S R Gray1, H Rawsthorne, B Dirks, T G Phister. 1. Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC 27695-7624, USA.
Abstract
AIMS: In this article, a quantitative real-time PCR assay for detection and enumeration of the spoilage yeast Dekkera anomala in beer, cola, apple cider, and brewing wort is presented as an improvement upon existing detection methods, which are very time-consuming and not always accurate. METHODS AND RESULTS: Primers were designed to exclude other organisms common in these beverages, and the assay was linear over 6 log units of cell concentrations. The addition of large amounts of non-target yeast DNA did not affect the efficiency of this assay. A standard curve of known DNA was established by plotting the C(t) values obtained from the QPCR against the log of plate counts on yeast peptone dextrose medium and unknowns showed exceptional correlation when tested against this standard curve. The assay was found to detect D. anomala at levels of 10-14 CFU ml⁻¹ in either cola or beer and at levels of 9·4-25·0 CFU ml⁻¹ in apple cider. The assay was also used to follow the growth of D. anomala in brewing wort. CONCLUSIONS: The results indicate that real-time PCR is an effective tool for rapid, accurate detection and quantitation of D. anomala in beer, cola and apple cider. SIGNIFICANCE AND IMPACT OF THE STUDY: This method gives a faster and more efficient technique to screen beer, cola, and cider samples and reduce spoilage by D. anomala. Faster screening may allow for significant reduction in economic loss because of reduced spoilage.
AIMS: In this article, a quantitative real-time PCR assay for detection and enumeration of the spoilage yeastDekkera anomala in beer, cola, apple cider, and brewing wort is presented as an improvement upon existing detection methods, which are very time-consuming and not always accurate. METHODS AND RESULTS: Primers were designed to exclude other organisms common in these beverages, and the assay was linear over 6 log units of cell concentrations. The addition of large amounts of non-target yeast DNA did not affect the efficiency of this assay. A standard curve of known DNA was established by plotting the C(t) values obtained from the QPCR against the log of plate counts on yeastpeptone dextrose medium and unknowns showed exceptional correlation when tested against this standard curve. The assay was found to detect D. anomala at levels of 10-14 CFU ml⁻¹ in either cola or beer and at levels of 9·4-25·0 CFU ml⁻¹ in apple cider. The assay was also used to follow the growth of D. anomala in brewing wort. CONCLUSIONS: The results indicate that real-time PCR is an effective tool for rapid, accurate detection and quantitation of D. anomala in beer, cola and apple cider. SIGNIFICANCE AND IMPACT OF THE STUDY: This method gives a faster and more efficient technique to screen beer, cola, and cider samples and reduce spoilage by D. anomala. Faster screening may allow for significant reduction in economic loss because of reduced spoilage.