This study evaluated survival of a radiation-resistant organism, Streptococcus faecium, as a potential indication of safety of beef loaf and potatoes after microwave-heating in a hospital cook/chill foodservice system. The cook/chill system was simulated in a laboratory three times for both beef loaf and potatoes. Beef loaf (15 kg) was initially cooked to 66 C in a convection oven (156 C), chilled 24 h at 6 C, cut into 100-g portions, inoculated on the external surface with S. faecium (1 × 108 CFU/g), chilled 2 h, and microwave-heated for 20, 50, 80 or 110 sec. Dehydrated potatoes (5.7 kg) were reconstituted to 79 C over direct heat, chilled to 37 C, inoculated internally with S. faecium (1 × 106 CFU/g), stored chilled 24 h at 6 C, portioned into 100 g/portion, chilled 2 h at 6 C and microwave-heated for 25, 45, 65 or 85 sec. Results indicated that increasing the time of microwave-heating for portions of beef loaf or potatoes decreased the count on KF agar regardless of internal or external inoculation procedure. Eighty or 85 sec of microwave-heating of beef loaf or potatoes resulted in portions with similar numbers of bacteria as determined by KF agar, but mean internal end temperatures ranged from 66 to 95 C.
1Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison.
2Present address: Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48823.