Location: Food Safety and Intervention Technologies Research
2020 Annual Report
Objectives
1: Further studies on the ARS-patented use of RFP for shell eggs through the development of pilot plant and commercial prototypes of continuous RFP equipment for multiple eggs.
2: Further studies on the use of innovative technologies to reduce microorganisms on fresh produce, and minimally preserved, brined, and fresh-cut refrigerated vegetables.
3: Evaluate the use of biochars to reduce pathogens in manures, compost, and soils used for the production of fresh (both conventional and organic) produce.
Approach
A pilot plant-scale radio frequency pasteurization (RFP) unit will be developed, capable of continuously processing multiple shell eggs. Initial efforts will use a 60 MHz RFP unit similar to the unit used to write the ARS patent. The single-egg RFP unit is capable of pasteurizing shell eggs with significantly better quality than industry eggs (currently pasteurized using hot water immersion). RFP operating parameters will be optimized, while experimental factors to be investigated will include cooling water flow rate, cooling water conductivity, cooling water temperature, and amount and duration of RF power applied. Equally important for reducing pasteurization operating costs is reducing equipment costs. To this end, we will study egg roller minimum rotation speed, and feasibility of adjusting frequency to 40.68 MHz, which is within the radio band internationally reserved for industrial, scientific and medical purposes. Optimized RF operating and equipment costs will be estimated. Quality and functionality characteristics of RFP eggs will be evaluated. The RFP process will be scaled up by developing RF power supplies, matching networks, and power distribution schemes to evenly heat hundreds of egg simultaneously. Finally, a continuous RFP pilot plant unit will be designed and assembled, which will convey eggs through the unit. To reduce microorganisms on fresh and fresh-cut vegetables, several innovative technologies will be researched. The ability of novel washes, developed during the previous project cycle, to remove pathogenic biofilms will be investigated. Bacterial cell surface charges will be determined using hydrophobic and electrostatic interaction chromatography. Also, the occurrence of sublethal injury to pathogens, following treatment with the produce wash, will be determined. The previously-developed antimicrobial wash will be improved with additional ingredients and pH adjustment. Wet steam technology has been successfully applied to cantaloupes, and will be extended to other produce. Finally, pilot plant scale testing of the produce intervention technologies will be conducted and costs of applying them estimated. In order to evaluate the use of biochars to reduce pathogens in manures, compost, and soils, non-pathogenic bacteria will be validated as surrogates for pathogenic bacteria in soil and manure survival studies with biochar. Antimicrobial efficacy of biochar will be optimized by adjusting production time and temperature as well as by comparing various biofeedstocks. The optimized biochar will be evaluated to determine its potential to inactivate surrogate bacteria in compost, in lab and greenhouse settings as well as in scaled-up field experiments. Cost estimates for applying lethal doses of the optimized biochar to compost and fields will be determined.
Progress Report
In produce-related research, a new solution aimed at reducing browning of fresh-cut apples pieces and, at the same time, reducing microbial populations was developed by combining specific short chain organic acids, generally regarded as safe (GRAS). A hurdle technology using the above solution and combining it with non-thermal intervention technologies to lower or kill pathogenic bacteria after treatment was investigated. The new antibrowning-antimicrobial solution led to 8 log inactivation of Salmonella, E. coli O157:H7 and Listeria monocytogenes in vivo and a 3.8 log inactivation of attached bacteria on produce surfaces. A combination treatment with UV-light and 0.5 kGy of irradiation led to a 5 log reduction, suggesting that these treatments would reduce bacterial populations on produce, minimizing incidence of foodborne illness, saving the produce industry costly recalls, and improving consumer confidence.
Risks associated with human pathogens on fresh fruit and vegetables remain a concern for consumers. We developed a patent-pending combination of organic acids and GRAS additives that effectively inactivates human pathogens on a variety of fruits and vegetables. Isopropyl citrate (IC) (0.16% acidulant) plus 0.05% total concentration of two GRAS surfactants (0.025% sodium-2-ethyl-hexyl sulfate (EHS) and 0.025% sodium dodecylbenzene-sulfonate (SDBS)) inactivated L. monocytogenes in suspension by up to 7.0 log CFU/mL within 2 min, while 0.27% IC plus surfactants inactivated Salmonella and E. coli O157:H7 by up to 6.54 log CFU/ml (99.9999+%). On grape tomatoes, 0.54% IC plus 0.05% total concentration of EHS + SDBS inactivated L. monocytogenes, E. coli O157:H7 and Salmonella by 4.2 (99.994%), 4.9 (99.998%), and 5.5 log CFU/g (99.999+), respectively. A patent pending combination of 0.35% lactic or citric acids plus 0.05% total concentration of two surfactants (0.025% EHS and 0.025% SDBS) inactivated up to 7.0 log CFU/ml (99.99999+%)of L. monocytogenes, Salmonella and E. coli O157:H7. On grape tomatoes, 0.61% lactic or citric acids plus 0.05% total concentration of EHS + SDBS inactivated L. monocytogenes, E. coli O157:H7 and Salmonella by up to 4.0 (99.99%), 4.4 (99.996%), and 4.9 log CFU/g (99.998%), respectively. Newly created antimicrobial solutions may provide alternatives for the decontamination of fresh produce.
