Purpose: The objective of this study was to investigate the thermal inactivation of desiccation-adapted Salmonella spp. in aged chicken litter and to examine potential cross-tolerance of desiccation-adapted Salmonella spp. to heat treatment.
Methods: A mixture of four Salmonella serotypes was inoculated into the finished compost with 20, 30, 40, and 50% moisture contents for a 24-h desiccation adaptation. Afterwards, the compost with desiccation-adapted cells was added into the aged chicken litter with the same moisture contents for heat treatments at 70, 75, 80, and 150°C. Recovery media were used to allow injured cells to resuscitate.
Results: A 5-log reduction of the desiccation-adapted Salmonella cells in chicken litter with 20% moisture content required >6, >6, and 4~5 h exposure at 70, 75, and 80°C, respectively, whereas the same reduction in non-adapted control with 20% moisture content was achieved within 1.5~2, 1~1.5, and 0.5~1 h at 70, 75, and 80°C, respectively. Time required to obtain a 5-log reduction in desiccation-adapted cells gradually became shorter as temperature and moisture content were increased. At 150°C, desiccation-adapted Salmonella survived for 50 min in chicken litter with 20% moisture content, whereas control cells were detectable by enrichment until only 10 min.
Significance: Our results demonstrated that the thermal resistance of Salmonella in aged chicken litter was increased significantly when the cells were adapted to desiccation. Therefore, the chicken litter processors need to validate and modify their heating process in order to eliminate Salmonella that may be subjected to dry stress.