Rapid Enumeration of Psychrotrophic Bacteria in Raw and Pasteurized Milk

A plating method was developed to enumerate psychrotrophic bacteria in raw and pasteurized milk. Standard Methods agar plates were prepared according to Standard Methods for the Examination of Dairy Products, and incubated at 21 C for 25 h (21 C-25 h). Counts obtained by this method were in very good agreement with those obtained by the standard psychrotrophic count. The correlation coefficients between counts obtained by the 21 C-25 h method and by the standard psychrotrophic count method for 132 samples of raw milk and 190 samples of pasteurized milk were 0.992 and 0.996, respectively.