Poultry litter is attractive to conventional and organic producers alike because of the organic matter and nutrients it contains. But Salmonella cells may adapt to the dry conditions in poultry litter and become more heat resistant during subsequent heat treatments, according to a research hypothesis. To help poultry litter processors produce a product with a reduced risk of Salmonella, Dr. Xiuping Jiang, a professor of food microbiology at Clemson University, Clemson, S.C., is looking at the role moisture and poultry litter types combined with heat play during treatment in commercial plants. The research, titled "Validating a physically heat-
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Key Take-Aways * Salmonella adapted to desiccation may become more heat resistant during poultry litter heat treatments * Project seeks non-pathogenic Salmonella surrogates and indicator microorganisms to validate heat treatments * Trials look at the role moisture levels of 35~37% and 40~45% play in Salmonella deactivation during litter heat treatments |
treated process for poultry litter in industry settings using the avirulent Salmonella surrogates or indicator microorganisms," is about midway through the two-year project.
Ultimately, Jiang said, she hopes to produce guidelines, including residence time, temperature and moisture levels, and tools to help the fertilizer industry modify their practices to enhance the microbiological safety of their products. Not only should the project benefit litter processors, but she said it also is expected to provide greater assurances to fruit and vegetable growers who want to use the animal by-product as a soil amendment. "They will have the confidence that the (poultry litter) plant is processing it the right way," Jiang said.
Joining Jiang as co-principal investigator is Dr. Annel Greene, professor and director of the Animal Co-Products Research & Education Center at Clemson University. The two are working closely with a commercial turkey litter processor and a commercial chicken litter processor to validate their initial laboratory trials and to ensure their research represents real-world processes in commercial facilities.
"They are very involved," Jiang said of the cooperating processors. "They want to know every detail, and they want to know how the results can help them improve product safety. They have several people helping us with our trials because we are not that familiar with their processes." Because turkeys and chickens are fed different diets and raised differently, the composition - including microbial make-up - of the litters differ. That is why Jiang said it is important to work with processors of each material.
Through previous CPS-funded work, Jiang identified Salmonella Senftenberg to be the most heat-resistant serotype found in chicken litter, and it will be used as the benchmark for surrogate selection. In the current study, initial laboratory trials show strong correlation in thermal inactivation rates between this Salmonella serotype and indigenous enterococci organisms also found in poultry litter. Jiang said they believe Enterococcus faecium NRRL B-2354, identified as a Salmonella surrogate for almond pasteurization, may also fill that role in litter processing.
In August, Jiang conducted a pilot test at a cooperating processor by using color-coded MicroTracers to examine resident treatment times as a batch of poultry litter traveled through the 15-meter-long rotating dryer. As she learned, the heat fluctuated during the treatment - temperatures were much higher near the inlet and declined rapidly as the litter moved through the dryer. This differs from their laboratory trials, which used a constant temperature throughout litter treatment. "The results from those plants are probably more realistic," Jiang said. She said their original customized sampling container didn't work as expected during the pilot run due to the shear forces generated by the rotating dryer. But they modified the sampling container by lining it with stainless steel mesh to keep the litter sample bag intact yet expose it to the surrounding heat and moisture of processing. They successfully tested it during their trial in October. During that and subsequent tests, sample containers of the Salmonella surrogate in poultry litter with moisture levels of 35~37 percent and 40~45 percent are shipped overnight to the cooperating processor, added to the dryer inlet and collected at the exit end. The containers are shipped overnight to Jiang's lab, where the samples are analyzed immediately for populations of the Salmonella surrogate along with indigenous enterococci and total aerobic bacteria.
Project abstract may be found on the Center for Produce Safety website:
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