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United States Department of Agriculture

Agricultural Research Service


Location: Food Safety and Intervention Technologies Research

2012 Annual Report

1a. Objectives (from AD-416):
1. Develop new effective chemical and physical decontamination interventions for produce and/or improve the performance of current interventions such as gas-phase antimicrobials and cold plasma. Develop protocols for implementing interventions within a multi-step approach that improves decontamination efficacy, retains product quality and/or enhances the efficiency and practicality of the effective interventions. a. Develop and optimize gas-phase antimicrobial treatments and precision thermal treatments. b. Develop and optimize cold plasma and irradiation as non-thermal antimicrobial treatments. 2. Understand ecological factors that influence treatment decontamination efficacy, including interaction of human pathogens with native microorganisms and behavioral factors such as attachment, internalization and biofilm formation. Use this information to develop and evaluate biological-based intervention strategies for pathogen reduction while maintaining product quality. 3. Develop and evaluate process models, including economic analysis models, in order to identify barriers to commercialization and to facilitate technology transfer and commercial adoption of interventions and intervention combinations.

1b. Approach (from AD-416):
As part of this project, new and/or improved antimicrobial intervention technologies will be developed and optimized, focusing on chemical and non-thermal physical interventions. Physical and chemical treatments include the use of hot water pasteurization, gaseous chlorine dioxide, cold plasma, hydrogen peroxide vapor, and ionizing radiation alone or in combination. The microbial ecology of human pathogens on the surfaces of commodities, including attachment, biofilm formation and internalization, can alter the efficacy of the intervention. Research to better understand this aspect of pathogen biology, as well as interactions with native microflora including spoilage organisms, will be used in an iterative approach; this data will assist in the development and optimization of intervention strategies, including microbial antagonist-based biological controls. Initial studies will concentrate on high-risk produce commodities, such as leafy greens and tomatoes, and will also focus on additional products identified as contributing to foodborne illnesses. Intervention strategies will be examined for their effects on product quality and shelf-life. To facilitate industry implementation of promising treatments and treatment combinations, engineering process models and economic models will be developed to identify key barriers to commercialization during scale-up. This information will guide research efforts to address the most important aspects of successful implementation. Effective, cost-efficient intervention technologies will be transferred to industry to reduce the risk of produce-related outbreaks of foodborne illness.

3. Progress Report:
Consumption of fresh fruits and vegetables is an important part of healthy diet and anti-obesity efforts. However, contamination of produce such as cantaloupe, tomato, sprouts, nuts and jalepeno peppers, is a continuing serious problem. Our research under Objective 2 seeks to determine how pathogens persist on produce. This information will help guide our efforts to inactivate them. On artificially inoculated peppers, ARS researchers in Wyndmoor, PA recovered > 90% of Salmonella from the stem and calyx and only a small proportion from the fleshy pods. We showed that Salmonella grew by 3 logs (over a thousand fold) on peppers after incubation at 20C for 48 hr and could survive for at least 8 weeks on peppers stored at 4C. Under Objective 1, we tested a variety of antimicrobial treatments, both chemical and physical. By immersing inoculated peppers in various antimicrobial solutions for 10 min, we were able to reduce Salmonella on stem/calyx by 96.8-98.0% and on flesh by 99.2-99.6%. Using a 0.5 mg/l treatment of another type of chemical, chlorine dioxide, we reduced Salmonella on inoculated mung bean seeds and mung bean sprouts by 99.999%. This 15 minute treatment is commercially feasible and can enhance the safety of the sprouts. Although these intense levels of conventional chemical treatments show promise, there remains a critical need for novel, non-chemical antimicrobial interventions. Using an innovative new technology, cold plasma, we inactivated both Salmonella and Escherichia coli O157:H7 on dry almonds. Because the speed of the treatment is very important to processors, we used rapid treatments of 10 or 20 seconds, applied to the inoculated almonds at 2, 4 or 6 cm from the cold plasma emitter. The greatest inactivation we obtained was a 95.4% reduction of E. coli O157:H7. We found that air was generally a more effective cold plasma feed gas than nitrogen. Cold plasma therefore shows promise as a nonthermal treatment for tree nuts. Using a 45-second, direct-from-field treatment in 70C (160F) hot water, we eliminated coliforms and reduced total plate count on cantaloupe by at least 99.9%. This process can be integrated with existing commercial processing facilities & equipment. We’re collaborating with an industry partner to evaluate the quality, shelf-life, and sensory quality of fresh and fresh-cut cantaloupes treated with the ERRC hot water process. We also found that a longer hot water treatment of 3.5 minutes reduced Salmonella on fresh green tomatoes by up to 99.9999% without obvious visual injury and without changes to maturation. This promises to be a flexible, effective and economical antimicrobial process for intact fruits and vegetables. In our research with human norovirus, we found that high pressure processing (HPP) effectively disrupts the structure and function of the human norovirus capsid at pressure levels of 700-900MPa, for a holding time of 1 – 5 minutes. Since norovirus is a pathogen of concern for fresh foods, this information will help us design ways to use HPP so foods will be safer to consume. Overall, our research is on schedule for all our Objectives, and is seeing significant interest from our stakeholders.

