1a. Objectives (from AD-416):
The overall goal of this research is to reduce the risk of foodborne illness associated with the consumption of produce and shell eggs. Effective postharvest intervention technologies for these foods have proven difficult to implement and, therefore, are on the FDA Center for Food Safety and Applied Nutrition's list of highest research priorities. This new project was formed to apply proven engineering expertise to the development of efficient intervention strategies for challenging foods such as shell eggs, fresh produce and frozen produce. While other projects continue looking at intervention methods such as hot water immersion, irradiation and cold plasma for these types of foods, the proposed project will research novel technologies including microwave, radio frequency, UV, and flash steam. The specific objectives of the research program are as follows: 1: Develop, evaluate, and validate through laboratory and pilot-plant processing the effect of single and combinations of intervention technologies on pathogen reduction in eggs. Specifically, conduct research to "pasteurize" shell eggs using technologies, such as microwave heating or ozone-based combination treatments. 2: Develop, evaluate, and validate through laboratory and pilot-plant processing the effect of single and combinations of intervention technologies on pathogen reduction in fresh produce. For example, engineer flash steam and UV treatments and develop antimicrobial/antioxidant compounds of GRAS origin as a processing aid for fruits and vegetables. 2A: Develop and evaluate a hurdle approach to inactivate Salmonella spp. and E. coli O157:H7 from tomato stem scar tissue. Application of thermal energy to the stem scar region of the tomato will be employed for the destruction of pathogens and to expose bacteria to subsequent treatments including antimicrobial immersion. 2B: Develop and evaluate a novel approach to inactivate Salmonella and E. coli O157:H7 on berries by an antimicrobial water agitation treatment. Aerated turbulence and vacuum will be applied to berries in order to remove particulate matter and expose niches within the host tissue to antimicrobials. 2C: Develop and evaluate a hurdle approach to inactivate Salmonella spp., L. monocytogenes and E. coli O157:H7 on fresh fruits and vegetables using individual treatments or a combination of antimicrobials and flash steam. 3: Develop, evaluate, and validate through laboratory and pilot-plant processing the effect of single and combinations of intervention technologies on pathogen reduction for frozen fruits and vegetables. Currently some vegetables are processed through snap freezing. It might be possible to develop a steam pasteurization processing technology that would allow vegetables to be stored refrigerated instead of frozen while having a stable shelf life.
1b. Approach (from AD-416):
Radio frequency (RF) heating intervention technology will be developed that requires less time to pasteurize shell eggs than hot water immersion. A 4 kW RF unit will be modified to enable the application of RF energy to a shell egg. Another option to improve heating uniformity is to immerse the shell eggs in a liquid while applying RF energy. In addition, nonthermal ozone treatment of shell eggs will be evaluated for reducing Salmonella. Combinations of these technologies, such as ozone and RF, will be investigated. Shell eggs will be sent to Dr. Deana Jones (Athens, GA) for extensive quality tests including foaming ability, Haugh unit, yolk index, as well as turbidity and viscosity of the egg white. Tomatoes will be inoculated and the current practice of trimming stem-scar tissue will be tested to determine if subsequent cross-contamination of tomatoes occurs during traditional stem-scar removal. Vacuum perfusion sanitization will be used in combination with chemical sanitizers for the decontamination of Salmonella and E. coli from tomatoes. A novel localized heat treatment for the physical inactivation of Salmonella within the stem scar of tomatoes will be developed. Our engineers will modify existing technology currently used for the electrical thermal dehorning of sheep, goats and cattle. Berries will be inoculated and a hurdle approach to decontaminating berries will be applied by the use of sanitizers in combination with physical treatments such as applied vacuum perfusion, or aerated turbulence of water. Fruit (including melon, apple, tomato, pepper, mango, cucumber, and pear) surfaces will be inoculated and a novel antimicrobial treatment will be developed that will not impact the sensorial quality. The kinetics and mechanism of inactivation of the developed antimicrobial wash solutions will be investigated. Flash steam technology will be used to inactivate bacteria on such fruits and vegetables as peppers, cantaloupes, mangoes, green onions, parsley, cabbage, cucumbers, and radishes. The produce will be evaluated for thermal and mechanical damage using a texture analyzer and colorimeter. Frozen fruit (e.g., berries) and vegetables (e.g., corn and peas) will be inoculated and GRAS antimicrobial compounds will be used to sensitize foodborne pathogens to UV light inactivation and inhibit growth of pathogens on thawed fruits and vegetables. The bacterial inactivation using pulsed UV bulbs, that provide higher intensities than 254 nm UV bulbs, will be investigated. The latest technology to emerge is UV-LED (light-emitting diode). UV-LEDs are compact, do not fail as quickly as other types of UV bulbs, and have a potential for significant energy savings.
