Location: Microbial and Chemical Food Safety
2025 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 (STEC), 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 raw fruits and vegetables or due to cross-contamination from fresh produce to other foods and food preparation surfaces.
Previous studies, in this project plan, have demonstrated that biochar may be an effective matrix for filtering E. coli from pathogen-contaminated water, as well as for inactivating foodborne pathogens in agricultural soils and compost. Under Objective 1, we previously examined optimal temperatures requisite to produce antimicrobial biochar, which would have utility in inactivating foodborne bacterial pathogens as soil amendments. We also determined that increasing the filter matrix ratio to 50:50 biochar:sand, increasing the length of the biochar:sand filters from 4.25 to 8.5 inches, and pre-wetting biochar to ca. 78% moisture before constructing filters, in contrast to construction with dry biochar, enhanced E. coli reduction.
Recent experiments, related to Objective 1, have made significant progress in constructing sand:biochar irrigation water filters to test the filtration capacity of various types of biochar. A total of 26 different types of biochar were tested in biochar:sand irrigation water filters, including (1) those made in-house, (2) those provided by collaborators, and (3) commercially produced and purchased biochars. Biochars were produced by slow-pyrolysis and fast-pyrolysis with various organic feedstocks. Seventeen different organic agricultural byproduct biofeedstocks were used to produce the irrigation water filter biochars, including corn stover, almond shell, walnut shell, cocoa shell, horse litter, guayule leaf, miscanthus straw, wheat straw, switchgrass, oilseed rape straw, rice husk, pine, eucalyptus, softwood, hardwood, hardwood pellets, and paper. E. coli reduction ranged from ca. 0.10 to >4.57 log colony forming units (CFU) per ml of water in simulated irrigation water. Biochar that reduced >4.5 log CFU per ml eliminated 100% of E. coli from irrigation water, thus further studies should test higher inoculation levels of E. coli to determine maximum reductions achieved by the biochar. The greatest reductions of E. coli were achieved by biochars anoxically pyrolyzed from paper (generated in-house) at 700 degrees Celsius, as well as by two softwood biochars produced by U.S. biochar manufacturers.
Under Objective 3, significant progress was made in inactivating foodborne pathogens in laboratory assays by using antimicrobial (sanitizers) generally recognized as safe. Pathogen reductions were quantified by minimum inhibition concentrations (MIC) of antimicrobials on pathogens by dilution assays as mixtures of Salmonella Typhimurium and L. monocytogenes in antimicrobial suspensions for 0, 2, 4, 6, 10 and 24 h (30 degrees Celsius) and by optical density (OD600) assays. Significant pathogen reductions by antimicrobials were documented in liquid substrates following 24-h storage. The MIC of antimicrobials ranged from 500-5,000 µL. The reduction of Salmonella Typhimurium and L. monocytogenes ranged from 5-7 log CFU/mL. Bio-based sophorolipids, applied as antimicrobials on foodborne pathogenic bacteria, significantly inactivated pathogens. At 0.05 and 0.5 mg/mL of sophorolipids from palmitic, oleic and stearic acids in liquid substrates, >2.5 log of L. monocytogenes, Salmonella Typhimurium, and E. coli O157:H7 were inactivated, when inoculated at 6 log CFU/ml. Similarly, the bio-based sophorolpids of palmitic, oleic and stearic acid applied at 5%, as agar amendments, also significantly inhibited bacterial growth. The organic-acid based antimicrobials, consisting of USDA-ARS-developed Lacop, and protein isolates, applied as agar amendments at 10-50% concentration, resulted in significant reductions of bacterial pathogens. The antimicrobial compounds inactivated >3 log CFU/ mL of Salmonella, E. coli O157:H7 and L. monocytogenes, after 2 h of storage.
Accomplishments
1. Elimination of E. coli from irrigation water by biochar-sand filters. Shiga toxin-producing E. coli have been implicated in foodborne illness outbreaks from fresh fruits and vegetables, as a result of contaminated irrigation water. ARS researchers in Wyndmoor, Pennsylvania, continuing work from the previous year, advanced the proficiency of biochar:sand irrigation water filters by testing 26 types of biochar to reduce E. coli in irrigation water. Biochars were pyrolyzed from 17 different organic agricultural byproduct biofeedstocks (including corn stover, almond shell, walnut shell, cocoa shell, horse litter, guayule leaf, miscanthus straw, wheat straw, switchgrass, oilseed rape straw, rice husk, pine, eucalyptus wood, mixed softwood, mixed hardwood, mixed hardwood pellets, and paper). Two biochars (one commercially produced biochar from softwood, and one paper biochar, pyrolyzed in-house in Wyndmoor, Pennsylvania), reduced >4.5 log colony forming units (CFU) of E. coli per milliliter of irrigation water, what was 100% reduction of inoculated E. coli. These results may be used by agriculturalists to reduce or eliminate pathogenic E. coli from irrigation water to minimize the contamination of fresh fruits and vegetables and, thus, prevent costly fresh produce recalls and foodborne illness outbreaks.
2. Inactivation of Salmonella, E. coli O157:H7, and Listeria monocytogenes by bio-based sophorolipids antimicrobials. Foodborne illnesses continue to occur due to foods contaminated with pathogenic bacteria. The advancement of food-grade antimicrobials to inactivate foodborne bacterial pathogens, or either to prevent their growth in foods, is a major component in reducing illnesses and costly food product recalls. Researchers at the ARS in Wyndmoor, Pennsylvania, made significant progress in inactivating foodborne pathogens in laboratory assays by bio-based sophorolipids antimicrobials, developed in-house. Novel bio-based sophorolipids were created from palmitic, oleic, and stearic acids, and tested in liquid and agar media. Results indicated that the novel antimicrobials were highly effective in inactivating the foodborne bacterial pathogens, Salmonella, Listeria monocytogenes and E. coli O157:H7 were reduced at populations of up to 7 log colony forming units (CFU) of E. coli per milliliter of suspension. This technology may be further developed, and, if approved for industry use by the food industry, could then assist in inactivating bacterial pathogen, or preventing the growth of these microorganisms, in foods, thus reducing foodborne illness outbreaks.
Review Publications
Gurtler, J., Mullen, C.A. 2024. Inactivation of E. coli O157:H7 in fresh dairy manure compost by alkaline slow-pyrolysis walnut hull biochar. Journal of Food Protection. 88. https://doi.org/10.1016/j.jfp.2024.100438.
Nam, S., Olanya, O.M., Jordan, J.H., Uknalis, J., He, Z., Kashem, M., Fang, D.D. 2025. From cotton gin byproduct to nano-in-nano structured hybrid composite for effective pathogen control. Frontiers in Nanotechnology. 7: 1567693. https://doi.org/10.3389/fnano.2025.1567693.
Fan, X., Gurtler, J., Baik, J.I., Garner, C.M., Vinyard, B.T. 2025. Effectiveness of UVC-assisted Fenton reaction wash-based system to inactivate Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes on cherry tomatoes. Journal of Food Protection. 88(8). https://doi.org/10.1016/j.jfp.2025.100555.