4. Accomplishments
1. Cold plasma inactivates pathogens on almonds. Contamination of raw nuts, including almonds, is a food safety concern. ARS researchers at Wyndmoor, Pennsylvania used rapid cold plasma treatments, 10 or 20 seconds, to inactivate both Salmonella and Escherichia coli O157:H7 from dry almonds. Inoculated almonds were treated with at 2, 4 or 6 cm from the cold plasma emitter. The greatest effect observed was a 95.4% reduction of E. coli O157:H7. The interaction of treatment time with distance from plasma emitter head was complex, and isolate-dependent. In general, air was a more effective cold plasma feed gas than nitrogen. This treatment is waterless, contact-free and uses no antimicrobial chemicals. Short pulses of atmospheric pressure cold plasma therefore show promise as a nonthermal treatment for tree nuts, a technological advance which will have applications in improving the safety of this commodity for producers and consumers.

2. Finding the ‘Danger Zone’ on a jalapeño pepper. Consumption of Salmonella-contaminated jalapeño peppers has been implicated in foodborne illness outbreaks. Working with artificially inoculated peppers, ARS researchers at Wyndmoor, Pennsylvania recovered > 90% of the introduced Salmonella from the stem/calyx and recovered only a small proportion from fleshy pods. Salmonella grew by 3 logs on peppers after incubation at 20C (68F) for 48 hr and could survive for at least 8 weeks on peppers stored at 4C (40F). Immersion of inoculated peppers in 200 ppm of sodium hypochlorite, acidified sodium chlorite, or peroxyacetic acid for 10 min could reduce the number of Salmonella on stem/calyx by 96.8-98.0% and on flesh by 99.2-99.6%. By clearly identifying where pathogens reside on peppers, processors will be better able to provide safer produce to consumers.

3. A simple treatment to eliminate Salmonella from tomatoes. Numerous Salmonella outbreaks have been associated with fresh tomatoes. ARS researchers at Wyndmoor, Pennsylvania dipped artificially contaminated green tomatoes in hot water for 3.5 minutes. This treatment at 70C (160F) reduced Salmonella by up to 99.9999% without visible injury or changes to maturation. When combined with refrigerated storage, the treated tomatoes remained free of Salmonella. This chemical-free process of surface pasteurization holds promise for use in the fresh produce industry, and can enhance the microbiological safety of tomatoes.

4. Safer, cleaner cantaloupes in 45 seconds. Cantaloupes have been implicated in some of the deadliest foodborne illness outbreaks due to contamination with Salmonella and Listeria monocytogenes. A surface pasteurization process developed by ARS researchers at Wyndmoor, Pennsylvania is now being tested commercially for whole cantaloupe. A very brief, direct-from-field treatment in 70C (160F) hot water reduces total plate count by at least 99.9% and total coliforms to non-detectable levels. This 45 second process dovetails in existing commercial cantaloupe processing lines. Collaboration between ERRC and the industry partner is underway to evaluate the effect of this commercial process on microbial quality, shelf-life, and sensory quality of fresh and fresh-cut cantaloupes.

Review Publications
Niemira, B.A. 2012. Cold plasma decontamination of foods. Annual Review of Food Science and Technology. 3:125-142.

Niemira, B.A., Boyd, G. 2012. Cold plasma reduction of Salmonella and Escherichia coli 0157:H7 on almonds using ambient pressure gases. Journal of Food Science. 77:M171-175.

Gunduz, G.T., Niemira, B.A., Gonul, S.A., Karapinar, M. 2012. Antimicrobial activity of oregano oil on iceberg lettuce with different attachment conditions. Journal of Food Science. 77(7):412-415.

Fangfei, L., Huang, P., Neetoo, H., Gurtler, J., Niemira, B.A., Chen, H., Jaing, X., Li, J. 2012. High pressure inactivation of human norovirus virus-like particles: evidence that the capsid of human norovirus is highly pressure resistant. Applied and Environmental Microbiology. DOI: 10.1128/AEM.00532-12.

Last Modified: 06/25/2017
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