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United States Department of Agriculture

Agricultural Research Service

2011 Annual Report

1a.Objectives (from AD-416)
Determine the kinetics and mechanisms of inactivation of pathogens and their surrogates by PEF and RFEF technologies; Develop, evaluate and validate PEF and RFEF alone and in combination with other processes to ensure safety and security of fresh apple cider, fresh orange juice and liquid egg; and Evaluate quality, shelf life and cost of products processed by PEF, RFEF and combinational processes, and packaged aseptically or with antimicrobial agents, in comparison to thermal pasteurization.

1b.Approach (from AD-416)
Integrate disciplines of microbiology, engineering and chemistry to provide consumers with safe and high quality food products. Our microbiologists will lead the research in determining the mechanisms and kinetics of microbial inactivation, microbial shelf-life evaluations and product safety evaluations. Our engineers and food technologists will develop and validate novel processes and packaging technologies and evaluate associated cost. Our chemist and food technologists will lead the quality and shelf-life evaluations and consumer acceptance studies. From a food product point of view, the raw food materials will be processed and packaged to ensure safety and to maintain the fresh quality. Process conditions will be determined to achieve the food safety objectives set forth by the log reduction required for the pathogen of concern. Kinetics of microbial inactivation and models provide process set points to achieve food safety objectives. The kinetic models also serve as tools for risk assessment when deviations take place in raw product composition, microbial load and/or processing conditions. Identification of the mechanisms of microbial inactivation will help understand the process and define the direction in process optimization. We will also work with our collaborators in regulatory agencies, industry and other ARS laboratories, to identify the pathogens of concern and suitable surrogates and to define food safety objectives for each product.

3.Progress Report
This is the final year of this project. Essentially, all of the milestones were fully met in all three objectives, all of which fall under National Program 108, Component I.D., Intervention and Control Strategies. Objective 1 was to investigate kinetics and mechanisms of inactivation of nonthermal intervention methods for liquid foods. Kinetics of inactivation by radio frequency electric fields (RFEF), pulsed electric fields (PEF), and thermal processing were determined over the course of the project. The Survival and growth models for Escherichia coli O157:H7, L. monocytogenes and Salmonella spp. in apple cider during storage were completed. Addition of an antimicrobial combination, nisin and EDTA, caused a decline in the populations for all pathogens tested, suggesting possible addition of this combination to freshly prepared apple cider could enhance its microbial safety and prevent costly recalls. Escherichia coli K-12 in apple juice was treated with a combination of RFEF and UV-light and it was determined that RFEF treatment causes more injury to the bacterial cells leading to more cellular leakage than UV-light treatment. Thermal inactivation experiments were completed using the capillary tube method for Salmonella suspended in liquid whole egg. This data was provided to FSIS, Washington, D.C., for mathematical modeling for new industry compliance guidelines. Antimicrobials were found that sensitized Salmonella in liquid whole egg to thermal pasteurization. Objective 2 of the project was to develop PEF and RFEF processes for liquid foods. A laboratory scale PEF, RFEF and thermal processing system was developed. In addition, a larger, pilot scale PEF, RFEF and thermal processing system was developed. A patent application was filed on the nonthermal RFEF process. Another pilot scale system was developed that used super critical carbon dioxide to pasteurize fruit juices at 38 ºC to minimize quality degradation. The project's third objective was to evaluate quality, shelf life and cost of the processes developed. The cost of RFEF pasteurization of juices was determined to be less than 2 cents per gallon.

1. Determined liquid egg pasteurization parameters for FSIS. A model that predicts lethality of Salmonella for given times and temperatures was needed. A model was developed by ARS researchers at Wyndmoor, PA, and it confirmed that the current pasteurization requirements for 10% salted liquid whole egg of minimum temperatures and times (i.e. 63.3 deg C for 3.5 min, or 62.2 deg C for 6.2 min) are not sufficient to completely Salmonella and are estimated to provide ca. 99.99-99.999% CFU/ml of destruction. This model will assist the USDA, FSIS in issuing pasteurization performance standards and provide industry guidance for designing pasteurization processes that will ensure safe product.

2. The use of bottles with antimicrobial coatings inactivated Salmonella in liquid egg. Salmonellosis is a leading cause of foodborne illness in the United States. In this study, an antimicrobial bottle coating method was developed by ARS researchers at Wyndmoor, PA, to reduce the risk of outbreaks of human Salmonellosis caused by contaminated liquid eggs. Glass jars were coated with a mixture of polylactic acid (PLA) polymer and antimicrobial compounds and the efficacy of bottle coatings in inactivating Salmonella in liquid egg white was investigated. The PLA bottle coatings with antimicrobials effectively inactivated Salmonella in liquid egg albumen and the synergistic bactericidal effect was found when two or more antimicrobials were used together. This study demonstrated the potential of applying the antimicrobial bottle coating method to liquid eggs, and possibly other fluid food products.

