FACTORS INFLUENCING THE RECOVERY OF PSYCHROTROPHIC, MESOPHILIC AND THERMOPHILIC BACILLUS SPP FROM BULK RAW-MILK

Because of the wide range of physiological properties found in the gen us Bacillus one of the main problems in the standard procedure for iso lating these organisms from milk and dairy products is the difficulty in defining conditions which are suitable for the activation and outgr owth of all spores present. This study investigated the effects of var ious raw milk heat treatments, the addition of L-alanine (a nutrient e ncouraging germination) to the milk after heat treatment, different in cubation temperature-rime combinations and two confirmatory media on t he recovery of psychrotrophic, mesophilic and thermophilic Bacillus sp p occurring in raw bulked milk. There was no significant difference (p >0.05) between the confirmatory media used, ie, starch milk agar and m ilk plate count agar. However, it was found that heat treatment, addit ion of L-alanine and the incubation period had significant effects on the recovery of the organisms from raw milk. The highest numbers of ps ychrotrophic and mesophilic spores were recovered after a heat treatme nt of 80 degrees C for 10 min followed by the addition of L-alanine to the milk at 0.1 % w/v, and incubating at 6.5 degrees C for 15 days fo r the former find 30 degrees C for 15 days for the latter. The highest numbers of thermophilic spores were recovered from raw milk by a heat treatment of 80 degrees C for 30 min, addition of L-alanine and incub ating at 55 degrees C for 7 days.