2. Materials and methods
2.1. Challenge tests and Salmonella growth models
Primary and secondary Salmonella growth models were developed
based on experimental data generated from inoculation of
sterile ground pork meat.
Packages of approx. 500 g of modified atmosphere packaged
(MAP) ground lean pork were obtained from a local retailer. The
packages used for preparing sterile meat were mixed manually in
a sterile bag for 10 min. Portions of 100 3 g were vacuum packaged
and frozen at 18 C. Sterilization of volumes of 5 times 100 g
of frozen samples was done by irradiation at a dose of 5 kGy for
523 min, followed by freezing at 18 C. Prior to challenge tests
100 g portions of vacuum packed sterilized ground meat were
defrosted in water at a temperature of approx. 40 C for 30 min.
Three Salmonella strains, previously isolated from pigs and
characterized by the National Food Institute at the Technical
University of Denmark, were studied. Salmonella Typhimurium
DT104 (77-20547) carried resistance to ampicillin, chloramphenicol,
florfenicol, streptomycin and sulfa. Salmonella Typhimurium
DT12 (R77) was resistant to rifampicin and Salmonella Derby (77-
20390) carried resistance to gentamycin, streptomycin, sulfa and