30. Recent developments in detection and identification methods for beer spoilage lactic acid bacteria

Koji Suzuki (1); (1) Asahi Breweries, Ltd., Moriya, Ibaraki, Japan

Technical Session 9: Brewing Microbiology
Monday, August 15  •  9:45–11:30 a.m.
Plaza Building, Concourse Level, Governor’s Square 14

Beer spoilage lactic acid bacteria (LAB) are defined as those exhibiting growth capabilities in beer despite the presence of hop bitter acids and other inhibitory factors for growth. Beer spoilage LAB are considered as a subgroup of microorganisms that have chosen beer brewing environments for their habitat and progressively developed various defense mechanisms to survive in beer. Under these evolutionary backgrounds, detection and identification methods have been developed to target two genetic markers, hop resistance genes and glucosyltransferase genes, that are found to be spreading among beer spoilage LAB through horizontal gene transfer. These two groups of genetic factors are known to confer competitive advantages in beer brewing environments and help beer spoilage LAB to survive in beer. For instance, hop resistance genes confer resistance to hop bitter acids—major antibacterial agents in beer. On the other hand, glucosyltransferase produces extracellular polysaccharides (EPS) around the cells of beer spoilage LAB. EPS act as a protective barrier against pasteurization processes and disinfectants used in breweries, making the beer spoilage LAB strains with glucosyltransferase genes hard to eradicate from brewing environments. Taking advantages of these phenomena, the species-independent detection methods targeting the above genetic factors help brewers detect and identify LAB strains belonging to as yet uncharacterized beer spoilage species. In addition, the species-independent methods lead to more accurate evaluation of the beer spoilage ability and other threatening characters of detected LAB strains, which cannot be fully assessed by conventional species-specific approaches. On the other hand, the profound adaptation to beer brewing environments by spoilage LAB has given rise to another problem—the emergence of hard-to-culture beer spoilage LAB that fail to grow in quality control laboratory media. In the face of this problem, a novel culture-independent method using a pressure cycling technology and PCR has been developed to comprehensively detect beer spoilage LAB strains, including hard-to-culture ones. This culture-independent method enables the detection and identification of beer spoilage LAB within 8 hr, and the detection limits are a few cells/300 mL of beer. This level of sensitivity and swiftness enables rapid action for brewers without waiting for results from traditional culture media. An additional less laborious approach has also been developed to use a new culture medium for hard-to-culture LAB, in combination with a microcolony method that allows the detection of beer spoilage LAB within 3 days. When coupled with the fluorescence in situ hybridization test, the beer spoilage LAB strains can be identified to the species level immediately after detection by the microcolony method. In this lecture, recent developments in the detection and identification methods for beer spoilage LAB will be reviewed.

Koji Suzuki obtained an M.S. degree in agricultural chemistry from Tokyo University, Japan. He joined Asahi Breweries, Ltd. in April 1992 as a microbiologist. Since April 2013, he has functioned as manager and principal researcher in the Quality Control (QC) Center and mainly supported microbiological QC activities in breweries and food manufacturing facilities. He received a Ph.D. degree from Tokyo University in 2004 and two awards from the Brewing Society of Japan in 2007 and 2009 for his work concerning hop resistance in beer spoilage lactic acid bacteria. In 2011, he also received a prestigious technology award from the Japan Society for Bioscience, Biotechnology, and Agrochemistry. At present, he lectures on fermentation food science at Meiji University and serves on the editorial board of the Journal of the Institute of Brewing. He has authored many original and review papers, as well as several book chapters, such as those published in Beer in Health and Disease Prevention (Elsevier Science; 2008) and Brewing Microbiology (Elsevier Woodhead; 2015). He is currently a vice chair of the BCOJ Analysis Committee and also serves as a member of the Industry-Government-Academia Collaboration Committee in the Japanese Society for Food Science and Technology.