Location: Food Safety and Intervention Technologies Research
2019 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
Scaling-up of the radio frequency pasteurization (RFP) process for shell eggs continued. A 54-egg RFP unit is being assembled in collaboration with a CRADA industry partner. A branch line splitter, which distributes the power from one RF generator to many eggs, was assembled from inexpensive parts and tested. It was compared to a commercial 90-degree hybrid splitter, which divides the power between eggs exactly 50:50 but is prohibitively expensive. The branch line splitter divides the power 56:44, which is acceptable, at a fraction of the cost of the commercial splitter. The cost savings of using branch line splitters in a large-scale RFP unit is estimated to be $100K. In other RFP research, the efficacy of RF in combination with hot water spraying (HWS) on the inactivation of Salmonella in shell eggs was compared to that of the current method which uses hot water immersion (HWI). HWS is of interest because eggs are already sprayed with warm water during RF processing. The results indicated that the pasteurization times were comparable for RF/HWI and RF/HWS (19.5 and 24.5 min, respectively). In addition, the quality of the eggs from both treatments were essentially the same. These results showed that HWS, which simplifies the RF pasteurization process, is an attractive alternative to HWI.
In produce-related research, the surface charge and hydrophobicity of strains of Salmonella, Escherichia coli and Listeria monocytogenes were determined and the initial bacterial attachment on produce 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 apples pieces and, at the same time, reducing microbial populations was developed by combining specific short chain organic acids generally regarded as safe (GRAS). Also, a bioluminescent ATP assay that achieves results within minutes was compared to conventional microbial determination that requires 2-3 days incubation before results are acquired. The results were very comparable to plate count methods but not on antimicrobial washed fruits due to low bacterial count after treatment. The new antibrowning-antimicrobial solution also disrupted biofilms on the surfaces of treated fruits. An invention disclosure for this novel antibrowning-antimicrobial solution has been filed. This treatment and determination would save produce industry time and money in investigating microbial load on produce.
Regarding research on biochar soil amendments for the safer production of produce, studies were conducted determining the minimum concentrations of biochar capable of inactivating attenuated E. coli O157:H7 in soil as well as if biochar was capable of reducing the pathogen in dairy manure compost. 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. Soil was amended with fast-pyrolysis biochar generated at 600°C in a newly-constructed bioreactor. Pathogen populations after only one week of storage were (biochar concentrations in parentheses) 6.93 log CFU/g (0%), 5.89 log (1.0%), 3.80 log (1.5%), 3.78 log (2.0%), 3.25 log (2.5%), 1.46 (3.0%), and 0.00 (3.5%). When fresh dairy compost was supplemented with 10% walnut cyclone biochar from a collaborator, no growth was detected throughout 7 weeks of storage which was attributed to high pH in compost (10.76). However, when compost was supplemented with 10% high-temp walnut biochar (pH 8.71 in compost) from the collaborator, populations remained as high as 9.05 log CFU/g up to week 4, compared with the no-biochar control, which was 9.34 log. Further, when 3.5% of the same biochar was inoculated in soil, populations were reduced to 4.42 log as compared with the no-biochar control, which was 6.46 log, indicating biochar may have a greater antimicrobial efficacy in soil as compared with fresh dairy compost. Results should provide guidance on the application of biochar added to compost or soil to inactivate foodborne pathogens.
Accomplishments
1. Novel antimicrobial antibrowning solution for fresh-cut produce. The ARS- developed antimicrobial-antibrowning solution was able to kill viable populations of Listeria monocytogenes, Salmonella or Escherichia coli O157:H7 bacteria and reduced their populations to below detectable levels on treated fresh-cut fruits. This antimicrobial-antibrowning solution will reduce foodborne outbreaks and produce recalls by the industries. Invention disclosure has been filed and work is in progress with an industry partner for possible licensing and patent application.
2. Inactivation of E. coli O157:H7 in manure by supplementing with biochar. ARS researchers in Wyndmoor, Pennsylvania have demonstrated that biochar is antimicrobial to foodborne pathogens in crop soil. Fresh dairy compost was supplemented with 10% walnut cyclone biochar from a collaborator. The 10% biochar supplement inactivated 7.95 log of the pathogen within 7 days. No E. coli was detected in the biochar-supplemented compost throughout 7 weeks of storage which was attributed to high pH in compost (10.76). This result provides guidance on the application of biochar to compost or soil to inactivate foodborne pathogens.
Review Publications
Ukuku, D.O., Niemira, B.A., Uknalis, J. 2019. Nisin-based antimicrobial combination with cold plasma treatment inactivate Listeria monocytogenes on granny smith apples. LWT - Food Science and Technology. 104:120-127. https://doi.org/10.1016/j.lwt.2018.12.049.
Yang, Y., Geveke, D.J., Brunkhorst, C.D., Sites, J.E., Geveke, N., Tilman, E.D. 2019. Optimization of the radio frequency power, time and cooling water temperature for pasteurization of Salmonella typhimurium in shell eggs. Journal of Food Engineering. 247:130-135.
Ukuku, D.O., Mukhopadhyay, S., Olanya, O.M. 2018. Survival and growth of transferred salmonella and aerobic mesophilic bacteria from melon rinds to fresh juices during juices preparation. Frontiers in Sustainable Food Systems. https://doi.org/10.3389/fsufs.2018.00078.
Gurtler, J., Fan, X., Jin, Z.T., Niemira, B.A. 2019. Effects of antimicrobials on the thermal sensitivity of foodborne pathogens: A review. Journal of Food Protection. 82(4):628-644. https://doi.org/10.4315/0362-028X.JFP-18-441.
Singh, A., Geveke, D.J., Jones, D.R., Tilman, E.D. 2019. Can acceptable quality angel food cakes be made using pasteurized shell eggs? The effects of mixing factors on functional properties of angel food cakes. Food Science and Nutrition. 7: 987-996.
Guo, M., Jin, Z.T., Gurtler, J., Fan, X., Yadav, M.P. 2018. Inactivation of E.coli O157:H7 and Salmonella on fresh strawberries by antimicrobial washing and coating. Journal of Food Protection. 81(8):1227-1235.
