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United States Department of Agriculture

Agricultural Research Service


Location: Food Safety and Intervention Technologies

2009 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
Thirty strains of Salmonella were screened for thermal resistance in liquid whole egg. The four most resistant strains were two strains of S. Enteritidis phage type (PT) 8, one of PT 13 and one of Oranienberg. These strains are being used in a collaborative FSIS liquid egg thermal kinetics study.

D values for a four-strain cocktail of Salmonella Enteritidis and Oranienberg in liquid egg yolk were 1.91 min at 58C, 0.70 min at 60C, 0.28 min at 62C, 0.11 min at 64C and 0.04 min at 66C. These values are higher than what has been reported in the literature. Ongoing studies are fitting yolk pasteurization data to a mathematical model with the assistance of FSIS.

E. coli O157:H7 and surrogate E. coli 35218 were inoculated into strawberry juice with or without the addition of 750 ppm sodium benzoate, 450 ppm potassium sorbate and 2.7% citric acid and treated by pulsed electric field treated at 45, 50 and 55C with a field strength of 18.6 kV/cm for 150 microseconds. Inactivation of surrogate E. coli at 45, 50, and 55C were 2.86, 3.12, and 3.79 log CFU/ml, respectively, in plain juice (pH 3.4), and 2.75, 3.52, and 5.11 with the addition of benzoic and sorbic acids (pH 3.5). Inactivation of E. coli O157:H7 under the same conditions were 3.09, 4.08, and 4.71 log CFU/ml, respectively, and 2.27, 3.29, and 5.40 with antimicrobials. E. coli O157:H7 in juice with antimicrobials and 2.7% citric acid (pH 2.7) treated with PEF was reduced by 2.60, 4.32 and 6.95 log CFU/ml at 45, 50 and 55C while the surrogate E. coli decreased by 3.54, 5.69, and 7.13 log under the same conditions.

RFEF has recently been shown to be effective at reducing gram positive bacteria, a group that includes the human pathogen Listeria monocytogenes. There was a total lack of research on the ability of RFEF to injure gram positive bacteria. The population of Lactobacillus plantarum in apple cider at 55 C was inactivated by more than 99% and a further 94% of the survivors were injured. The results of this study and previous studies point to the possibility of using RFEF processing to pasteurize apple cider containing gram negative and gram positive bacteria.

UV-light treatment at 40Calone caused 6.5 log reduction of E. coli in apple juice while RFEF at 40C caused 1.5 log reduction. Percent injury caused by individual RFEF and UV-light processing averaged 95% and < 1%, respectively. A combination of the two processing treatments did not increase cell injury or leakage of UV-substances. The combination treatment was not synergetic.

1. Acidity and nonthermal processes are synergistic in inactivating microorganisms: Storage conditions and pH of media necessary for the resuscitation of Radio Frequency Electric Fields (RFEF) damaged E. coli cells in apple juice were investigated. RFEF treatment damaged the surface structure of E. coli cells and addition of calcium and magnesium chloride aided recovery of the injured cells during storage at 23C for 24 h. Injured cells stored at 5C for 24 h could not repair but died off suggesting that RFEF treatment and cold storage of treated juice as a good combination process for apple juice.

2. Pulsed electric field inactivates E. coli and Salmonella in orange juice: Twenty non-pathogenic bacteria were tested as potential surrogate organisms for E. coli O157:H7 treated in orange juice by pulsed electric field. Non-pathogenic E. coli 35218 most closely resembled the inactivation curve of E. coli O157:H7. Treatment conditions of 55C and 28 kV/cm for 75 microseconds resulted in 4.0 log CFU/ml and 100% injury of both bacteria.

3. Supercritical carbon dioxide achieved 5-log reduction to E. coli: A newly developed pilot-plant scale system using a gas-liquid contactor may be more efficient than previous systems because it was designed to operate at a lower pressure. The bactericidal effect of this new system on Escherichia coli K12 in buffered peptone water was evaluated. Results showed that a 99.999% reduction of E. coli was obtained at all tested temperatures (34, 38, and 42C). Storage test results after processing with SCCO2 showed that the number of cells further decreased at refrigerated temperature (4C) but increased at room temperature (25C) after 7 days. This new SCCO2 system appears promising for nonthermal liquid food pasteurization.

4. Nonthermal processes extended shelf life of fruit juices: Non-thermal processes like pulsed electric field (PEF) and ultraviolet (UV) light are developed as alternative pasteurization technologies to thermal process to enhance the microbial safety of fresh juice while preserving organoleptic and nutritional qualities. The effect of PEF, UV and thermal processes on apple cider quality are compared at conditions optimized to achieve equivalent 6 log reductions of E. coli. PEF extended the shelf-life of apple cider by inactivating spoilage microorganisms compared to UV processing, and better preserved the freshness (aroma and color) over traditional thermal processing. PEF process is the best choice among the three technologies studied. The information will help the juice industry to adopt PEF technology to better preserve the freshness of fruit juices.

