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 was made on all objectives, all of which fall under National Program 108 – Food Safety, Component 1 – Foodborne Contaminants, Problem Statement 5, Intervention and Control Strategies. Progress on scaling up the radio frequency pasteurization (RFP) technology continued. The ARS patented RFP technology inactivates 99.999% of Salmonella in shell eggs in 1/3 the time of the current commercial process. Assembly of the 4-egg RFP unit was completed. Testing confirmed that the unit can uniformly pasteurize 4 eggs simultaneously. In addition, a 16-egg RFP unit is being assembled in collaboration with a CRADA industry partner. The rapidity of RFP results in eggs that retain their fresh-like appearance and significantly more functionality, especially of the heat sensitive egg whites. Angel food cakes, containing egg whites, made from RFP eggs had 40% more volume than those made from egg pasteurized using the commercially available process. In produce-related research, the surface charge and hydrophobicity of strains of Salmonella, Escherichia coli and Listeria monocytogenes were determined using electrostatic and hydrophobic interaction chromatography. Initial bacterial attachment was highest for individual strains of E. coli and lowest for L. monocytogenes, but Salmonella exhibited the strongest attachment during storage. A new solution aimed at reducing browning of fresh-cut apple pieces and, at the same time, reducing microbial populations was developed by combining specific short chain organic acids generally regarded as safe (GRAS). An invention disclosure for this novel antibrowning-antimicrobial solution has been filed. Also, flash steam technology was developed and used to inactivate bacteria on fruit surfaces. The flash steam treatments of whole cantaloupe surfaces before fresh-cut preparation reduced microbial populations on melon whole surface and transfer to fresh-cut pieces. Treatments also reduced biofilms on the surfaces of treated melons. The flash steam technology, as well as the RFP of shell eggs, were featured in AgResearch Magazine, as well as many other news outlets. Regarding research on soil amendment for the safer production of produce, a study was conducted to evaluate survival of 22 strains of avirulent E. coli and Salmonella in crop soil with 10% fast-pyrolysis switchgrass biochar. The goal was to validate effective surrogate strains of bacteria to use in future studies, as there is danger in conducting experiments with pathogenic (virulent) strains, which could lead to illness through dust aerosolization and infection of laboratory workers. Twenty-two soil samples were amended with 10% biochar and inoculated with 5 strains of non-toxigenic E. coli O157:H7, ten strains of non-pathogenic E. coli, and seven attenuated vaccine strains of Salmonella, respectively. Samples were held 9 weeks. By 7 days, two salmonellae and four E. coli were undetectable. Eight strains were undetectable by week 3. Twelve strains were undetectable by week 7, including all non-toxigenic O157:H7. At 9 weeks of storage, only seven of the twenty-two strains were still detectable. These results identified suitable surrogate bacteria, to be used in the place of virulent pathogenic strains, for use in future biochar-soil decontamination studies. This now provides researchers validated bacterial surrogates to use in biochar/soil studies which should significantly increase worker safety.
1. Pasteurizing multiple eggs using radio frequency. Raw shell eggs can be contaminated with Salmonella, posing an ongoing health risk. The ARS-patented radio frequency pasteurization (RFP) process produced safer eggs with exceptional quality, treating one egg at a time in the lab-scale prototype. ARS researchers at Wyndmoor, Pennsylvania, in collaboration with a CRADA industry partner, assembled and tested a RFP unit that can simultaneously pasteurize four eggs, thus paving the way for larger, commercial scale, RFP units. This technology has the potential to address a significant, widespread source of foodborne illness and make shell eggs safer for the American consumer to handle and consume.
2. New method kills food-poisoning bacteria. Cantaloupe rind surfaces are sometimes contaminated with Listeria monocytogenes, Salmonella or Escherichia coli O157:H7 bacteria. A novel antimicrobial solution was developed that kills these pathogenic bacteria and reduces their populations to below detectable levels on fresh-cut pieces of melons. ARS researchers at Wyndmoor, Pennsylvania licensed this antimicrobial solution to an industry partner and an invention disclosure was filed. Produce washed with the antimicrobial solution will be safer.
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