Regarding research on biochar soil amendments for the safer production of produce, studies were conducted with a newly-constructed lab-scale, muffle furnace pyrolyzer to generate biochar with the goal of having antimicrobial properties. Pyrolysis conditions consisted of the following: First, finely ground mixed hardwood chips were pyrolyzed for 30 min. at temperatures of 350, 400, 450, 500, 550, and 600°C. The resulting biochar was added at a 10% concentration (wt.:wt.) into cultivable soils inoculated with ca. 7 log CFU/g of four-strain cocktail of attenuated E. coli O157:H7 and held for four weeks. Populations over time did not differ from the no-biochar control samples. Next, finely ground switchgrass was pyrolyzed at 500°C for times of 15, 30, 45, 60, 75 and 90 min. The biochar was then challenged in soil with E. coli O157:H7, as described above and the results were the same, with no difference in populations over time in comparison to no-biochar control samples. A major limitation with this means of biochar production is that once the target pyrolysis time and temperature is reached, and the muffle furnace is turned off, the system must cool to room temperature overnight before the chamber can be opened, for safety purposes. During this cooling period, the temperature remains high for a period of time; hence, the biochar may be over processed, and the antimicrobial properties of the biochar may dissipate. Efforts are underway to secure a biochar reactor that can eject biochar samples at the target pyrolysis time and temp, which does not require extended time periods for cooling down.
In other work, a patent application was filed for a novel combination of surfactants and acidulants for the inactivation of foodborne pathogens in solution or on fresh produce.
Accomplishments
1. New antimicrobial anti-browning solution for fresh-cut fruits. Human pathogens can survive on fresh fruit, creating a safety hazard for consumers. ARS researchers at Wyndmoor, Pennsylvania, developed and filed for a patent for a new antimicrobial solution, which also stops browning in cut fruits. The antimicrobial and anti-browning solution can kill Listeria, Salmonella, or E. coli bacteria on treated freshly-cut fruits. The treated fruit has low microbial counts, are safe, and will help to reduce costly recalls of the fresh-cut fruits by produce industries.
Review Publications
Gurtler, J. 2020. Two generally recognized as safe surfactants plus acidulants inactivate Salmonella, Escherichia coli 0157:H7, and Listeria monocytogenes in suspension or on dip-inoculated grape tomatoes. Journal of Food Protection. 83:637-643.
Rodriguez, A.B., Olanya, O.M., Ukuku, D.O., Niemira, B.A., Orellana, L.E., Mukhopadhyay, S., Cassidy, J.M., Boyd, G. 2019. Reduction of Listeria monocytogenes on post-harvest carrot and tomato by radiation, santizer and biocontrol treatments and their combinations. LWT - Food Science and Technology. 118:1-8.
Leng, J., Mukhopadhyay, S., Sokorai, K., Ukuku, D.O., Fan, X., Olanya, O.M., Juneja, V.K. 2019. Inactivation of Salmonella in cherry tomato stems cars and quality preservation by pulsed light treatment and antimicrobial wash. Food Control. 110:107005. https://doi.org/10.1016/j.foodcont.2019.107005.
Gurtler, J., Mullen, C.A., Boateng, A.A., Masek, O., Camp, M.J. 2020. Biocidal activity of fast pyroloysis biochar against E.coli 0157:H7 in soil varies based on production temperature or age of biochar. Journal of Food Protection. 83:1020-1029.
Gurtler, J., Juneja, V.K., Jones, D.R., Pruohit, A. 2019. Thermal inactivation kinetics of three heat-resistant Salmonella in whole liquid egg. Journal of Food Protection. 82(9):1465-1471.
Fan, X., Sokorai, K., Gurtler, J. 2019. Advanced oxidation process for the inactivation of Salmonella Typhimurium on tomatoes by combination of gaseous ozone and aerosolized hydrogen peroxide. International Journal of Food Microbiology. 312. https://doi.org/10.1016/j.ijfoodmicro.2019.108387.
Yu, Y., Jin, Z.T., Fan, X., Gurtler, J. 2019. Effects of carvacrol wash and ally isothiocyanate vapor treatment to extend the shelf life of blackberries. Jacobs Journal of Food and Nutrition. 6(4):46-57.
Wang, L., Fan, X., Gurtler, J., Wang, W. 2019. Interaction of gaseous chlorine dioxide and mild heat on the inactivation of Salmonella on almonds. Journal of Food Protection. 82(10):1729–1735. https://doi.org/10.4315/0362-028X.JFP-19-114.
Berrios-Rodriguez, A., Ukuku, D.O., Olanya, O.M., Cassidy, J.M., Orellana, L.E., Mukhopadhyay, S., Niemira, B.A. 2019. Nisin based organic acids inactivation of Salmonella on grape tomatoes: efficacy of treatment using bioluminescences ATP assay. Journal of Food Protection. 83(1):68-74. https://doi.org/10.4315/0362-028X.JFP-19-275.
Mukhopadhyay, S., Sokorai, K.J., Ukuku, D.O., Fan, X., Olanya, O.M., Juneja, V.K. 2019. Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli 0157:H7, microbial loads and apparent quality of spinach leaves. Food Microbiology. 82:127-134. https://doi.org/10.1016/j.fm.2019.01.022.
Olanya, O.M., Hoshide, A.K., Oluwatosin, I., Ukuku, D.O., Mukhopadhyay, S., Niemira, B.A., Ayeni, O. 2019. Cost estimation of listeriosis (Listeria monocytogenes) occurrence in South Africa in 2017-2018 and its food safety implications. Food Control. https://doi.org/10.1016/j.foodcont.2019.02.007.
Gurtler, J., Keller, S.E., Fan, X., Olanya, O.M., Jin, Z.T. 2020. Survival of desiccation-resistant salmonella on apple slices following antimicrobial immersion treatments and dehydration. Journal of Food Protection. 83:902-909.
