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 process (RFP) was developed to rapidly pasteurize shell eggs. It works by using penetrating radio frequency (RF) energy to quickly heat the yolk, which is the egg component most favorable to harboring Salmonella. As the egg is rotated, RF energy and cooling water are simultaneously applied to the egg. This initiates pasteurization of the yolk while maintaining a low temperature in the heat-sensitive egg white, thus preventing hazing. Immediately after the RF heating process, the egg is placed in hot water to pasteurize the egg white and to complete pasteurization of the yolk. Radio frequency pasteurization of shell eggs, invented by ARS engineers in Wyndmoor, Pennsylvania, was 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 eggs that retain their fresh-like appearance and significantly more functionality. Substantial progress was made in scaling up the process. A prototype RFP unit was assembled and tested that can process four eggs simultaneously. Work is ongoing to maximize processing uniformity of the eggs. In addition, a larger RFP unit is being assembled in collaboration with a funded-CRADA industry partner. In produce-related research, ARS scientists in Wyndmoor, Pennsylvania evaluated the washing of tomatoes with 63 sanitizers. Some of the sanitizers achieved an inactivation of 99.999% of Salmonella. A new organic antimicrobial wash was developed in partnership with a funded-CRADA industry partner. The results showed that the new formulation kills up to 99.97% of inoculated pathogens on grape tomatoes and apples, and up to 99.0% percent on spinach and cantaloupe rind. The formulation received a non-objection letter from Health Canada as well as approval from the FDA for use as an antimicrobial produce wash and was also approved as USDA Certified Organic (OMRI). A patent on the produce wash has been filed. Low level concentrations of the produce wash (0.2, 0.3, and 0.4%) inactivated greater than 99.999% of Listeria, Salmonella and E. coli. In the presence of an interference substance (5 percent apple juice), reductions for 0.5 and 0.4% concentrations of the produce wash, respectively, were E. coli (6.25, 5.06), Salmonella (6.78, 6.18), and Listeria (6.69, 2.94). A second antimicrobial wash solution was independently developed by ARS researchers in Wyndmoor, Pennsylvania that reduces Salmonella, E. coli O157:H7 and Listeria monocytogenes on produce surfaces. All ingredients used in making the wash are considered generally recognized as safe (GRAS). 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. An invention disclosure for a patent application for the wash was submitted. The effect of quick freezing on bacterial populations inoculated on baby spinach and in combination with the wash was investigated. Baby spinach treated with the wash and then frozen at -80 C for 1 h reduced the human bacterial populations to below detection, while even native spinach microflora was reduced by 99.9%. A wet steam intervention treatment was also developed that kills human bacterial pathogens on cantaloupe surfaces and reduces transfer to fresh-cut cantaloupe. The wet steam process did not affect sensory 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. The combination treatment did not affect the tomatoes’ firmness and color during storage. The feasibility of inactivating bacteria using UV energy supplied by light emitting diodes (UV-LED) was investigated. UV-LEDs have only very recently become commercially available. Compared to conventional UV mercury bulbs, UV-LED bulbs may be more energy efficient as well as more environmentally friendly. Using an experimental system that was designed and assembled in-house, E. coli inoculated onto the surface of a tomato was reduced by 99.7 percent after 150 seconds of UV-LED exposure. In other research, in order to mitigate transfer of bacterial pathogens from soil to fresh produce, studies examined the effects of mycorrhizal fungi as well as a biofuel production byproduct (pyrolysis biochar) on bacterial survival in soil. Long-term shelf stability of whey protein during adverse storage conditions was established and efficacy was found to be dependent on packaging, temperature and humidity.
1. Radio frequency pasteurization of shell eggs scaled-up. Radio frequency pasteurization (RFP) produces safer eggs with exceptional quality; however, larger scale equipment is needed to make the process economical. Based on the ARS-patented RFP prototype (U.S. 8,973,492), which is capable of killing 99.999% of Salmonella, ARS engineers in Wyndmoor, Pennsylvania designed and built a RFP unit that can simultaneously process four eggs. A larger scale RFP unit is being assembled, in collaboration with a CRADA industry partner, which will facilitate commercialization of RFP.
