Preincubation Test to Rapidly Identify Post-Pasteurization Contamination in Milk and Single Cream

A test involving preincubation of samples at 21°C for 25 h in the presence of a mixture of nisin:penicillin:crystal violet to prevent growth of gram-positive organisms was used to identify post-pasteurization contamination of milk and single cream. This test (P-INC test) could successfully predict the level of contamination after storage at 6°C for 7 din 85% of milk samples and 86.1% of cream samples studied. A Bacillus sp. which was resistant to the inhibitors used in the test was isolated from only cream samples. However, growth of this organism did not significantly affect accuracy of the test.