GROWTH-CHARACTERISTICS OF POST-PASTEURIZATION CONTAMINANTS ISOLATED FROM PASTEURIZED MILK

Nine organisms were isolated from separate pasteurized milk samples af ter they had been incubated at 6 degrees C for 5 d (European Union pre incubated count, PIG); four from high count samples (> 5 x 10(6) cfu/m l) and five from low count samples (< 10(3) cfu/ml). When the organism s were harvested without overt stress being applied and subjected to a simulated PIC using UHT whole milk, all except one isolate gave compa ratively high (> 10(6) cfu/ml) counts. The imposition of a heat stress at 50 degrees C prior to a simulated PIC resulted in a segregation of the isolates into those giving high and those giving low counts, whic h reflected the PIC values of the milk samples from which they were or iginally isolated. When the isolates were subjected to a cold stress ( 25 to 4 degrees C) and inoculated into nutrient broth at 4 degrees C, the high count isolates were found to have significantly (P < 0.05) sh orter lag phases than the low count isolates.