Abstract
Brettanomyces bruxellensis is a wine spoilage concern in wineries around the world. In order to maintain wine quality during storage and ageing, it is imperative to control and monitor this yeast. Being a fastidious slow growing yeast, which requires 5 to 14 days of incubation for visible growth in agar plates, it is difficult to detect growth (colonies) by conventional agar plate count method. Yeast enumeration by impedance was investigated because previous research using other microorganisms has shown that it is potentially faster than plate counting. The relationship between plate counting and impedance detection times was investigated for Brettanomyces inoculated in red wine samples. A linear relationship between log plate count concentrations and impedance detection times was found. Incubation time was reduced from 120 h down to 0.9 and 57.7 h for samples with 6.7 × 107 and 1.8 × 102 cfu/mL, respectively, using the ‘indirect’ impedance method. The ‘direct’ method also reduced the incubation times to 9.5 and 81.9 h, for the same concentrations. The ‘indirect’ impedance method has the potential to be used by the wine industry to control and monitor the Brettanomyces numbers in wines.
Highlights
Brettanomyces bruxellensis is a wine spoilage concern in wineries around the world
The yeast Brettanomyces bruxellensis is one of the major spoilage organisms faced by the wine industry, which leads to economic losses worldwide [3,4]
According to the method used by van Wyk and Silva (2017), the yeast was first streaked onto yeast extract peptone dextrose (YPD) agar and incubated for 5 days at 28 ◦ C
Summary
In 2015, the average global wine production was approximately 2.8 × 1010 L [1,2]. The yeast Brettanomyces bruxellensis (the anamorph Dekkera bruxellensis) is one of the major spoilage organisms faced by the wine industry, which leads to economic losses worldwide [3,4]. Malacrino et al (2001) found that flow cytometry in combination with fluorescent dyes can be used to estimate yeast and bacteria counts in wines [10] This is a rapid enumeration method, with high specificity and the ability to analyze the physiological state of cells [8]. Due to the lower growth rate of Brettanomyces compared to other yeasts, new technologies, including impedance, could have the potential to reduce detection and enumeration times. The impedance enumeration method measures the change in impedance caused by microbial growth in a selective medium under an alternating current (AC) field. Impedance detection time is defined as the time from the start of the measurement period until the signal exceeds the specified M- or E-value threshold For both methods, impedance is evaluated based on the growth of microbial cells added to the BacTrac measuring vials. Filter sterile red wine samples were inoculated with only B. bruxellensis with the main objectives: (i) to investigate the relationship between plate counting and impedance detection times in red wine; and (ii) to validate and compare the ‘direct’ and ‘indirect’ impedance methods using a different red wine
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