VIABILITY LOSS OF SALMONELLA SPECIES, STAPHYLOCOCCUS-AUREUS, AND LISTERIA-MONOCYTOGENES IN COMPLEX FOODS HEATED BY MICROWAVE-ENERGY

The chemical composition of five foods (UHT milk, beef broth, pudding, cream sauce, and liquid whole egg) was examined to determine factors important in achieving uniform temperatures within foods heated in a 7 00 W microwave oven. Proximate analyses were performed on all food sys tems to relate their chemical composition to temperatures and to destr uction of microwave-heated Salmonella species, Listeria monocytogenes Scott A and V7 and Staphylococcus aureus ATCC 25923. Microwave heating times were chosen such that the final mixed mean temperature achieved by systems was 60 degrees C for Salmonella spp. and L. monocytogenes, and 65 degrees C for S. aureus. The amount of destruction of Salmonel la spp. varied from 3.17 log CFU/ml in UHT milk to 0.44 log CFU/ml in beef broth. L. monocytogenes strains incurred the greatest amount of d estruction in pudding (2.39 log CFU/g), while the least amount of dest ruction was observed in cream sauce (1.63 log CFU/ml). There were no s ignificant differences in the amount of destruction of S. aureus heate d in the five foods. The pH and a(w) of these foods did not affect sur vival of thermally stressed Salmonella, L. monocytogenes, or S. aureus cells. Of the food components examined, sodium content was the primar y influence on the uniformity of temperatures achieved within foods, a nd, in turn, on the survival of bacteria.