Location: Microbial and Chemical Food Safety
2023 Annual Report
Objectives
Objective 1: To mitigate issues with bacterial pathogen-contaminated irrigation waters, examine the use of biochar as an antimicrobial and filtration intervention, for example, combining biochar filtration with ARS pre-existing zero-valent water filtration technology.
Objective 2: Examine the use of adding biochar to compost piles, in order to inactivate pathogens in the compost, but especially the problematic “toes” of manure piles.
Approach
The approach of project will follow two objectives. The first objective will evaluate the ability of biochar filters to remove pathogenic bacteria from surface irrigation waters with or without zero valent iron and sand-composite filtration. Biochar pyrolysis will be optimized for this purpose by altering the residence time, temperature and biofeedstock with an in-house biochar slow-pyrolysis reactor. The optimized water filtration units will then be scaled up to reduce pathogens in irrigation water, lowering the risk of foodborne illness from irrigated fresh produce. Second, pyrolysis will be further optimized for maximal antimicrobial efficacy of biochar. This biochar will then be utilized in lab-scale and field-trial dairy and poultry compost experiments with the goal of more rapidly inactivating EHEC and Salmonella. Successful results will allow for shorter composting times prior to field application, which will decrease the chances for pathogenic bacteria to survive the process and contaminate field crops. Stakeholders will be consulted and collaborated with for all objectives, and technology will be transferred to the appropriate entities. Overall, the results and outcomes from this project plan will increase the safety of fresh fruits and vegetables and lower the burden of human-related illnesses caused by foodborne pathogens by providing practical intervention solutions for farmers, packers, processors and distributers of fresh produce, related to foodborne pathogens.
Progress Report
Surface waters used for irrigating fruit and vegetable crops sometimes become contaminated with pathogens such as enterohemorrhagic-Shiga toxin-producing Escherichia coli (EHEC), Salmonella or Listeria monocytogenes, which has led to foodborne outbreaks in recent years. Microbial pathogens can also be transferred to produce in fields via composted dairy and poultry manures (biological soil amendments of animal origin [BSAAO]) applied to farmland. The resulting effect is potential contamination of fresh produce, which can lead to human foodborne illnesses from uncooked fruits and vegetables or due to cross-contamination from fresh produce to other foods and food preparation surfaces.
Past studies have demonstrated that biochar may be an effective matrix for filtering Escherichia coli (E. coli) from pathogen-contaminated water, as well as for inactivating foodborne pathogens in agricultural soils and compost. Under Objective 1, project scientists previously examined optimal temperatures requisite to produce antimicrobial biochar, which would have utility in inactivating foodborne bacterial pathogens as soil amendments. In these studies, it demonstrated that the primary factor influencing the inactivation of bacterial pathogens by biochar is alkaline pH, which is enhanced at higher pyrolysis temperatures. In our studies, it was determined that a pyrolysis reactor temperature of 700 degrees Celsius for 1 h appears to be the optimal time/temperature combination to produce antimicrobial alkaline biochar.
Recent ongoing experiments, related to Objective 1, have made significant progress into further optimizing antimicrobial biochar production by examining the pyrolysis of various organic biofeedstocks including switchgrass, switchgrass pellets, hardwood (oak) shavings, paper, walnut hulls, etc. Results indicate that of all the biofeedstocks examined, paper biochar, pyrolyzed under anoxic conditions with nitrogen flush for 1 h at 700 degrees Celsius (P700C), was the most biocidal biochar tested. Studies then addressed the ability of between 1.0 and 6.5% P700C biochar to inactivate a two-strain composite of E. coli O157:H7 (EHEC) in soil. Results demonstrated that while 1.0-2.0% concentrations reduced varying populations of EHEC, the most consistent and significant results occurred by the addition of at least 2.5% P700C biochar to soil, which inactivated 6 log CFU of EHEC within one week of application. Furthermore, when a two-strain composite of Salmonella serovars were challenged by P700C biochar amendment in soil, Salmonella populations were less resistant to inactivation than were populations of EHEC, declining by greater than 6.5 log within one week by application of only 2.0% P700C biochar.
Under Objective 2, significant progress was made in evaluating the ability of P700C biochar to inactivate Salmonella in 2-year-old commercial poultry litter (previously used to raise between 10 and 12 flocks of broilers) at various moisture levels, per milestone 2, listed above. Results indicate that survival of Salmonella in commercial poultry litter declines commensurate with increasing P700C biochar amendment concentrations. When Salmonella was inoculated into poultry litter at a 50% moisture level, populations in the 0% biochar (control) litter decreased by 6 log CFU within one week’s time. However, at a 30% moisture level, only 5 log of Salmonella were reduced within one week in no biochar (control) litter, while populations dropped by 7 log in one week in litter at 30% moisture by the addition of every concentration of P700C biochar between 0.5 and 3.0%. Previous studies have indicated that Salmonella survival decreases with increasing numbers of consecutive flocks that are raised on poultry litter. This fact may account for the rapid reduction of Salmonella populations in our 2-year-old, 0% biochar (control) litter in these experiments. Ongoing experiments will examine the survival of Salmonella with and without biochar amendment in fresher broiler litter on which fewer flocks have been raised. Salmonella inoculated into less used poultry litter should survive longer in no biochar (control) samples; hence, the greater need for a bacterial pathogen-reducing intervention, such as amending with biochar.
Accomplishments
1. Optimal pyrolysis. Optimal pyrolysis conditions were determined for generating alkaline biochar capable of inactivating Salmonella and E. coli O157:H7 in crop soil. Foodborne pathogens, such as E. coli O157:H7 and Salmonella, have been known to be present in crop soil, often from biological soil amendments, which can contaminate fresh produce and lead to human foodborne illnesses. Prior research has determined that biochar, amended into crop soil, is capable of inactivating these foodborne pathogens, primarily based on the alkalinity of biochar. ARS researchers in Wyndmoor, Pennsylvania, determined that the optimal biofeedstock and pyrolysis conditions for producing alkaline biochar were heating paper at 700 degrees Celsius for 1 h, in the absence of oxygen. Biochar produced under these conditions was capable of inactivating high populations of E. coli O157:H7 at 2.5% biochar concentration in soil as well as inactivating high populations of Salmonella at only 2.0% biochar concentration in soil. These results may provide practical means for fresh produce growers to inactivate foodborne pathogens in crop soil and prevent contamination of fresh produce and human illnesses.
Review Publications
Wang, L., Fan, X., Gurtler, J. 2022. Reduction of Salmonella enterica Typhimurium populations and quality of grape tomatoes treated with dry and humidified gaseous ozone. Postharvest Biology and Technology. 193:112061. https://doi.org/10.1016/j.postharvbio.2022.112061.
Fan, X., Gurtler, J., Mattheis, J.P. 2023. Possible sources of Listeria monocytogenes contamination of fresh-cut apples and antimicrobial interventions during antibrowning treatments: A review. Journal of Food Protection. 86:100100. https://doi.org/10.1016/j.jfp.2023.100100.
