Validating Thermal Inactivation of Salmonella spp. in Fresh and Aged Chicken Litter

Abstract

Our results revealed that a 7-log reduction of Salmonella can be achieved by exposing fresh chicken litter for 80.5 to 100.8, 78.4 to 93.1, and 44.1 to 63 min at 70, 75, and 80°C, respectively, depending on initial moisture contents. However, the aged chicken litter requires more heat treatment.A pproximately 14 million tons of poultry litter, most of which was broiler litter (68%), was produced on U.S. poultry farms in 1990, and over 90% of poultry litter is applied to agricultural land (22). However, the direct application of this waste material to agricultural land can be harmful to the environment due to nutrient and pathogenic microorganisms in runoff (14,29). Salmonella-contaminated litter can be a potential source of produce contamination in the agricultural field due to the prolonged survival of Salmonella in the environment (9, 17). Heat treatments are usually recommended to reduce or eliminate potential pathogenic microorganisms in animal wastes. To produce a heattreated product that tests negative or at less than the detection limit for Salmonella, the temperature range of 65 to 80°C for 30 to 60 min was recommended by different organizations or federal agencies (11,23,33). The California Leafy Green Marketing Agreement (LGMA) has a strict guideline for physically heattreated animal manure. A minimum temperature of 150°C for 60 min, resulting in a moisture content of less than 30%, and a negative result or a result that is less than the detection limit for fecal coliforms, Salmonella, and Escherichia coli O157:H7 are required (3). However, there were no defined heat sources (dry versus moist heat), varying time-temperature requirements, and microbial standards among the guidelines.Most research on heat inactivation of pathogens has shown that dry heat requires a much higher temperature than moist heat to achieve comparable pathogen inactivation in sludge (4,24,37). In contrast, there are few quantitative data on the effects of dry heat on pathogen inactivation. examined thermal inactivation of Salmonella artificially inoculated in sludge using dry heat. Salmonella populations were reduced by ca. 6 logs after 30 min and by more than 8 logs after 90 min at 80°C. Davey (8) calculated that the time required to inactivate clumps of bacteria heated in dry air is about 19 times more than in moist heat.The purpose of this study was to evaluate thermal inactivation of Salmonella spp. in chicken litter under different temperatures, moisture levels, and litter compositions.Preparation of chicken litter. Fresh chicken litter was collected daily from a chicken house of laying hens (single-comb white leghorns), which were raised on the Morgan poultry farm, Clemson, SC. The majority of the litter was feces mixed with a small amount of feathers and wasted feeds. The litter was dried under a hood until the moisture content was reduced to less than 30% and then ground to a particle size of less than 3 mm (sieve pore size, 3 by 3 mm). Aged chicken litter was collected from a local poultry farm (Westminster, SC) where 4...

Drying of Poultry Manure for Use as Animal Feed

“…The authors observed that the aerobic and anaerobic microbial counts could be significantly reduced if the moisture content of the sample was reduced to less than 10%. Kim et al (2012) studied the thermal inactivation of Salmonellae in broiler litter by dry heat and found that the temperature and moisture content affected the survival of Salmonellae in the litter. They reported the time required for a 7 log reduction in Salmonellae at 30% moisture content to be 80, 78 and 44 min for the 70, 75 and 80°C drying conditions respectively.…”

Thermal Inactivation of Desiccation-Adapted Salmonella spp. in Aged Chicken Litter

“…However, chicken litter may contain loads of human pathogens, such as Salmonella spp., that have great potential to directly or indirectly contaminate fresh produce and cause food-borne disease outbreaks (1). Currently, high-temperature processing is the most commonly applied method to reduce or eliminate potential pathogens in chicken litter (1,4).…”

Effects of Chicken Litter Storage Time and Ammonia Content on Thermal Resistance of Desiccation-Adapted Salmonella spp

“…However, some pathogenic cells may become acclimatized to hostile environments during stockpiling or composting, which can cross-protect them against subsequent thermal treatment (1, 7). A limitation regarding most published thermal inactivation studies on pathogens in compost and manure is that the conclusions are primarily based on using nonstressed cells (5,6), and the data obtained from these studies can be misinformed or biased. Currently, the use of stressed cells in the challenge studies on validating the efficacy of heat-based hurdles for food-borne pathogens is still novel, and few examples of quantitative assessments are available in the published literature (8,9).…”

“…Notably, chicken litter is a heterogeneous waste product with variable compositions and differences in physical, chemical, and microbiological properties, which can be affected by storage time and other factors (6). In addition to composting, physical dry-heat treatment after composting or without composting is one of the most commonly used methods to eliminate potential pathogens in chicken litter (6). The storage time of chicken litter may, to some extent, affect the thermal inactivation of food-borne pathogens.…”

“…Temporary storage should thus be provided until conditions are proper for direct application on land or until the litter can be composted or further heat processed. Notably, chicken litter is a heterogeneous waste product with variable compositions and differences in physical, chemical, and microbiological properties, which can be affected by storage time and other factors (6). In addition to composting, physical dry-heat treatment after composting or without composting is one of the most commonly used methods to eliminate potential pathogens in chicken litter (6).…”