3. Progress Report:
Radio frequency pasteurization (RFP) of shell eggs, invented by ARS engineers at Wyndmoor Pennsylvania, was recently granted patent rights (U.S. 8,973,492). The process inactivates 99.999% of Salmonella (inoculated) in shell eggs in 1/3 the time of the conventional hot water process and results in a significantly superior quality egg. Substantial progress was made in scaling up the process in collaboration with a funded-CRADA industry partner. A prototype RFP unit was assembled and tested that can process multiple eggs simultaneously. Work is ongoing to maximize processing uniformity of the eggs. In addition, an even larger RFP unit is being designed. Recently, a postdoc researcher was appointed to evaluate the quality of the RFP eggs. In produce-related research, a new organic antimicrobial wash was developed in partnership with a funded-CRADA industry partner. The results showed that the formulation kills up to 99.97 percent of inoculated pathogens on grape tomatoes and apples, and up to 99.0 percent on spinach and cantaloupe rind. The new formulation received a non-objection letter from Health Canada for use as an antimicrobial produce wash. The formulation was also approved as USDA Certified Organic (OMRI). In other research, a thermal cauterization technique was able to inactivate greater than 99.999 percent of Salmonella from tomato stem scars; however, a sonication wash technique only inactivated 68 percent of Salmonella on strawberries. Viral inactivation experiments were also run, analyzing Tulane virus as a useful surrogate for cold plasma treatment in comparison to Murine Norovirus. A second antimicrobial wash solution, named Lovit, independently was developed that reduces Salmonella, E. coli O157:H7 and Listeria monocytogenes on produce surfaces. Inactivation using this wash solution achieved 99.99% kill and prevented transfer of these pathogens to the interior flesh during fresh-cut preparation. This antimicrobial solution was also shown to reduce the browning reaction on fresh-cut apples and pears. A wet steam intervention treatment was also developed that kills human bacterial pathogens on cantaloupe surfaces and reduces transfer to fresh-cut pieces. The wet steam process did not affect sensorial characteristics of the fresh-cut melons. In addition, combining ultraviolet-C (UV-C) light treatment with antimicrobials to inactivate Salmonella Enterica on plum tomatoes was investigated. The combined UV-C and antimicrobial treatment effectively inactivated Salmonella on tomatoes during storage at 4 deg C. The combination treatment did not affect the tomatoes’ firmness and color during storage.
1. Radio frequency process to pasteurize shell eggs is scaled-up. Radio frequency pasteurization (RFP) produces safer eggs with exceptional quality; however, larger scale equipment is needed to process more eggs. Based on the ARS-patented RFP prototype (U.S. 8,973,492) which is capable of killing 99.999% of Salmonella, ARS engineers at Wyndmoor, Pennsylvania, designed and built a RFP unit that can simultaneously pasteurize multiple eggs. The multiple egg unit is being used to design an even larger unit in order to facilitate commercialization of RFP. Pasteurization of all shell eggs in the U.S. would reduce cases of Salmonella illnesses by an estimated 110,000 annually.
2. Antimicrobial wash solution developed for fresh and fresh-cut produce. A produce wash solution, called Lovit, was developed by ARS Researchers at Wyndmoor, Pennsylvania. The novel wash inactivates 99.99% of human bacterial pathogens on produce surfaces and minimizes transfer of these pathogens to the interior during fresh-cut preparation. It also slows down the browning reaction on fresh-cut apples and pears. All ingredients used in making the wash are considered generally recognized as safe (GRAS). A patent application has been filed and a company has filed for licensing. This innovation is the basis of a forthcoming article in AgResearch Magazine.
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Ukuku, D.O., Geveke, D.J., Mukhopadhyay, S., Olanya, O.M., Juneja, V.K. 2014. Survival, injury and inactivation of Escherichia coli 0157:H7, salmonella and aerobic mesophilic bacteria in apple juice and cider amended with nisin-edta. Journal of Food Processing and Technology. 5:385.