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:
A radio frequency (RF) energy process was developed that has great potential to substantially increase the number of eggs pasteurized in the US, thus significantly reducing illness from Salmonella bacteria. The collaboration continues with ARS scientists at Athens Georgia to evaluate the egg quality. Also, shell eggs were treated with ozone, an oxidizing antimicrobial agent. The reduction of Salmonella using the ozone was insignificant, probably due to the difficulty of the ozone to penetrate the shell. Studies were performed on the efficacy of sanitizers against Salmonella and E. coli O157:H7 on strawberries as well as on tomato stem scars. Sanitizers inactivated over 99.999% and 99.9% of these pathogens on tomato stem scars and strawberries, respectively. Results indicated that vacuum perfusion did not increase the inactivation of bacteria on fruits washed with antimicrobial solutions. A paper was published in the International Journal of Food Microbiology detailing the research. Work continued on a 36-month CRADA entitled, “Development of Produce Wash for Microbial Decontamination of Fresh Fruits and Vegetables”. Work also continued on a 5-year NIFA-funded project in conjunction with the University of Delaware, entitled, “Inactivation of Enteric Foodborne Viruses in High Risk Foods by Non-Thermal Processing Technologies”. An Auburn University postdoctoral research associate began work on a 2-year NIFA-funded Fellows project investigating the role of fast-pyrolysis biochar in accelerating the inactivation of E. coli O157:H7 and Salmonella in crop soil over time, in order to inhibit the contamination of fresh produce. Another scientist is researching the behavior of Salmonella spp. on inoculated fresh-cut cantaloupe pieces processed with organic acids stored at different temperatures and the overall acceptability of the treated cantaloupe cubes. Sodium lactate treatment resulted in the highest acceptability score, 8 (with 10 being the highest rating), and it provided an additional viability loss of 30 percent for Salmonella spp. Finally, membrane damage and viability loss of E. coli O157:H7 and Salmonella spp. in apple juice treated with heat and with nonthermal high hydrostatic pressure and were investigated to understand the relationship of heat and pressure on mechanism of inactivation. A 350 MPa pressure at 35 C led to the collapse of the bacterial membrane. The damaged bacteria did not recover during refrigerated storage. Manuscripts on these last two studies have been accepted for publication in scientific journals. Using an experimental UV light emitting diode (UV-LED) system, that was designed and assembled in-house, E. coli was reduced by 99.999% and 99.7% in a liquid solution and on the surface of a tomato, respectively. This is the first study to show that bacteria on foods can be inactivated using nonthermal UV LED technology. The next step is to study the energy costs of the UV-LED process.
1. Shell eggs pasteurized using innovative RF process look great. Pasteurization of all shell eggs in the U.S. would reduce Salmonella illnesses by approximately 110,000 annually, yet only about 1 percent of eggs are currently pasteurized because the process is costly and damages the egg white appearance. ARS researchers, at Wyndmoor, Pennsylvania, developed a radio frequency (RF) energy process that eliminates 99.999 percent of Salmonella, that may be present in eggs. The RF process is significantly faster than the current pasteurization process, by more than 50 percent, and the egg whites look perfect. The ARS has filed for patent protection and several companies have expressed interest in licensing the technology. RF pasteurization substantially reduces the threat of illness from uncooked and undercooked shell eggs, allowing consumers to enjoy their favorite recipes and styles.
Ukuku, D.O., Mukhopadhyay, S., Onwulata, C.I. 2013. Effect of storage temperature on survival and recovery of thermal and extrusion injured Escherichia coli populations in whey protein concentrate and corn meal. Foodborne Pathogens and Disease. Volume 10(1):62-68.