FOOD 3230 Study Guide - Health Canada
1 Dec 2012
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Result (cfu/g or cfu/ml) = initial dilution subsequent dilution ave count / volume (ml) Initial dilution is the first dilution which dilutes the original solid or liquid sample in buffer. In lab 1 shrimp tests, the initial dilution was prepared by putting 25g shrimp into 225ml buffer. Subsequent dilution is the following 10 fold dilutions. In lab 1, they were prepared by transferring 1ml sample from initial dilution (in stomach bag) to test tube with 9ml buffer. The further dilutions were prepared in the same way. So the dilutions in there test tubes were 10-2, Ave count is typical colony number on the plate. If 2 or more parallel tests are performed, the number is average number of each test. Volume (ml) is volume of diluted sample added on the plate. Normally, pour plate method requires 1ml and spreading method need 0. 1ml. Note: you do not need to calculate all colony number from all dilutions.
