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United States Department of Agriculture

Agricultural Research Service

2010 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
Progress was made on all three objectives, all of which fall under National Program 108, Component I.D., Intervention and Control Strategies. Regarding research on the kinetics of inactivation in liquid egg, the selection of Salmonellae strains for thermal challenge studies was optimized with two strains of heat-resistant Salmonella Enteritidis phage type 8 and one strain of Salmonella Oranienburg. Furthermore, thermal experiments were completed using the capillary tube method for the inactivation kinetics of Salmonella in plain liquid whole egg and liquid egg yolk + 10% salt. All of this data was provided to Dr. Harry Marks, USDA FSIS, Washington, D.C., for mathematical modeling for new industry compliance guidelines. A FSIS/ARS funded project was established titled “Evaluation of Thermal Inactivation Kinetics of Salmonella in Liquid Egg Products” which was used to launch a cooperative agreement with Drexel University. Research concentrated on testing antimicrobials used for sensitizing Salmonella to thermal pasteurization in liquid whole egg. Research on the pilot plant scale pulsed electric fields (PEF) system made significant progress. A preliminary study was performed on PEF inactivation of E. coli in buffered peptone water and strawberry puree to determine the effect of electric field strength and temperature. A state-of-the-art high speed real-time continuous data acquisition system was developed for the pilot plant PEF system. The data acquisition system should meet a requirement for FDA approval of PEF processing. Experiments were performed using the laboratory scale PEF system as well. The effect of PEF was estimated on surface hydrophobicity and cell surface charge of E. coli O157:H7. The injury of E. coli was determined and correlated with changes in cell surface charge. PEF treated apple juice was collected and amended with either 0.1% pyruvate or catalase to investigate the effect of these additives on the surviving populations of PEF injured E. coli cells. The results of this study suggest that disruption of bacterial cell membrane protein is also part of the inactivation mechanism of PEF. Finally, PEF processing of liquid egg albumen was tested.

1. Antimicrobial packaging inactivates E. coli O157:H7 and Listeria monocytogenes: Beverages can occasionally become contaminated by the pathogen E. coli O157:H7 and Listeria monocytogenes, leading to product recalls and foodborne illness outbreaks. Antimicrobial packaging films and coatings were developed, by ARS researchers at Wyndmoor, PA, for pathogen control in strawberry purees, milk and liquid egg products. Generally recognized as safe (GRAS) antimicrobial compounds, singly and in combinations, were incorporated into polylactic acid polymer films or coated on glass jars. The antimicrobial treatments inactivated more than 99.99 percent of E. coli O 157:H7 in strawberry purees and completely inactivated L. monocytogenes in milk and liquid egg white. The antimicrobial coating has the potential to reduce product recalls and foodborne illness outbreaks due to contamination by E. coli O157:H7 or Listeria monocytogenes.

2. Supercritical carbon dioxide CO2 destroys spoilage bacteria in apple cider at low temperatures: Spoilage bacteria in apple cider, such as Lactobacillus plantarum, may cause undesirable flavors and damage to the container by fermentation during storage, resulting in shortened shelf-life of the product. Thermal processing is the most effective way to kill spoilage bacteria in apple cider; however, this method may cause side effects such as destruction of nutrients and off-flavors. To kill bacteria without deterioration of apple cider quality, nonthermal supercritical carbon dioxide technology has been developed by ARS researchers in Wyndmoor, PA. A 99.999% kill of L. plantarum was obtained at 42C. Microscopic imaging confirmed that supercritical CO2 also caused injury of L. plantarum. Refrigeration after processing prevented re-growth of L. plantarum during storage for 28 days. This study indicates that supercritical CO2 can kill spoilage bacteria in apple cider at low temperatures, thus extending the shelf-life of the cider without any of the side effects produced by heat.

3. Nonthermal processing may cost more than traditional thermal processing: Novel nonthermal intervention technologies such as high pressure processing and pulsed electric fields processing are being developed to produce safer, natural and more nutritious food. Although research has shown the benefits of these technologies, there are no studies comparing the costs to that of traditional thermal processing. An analysis was performed, by ARS researchers in Wyndmoor, PA, on the costs to process orange juice by these three technologies. Preliminary results showed that thermal pasteurization was 4 cents/kg and 5 cents/kg cheaper than PEF and HPP, respectively, based on a 3000 L/h production scale. This project will be useful to food manufacturers by increasing the knowledge of these new nonthermal technologies, which are more expensive than thermal processing, but offer benefits to the consumer.

4. Centrifugal film UV irradiator inactivates E. coli in grapefruit juice: ARS researchers in Wyndmoor, PA performed inactivation studies on grapefruit juice using a laboratory scale UV light system from Dill Instruments. Nonthermal UV processing reduced E. coli in grapefruit juice by more than 99.999%. Storing UV processed grapefruit juice at refrigeration temperatures for 14 days further reduced E. coli to below detectable levels. These results suggest that grapefruit juice may be nonthermally pasteurized using a UV device that centrifugally forms a thin liquid film.

Review Publications
Ukuku, D.O., Zhang, H.Q., Latiful, B., Yamamoto, K., Kawamoto, S. 2009. Leakage of Intracellular UV Materials of High Hydrostatic Pressure-Injured Escherichia Coli O157:H7 Strains in Tomato Juice. Journal of Food Protection. 72(11):2407-2412.

Gurtler, J., Kornacki, J.L. 2009. Comparison of supplements to enhance recovery of heat-injured Salmonella from egg albumen. Letters in Applied Microbiology. 503-509.

Beuchat, L.R., Kim, H., Gurtler, J., Lin, L., Ryu, J., Richards, G. 2009. Cronobacter sakazakii in foods and factors affecting its survival, growth, and inactivation. International Journal of Food Microbiology. 136:204-213.

Ukuku, D.O., Geveke, D.J. 2010. A combined treatment of UV-light and radio frequency electric field for the inactivation of Escherichia coli K-12 in apple juice. International Journal of Food Microbiology. 138:50-55.

Yuk, H., Geveke, D.J., Zhang, H.Q. 2010. Efficacy of supercritical carbon dioxide for nonthermal inactivation of Escherichia coli K12 in apple cider. International Journal of Food Microbiology. 138:91-99.

Gurtler, J., Rivera, R.B., Geveke, D.J., Zhang, H.Q. 2010. Selection of surrogate bacteria in place of E. coli O157:H7 and Salmonella Typhimurium for pulsed electric field treatment of orange juice. International Journal of Food Microbiology. 139:1-8.

Sampedro, F., Geveke, D.J., Fan, X., Zhang, H.Q. 2009. Effect of PEF, HHP and Thermal Treatment on PME Inactivation and Volatile Compounds Concentration of an Orange Juice-Milk Based Beverage. Innovative Food Science and Emerging Technologies. 10:463-469.

Yuk, H., Geveke, D.J., Zhang, H.Q., Jin, Z.T. 2009. Comparison of aluminum thermal-death-time disks with a pilot-scale pasteurizer on the thermal inactivation of Escherichia coli K12 in apple cider. Food Control. 20:1053-1057.

Behling, R.G., Eifert, J., Erickson, M.C., Gurtler, J., Kornacki, J.L., Line, J.E., Radcliff, R., Ryser, E.T., Stawick, B., Yan, Z. 2010. Selected pathogens of concern to industrial food processors: infectious, toxigenic, toxico-infectious, selected emerging pathogenic bacteria. In: Kornack, J.L. Editor. Principles of Microbiological Troubleshooting in the Industrial Food Processing Environment. New York, NY: Springer. 140 p.

Last Modified: 11/28/2015
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