Developing a Two-step Heat Treatment for Inactivating Desiccation-adapted Salmonella in Aged Chicken Litter

Introduction: Chicken litter may contain a variety of human pathogens, such as Salmonella, that can potentially contaminate fresh produce as an organic fertilizer. Some bacterial cells become acclimatized to desiccation condition in stockpiled chicken litter and develop cross-protection to subsequent dry-heat processing. Dry-heat treatment alone may not readily decrease the desiccation-adapted pathogenic cells to safe levels, resulting in the survival of some heat-resistant desiccation-adapted cells.

Purpose: The objective of this study was to evaluate the effectiveness of a two-step heat treatment for aged chicken litter on elimination of desiccation-adapted Salmonella.

Methods: Aged chicken litter with 20, 30, 40, and 50% moisture contents was inoculated with a mixture of four Salmonella serotypes for a 24-h desiccation adaptation. Afterwards, the chicken litter with desiccation-adapted cells was added into litter with the same moisture contents for a 1-h wet-heat treatment at 65°C and 100% RH inside a water bath. The inoculated litter was then dry-heated in a convectional oven at 85°C for 1h to the desired moisture level (<12%).

Results: After wet-heat treatment, the populations of Salmonella in aged chicken litter at 20 and 30% moisture contents decreased from 6.7 log CFU/g to 3.3 and 3.0 log CFU/g, respectively, and after subsequent dry-heat treatment, the populations decreased to 3.0 and 2.6 log CFU/g, respectively. Salmonella cells in litter samples at 40 and 50% moisture contents were only detectable by enrichment for 40 and 20 min of wet-heat treatment, respectively. Moisture contents in all samples were reduced to <12% after drying process.

Significance: Our results demonstrated that the two-step heat treatment was effective in reducing >5.5 logs of desiccation-adapted Salmonella in chicken litter with moisture content at or above 40%. Therefore, the findings from this study provide the industry with a cost-effective heat treatment method for processing chicken litter.