2. Antimicrobial produce wash receives FDA approval. A patent-pending produce wash was developed jointly with a CRADA industry partner and ARS researchers in Wyndmoor, Pennsylvania. This antimicrobial solution has been shown to inactivate foodborne pathogens on produce and in wash waters which assists in preventing cross contamination of fruits and vegetables during washing. Besides being approved for use in Canada and receiving USDA-Organic Materials Review Institute Certified-Organic Status, the FDA recently approved the produce wash to be used on fresh and fresh cut fruits and vegetables. This approval by the FDA has allowed the industry cooperator to begin selling the product to fresh produce processors.
5. Significant Activities that Support Special Target Populations:
Geveke, D.J., Gurtler, J., Jones, D.R., Bigley, A.R. 2016. Inactivation of salmonella in shell eggs by hot water immersion and its effect on quality. Journal of Food Science. 81(3):M709-M714.
Miks-Krajnik, M., Yoon, Y., Ukuku, D.O., Yuk, H. 2016. Growth dynamics of specific spoilage organisms and associated spoilage biomarkers in chicken breast stored aerobically. Food Microbiology and Safety Journal. DOI:10.1111/1750-3841.13371.
Ukuku, D.O., Mukhopadhyay, S., Geveke, D.J., Olanya, O.M., Niemira, B.A. 2016. Minimal thermal treatments for reducing bacterial population on cantaloupe rind surfaces and transfer to fresh-cut pieces. Journal of Food Protection. doi: 10.4315/0362-028X.JFP-16-046.
Krajnik, M., Yoon, Y., Ukuku, D.O., Hyun, G. 2016. Volatile chemical spoilage indexes of raw Atlantic salmon (salmo salar)stored under aerobic condition in relation to microbiological and sensory shelf lives. Food Microbiology. 53:182-191.
Ukuku, D.O., Onwulata, C.I., Mukhopadhyay, S., Thomas-Gahring, A.E., Chau, L.I., Tunick, M.H. 2016. Changes in microbial populations of WPC34 and WPC80 whey protein during long term storage. Journal of Food Processing and Preservation. doi: 10/1111/jfpp.12743.
Geveke, D.J., Aubuchon, I., Zhang, H.Q., Boyd, G., Sites, J.E., Bigley, A. 2015. Validation of a pulsed electric field process to pasteurize strawberry puree. Journal of Food Engineering. 166:384-389.
Geveke, D.J., Trujillo, F. 2014. Nonthermal processing by radio frequency electric fields. Book Chapter. Sun, D.W, editor. Emerging Technologies for Food Processing 2nd Edition. Amsterdam:Elsevier Academic Press. p. 259-269.
Ukuku, D.O., Geveke, D.J., Chau, L.I., Niemira, B.A. 2016. Microbial safety and overall quality of cantaloupe fresh-cut pieces prepared from whole fruit after wet steam treatment. International Journal of Food Microbiology. doi: 10.1016/j.ijfoodmicro.2016.05.019.
Ojwang, D.J., Nyankanga, R.O., Olanya, O.M., Ukuku, D.O., Imungi, J. 2016. Yield potential of pigeon pea cultivars. Subtropical Agriculture and Environments. 67:1-12.
Ukuku, D.O., Latiful, B., Kassama, L.S., Mukhopadhyay, S., Olanya, O.M. 2015. Survival, injury and inactivation of human bacterial pathogens in foods: effect of non-thermal treatments. Book Chapter. p. 82-96.
Ukuku, D.O., Latiful, B. 2015. Foodborne illness and microbial agents. Book Chapter. Foodborne Pathogens and Safety (Food Biology Series);Bari,Md.L.,Ukuku, Dike (editors) CRC Press, Taylor and Francis Group.Boca Raton, Florida, USA. p. 16-34.
Ukuku, D.O., Mukhopadhyay, S., Juneja, V.K., Rajkowski, K.T. 2014. Evaluating natural antimicrobials for food application, in natural antimicrobials for food safety and quality. Book Chapter. Oxford, UK: Woodhead Publishing. p. 185-202.