity, membranes, and target DNA sequences were intact. VBNC was determined by quantitative PCR and epifluorescence microscopy. Viable B1b cell size decreased following mSO2 exposure observed by epifluorescence microscopy. Resurgence of culturable F3 and B1b populations in all levels of mSO2 treated wines were detected on non-selective media. Wines (without and with mSO2 additions) filtered through 1.2 µm pore size filters removed B1b from a ‘Syrah’ wine, but failed to remove F3 from a blended wine. A membrane with a pore size of 0.8 µm successfully removed F3 from the blended wine. A simplified 4EP quantification method for wines by liquid-liquid extraction and GC-MS set for selective ion monitoring at m/z 107 was evaluated. Results from this method were linear, accurate, and reproducible between 50 to 3,200 µg/L 4EP, encompassing reported human sensory threshold. 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 of F3 and B1b increased in wine following mSO2 treatment, without increasing 4EP levels (remained >1,500 µg/L).