17A-12 |
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H. CHUNG, R. J. McCarthy, and P. Courtney. Ohio State University, Columbus, OH 43210 Propionibacterium species are responsible for eye and flavor formation in Swiss cheese. They are introduced as starter cultures or as part of the natural microflora of the milk or cheesemaking environment. The objective was to isolate and characterize Propionibacterium strains from commercial starter cultures and Swiss cheeses. Propionibacterium colonies from 7 Swiss-style cheeses, 2 manufactured in Switzerland and 5 in the U.S., were selected on lithium-glycerol agar medium. Forty colonies from each cheese were genetically typed by pulsed field gel electrophoresis (PFGE). In addition, Propionibacterium strains were isolated from commercial starter cultures. DNA from each isolate was digested with XbaI prior to PFGE. Comparisons between the normalized PFGE band profiles were made using the Dice similarity coefficient, and cluster analysis was performed using the unweighted pair group method with arithmetic average clustering algorithm. PCR using species-specific primers determined the species of each strain. Thirty-nine different Propionibacterium strains were identified, 23 from the cheeses and 16 from starter cultures. The individual cheeses had 1-8 different strains. Thirty-eight strains were classified as P. freudenreichii. Strain P572/107 was identified as either P. freudenreichi or P. acidipropionici using the PCR method. Cluster analysis of PFGE profiles revealed three major groups with an overall similarity of 15%. Group 1 contained only strain P572/107. Group 2 contained all of the strains isolated from U.S.-produced cheeses and one isolate from a Swiss-manufactured cheese. Group 3 contained all starter culture isolates except P572/107 and four isolates from Swiss-manufactured cheeses. Cheese isolates tended to cluster with other strains isolated from the same cheese. Extensive genetic diversity in dairy Propionibacteriumstrains was observed. Strains from the same source or geographic location tended to have high similarity. Understanding strain diversity and distribution may help identify new strains and genetic markers associated with commercially important traits.
Session 17A, Dairy Foods: Cheese and microbiology
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