1a. Objectives (from AD-416):
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.
1b. Approach (from AD-416):
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.
3. Progress Report:
Progress on scaling up radio frequency pasteurization (RFP) of shell eggs continued. The ARS patented RFP technology kills 99.999% of Salmonella in shell eggs in 1/3 the time of the current commercial process. Assembly of a third generation RFP unit is nearing completion. The unit is currently capable of simultaneously processing 9 eggs. Work is ongoing to maximize processing uniformity of the eggs and to increase the number of eggs processed. A fourth generation, large-scale RFP unit is being assembled in collaboration with a CRADA industry partner. Two major advancements were made that will facilitate commercialization of RFP; (1) the equipment was modified to operate at a frequency of 40.68 MHz, which is an international frequency reserved for industrial, scientific and medical (ISM) purposes rather than the non-ISM (60 MHz) frequency previously used, and (2) matching was obtained using inexpensive ferrites instead of with a matching network costing $10-100K. A second patent (U.S. 9,883,682) was awarded for RFP. Also, the effect of RF power, treatment time and cooling water temperature on the inactivation of Salmonella Typhimurium was investigated. Five operating conditions (of various power, time, and cooling water temperature) achieved more than 99.999% kill without any observable quality change. The results showed, for the first time, that RFP is a flexible process. This study will help to determine the processing parameters of RF for the food industry. In produce-related research, fruits and vegetables were inoculated with Salmonella, Escherichia coli and Listeria monocytogenes. Bacterial attachment was highest for spinach and lettuce compared to cucumber, apples and tomatoes. Salmonella exhibited the strongest attachment. In another study, a solution with dual purpose (antibrowning/antimicrobial) for treatment of fresh-cut produce was developed and tested against E. coli O157:H7, Salmonella spp. and L. monocytogenes bacteria inoculated on melon, apple, tomato, cucumber, and pear surfaces. The antibrowning-antimicrobial solution was effective in reducing bacterial populations and inhibiting browning reaction. An invention disclosure on the novel antimicrobial-antibrowning treatment has been filed. Also, a hurdle technology using a combination of cold plasma and antimicrobial treatment was developed to inactivate bacteria on fruits surfaces. Regarding research on soil amendment for the safer production of produce, a study was conducted to evaluate survival of non-pathogenic surrogate strains of E. coli in soil with 10 percent biochar. The rationale for using biochar as a soil amendment is to mitigate the potential for foodborne pathogen contamination in cultivable soils to prevent transfer from soil to fresh produce commodities, which could subsequently infect humans. Five types of biofeedstock were used to produce the pyrolysis biochars including (1) switchgrass, (2) wheat straw, (3) miscanthus grass, (4) oil rapeseed straw, and (5) rice hulls. Results should provide guidance on biofeedstock type that go into producing biochar with the greatest biocidal activity to inactivate foodborne pathogens in the soil.
1. Improvements in radio frequency pasteurization of shell eggs. Raw shell eggs can be contaminated with Salmonella, causing illnesses and recalls. The ARS-patented radio frequency pasteurization (RFP) process produced safer eggs with exceptional quality in a small-scale prototype. ARS researchers at Wyndmoor, Pennsylvania, in collaboration with a CRADA industry partner, assembled and successfully tested a larger-scale RFP unit, thus paving the way for a commercial-scale RFP unit. In addition, two breakthroughs were achieved that will facilitate commercialization. The first was the modification of RFP to operate at 40.68 MHz, which is an international frequency reserved for industrial, scientific and medical purposes. The second was another modification of the RFP to enable inexpensive ferrites to provide a match between the eggs and equipment. This will save between $10 to $100K per RFP unit. This technology has the potential to address a significant, widespread source of foodborne illness and make shell eggs safer for the American consumer.
Geveke, D.J., Bigley, A., Brunkhorst, C., Jones, D.R., Tilman, E.D. 2018. An improved radio frequency method to pasteurize salmonella in shell eggs. International Journal of Food Science and Technology. https://doi.org/10.1111/ijfs.13843.
Mukhopadhyay, S., Sokorai, K.J., Ukuku, D.O., Jin, Z.T., Fan, X., Olanya, O.M., Juneja, V.K. 2018. Inactivation of Salmonella in tomato stem scars by organic acid wash and chitosan-allyl isothiocyanate coating. International Journal of Food Microbiology. 266:234-240.
Fan, X., Gurtler, J., Sokorai, K.J. 2018. Type of tomatoes and water rinse affect efficacy of acid washes against salmonella enterica inoculated on stem scar areas of tomatoes and on product quality. International Journal of Food Microbiology. 280:57-65.
Lacombe, A., Niemira, B.A., Gurtler, J., Kingsley, D.H., Li, X., Chen, H. 2018. Surfactant-enhanced disinfection of the human norovirus surrogate, Tulane virus, with organic acids and surfactant. Journal of Food Protection. 81:(2)279-283.
Yan, R., Yun, J., Gurtler, J., Fan, X. 2017. Radiochromic film dosimetry for UV-C treatments of apple fruit. Postharvest Biology and Technology. 127:14-20.
Yan, R., Liu, Y., Gurtler, J., Fan, X. 2017. Sensitivity of pathogenic and attenuated E. coli O157:H7 strains to ultraviolet-C light as assessed by conventional plating methods and ethidium monoazide-PCR. Journal of Food Safety. doi: 10.1111/jfs.12346.
Hu, M., Gurtler, J. 2017. Selection, validation and utility of pathogen surrogate bacteria used in food safety challenge studies: A Review. Journal of Food Protection. 80:1506-1536.
Gurtler, J. 2017. Pathogen decontamination in crop soil: A review. Journal of Food Protection. 80:1461-1470.