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:
For objective 1, pasteurization of shell eggs, experiments on evaluating the hot water immersion method have been completed. Salmonella was reduced by 4.5 log (99.997%) following treatment at 56.7 deg C for 60 min. The quality of the hot water pasteurized eggs was evaluated. In addition, pasteurized eggs were refrigerated for 4 weeks to determine the fate of the surviving Salmonella. Regarding objective 2, pathogen reduction in fresh produce, a scientist investigated the cross-contamination of Salmonella-inoculated tomato stem scars after removing them with a knife and then slicing the same tomato with the same knife. Approximately 30% of tomatoes became contaminated; however, stem scars that were entirely removed (without the knife blade touching the inoculated stem scar) did not further contaminate the tomato. Experiments were performed on inactivating Salmonella and E. coli O157:H7 on strawberries by means of more than 50 different sanitizing wash combinations. In addition, a scientist became the ADODR on a 36 month CRADA entitled, “Development of produce wash for microbial decontamination of fresh fruits and vegetables.” The industry partner will provide $65,000 to ARS. Work continued on optimizing high pressure processing of foods for inactivating pathogenic bacteria and viruses. One manuscript was published in Applied and Environmental Microbiology. A scientist completed studies investigating the internalization of Salmonella and E. coli O157:H7 into both leek and baby Romaine lettuce as affected by mycorrhizal fungi in the soil. Results showed that fungi may increase the survivability of Salmonella and E. coli O157:H7 in leek plants but not in baby Romaine lettuce. A novel antimicrobial wash solution containing certain short chain organic acids generally regarded as safe is being developed. The ability of microbial inactivation by individual organic acids was tested to optimize effective concentrations. Treatment of melons, cucumber and tomatoes with the novel antimicrobial solution at ambient temperature and 60 deg C for 3 minutes resulted in a population reduction of 4.5 and 6 log (99.997 and 99.9999%), respectively. In addition, research was undertaken to investigate bacterial surface charge and strength of attachment for non-pathogenic surrogates (E. coli ATCC 25922 and ATCC 35218) and human bacterial pathogens (Salmonella serovars, E. coli O157:H7 and Listeria monocytogenes) on cantaloupe surfaces. The information will provide the food processing industry and research institutions the necessary parameters of specific bacterial surrogates for pilot plant studies. For objective 3, pathogen reduction for frozen fruits and vegetables, a nonthermal UV-LED experimental system was designed and assembled. Preliminary experiments indicated that E. coli is inactivated by the UV-LED system.