5. Developed antimicrobial packaging material to inactivate pathogens: Antimicrobial packaging systems using natural antimicrobials and biodegradable polymers have been developed to enhance food safety and extend food shelf-life. The generally regarded as safe antimicrobials, such and nisin, lactic acid, and nanoscale zinc oxide were integrated into biodegradable packaging materials (polylactic acid and/or pectin) to develop antimicrobial packaging systems used for liquid or solid foods. These packaging systems significantly inactivated or inhibited pathogenic Listeria monocytogenes, E. coli O157:H7, Salmonella enteritidis in orange juice, apple cider, strawberry purees, liquid egg, ready-to-eat meat, and milk. Antimicrobial food packaging provides an additional and final intervention hurdle for controlling food borne pathogens in packaged foods.

6.Technology Transfer


Review Publications
Jin, Z.T., Zhang, H.Q., Hermawan, N., Dantzer, W. 2009. Effects of pH and Temperature on Inactivation of Salmonella Tyhimurium DT104 in Liquid Whole Egg by Pulsed Electric Fields. Journal of Food Science and Technology. 44:367-372.

Jin, Z.T., Liu, L.S., Zhang, H.Q., Hicks, K.B. 2009. Antimicrobial activity of nisin incorporated in pectin and polylactic acid composite films against Listeria monocytogenes. International Journal of Food Science and Technology. 44:322-329.

Ukuku, D.O., Jin, Z.T., Zhang, H.Q. 2008. Membrane damage and viability loss of Escherichia coli K-12 and Salmonella entertidis in liquid egg by thermal death time disk treatment. Journal of Food Protection. 71(10):1988-1995.

Jin, Z.T., Zhang, H.Q., Sun, D., Su, J.Y., Sue, H. 2009. Antimicrobial Efficacy of Zinc Oxide Quantum Dots Against Listeria Monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7. Journal of Food Science. 74(1):M46-M52.

Azhuvalappil, Z., Fan, X., Zhang, H.Q., Rouseff, R.L. 2009. Impact of Thermal and Nonthermal Processing Technologies on Unfermented Apple Cider Aroma Volatiles. Journal of Agricultural and Food Chemistry. 57:924-929.

Sampedro, F., Geveke, D.J., Fan, X., Rodrigo, D., Zhang, H.Q. 2009. Shelf-Life Study of an Orange Juice-Milk Based Beverage after PEF and Thermal Processing. Journal of Food Science. 74(2):S107-S112.

Yuk, H., Geveke, D.J., Zhang, H.Q. 2009. Nonthermal inactivation of Escherichia coli K12 in buffered peptone water using a pilot-plant scale supercritical carbon dioxide system with gas-liquid porous metal contractor. Food Control. 20:847-851.

Geveke, D.J., Gurtler, J., Zhang, H.Q. 2009. Inactivation of Lactobacillus plantarum in apple cider using radio frequency electric fields. Journal of Food Protection. 72(3):656-661.

Ukuku, D.O., Zhang, H.Q., Huang, L. 2009. Growth parameters of escherichia coli O157:H7, salmonella and listeria monocytogenes and aerobic mesophilic bacteria of apple cider amended with nisin-EDTA. Foodborne Pathogens and Disease. 6(4):487-494.

Gurtler, J., Conner, D.E. 2009. Survival and Growth of Salmonella Enteritidis in Liquid Egg Products Varying by Temperature, Product Composition, and Carbon Dioxide Concentration. Foodborne Pathogens and Disease. 6(5):1-7.

Gurtler, J. 2009. Evaluation of plating media for recovering Salmonella from thermally treated egg albumen. Journal of Applied Poultry Research. 18:297-309.

Jin, Z.T., Zhang, H.Q., Li, S., Kim, M. 2009. QUALITY OF APPLESAUCES PROCESSED BY PULSED ELECTRIC FIELDS AND HTST PASTEURIZATION. International Journal of Food Science and Technology. 44:829-839.

Liu, L.S., Jin, Z.T., Liu, C., Hicks, K.B., Mohanty, A.K., Bhardwaj, R., Misra, M. 2008. A preliminary study on edible, antimicrobial extruded films made from pectin and other food hydrocolloids. Journal of Natural Fibers. 5(4):366-382.

Ravishankar, S., Zhang, H.Q., Kempkes, M.I. 2008. Pulsed electric fields. Food Science and Technology International. 14(5)429-432.

Wesche, A.M., Gurtler, J., Marks, B.P., Ryser, E.T. 2009. Stress, Sublethal Injury, Resuscitation and Virulence of Bacterial Foodborne Pathogens. Journal of Food Protection. 72(5):1121-1138.

Last Modified: 4/19/2014
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