Location: Food Safety and Intervention Technologies Research
2021 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 the 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). 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. 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 the incidence of foodborne illness, saving the produce industry costly recalls, and improving consumer confidence.
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 to have 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 a 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. The results were the same, with no difference in populations over time compared 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 temperature which does not require extended time or extended for cooling down.
Accomplishments
1. Antimicrobial treatment for fresh and fresh-cut fruits and vegetables. Risks associated with human pathogens on fresh fruit and vegetables remain a concern for consumers. ARS researchers at Wyndmoor, Pennsylvania, have developed a combination of organic acids and safe additives that kills pathogens such as Listeria monocytogenes, Salmonella, and E. coli on a variety of fruits and vegetables. These newly created antimicrobial solutions provide alternatives for safe decontamination of fresh produce.
Review Publications
Yang, Y., Geveke, D.J. 2019. Shell egg pasteurization using radio frequency in combination with hot air or hot water. Food Microbiology. https://doi.org/10.1016/j.fm.2019.103281.
