Since poultry obviously is a major target in Salmonella control efforts, Dr. Rajashekara’s team also tested their novel small molecules in chickens and found that these small molecules are effective in reducing Salmonella in infected chickens.
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“Small molecules are also compatible with the use of probiotics and they enhance the antimicrobial activity of certain antibiotics that are currently used to control Salmonella in poultry production systems,” Dr. Rajashekara says. “Our study highlights the importance of abiotic (environmental) and biotic (plant pathogens) factors in the survival and persistence of Salmonella in fresh produce. And we are very excited about the potential effectiveness of novel new generation small molecules against Salmonella. We believe our findings will allow the development of new strategies to prevent contamination of human bacterial foodborne pathogens at pre-harvest stages and to implement effective disinfection procedures post-harvest.”
Success with Steam Pasteurization
Vacuum steam pasteurization is proving to be effective for killing Salmonella on several low moisture foods, according to Teresa Bergholz, PhD, a food scientist with North Dakota State University, Fargo.
“Recently, a number of outbreaks of foodborne illness have been attributed to Salmonella on low-moisture foods,” Dr. Bergholz points out. “These foods were previously thought to be relatively low-risk for transmitting foodborne illness, as they typically do not support growth of microbes. With these latest developments, it is clear that effective preventative controls are needed to reduce the risk of human illness associated with low-moisture foods. To that end, we are finding that the use of vacuum steam pasteurization is expected to have greater efficacy against pathogens, as moist heat is more effective at inactivating microbes compared to dry heat.”
In Dr. Bergholz’s recent research funded by the North Dakota Agricultural Products Utilization Commission, she and her colleagues applied steam at lower temperatures to several low moisture foods, including flaxseed, quinoa, and sunflower kernels. “The lower temperatures are relative to greater than 212 degrees Fahrenheit, which is the temperature that would be required to produce steam if not under a vacuum,” she explains. “The results show that vacuum steam pasteurization for 2 to 5 minutes at temperatures ranging from 167 degrees Fahrenheit to 185 degrees Fahrenheit can effectively kill 5 logs of Salmonella.
“Now that we know vacuum steam pasteurization can be effective, using a USDA NIFA grant, we are currently evaluating if Salmonella serovars Agona, Enteriditis, Montevideo, and Tennessee differ in their susceptibility to vacuum steam pasteurization when inoculated onto whole flaxseeds,” Dr. Bergholz continues. “Our initial results indicate that the serovars have similar levels of inactivation. We are also interested in determining if the length of time the pathogen is present on the low moisture food prior to vacuum steam pasteurization impacts the ability of Salmonella to be killed by the treatment.”
Dr. Bergholz says many studies have shown that Salmonella can survive for months or even years on low moisture foods. “Now we want to know if that long-term survival could make Salmonella more resistant or more susceptible to the thermal treatment,” she mentions. “This work is still in progress.”
Another part of this project was to evaluate if vacuum steam pasteurization impacted the quality of the foods that were pasteurized, Dr. Bergholz adds. “In collaboration with food scientist Clifford Hall, PhD, who coordinates the NDSU pulse crops quality program, we measured chemical and microbial changes in whole and milled flaxseed over 28 to 36 weeks after pasteurization,” she relates. “Overall, we saw a reduction in the number of aerobic microbes, yeasts, and molds, and negligible changes in chemical parameters. Thus, we learned that vacuum steam pasteurization can be used to effectively inactivate pathogens and has minimal effects on chemical shelf-life parameters of flaxseed.”
Since poultry products have been frequently implicated in reported cases of salmonellosis, and since there has been little information available about the chicken’s intestinal microbiota and its role in resistance to disease causing pathogens, especially Salmonella, Hosni Hassan, PhD, a professor of microbiology in the Prestage Department of Poultry Science at North Carolina State University (NCSU), Raleigh, spearheaded a research project to tackle these issues.