17A-7 |
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N. A. KOCAOGLU-VURMA and P. D. Courtney. Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Ct., 110 Parker Food Science Bldg., Columbus, OH 43210-1007 Nonstarter Lactobacillus strains affect the quality of many cheese varieties. Nonstarter bacteria are present in the cheese, but were not intentionally added as part of the starter cultures during the processing. The objective of this study was to isolate and identify nonstarter Lactobacillus strains in high quality commercial Swiss cheese samples manufactured in Ohio or imported from Switzerland. Ohio Swiss cheeses were obtained directly from five cheese plants and two cheeses manufactured in Switzerland were purchased at a local supermarket. A one-gram sample, aseptically removed from the interior of the cheese, was homogenized in 2% sodium citrate solution, serially diluted and plated on Rogosa SL agar, a medium selective for the genus Lactobacillus. To differentiate the strains, eighty colonies were selected from each cheese and genetically typed by pulsed field gel electrophoresis. The species of each different strain was identified by PCR amplification and DNA sequencing of the spacer region between 16S and 23S rRNA genes. The sequences obtained from the isolates were compared to sequences in the GenBank database. The total number of Lactobacillus cells ranged from 4.8 x 104 to 7.1 x 107 CFU/g cheese. Strains belonging to L. casei, L. rhamnosus, and L. fermentum species were most frequently encountered. Lactobacillus casei strains predominated in the cheeses originating in Switzerland; whereas, the cheeses from Ohio contained a wider variety of Lactobacillus species, including different strains of L. casei, L. rhamnosus, L. gasseri, L. delbrüeckii, and L. fermentum. Characterization of nonstarter strains from high quality cheeses may lead to new adjunct cultures specific for Swiss cheese. Understanding the occurrence and types of nonstarter Lactobacillus in Swiss cheese will allow further studies of their role in cheese ripening and their effect on Propionibacterium fermentation.
Session 17A, Dairy Foods: Cheese and microbiology
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