ABSTRACT
Survival of Salmonella typhimurium in refrigerated water and a 30:70 mixture of ethylene glycol and water was studied. Survival was determined with an MPN procedure using 333 ml of the cooling medium. Initial populations were determined by spread plating 1 ml of sample on 3 plates of XLD. With water as the suspending medium, the temperature of the circulating water was 1°C. When the cooling medium was the glycol/water mixture, the temperature was -1°C. Low numbers of S. typhimurium were recovered from the cold water for 9 d and from the glycol/water mixture for 14 d. The initial population in the water was 310 CFU/ml and 630 CFU/ml in the glycol/water system. A preliminary survey of the pressure relationships in the cooling sections of HTST pasteurizers in 8 fluid milk plants showed that 3 had higher pressures on the coolant side than on the pasteurized side. Such a pressure relationship could result in the contamination of pasteurized milk with the cooling medium.
ABSTRACT
Mesophilic aerobic microbial populations in fresh ground beef were enumerated with a new system, Petrifilm™ SM Plates (PSM), and with the conventional aerobic plate count (APC) method using standard methods agar (SMA). Total colony-forming units were determined in 119 fresh ground beef samples (29 extra-lean, 30 lean and 60 regular) purchased at nine different retail markets over a period of 6 wk. Linear regression analysis of PSM vs. APC counts gave a slope of 0.963, an intercept of -0.027, and a correlation coefficient of 0.951. Mean log10 counts on PSM were 5.86 compared to 6.11 on SMA (P<0.01) or a mean log10 difference of -0.25. These analyses indicate that the Petrifilm SM method would be a possible alternative for the aerobic plate count method.
