Four frozen turkeys were used in the study. The turkeys were thawed in a refrigerator. The weight of the turkeys ranged from 11.7 to 25.5 pounds. Hence, they would take different times to cook. The carcasses were thoroughly washed, dried with a towel, and were stuffed with stuffing prepared using a standard recipe formulation. Cultures of Staphylococcus aureus, Salmonella typhimurium, and Clostridium perfringens were added to the stuffing of two turkeys. The population of each organism ranged from 100,000 per gram to 10,000,000 per gram of stuffing.
The stuffed turkeys were placed in a preheated, 350F oven and baked for 1 hour. The temperature of the oven was then reduced to 225F, and the turkeys were roasted an additional 12 hours. If the juice of the turkeys was pink, the turkeys were roasted an additional 1 to 2 hours at 300F, or 1 hour at 350F. A critical fact was that the final temperature of the stuffing was 165F. The longest time between start of cook and getting to above the safe temperature of 130F for the slowest cooking / largest turkey was about 8 hours.
As expected, no salmonellae or staphylococci was recovered. Actually, if the stuffing had been sampled at 140 to 150F, they would have found that these organisms would probably be dead, considering integrated lethality. Remember, 140F for 12.7 minutes gives a 7D reduction of Salmonella.
The results for C. perfringens were positive. A temperature of 165F for 10 seconds is very lethal for salmonellae and staphylococci, as these are vegetative pathogens. The spores of C. perfringens, of course, survive 165F. On the other hand, the vegetative cells of C. perfringens that cause illness are destroyed when the stuffing reaches about 145F. Thus, the turkeys cooked in this manner would be safe as long as they are above 130F. Of course, uneaten portions of the stuffing (and turkey) must be handled properly to prevent C. perfringens "toxinfection" from the outgrowth of the spores.
How long does one have in cooking to get above the safe temperature of 130F? Willardsen et al. (1978) reported on the multiplication of the C. perfringens vegetative cells in precooked hamburger during slow come-up in cooking. If the time to go from 50 to 130F was about 7.6 hours, the vegetative cells might multiply 10,000 to 1. If the time was 5.8 hours, the multiplication would be about 1,000 to 1. If the time was 3.5 hours, the multiplication would be about 10 to 1. By the time the hamburger reached 140F, the C. perfringens that had multiplied were all destroyed. They used C. perfringens strains that multiplied about one every 7.5 minutes at 113F. Common illness strains multiply more like once every 15 minutes at 113F. Hence, this experiment was looking for extremes of safety. The times would probably be twice that reported for more "normal" C. perfringens.
From a HACCP perspective, what would be our concern? It would be toxin production from S. aureus. However, in raw turkey / food, S. aureus does not multiply, because there are competitive spoilage microorganisms. Therefore, with raw turkey, it would not multiply during cooking. Even if it did, as on cooked turkey with 100 S. aureus per gram, which was slowly reheated, the fastest I have found S. aureus to multiply is about once every 20 minutes in milk--3 times slower than the C. perfringens experiment by Willardsen et al. It would have to multiply at least 1,000 to 1, or 10 generations, to make enough toxin to make anyone ill. The danger time to go from 50 to 130F in cooked food starting with 100 S. aureus per gram would be expected to be approximately 3 times that of C. perfringens, or 15 hours. Note, this shows that the FDA-required food reheating to 165F and holding for 15 seconds in less than 2 hours has absolutely no scientific validity. There is a small reason to set a minimum time for raw food cook come-up, but no justification for reheating as a safety control.
It is true that there is a phenomenon whereby Salmonella can double or triple in resistance to kill if it spends some time at about 110F, which it will during slow cooking. However, it makes no difference; 12.7 minutes at 140F gives a 10,000,000-to-1 kill (7D reduction). Assume that the time becomes 45 minutes. During slow cooking, the food still spends plenty of time at lethal temperatures to kill all vegetative organisms.
As a final point, remember, the code says that raw, potentially hazardous food must be held at 41F. There is no science for any temperature by itself. There must be time factored in, because Listeria monocytogenes, Yersinia enterocolitica , and Aeromonas hydrophila all begin to grow at 29.3F. If we choose 7 days at 41F as a control, which actually allows for about 10 multiplications of L. monocytogenes, 45F-4 days, 50F-2.4 days, and 110F-4.5 hours are precisely equivalent for growth (Snyder, 1998). When we use HACCP in retail food operations, no one needs to measure the refrigerators again in terms of hazard control.
There is getting to be an extensive body of science indicating that
below about 55 to 60F, food "spoils safe." The FDA has no justification
for imposing a raw food 41F cold-holding temperature. Epidemiological
experience of the last 100 years suggests that food held at 55 to 60F spoils
safe. From a HACCP point of view, I can find no science that justifies
any cold-holding temperature below 55 to 60F. There are many quality
reasons for keeping raw food at 28 to 32F. However, this is shelf
life, and the government does not regulate shelf life, except for baby
food because of slight nutrient loss.