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
The project has completed research in support of NP Component 1D (Pathogen Toxins and Chemical Contaminants-Intervention Strategies). Results of the research (described below) have addressed the Project Objectives. As a newly established Project, progress has been based on continuation of studies from the previous project (011), and establishment of new research. The impact of post-contamination storage time on the efficacy of irradiation was determined for leafy vegetables. Leaves of Romaine lettuce and baby spinach were dip inoculated in a cocktail of three strains of Salmonella. Leaves were stored at 4C to allow biofilms to form, then treated with either a sodium hypochlorite wash or increasing doses of irradiation. Chlorine washes yielded maximal reductions of 1.9 log cfu/g. From 0 h of storage, D10 (the dose required for a 90% reduction) increased from 0.28 kGy to a maximum of 0.34 kGy for spinach. For Romaine, D10 increased from 0.30 kGy at 0h to 0.37 kGy at 72 h. The biofilm habitat can reduce the efficacy of irradiation in eliminating pathogens from leafy vegetables. These results can be used to better establish best practices for incorporating irradiation into a lettuce/cut salad processing chain. Cold plasma was tested for ability to remove biofilms from food-contact surfaces. Salmonella and E. coli O157:H7 cultures were allowed to form adherent biofilms on glass. These were placed on a conveyor belt and passed at various line speeds under a plasma jet emitter. Optimized treatments of 15 seconds were able to reduce the most durable forms of E. coli O157:H7 biofilms by 3.03 log cfu/cm, and Salmonella biofilms by 2.12 log cfu/cm. Cold plasma shows promise as a rapid treatment for effectively inactivating persistent contamination on food contact surfaces. In collaboration with industry, two large scale field trials to evaluate chlorine dioxide (ClO2) were conducted. Trial data showed chlorine dioxide gas effectively penetrated fruit boxes and delivered a uniform treatment. Low dose gassing with ClO2 delayed mold development on whole pineapples and plantains, thereby increasing shelf life. Companion studies with pathogen-inoculated produce showed that ClO2 fumigation treatments reduced Salmonella by 4.5 log on tomato and 5 log on cantaloupe following 7 or 8 days of storage. The treatment also helped increase the shelf life. These data suggest the feasibility of ClO2 fumigation for enhancing the safety and shelf life of stored and shipped whole commodities. The research program on microbial ecology and biological control organisms was completely suspended after scientist died on October 17, 2010. Another scientist joined project 018 on July 18, 2011 and assumed the responsibilities for the microbial ecology research under the new plan.
1. Rapid treatment with cold plasma kills Salmonella and E. coli O157:H7. Cross-contamination of fresh produce from persistent pathogen reservoirs is a known risk factor in processing environments. Industry requires a waterless, zero-contact, chemical-free method for removing pathogens from food-contact surfaces. Cold plasma was tested by ARS researchers at Wyndmoor, PA, for its ability to remove biofilms from food-contact surfaces. Salmonella and E. coli O157:H7 cultures were allowed to form adherent biofilms for 24, 48 or 72 hours on a test surface (glass slides). These were placed on a conveyor belt and passed at various line speeds either 5cm or 7.5 cm under a plasma jet emitter. The frequency of cold plasma generation was varied from 23kHz to 48kHz. Optimized treatments of 5, 10 or 15 seconds were able to reduce the most durable forms of E. coli O157:H7 biofilms by 94.4%, 99.7% and 99.9%, respectively. These rapid treatments reduced the most durable forms of Salmonella biofilms by 88.0%, 97.4% and 99.2% respectively. Cold plasma effectively inactivated persistent contamination on food contact surfaces associated with fruits and vegetables processing.
2. Chlorine dioxide kills Salmonella on green tomatoes and cantaloupe. Tomatoes and cantaloupes are recurrent sources of contamination for human pathogens. Pilot scale ClO2 gas treatment of intact produce was conducted by ARS researchers in Wyndmoor, PA, at the ERRC. Green tomatoes and cantaloupe were inoculated to 10,000 cfu/g with Salmonella Montevideo or Poona, respectively, and stored at 4C or 12.5C for 24 h prior to treatment. ClO2 treatments consisted of 6 h fumigations at 0.4 or 0.8 mg/l (tomatoes) or 1.0 mg/l (cantaloupes). Tomatoes were stored at 18C, while cantaloupes were stored at 4C. Reductions of 99.997% on tomato and 99.999% on cantaloupe were seen following 7 or 8 days of storage, respectively. The treatment helped increase the shelf life of produce by reducing the spoilage microorganism populations on the surface. This process is a feasible method for enhancing the safety and shelf life of tomatoes and cantaloupe.
Niemira, B.A., Cooke, P.H. 2010. Escherichia coli O157:H7 biofilm formation and internalization on lettuce and spinach leaf surfaces reduces efficacy of irradiation and sodium hypochlorite washes. Journal of Food Science. 75(5):M270-M277.