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.

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Author notes

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.