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 collaborators, (USDA/ARS in 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
The project has just recently been certified by OSQR. The objectives, all of which fall under National Program 108, Component I.D., Intervention and Control Strategies, are significantly different from those of the last project. Progress was made on all three objectives. For objective 1, pasteurization of shell eggs, experiments have begun on evaluating the commercial method. Shell eggs were inoculated with salmonella and were immersed in hot water at various temperatures for various times. Salmonella was reduced by 4.5 log. The shelf life and quality of the eggs will be evaluated over the next six months. Regarding objective 2, pathogen reduction in fresh produce, vacuum perfusion sanitization was performed in conjunction with the use of chemical sanitizers for the decontamination of Salmonella from the stem scars of tomatoes. The vacuum perfusion method, in conjunction with sanitizers, did not significantly increase the level of Salmonella inactivation in the stem scars of tomatoes when compared with tomatoes that were not treated with vacuum perfusion treated tomatoes. Further studies with chemical sanitizers were sufficient to attain a = 5 log CFU/stem scar inactivation of Salmonella. Literature searches were conducted to determine the extent of cross contamination from trimming tomato stem scars as well as to assess the ability of antimicrobial immersions treatments to inactivate Salmonella and E. coli O157:H7 on berries. In addition, a project scientist recently became the ADODR on USDA-AFRI Grant, Award # 2011-68003-30005, for the project entitled “Inactivation of Enteric Foodborne Viruses in High Risk Foods by Non-Thermal Processing Technologies” which was subawarded $300,000 from the University of Delaware. The funds will be used to determine the effects of ultraviolet light, gamma irradiation, high pressure processing, antimicrobial sanitizers, and cold plasma treatment on human norovirus, hepatitis A virus, and rotavirus on strawberries, raspberries, blueberries, green onions, salsa, and other high risk foods. For objective 3, pathogen reduction for frozen fruits and vegetables, the design of a nonthermal UV-LED experimental system for improving the safety of frozen foods is ongoing.