3. Destroyed spoilage bacteria in orange juice at low temperatures using supercritical carbon dioxide (CO2). Thermal processing is the most effective way to kill microorganisms in orange juice; however, this method may cause side effects such as destruction of nutrients and off-flavors. To kill bacteria without deterioration of orange juice quality, a nonthermal supercritical carbon dioxide technology has been developed by ARS researchers at Wyndmoor, PA. Microscopic imaging confirmed that supercritical CO2 also caused injury. This study indicates that supercritical CO2 can kill microorganisms in orange juice at low temperatures, thus potentially minimizing side effects produced by heat.

4. Determined that nonthermal processing may cost more than traditional thermal processing. The main goal of the application of nonthermal technologies such as pulsed electric fields (PEF) and high pressure processing (HPP) is to produce safe, fresher and more nutritious food. However, despite extensive microbiological data available, cost analysis and environmental impact studies of these processes are still scarce. The present study by ARS researchers at Wyndmoor, PA, analyzed the cost and impact on the environment of pasteurization of orange juice by PEF, HPP and thermal processes. Nonthermal technologies were more costly and had more green-house emissions than traditional thermal pasteurization on orange juice processing. HPP was found to be the most costly technology whereas PEF and HPP had similar CO2 production. The information presented here will enable a better understanding of the industrial implementation of nonthermal processing.

5. Inactivated E. coli in liquid egg white using a centrifugal film UV irradiator. ARS researchers at Wyndmoor, PA, performed inactivation studies on liquid egg white using a UV light system that centrifugally forms a thin liquid film from Dill Instruments. Nonthermal UV processing reduced E. coli in liquid egg white by more than 99.999%. Processing at higher flow rates resulted in lower reductions of E. coli. These results suggest that liquid egg white may be nonthermally pasteurized using a low flow rate centrifugal UV irradiator.

Review Publications
Geveke, D.J. 2011. Radio Frequency Electric Fields as a Nonthermal Process. In: Zhang, H.Q., Barbosa-Canovas, G.V., Balasubramaniam, V.M., Farkas, D., Yuan, J.L., editors. Nonthermal Processing Technologies for Food. Chichester, West Sussex, UK: Wiley-Blackwell. p. 213-221.

Azhuvalappil, Z., Fan, X., Geveke, D.J., Zhang, H.Q. 2010. Thermal and non-thermal processing of apple cider: storage quality under equivalent process conditions. Journal of Food Quality. 33(5):612-631.

Ukuku, D.O., Geveke, D.J., Zhang, H.Q. 2010. Behavior of radio frequency electric fields injured Escherichia coli in nutrient and non nutrient media during storage. International Journal of Food Microbiology. 8(3&4):170-174.

Zhang, H.Q., Barbosa-Canovas, G.V., Balasubramaniam, V.M., Dunne, C.P., Farkas, D.F., Yuan, J.T. 2011. Nonthermal processing technologies for food. Malaysia: IFT Press. 640 p.

Yuk, H., Geveke, D.J. 2010. Nonthermal inactivation and sublethal injury of Lactobacillus plantarum in apple cider by a pilot plant scale continuous supercritical carbon dioxide system. Food Microbiology. 28:377-383.

Ukuku, D.O., Yuk, H., Zhang, H.Q. 2010. Behavior of pulsed electric field injured Escherichia coli O157:H7 cells in apple juice amended with pyruvate and catalase. Journal of Microbial and Biochemical Technology. 2(6):134-138.

Gurtler, J., Marks, H.M., Jones, D.R., Bailey, R., Bauer, N.E. 2011. Thermal inactivation kinetics of heat-resistant Salmonella Enteritidis and Oranienberg in 10% salted liquid egg yolk. Journal of Food Protection. 74(6):882-892.

Gurtler, J., Bailey, R., Geveke, D.J., Zhang, H.Q. 2011. Sodium benzoate, potassium sorbate, and citric acid induce sublethal injury and enhance pulsed electric field inactivation of E. coli O157:H7 and nonpathogenic surrogate E. coli in strawberry juice. Food Control. 22(2011)1689-1694.

Jin, Z.T., Gurtler, J. 2010. Inactivation of Salmonellae in liquid egg white by antimicrobial bottle coating with allvl isothiocyanate, nisin and ZnO nanoparticles. Applied and Environmental Microbiology. 110(3):704-712.

Last Modified: 10/4/2015
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