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Microbial trends in Cheddar cheese produced in different regions of the United States |
N. A. KHILLA1, T. Considine2, E. Vedamuthu, and N. Y. Farkye. (1) Dairy Products Technology Center, California Polytechnic State University, San Luis Obispo, 1 Grand Avenue, San Luis Obispo, CA 93407, (2) Dairy Products Technology Center, California Polytechnic State University, 1 Grand Avenue, San Luis Obispo, CA 93407 Cheddar cheese is the most popular variety consumed in the US. Microflora indigenous to specific plants are believed to be responsible for the unique flavor of Cheddar. Its flavor is also influenced by starter bacteria, non-starter lactic acid bacteria (NSLAB) rennet, ripening conditions and the overall microbial ecology of the cheese. Commercial Cheddar cheeses were obtained directly from manufacturers in 7 states. The cheeses had been ripened for 2 months (group A) and 7-10 months (group B) before receipt. On arrival, cheeses were stored at 8°C and sampled at day 0 (initial sampling) and at 3, 6 and 9 months (equivalent to 2, 5, 8 and 11 months old for group A and 7, 10, 13 and16 months old for group B) of ripening for starter and NSLAB. The samples were enumerated on M17, MRS and Rogosa agar. In general, starter colonies enumerated on M17 decreased over the six month period from 106 to 104CFU/g. Colonies enumerated on MRS demonstrated an overall growth trend in NSLAB by an increase of approximately one to four log cycles. Colonies enumerated on Rogosa increased approximately by one log cycle. Microbial samples were also taken to qualitatively assess citrate utilization on Reddy’s agar plates. Approximately 35% of group B cheeses contained organisms that demonstrated the ability to use citrate. Colonies grown on Reddy’s agar were then inoculated into a 10% skim milk to screen for acid production and milk coagulation. Twenty-two percent of the samples contained organisms that coagulated skim milk within 48 h at 32ºC. Representative colonies (~1000) were stocked in glycerol, Gram-stained, catalase tested and screened for casein hydrolysis; ~11% of the samples had the ability to hydrolyze casein. Similar results for milk coagulation, Gram-stains, catalase and casein hydrolysis were observed for group A cheeses.
Session 28, Dairy Foods: Developments in microbiology and chemistry of cheese
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